turbidites [a.h. bouma & a. brouwer, 1964]

DEVELOPMENTS I N S E D I M E N T O L O G Y

3

T U R B I D I T E S

E D I T E D B Y

A.H. B O U M A Geological Institute

State University, Utrecht

The Netherlands

and

A. B R O U W E R

Geolagical Institute

State University, Leyden

The Netherlands

E L S E V I E R P U B L I S H I N G C O M P A N Y

A M S T E R D A M LONDON N E W Y O R K

1964

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INTRODUCTION

A A R T BROUWER

Department of Stratigrnphy and Palaeontology, University, Leyden (The Netherlands)

Few terms recently introduced into the geologists’ jargon seem to have been so easily and so generally incorporated as the term “turbidite”. This is certainly a remarkable phenomenon since many geologists are usually reluctant to denote sedimentary rocks by names that are so obviously related to origin. One possible explanation is that rocks with turbidite characteristics are of widespread occurrence, and can easily be recognized in the field once attention has been directed towards their diagnostic features. Still, notwithstanding the genetical significance of the term, many problems related to both the mode of origin and to the environmental conditions favourable to their formation, remain unsolved.

The problem of turbidite sedimentation has been approached from two different sides, firstly by students of modern deep-sea deposits, and secondly by students of flysch and flysch-like deposits.

The concept of turbidity currents was first suggested by DALY in 1936 in connection with research on the mode of origin of submarine canyons. This suggestion seemed a fruitful one, and the idea of mass movements by currents of high density was soon adopted by other geologists. Among them Ph. H. Kuenen should be noted in particular. Via both field studies and ingenious laboratory experiments he made invaluable contributions towards a better understanding of this fascinating type of sediment. It soon became clear that many flysch and flysch-like sediments show the same characteristics as those laid down by turbidity currents, even to such a degree that turbidites and flysch sometimes give the impression of being two names for one kind of deposit. There can be no doubt that both originate from the same mechanism, as has repeatedly been pointed out. Recently NESTEROFF and HEEZEN (1963) made a careful point- for-point comparison of these deposits. Their conclusion seems inescapable: “Toute une skrie de caracthres pktrographiques similaires nous permet d’affirmer que les turbidites sont les dkpdts modernes correspondants aw flyschs des skries gkologiques”. Kuenen reaches the same conclusion in his contribution to the present volume. Never- theless, few seem alarmed by the conclusion that two types of sediments, originating under different environmental conditions, exhibit the same set of characteristics.

The termflysch was introduced by the Swiss geologist B. Studer using adistinct stratigraphical meaning as early as 1827, although the word itself seems to be much older (STUDER, 1827). The sediments thus denoted were so clearly related to the oncoming Alpine movements that the meaning of the term has gradually been broadened to

2 INDRODUCTION

include all similar kinds of sediments connected with strong geosynclinal instability, without any references to place or time. Much to the distress of several Swiss geologists the term flysch has thus become a member of the family of tecto-facies terms rather than a distinct element in the Alpine stratigraphical succession. Perhaps the Lower Carboniferous Culm facies, with its remarkable distribution amidst a predominantly calcareous facies, was one of the first to which the term flysch was applied outside the Alpine orogene. Afterwards certain members of the Caledonian geosynclinal succession have also been referred to as flysch, or more precisely, as flysch-like sediments. It is certainly somewhat distressing to encounter the same characteristic lithological features and comparable palaeontological characteristics in many modern deep-sea sands. Perhaps Dietz’s recent suggestion that eugeosynclines are developed on the oceanic crust marginal to the continents offers a way out of this dilemma (DJETZ, 1963).

The papers of the present volume were originally gathered in order to be published in a special issue of the International Association of Sedimentologists’ quarterly Sediinentology, but the response was such that it soon became obvious that the under- taking went beyond the possibilities of Sedimentology. Publication of the papers in more than one issue would certainly have lessened their value. Therefore an offer made by the Elsevier Publishing Company to publish the papers together in a special volume was gratefully accepted.

The authors of the papers in this volume do not claim that they present a complete and final answer to the many problems connected with the origin of turbidites both in modern seas and in successions of the geological past. They do, however, represent many aspects, and certainly all of the more important ones, of these puzzling rocks. Looking at the bibliography on turbidites, which we are pleased to include, the reader may receive the impression that turbidites have been studied from every possible point of view and in the remotest corners of our planet. It may thus seem that an explanation of these rocks, if not yet arrived at, is at least quite nearby. This, however, is completely erroneous. Large as our knowledge may appear, still more is to be learned. The main function of the present volume is to stimulate discussion and research.

REFERENCES

DALY, R. A., 1936. Origin of submarine “canyons”. Am. J . Sci., 31 : 401-420. DIETZ, R. S., 1963. Alpine serpentines as oceanic rind fragments. Bull. Geol. SOC. Am., 74 : 947-952. NESTERHOFF, W. D. et HEEZEN, R. C., 1963. Essais de comparaison entre les turbidites rnodernes et le

STUDER, B., 1827. Geognostische Fkmcrkungen uber einige Theile der nordlichen Alpenkette. flysch. Rev. Gdograph. Phys. Gkol. Dyn., Sdr. 2,1962,5 (2) : 115-127.

Z . Mineral.. 1 : 1-52.

DEEP-SEA SANDS AND ANCIENT TURBIDITES

PH. H. KUENEN

Geological Institute, State University at Groningen (The Netherlands)

SUMMARY

It is shown that deep-sea sands have been emplaced by turbidity currents except for a few slumped beds near slopes. The evidence from deep-sea topography and bottom sampling allows no other interpretation. The known depth range is from many thousands to one thousand metres and a doubtful case in 20 metres. Single beds may extend hundreds of kilometres. The vast scale on which these currents can act is thus established beyond doubt. The structural features of these unquestionable turbidites are closely matched in a number of ancient flysch-like sequences of the alternating type. More or less complete paleontological evidence for depths of the latter greater than neritic is obtained here and there, and the total lack of shallow-water features (littoral, paralic, and shallow-neritic) in many such formations confirms the conclusion that they are of deep-water origin. Sole markings and other sedimentological features add their testimony. Some alternative explanations have been proposed for deep-sea sands (slumping, creep, liquefaction, normal currents), or for flysch-like rocks (creep, normal marine currents, tectonic or climatic rhythms, coastal or deltaic environments, etc.), but all these suggestions are opposed by clear evidence in the majority of flysch- like sequences, or there are serious theoretical objections.

However, there are also certain differences between normal deep-sea sands and the most typical of flysch formations in the Alps and elsewhere. These dissimilarities in sorting, grain size, organic remains, etc. are not indicative of a different mechanism of transportation, but of a different geographical setting of the geosynclinal trenches compared to present-day marine basins. There are also turbidite formations which are not classifiable as flysch, and there are pelagic formations which contain a few turbidites.

Between obvious turbiditic flysch beds there are individual beds emplaced by slumping or precipitation; there are also flysch-like formations that originated in insignificant depths, which follows from paleontological and sedimentological evidence. Whether turbidity currents can be invoked in shallow water is less certain - perhaps sheet floods were active. Where, in ancient rocks, only a few of the typical turbidite features are present, or where exposure is poor, the environment of deposition and mechanism of transportation must remain in doubt. The divergent features of sediments formed in several other environments are briefly indicated.

4 PH. H. KUENEN

INTRODUCTION

In the deep sea beyond the edge of the shelf, numerous sand beds have been discovered that are neither of volcanic, nor of eolian or organic origin. They are usually referred to as deepsea sands, although gravels and silts are included. Their origin was long sought in subsidence or sliding, but interstratification with normal pelagic deep-sea sediment rules out the first suggestion, and the great distance to steep slopes in many cases argues against the second surmise. Hence, they were tentatively attributed by KUENEN (1950) to turbidity currents. Since then, many marine geologists have collected data on this question. The accumulated evidence showing that the great majority of deep-sea sands outside canyons have been deposited by turbidity currents is now overwhelming. The location and topographic conditions give highly valuable information on the mechanism of flow, and on the gigantic scale at which it can act. Study of cores shows which sedimentary features to expect in the deposits of such currents. All this information can be applied by hard-rock geologists confronted with the problem of explaining the origin of marine formations with graded g b a c k e s alternating with shale beds. But many field-workers appear to be unfamiliar with the findings of marine geologists and vice versa. The present paper aims at bringing together the widely scattered results of work at sea and showing the surprising extent to which the features of deep-sea sands and certain ancient arenites tally with each other. In fact, for many flysch-like sequences the origin in bathyal depths by turbidity currents can hardly be doubted.

There is no need to trace here the stages by which the concept of turbidity flow developed from DALY’S first rough sketch, in 1936, to our present much more detailed understanding a quarter of a century later. The first problem to be formulated was that of explaining the origin of submarine canyons. It is still controversial, because the degree to which turbidity currents can erode is an open question. Experimental work on turbidity flow by the present author ( KUENEN, 1937) showed the suggested mechanism to be a reality. More detailed experiments (KUENEN, 1950; KUENEN and MIGLIO- RINI, 1950) were undertaken largely in an attempt to explain the origin of ancient graded graywackes. When the results were applied to certain rock formations the line of thought proved encouraging from the very start. Soon, the findings in the deep sea were bringing even fuller and more precise evidence in favour of the importance of this newly discovered mode of transport. One of the more spectacular results was to show that the activity of this mechanism extends out from the continents to many hundreds of kilometres across the deep ocean floor. The ability to measure depths and slopes and to locate source areas are among the most useful advantages the marine geologist has over his hard-rock colleague.

In later years wider application of the concept of turbidity currents to ancient deposits has supplied fruitful results, not only in understanding the emplacement of the beds themselves, but also in smoothing out paleontological difficulties. Paleogeo- graphy and even structural geology have benefited by the new light supplied by the study of turbidite formations. However, although few geologists deny the action of

DEEP-SEA SANDS AND ANClENT TURBlDlTES 5

turbidity currents in general, there are a number of colleagues who have strong doubts whether the notion can be used for the cases they happen to be familiar with, or they have suggested alternative mechanisms. In geology, snags are bound to be revealed as soon as any general concept is applied to a specific case, but some of the fancied objections can be disposed of by referring to the deep-sea floor for evidence. For example, several authors have denied that turbidity currents can be responsible for depositing laminated beds, although deep-sea turbidites are usually laminated. In contrast when extravagant claims have been made for turbidity currents, a better understanding of the phenomena in the oceans would have led to a more cautious approach. Marine geologists unfamiliar with ancient rocks have suggested creep or slumping to explain flysch rocks, because they have not taken the evidence for current action into account. It is obvious that the results of work at sea, in the field, and in the laboratory should be interrelated. A study of ancient and recent basins off southern California by GORSLINE and EMERY (1959) shows how fruitful such a double approach can be.

EVIDENCE FOR TURBIDITY CURRENTS 1N THE OCEAN

There are several independent sources of evidence for the action of turbidity flow in the present oceans and marine basins.

Ocean-joor topography

The topography of the ocean floor provides some of the strongest evidence for turbidity currents. At the mouths of submarine canyons, such as the Hudson, Monterey, Mediterranean, and Mississippi canyons, great, low-angle fans have been built. These are incised radially by one or more leveed channels. At their outer limits these sub-sea fans merge gradually into adjoining abyssal plains. Although this means that the slope \has,therdsunk below the value of 1 in 1,OOO or at least 1 in 500, the featureless expan- ses beyond continue to drop away from the fans. It is obviously impossible to ascribe such shapes to tectonic forces, so that a depositional morphology has to be assumed. The features can only be attributed to a bottom-hugging, gravity-driven, depositing current. No other type of ocean current could be bound to plains sloping in a constant direction and away from the source of supply, and it can hardly be doubted that the canyons are the source channels along which the sediment has arrived. In inland seas and in the Atlantic, the abyssal plains occupy the entire expanse of the deepest areas, leaving no rough topography except that which rises above them. Many deep-sea trenches throughout the oceans are floored by a narrow abyssal plain with a longitudinal slope, but in the Pacific most of the deep-sea floor is rough with a relief of several hundreds of metres. The abyssal plains are restricted to broad fringes along the North American continent about 2,000 kilometres across, and to narrower archipelagic aprons around volcanic islands; elsewhere, the plains are missing. Significantly, this is where

6 PH. H. KUENEN

deep-sea troughs, basins, ridges, or great distances intervene between land areas and the abyssal floor, and these topographic features must be responsible for excluding the smoothing mechanism. The only manner in which this obstruction can act is by barring transport over the bottom. This surmise is confirmed by the situation off British Columbia, where a patch of rough topography occurs in the middle of the abyssal plain directly behind a short ridge parallel with the continental terrace (MENARD, 1955).

Two or three cases are known in which basins have become filled with sediment to the lowest point in the rim. Here the surplus spills over into the neighbouring basin that has thus acquired an abyssal plain of its own. In one case, the Biscay and Iberia plains (LAUGHTON, 1960), the connection is a short meandering channel with a sub- sea fan at its lower end1.

It is worth noting that beyond the leveed channel on the subaqueous slope of the RhBne delta in Lake Geneva, a perfect example of an abyssal plain is found.

Coarse strata ubiquitous on abyssalplains

Every single long core taken by the Lamont Observatory piston sampler on abyssal plains or sub-sea fans - and there are many - contains at least one deep-sea gravel-, sand- or silt-bed, and in many samples there are several such beds always separated by normal pelagic sediment. According to NESTEROFF (1961) each abyssal-plain core of 10m length has 10-30 sand or silt layers. Such beds have never been encountered on isolated hills or ridges, not even on those rising no more than a hundred metres from the middle of abyssal plains, as, for instance, in the Gulf of Mexico (EWING et al., 1958). Neither do they occur on steeper continental or insular slopes, or on irregular topography beyond abyssal plains or archipelagic aprons. This distribution is only compatible with a supply along the bottom under the influence of gravity. The mechanism carrying the coarse sediment on its long journey out from the continent or island is unable to raise it up off an abyssal plain. The only condition under which deep-sea sand is lifted above the sea floor, is along the edge of those channels which are bordered by levees. The conditions just described are duplicated in the Mediterranean (BOURCART~~ al., 1960,1961 ; BOURCART and Ross, 1962; GENNESSEAUX, 1962) and Adriatic (VAN STRAATEN, 1964).

The pelagic beds between the sands are significant because they are known to accumulate slowly, and each of them represents several to many thousands of years. The normal condition on the deep-sea floor is, therefore, one of only slight bottom currents, so weak as to allow clay to settle out. During deposition of a deep-sea sand a powerful current is obviously active to ensure the supply, but the crucial point is that no such current occurs when there is no coarse sediment available. This means that current and coarse sediment are parts of one and the same phenomenon.

The relation is actually so close that, as the grain size of the deposits diminished upwards during deposition of a graded bed, the current must have slackened concom- itantly to allow settling out, with no fluctuation sufficient to cause erosion during

One feature of several abyssal plains is admittedly. still obscure: that of the occurrence of single deep-sea channels crossing them.

DEEP-SEA SANDS AND ANCIENT TURBIDITES 7

this gradual slackening. This is in sharp contrast with tidal and wind-driven currents or rivers, because all these flow irrespectively of whether there is sediment available or not. The result is that with these currents local temporary erosion is a universal phenomenon.

Two independent features prove that a bed of deepsea sand is deposited in a very short time. Several cases have been noted (ERICSON et al., 1952; EWING et al., 1958, p.1046) that burrowing organisms have reworked the upper few centimetres of such beds, but have left the remainder undisturbed. Obviously sedimentation was so swift that no reworking could take place, but later, during the slow accumulation of the covering deep-sea deposit, the bottom fauna was again active. The other indication of swift sedimentation is the absence of features pointing to fluctuations in the supplying current due to external variations. Evidently the bed was produced by a current too powerful or too short-lived to be affected by tides or climatic fluctuations. In cases where the pelagic deposit, like red clay, is a solution residue of carbonate-rich sediment, the presence of lime in the deepsea sands also proves swift accumulation of the bed preventing extraction of CaCO,.

Highly significant data confirming the origin of abyssal plains by turbidity currents, the continuation of single beds over distances of 100 km, and the accumulation of sediment in basins and trenches up to thicknesses of one or more kilometres has been obtained by J. Ewing and others of the Lamont Observatory using the new reflection profiler. (J. EWING et al., 1960, 1962; J. EWING and M. EWING, 1962; M. EWING and J. EWING, 1963).

Deep-sea sands are foreign to environment

Deep-sea sands tend to contain shallow-water benthonic Foraminifera, remains of calcareous Algae, large shells, plant remains, reworked fossils, and other components that are derived from the neritic sea floor on the shelf (PHLEGER, 1951; ERICSON et al., 1952; SHEPARD and EINSELE, 1962). The lime content is in many cases, much higher or lower than that of the pelagic deposits, accumulating in situ on adjoining slopes just above the abyssal plains. In contrast, the deep-sea sediment between the successive sand beds, is evidently formed in situ and contains pelagic or deepbenthonic organisms. It is similar to the sediment accumulating on the lower parts of adjacent slopes. (See Appendix, Note 1 and 2.)

Size of currents

The distances to which oceanic turbidity currents apparently spread out over the abyssal plains range up to 2,000 km. Obviously, this implies a huge volume for such flows, and it is born out because some idea of the great size can be obtained from the height of channel levees over the channel floor on sub-sea fans. The flows must have topped these natural dikes to build them up. Depths of 100-150 m at the very least are found, coupled with a breadth of several kilometres. SHEPARD (1962b) has suggested

8 PH. H. KUENEN

that the channels may have been deepened after the build-up of the levees. But as the concave walls of winding channels are steeper than the convex walls active erosion along the outer side of the bends must have accompanied any such deepening. The levees would then have been eaten away if they were merely left over from an earlier period with shallow channels. Evidently the levees are as youthful as any deepening of the channels and form trustworthy high water marks for the currents. For evidence concerning the large volumes of the resulting deposits see p.12, point 17. Obviously the amount of water involved was at least 10 times that of the sediment.

Turbidity current caused by an earthquake

The Grand Banks earthquake of 1929 caused the rupture, contortion, transportation, and burial of a number of submarine cables on the continental slope and deep ocean floor. Over a large area of the abyssal plain in the neighbourhood, a thick graded bed of silt was found 20 years later (HEEZEN and EWING, 1952,1955; HEEZEN, 1959). It was not covered by later pelagic sediment, and hence it had been emplaced a short time before. There can be no reasonable doubt that this bed was formed in consequence of the earthquake. As the material had travelled for great distances over slopes of less than l/l,OOO a slump is excluded. On the other hand a turbidity current triggered by the earthquake can explain all the observed phenomena satisfactorily.

Summary

From the foregoing list of arguments it follows that: vast amounts of sediment including coarse sand, pebbles, shallow-benthonic organisms and plant remains are carried off the shelf and are spread out extremely evenly over large areas of the deep-sea floor; that the grain size tends to decrease as the distance of travel increases; that existing normal bottom currents are not responsible for the emplacement; that the transportation is along the bottom and follows the direction of maximum slope available, even when it is less than 1 in 1,OOO, which is as much as to say that gravity provides the motive force; that the deposit shows graded bedding and lamination indicative of the action of a true, watery current; that the grading proves the velocity of the current is tied to the grain size of the load, load and current forming two features of the same phenomenon; that deposition is sudden, alternating with long intervals of normal pelagic accumulation; that the same action takes place in the Adriatic at one quarter the depth of the ocean, and, judging by the topography, also in Lake Geneva at 300 m; that sequences hundreds of metres thick are built up, levelling off the deepest parts of the basins reached by the currents.

Hence a series of short-lived, powerful currents carrying huge amounts of coarse sediment, travel spasmodically down the submarine slopes by gravity pull. This means no less than that the mechanism is that of turbidity current Jow, and that practically aN deep-sea sands are turbidites, apart from some slumps or winnowed sands of organic origin, and easily distinguishable eolian or volcanic sands.

DEEP-SEA SANDS A N D ANCIENT TURBIDITES 9

ALTERNATIVE MECHANISMS

Various alternative mechanisms have been invoked to account for the emplacement of deep-sea sands: slumping, creep, liquefaction and normal currents. The main objections to these suggestions will be briefly mentioned.

Slumping

Various sources of information indicate that sandy deposits are stable on subaqueous slopes of a few degrees, and that clay-rich sediment can slide on slight slopes, but comes to rest where the declivity is less than 1 %. This means that deep-sea sands, with their coarse grains in mutual contact and lying in positions where the materials must have been carried hundreds of kilometres across plains sloping less than 1 in l,OOO, cannot be attributed to slumping but must be accounted for by a far more mobile mechanism. The absence of distortions typical for slumping in deep-sea sands also militates against sliding.

This reasoning is strengthened by the observation already referred to, that deep-sea Jands tend to show graded bedding. The majority also show lamination and some even ripple lamination. These structures require settling from a passing flow and are incompatible with the fixation of a moving mass, that is with the manner in which a slump produces a slump sheet (KUENEN, 1956). (See Appendix, Note 3 and 4.)

Normal currents

Although no serious attempts have been made to explain deep-sea sands as the product of normal marine currents, there have been some passing suggestions to this effect and it is useful to realize what the objections are.

It should be recognized that currents in the deep-sea do not come and go like winds or wind-driven currents at the surface. There may be secular changes in velocity, but the volume of water involved is so great and the driving mechanism is of such a permanent character that deep-sea circulation is more constant even than the trade winds. Swinging currents (seiches) in basins are more spasmodic but cannot result in transportation in one direction. Bearing this in mind, it is obvious that the deep-sea sands of the oceans cannot be attributed to normal currents, because the sands form strata between clay-rich pelagic sediment. The sudden onset of sedimentation, the mixing of clay in the sand, the absence from slight elevations where currents should be concentrated, these are characteristics of deep-sea sands, which show they are not the products of normal currents. It is likewise obvious that the origin of sub-sea fans and abyssal plains requires a mechanism driven by bottom slope, and hence not normal marine currents. (See Appendix, Note 5.)

PROPERTIES OF DEEP-SEA TURBIDITES

If the validity of the foregoing deductions is conceded, study of deep-sea sands should

10 PH. H. KUENEN

reveal a number of features by which ancient turbidites can be recognized, besides teaching us much as to the conditions under which they may have originated. Com- bining the information obtained from many localities, largely from the Lamont cores the following significant features of deep-sea turbidites can be listed. Naturally, there are few localities in which they have all been ascertained together.

(I) The coarsest particles can reach the size of medium pebbles (rock and shell material have both been encountered), but many beds contain nothing beyond the size of fine silt. Generally speaking, at any one locality the maximum grain size increases with the thickness of the bed.

I I I I I I

Fig.1. Five averages of samples taken at 2 cm intervals from a deep-sea sand cored by the Lamont Observatory in 4,810 m depth on the Hudson sub-sea fan. Depth in core: 1 = 0-4 cm, 2 = 4-18 m,

3 = 18-24 cm, 4 = 24-48 cm, 5 = 48-72 cm. The grading is well developed.

(2) Grading is visible in only half of the beds, but careful mechanical analysis shows at least a slight tendency to grading in the majority of occurrences. (In a wet sample the grading probably does not show up as well as in a consolidated rock.) NESTEROFF (1 961) even claims that all turbidites of abyssal plains are graded, rendered more obvious by colour change, due to lime. Repeated grading has also been noted, where deposition evidently came from a few flows at short' intervals or pulses of a composite flow. In the coarser beds grading tends to be very obvious. Forams of about 500 p tend to be concentrated in thin zones where the quartz grains are 250 p.

The writer is able to add an analysis made by D. J. Doeglas on a deep-sea sand obtained from the Lamont Observatory (core number A 164-14; 36'6' N, 67'19'W; 4,810 m on the Hudson sub-sea fan). The result is shown in Fig.1 (about 6Xfiner than 16 p and 3.5 % below 2 p).

(3) At any level in a bed the sorting tends to be moderate to good and it improves with decrease in grain size. The great majority of deep-sea sands, although well sorted to look at, are found on analysis to contain a considerable proportion of silt and clay


(SHEPARD, 1961; BOURCART and Ros, 1962). Many layers consist almost entirely of silt and clay with a small admixture of sand-sized grains at the bottom. SHEPARD and EINSELE (1962) point to the similarity between sands of adjacent beaches and deep-sea sands but for higher lutite content of the latter.

(4) Most beds consist of inorganic matter, but some are rich in remains of Fora- minifera, molluscs, Halimeda, echinoid spines, or other calcareous particles. Much or nearly all of this material is easily shown to belong originally in neritic depths, and reworked older fossils have also been identified. The sand may be rich in feldspar and mica; glauconite can be plentiful and pyrite also occurs. The quartz is mostly angular.

(5) Several beds contain twigs in the sandy parts and fine plant remains interspersed between the fine sand and silt particles at higher levels in the beds. They may occur in such profusion as to produce a dark lignitic stratum.

(6) In most beds the fine sand or silt shows lamination. If the lower part of the turbidite is medium or coarse sand, then lamination is absent in that part1.

(7) Current ripple lamination occurs quite commonly, and in most cases is found lying on and covered by horizontal lamination.

(8) Contorted lamination strongly recalling so-called convolute lamination has been found, but the possibility could not be excluded that one was dealing with distortions due to faulty sampling. Now, however, VAN STRAATEN (1964) has found absolutely typical convolute lamination in the upper, silty part of a sandy turbidite 17 cm thick. This bed was cored at 1,200 m depth in the Adriatic.

(9) Lumps of mud occur in some deep-sea sands. (10) The thickness of the beds varies between a few millimetres and at least 6 m. (ZZ) The lower margin is abrupt and clean-cut; the upper margin may be sharply

drawn, but in other cases the top merges imperceptibly into the covering normal pelagic deposit.

(22) Deposition of some turbidites is shown to have been “instantaneous”, because only the upper part is reworked by burrowing.

(13) Irregularities at the bottom of some beds could be erosional sole markings but might stem from distortion of the core in question. However, slight erosion can be deduced from the common presence of a thin film of forams and pteropods at the base. According to the present author this is a winnowed residue of the underlying pelagic clay with shells (occasionally heaped up to 10 mm thickness, but usually one or two shells thick). NESTEROFF (1961) believed this film denoted the upper end of the turbidite and hence that no pelagic sediment is present between the turbidites. He pointed out that the more powerful currents, that deposited coarser beds, had wafted away the shells. But this explanation holds as well if the shell film is held to represent a lag deposit. The latter view is preferable because pelagic sedimentation cannot be absent on abyssal plains (see also point 24) and because the film thickness is not correlated with the size of the underlying bed.

SHEPARD and EINSELE (1962, p.121) are wrong when implying that lamination in ancient turbidites is found only above an unlaminated base, for many flysch beds are laminated throughout.

12 PH. H. KUENEN

Neither is it logical that all currents first deposited forams with medium sand, then - after an interval of silt followed by clay - forams with clay and finally forams without any inorganic admixture. The three foram layers are here explained as: (a) current deposited, (6) pelagically settled, (c) winnowed.

If this view is accepted the interesting corollary follows that even at great distances across the abyssal plains the nose of the current exerts a slight erosion of the soft pelagic clay.

(14) The beds are divided from each other by normal (hemi-)pelagic clay or ooze (so-called blue mud, red clay, globigerina ooze) lacking all elements indicative of shallow water. This means that the organic remains of the alternating layers are strongly contrasted.

(15) Where several beds above each other show current lamination the indicated directions of flow tend to be parallel to one another (observed by Van Straaten on cores of the Lamont Observatory).

(16) Deep-sea turbidites occur in thick extensive formations. This follows both from the seismically ascertained thickness of soft fill with internal reflections and from the burial of irregular topography. That the bedding must be of great regularity can be deduced, among others, from the extreme flatness of abyssal plains.

(17) Individual deep-sea turbidites are known to cover enormous areas. EMERY (1960) mentions two basins off California, in which presumably sandy beds just below the sea floor have been traced for 16 km by echo-sounder. ERICSON et al. (1952) traced three beds for 45 km in the Puerto Rico Trough (see also VAN STRAATEN, 1964).

Excellent examples are known from the Sigsbee abyssal plain in the Gulf of Mexico (EWING et al., 1958). A graded calcareous layer has been cored there over an area of at least 6,000 km2 and another bed over 10,000 km2; the most widely separated occurrences of the latter are 220 km apart. The known thickness of the former ranges from 8-80 cm; this should be reduced to half in the compacted state, and it is not, therefore, a thick layer. Its present volume is of the order of 3 km3. Oceanic beds several times as thick should have volumes of dozens of cubic kilometres. The Grand Banks earthquake resulted in a turbidite covering 100,000 km2 and a volume of at least 100 km3.

(28) The wide variety of recent deep-sea sands is not distributed arbitrarily. In the first place there are the differences resulting from available source materials. All variations between calcareous and lime-free turbidites have been found. The presence or absence of feldspar, gIauconite, plant remains, shell fragments, and shallow-water benthonic organisms depends on the nature of the source area; likewise the degree of abrasion and weathering of the grains and also to someextent the clay content. Winnow- ed coastal sands will produce a cleaner turbidite than poorly sorted material, or cases in which interbedded sands and muds have been set in motion together by a slide. These obvious conclusions are amply confirmed by data, e.g., for the basins off southern California.

(19) In the second place the location of the sample has a great influence. Beds tend to become thinner and finer grained and better sorted away from the source. At a


given locality the coarser beds usually belong to the thicker ones. GORSLINE and EMERY (1959) have shown that in submarine canyons the top, fine part of turbidites tends to be missing, so that they end upwards abruptly. The canyon sands probably contain less lutite than the sands deposited on abyssal plains. In canyons there are also slumped beds and non-graded beds (fluxo-turbidites?). On the sub-sea fans at the canyon mouths finer grain and lamination are encountered. Out beyond on the basin floor lamination is the main structure somewhat masking the grading, but sand is limited to lower parts of such beds so that there is still some grading. Gradational tops are more common at great distances from the source.

(20) The fine-grained beds between the recent turbidites show a wide variety in composition, but in each area they are uniform. Some basins have a rich autochtho- nous benthonic or pelagic fauna, others are practically devoid of bottom or pelagic life.

(21) Slopes of the ocean floor exceeding 5 or 10" are generally found to be free of deposit, or at least to carry only a thin cover. Nearly all deep-sea sands are found on bottom slopes of one degree or less. Some coarse sand has been transported for distances of 1,000 km or more on slopes of one in a thousand.

(22) Intervals between currents have been measured by radiocarbon dating on calcareous turbidites on the floor of the Tongue of the Ocean (BUSBY, 1962; RUSNAK et al., 1963). Frequencies range from one per 460 years to one per 10,000 years. Both the coarse and the fine material in the turbidites are older than the pelagic sediment upon which they rest. The turbidites are graded and range in thickness from a thin lamina to 20 cm. In some localities they form over 50 % of the deposit.

APPLICATION TO ANCIENT ROCKS

The first rocks that were attributed to the action of turbidity currents were the Oligocene graywackes of thi northern Apennines (KUENEN and MIGLIORINI, 1950). At that time and for the next few years, when some other sequences were identified as turbidite formations and their features described, little was then known concerning the deep-sea turbidites. Now that the mechanism by which the latter were deposited is no longer in doubt and so much has become known about their sedimentological features, the time has come for them to be used as criteria for the identification of ancient turbidites. However, it is important to place the main emphasis on recent turbidites from abyssal plains and sub-sea fans not in channels, for the ancient rocks are predominantly from flat featureless basin floors.

The most convincing case can be made out for the Plio-Pleistocene sequence of the Ventura Basin in southern California. The basin fill is 6,000 m thick and consists of a regular alternation of sandstones and shales. The top parts of the latter are very uniform and contain a rich fauna of benthonic Foraminifera. Thanks to the youth of these deposits, several species amongst the latter are still living in the adjacant Pacific. Natland (NATLAND and KUENEN, 1951) showed long ago that several of these species

14 PH. H. KUENEN

are restricted to great depth in the present ocean, whereas others are limited to somewhat smaller depths. By this means he was able to show that the depth of deposition low down in the succession was of the order of 1,500-2,OOO m, gradually decreasing upwards. Where extrapolation would indicate zero depth one actually encounters typical beach deposits covered by a terrestrial sequence.

In a recent paper NATLAND (1963) has amplified this picture and emphasized the faunal contrast between hemi-pelagic beds and turbidites. He has also shown convincingly that the current picks up forams all along its course and distributes them as clastics in its graded deposit.

Comparison of the sandy beds between these deep-water shales with deep-sea sands shows complete similarity. These beds are graded, slightly muddy sandstones, some with pebble sizes at the base, and usually with lamination in fine sand and silt sizes, ending with shale. Other features are mud pebbles, current ripple lamination, shallow-water fossils and re-worked older Foraminifera, plant remains from sticks to fine hashygreat horizontal extent of the beds, regular alternation of the sand beds with the shales, directional features indicating rather uniform directions of flow for the supplying currents, and finally complete absence of all features that indicate shallow water.

Inspection has also brought out some additional sedimentological properties of the Ventura sand beds, that fit in well with an origin by turbidity currents, but which have not yet been ascertained unequivocally in recent deposits on the actual deep-sea floor. These are: load casting at the base, slight current scour, pull-aparts, sand dikes, occasional slump structures and slump conglomerates, the latter restricted to local fans on the ancient sea floor. Then there is gradual disappearance of all typical properties as the beach deposits are approached going upwards in the sedimentary column. Finally, gradual decrease in grain size has been ascertained when tracing a bed in the direction of flow.

It is worth special attention that convolute lamination, one of the most ubiquitous features of the silty tops of ancient turbidites and also common in the Ventura Basin has now been discovered in the upper part of a deep-sea sand from the Adriatic by VAN STRAATEN (1964). The remarkable similarity between deep-sea sands and ancient turbidites is thereby rendered even closer.

The close analogy between these beds and both experimental and deep-sea turbidites, and the good match between the present offshore basins and the reconstructed former Ventura Basin, together help to establish the nature of the Ventura sequence beyond any reasonable doubt as resulting from turbidity currents flowing into a deep marine basin (see also WINTERER and DURHAM, 1962).

Later studies by EMERY (1960), EMERY and RITTENBERG (1952), CROUCH (1952), GORSLINE and EMERY (1959) have brought greater precision to this comparison between the present-day off-shore basins off southern California and the Pliocene Los Angeles Basin. Temperature was shown to be more important than pressure in limit- ing the occurrence of certain recent benthonic Foraminifera. Seven biozones were ascertained, the four deeper ones occurring in basins with sill depths of about 400,


1,OOO, 1,800, and nearly 3,000 m. Additional depths in the basin below the sill has no influence on the composition of the fauna. This means that the fauna gives a minimum value for the depths of the basin floor. The shales between the turbidites of the Los Angeles Oil Basin contain Foraminifera, proving for the Lower Pliocene a temperature of 3”C, equivalent to 1,200 m for the sill; in the Middle Pliocene 3”-3.5”C indicating 1,100 m; and 3.5”-8.5”C giving 1,O00400 m for the Upper Pliocene. The sandy beds of the same basin contain organisms that normally lived in water depths of 20-30 m and others that lived deeper. This contrast is of great significance because it establishes the juxtaposition of beds with animal remains from two environments of different depths, and also proves the occurrence in Pliocene times of warm shallow surface waters in the area. The possibility is thus excluded that the present deep-water fauna lived in those days in small depths because there happened to be cold water near the surface. (See Appendix, Note 6.)

Continuing the search for ancient turbidites one has to turn to older, pre-Pliocene sequences. In these the fossils cannot give quite such pertinent evidence because the depth of habitat is less certain for extinct species than for the Ventura and Los Angeles species that are still living in the ocean. It is, therefore, more satisfactory to use the sedimentological features for identifying such ancient turbidites. It turns out that there are many Tertiary formations that resemble deepsea turbidites and those of the Ventura Basin very closely. All the properties enumerated above are well developed and it is then found that the benthonic Foraminifera, if present, form what is held to be a deep-water assemblage. (For a recent example see GOHRBANDT et al., 1962.) Moreover, there is the same total lack of features that indicate shallow water. Exam- ples are the “macigno”, “marnoso arenacea” and Picene flysch of the northern Apennines, the Krosno Beds of Poland, most of the Gr6s d’Annot in the French Alps, and countless other flysch formations. Because of the lithification of the sandy beds (graywackes), the soles are exposed in most outcrops and these add some significant features to those already enumerated. Flute casts, groove casts, prod casts, etc., are all indicative of powerful current action preceded by a long period of quiet allowing the accumulation of a clay deposit and immediately followed by deposition of the sandstone itself. Measurement of current directions on these features brings out a remarkable uniformity, a result fitting the action of turbidity currents.

Against the weakened paleontological evidence for bathyal depth can be placed a rich collection of highly typical burrowings. Although the nature of the animals responsible can only be guessed at, the fact remains that the great majority of these so-called organic hieroglyphs have never been encountered in rocks of evident shallow- water origin. Burrows are lacking internally in the majority of the turbidites or restricted to the upper parts, just as in the deep-sea sands (SEILACHER, 1959); they may occur as casts on the soles, evidently re-excavated by the current prior to load dumping.

The Paleozoic and Precambrian also contain many turbidite formations, e.g., the Silurian and Ordovician of the Southern Uplands of Scotland, the Silurian around Aberystwyth in Wales, the Cambrian of the Harlech Dome, the Cambrian Bray Series south of Dublin, and parts of the Lower Carboniferous and Devonian in Germany.

16 PH. H. KUENEN

The burrowings in these formations closely resemble those in the Mesozoic and Tertiary turbidites. The Figtree Series invaded by the Archean granite of Natal and the Pretoria Series contain what are almost certainly turbidite formations. With their presumable ages of 3,000 million years and 2,000 million years respectively they are the oldest of such rocks known (KUENEN, in preparation). Some formations of fine pelagic material contain just a few coarser turbidites that were deposited at long intervals. An example has been described by Cmozzi (1957). TRUMPY (1960) claims that in the earlier stages of the Alpine geosyncline similar conditions were usual (“Biindnerschiefer”). There are also formations with many coarse slumps and turbidites of calcareous material that are not classified as flysch, but are nevertheless turbidite formations (KUENEN and CAROZZI, 1953).

An inventory of the features one can expect to find in ancient turbidite formations is almost identical with the list given above for recent deep-sea turbidites. A few comments can be made: (2) Grading may either be found in almost all beds of a formation, or less regularly, and there are cases in which it is even rare. (3) The admixture of lutite tends to produce dark sands (graywackes). According to CUMMINS (1962) the clay is partly secondary. (8) Convolute lamination is usually found combined with current ripple lamination and is a very common feature in most turbidite formations. (10) The maximum thickness can be at least 10 m. (11) Current rippled upper margins are found occasionally. (13) Sole markings are extremely frequent and vary from flute casts, groove casts, prod casts to bounce casts, typical burrowings, and less common kinds. However, ripple-mark does not occur as sole marking. (14) Shale or marl, poor in fossils, end the turbidites, capped with a hemi-pelagic stratum. The latter is not always present, because the time interval may have been too short or because the next current swept it away. This matter needs further study. (15) Current directions are normally sub-parallel over wide areas and through thick sequences. (1 7) Ancient turbidites have very seldom been traced beyond a single exposure, but their general appearance indicates that they must extend over wide areas, possibly with variable thickness. CAROZZI (1957) presented strong evidence for the tracing of individual beds over a distance of 3 0 4 km. (22) Estimated intervals for ancient turbidites range from one hundred to one million years, but centres around one thousand years. This is the same order of magnitude as measured for recent deposits.

For the identification of turbidites in ancient rocks considerable weight must be given to a number of negative features, namely, absence of winnowed sands, symmetrical sharp-crested wave ripple-mark of variable directions, reversing currents, beach structures, dune structures, swamps, river deposits, foreset beds, coarsely current- bedded laminations, megaripples, sun cracks, rain pits, tracks of land animals, salt pseudomorphs, reefs, biostromes, roots in situ, exclusively shallow neritic fauna in the fine grained beds, lack of lutites between the sandy beds, ripples in negative on the soles of the sand beds, etc. In fact, lack of all features indicative of proximity to sea level is typical of the great majority of well documented turbidite sequences. The possibility of shallow-water turbidites is dealt with on a later page (p. 18).

The present author has insisted throughout that no single feature is diagnostic of


turbidites, for each one can be encountered in deposits of quite different nature. It follows that it is seldom possible to be entirely sure whether a separate bed is a turbidite or not. There are few formations in which all the characteristics are present, let alone in which they have all been observed. But a geologist, who is all the time dealing with “convictions” or “reasonable certainties” of a lesser degree than possible in mathematics, can convince himself in many cases that he is examining the deposits of turbidity currents’.

The present writer claims to have proved in the foregoing pages, that there are a number of cases in which the emplacement of a flysch-like formation by turbidity currents cannot be doubted. But for each separate formation, the field-worker must assem- ble all evidence he can find to decide whether the rocks he is investigating may be or must be turbidites.

As it turns out that most formations containing turbidites are much like typical Alpine flysch - of the alternating type - as far as sedimentological features are concerned, in the sequel of this paper, where a non-committal term is preferable to “turbidite formation” the term “flysch-like formations” will be used. (Flysch of the kind consisting of shale or marl only, is not considered in this paper.)

The question arises what the deprhs were in which ancient turbidites were deposited. In the present seas, they have been found at all depths greater than 1,OOO m and on slopes of a few degrees to a few minutes. Obviously, no maximum can be given for the ancient formations, except for very small basins. Several lines of evidence indicate depths of the order of one or two thousand metres at the deepest end of ancient basins (KUENEN, 1959).

It is generally agreed that the accumulation of these formations was swift, and took place in unstable basins. In spite of this, a typical characteristic of most flysch-like formations is the uniformity in composition and stratification over wide areas and through thick sequences. The failure to build up above sea level, or to be replaced locally by a different facies, can be accounted for by assuming a deep environment in which a few dozen metres increase or decrease of depth made no radical difference in conditions on the bottom.

On the other hand, it is hard to imagine circumstances in a shallow, marine environment in which tectonic mobility of the floor and swift accumulation, held each other in such perfect balance that a uniform formation resulted.

The writer has pointed to the remarkable property of some flysch formations to thin away from the source, which feature is incompatible with the view that flysch-like formations of great thickness originated in shallow water (KUENEN, 1959; STANLEY, 1961). This remark finds support in the recently found thinning of the sediment away from land on the abyssal plain to the west of Canada (SHOR, 1962).

Taking all the sedimentological, paleontological and recent marine evidence into

This he can indicate briefly by using the term “turbidite”, in the same manner he uses diagnostic terms like “lava”, “tillite”, and “coprolite”, in contrast to descriptive terms like “andesite”, “loam with scratched boulders”, “rounded pellet”, and for the present problem “graded dark sandstone with laminated top”.

18 PH. H. KUENEN

account, the general conclusion is warranted that flysch-like formations have developed in bathyal (or abyssal) depths. They have evidently originated from slides on relatively steep slopes reaching to bathyal depths and these slides have been triggered by earthquakes, by oversteepening of depositional slopes, by storm surges, or by tectonic slope steepening. Liquefaction may have played a part.

However, although deep-water features are good additional evidence for the action of turbidity currents, and although the great majority of turbidite formations developed in bathyal depths, this does not exclude the possibility of turbidity currents acting in shallow water.

Daly’s original suggestion was that turbidity currents originated by storm-wave action on shallow shelves. Recently, PASSEGA (1962) has invoked the same mechanism. HEEZEN (1959, and earlier papers) has shown convincingly that rivers in spate (Magdalena and Congo Rivers) can produce turbitity currents flowing down into submarine canyons. VAN STRAATEN (1959) has presented good evidence for the deposition of sandy turbidites in a channel sloping 2” down the front of the RhBne delta in depths from 20-50 m. If such fluvio-marine turbidites occur in ancient formations, they should be found in channels and would not resemble flysch.

CUMMINS (1958) has suggested that certain continental sandstones can have been deposited by sheet floods, and that many of their features resemble those of turbidites. This is understandable because sheet flood and turbidity current are both highly charged flows of wide extent, appearing suddenly as foreign to the environment and dying out gradually. But it should be realized that a turbid sheet flood (or river in spate) is not a turbidity current because it is not flowing under stagnant water. But if such a flood were to cross a beach it would dive below the surface and become a turbidity current. A turbidite could then be formed at zero depth, in the manner that experimental turbidites are formed in tanks.

MANGIN (1962a) has recently discovered bird tracks in a Pyrenean flysch-like sequence. This remarkable finding is of great significance because it shows that some flysch-like sequences are of shallow-water origin, perhaps even continental. But according to DE RAAF (1964) there are half a dozen other exceptional features observable in this exposure, even rendering the term “flysch” open to question. (See Appen- dix, Note 7.)

ALTERNATIVE EXPLANATIONS FOR FLYSCH-LIKE ROCKS

Several authors have offered other explanations for the origin of flysch-like sequences. It has been suggested for instance that vertical oscillations from below to above wave base took place for each graywacke bed, or that each bed has been attributed to a tectonic uplift. Slow creep on the sea floor in bathyal depths is another suggestion. Invasion of oceanic currents over an oscillating bar into a shallow lagoon is yet another explanation, and “tsunamis” have also been held responsible (KUENEN, 1960b).

An endeavour to confront these hypotheses with the many sedimentary and paleon-


tological features usual in flysch-like rocks has not been made by the authors suggest- ing them. Any such attempt encounters many insurmountable difficulties. The analogy with deep-sea sands has been simply ignored. (See Appendix, Note 8.)

TURBIDITES AND FLYSCH

There is a strong link between the concepts of “flysch” and “turbidites”, but the terms are by no means synonymous. Much confusion has been caused by the many different meanings given to the term flysch. Most authors attach a certain orogenic connotation to it (“pre-paroxismal”), while others restrict the term to certain geological ages, or require certain petrographic features such as angular grains, unweathered minerals etc. Hence, the term “turbidite formation”, which is purely sedimentological and invokes a specific mechanism, cannot be equated with any definition of “flysch”.

However, it can be stated that the great majority of ancient turbidites have been encountered in formations that have previously been dubbed flysch (of the alternating type) or flysch-like Paleozoic and Precambrian formations. Besides, a large number, probably the great majority, of flysch formations are built up entirely or for the major part by turbidite sequences.

In seeking the mode of origin of flysch-type sediments, that is the mechanism of transportation and the environment, it is evident that the stratigraphic age, the subsequent tectonic history and the mineralogy of the grains are of no importance. The arguments based on such matters against the contention that turbidity currents have played a part can therefore bear no weight.

Furthermore, it is obvious that the known modern deep-sea sands differ from most of the typical flysch rocks in mor ethan one way. But these differences can be attributed to geographical setting because the present-day ocean basins in which nearly all deep-sea sands have been found are obviously very different from the geosynclinal basins of alpine orogenes. In general, slopes were steeper, shelfs narrower, supply more plentiful and of coarser grain, basins narrower and tectonically more active and waves slighter during periods of flysch sedimentation. Some graded deep-sea sands on flat floors contain gravel at their base, proving that turbidity currents are able to deposit such coarse material on basin floors. The fact that most flysch is on the average coarser grained than the average of deep-sea sands in no way militates against turbidity currents as the main factor in flysch deposition, but it does indicate a different supply and geographic setting.

Several authors have emphasized differences between samples taken in submarine canyons and flysch sandstones. Others have pointed out that the sea floor topography on the continental slopes is quite alien to the environment of flysch basins. However, it is much more pertinent to draw a comparison between the ancient rocks and the floors of present sea basins, and the similarity is then obvious. (See Appendix, Note 9.)

The claim that deep-sea sands are much cleaner than flysch sandstones may hold for the average calculated for many samples, but there are muddy deep-sea sands (see

20 PH. H. KUENEN

Fig.1) and clean flysch rocks. In flysch rocks, BOUMA (1962) found about 10 % smaller than 10 p, and much of this is not clay but calcite. Middleton measured only 4 % below 60 p in ancient turbidites. As noted above the clay may be partly secondary.

In some flysch formations one encounters dense, fine-graned limestone beds which have presumably been formed by precipitation. Various kinds of slumped deposits are also met with, like pebbly mudstones, sandy conglomerates, blocks that have slid (“Wild Flysch”) and slump structures. In most cases, these intercalations play a minor part between the beds that have the characteristics of turbidites and shales. They are to be expected in any formation deposited in deep water. Admittedly slumps can also form in shallow-neritic depths (“quake sheets”), so that they are not diagnostic.

DIFFERENCES BETWEEN TURBIDITES AND OTHER SEDIMENTS

In cases where all or most of the typical features, both positive and negative, listed above (pp.9,16) are found, it is safe to ascribe the sandy beds to the action of turbidity currents. However, there are also formations in which only part of the typical combination of features is encountered. The cause may be small size, small depth, or slight slope of the basin. Likewise, the nature of the available sediment may have been unfavourable or proximity to some source such as a delta may have been too close. The fewer typical features one encounters the less confidently can turbidity flow be invoked. But it is usually found that a well exposed, non-metamorphosed formation either obviously belongs to the category of turbidite sequence, or it is quite obviously of entirely different origin.

This statement requires amplification. In the first place there is one fundamental difference between normal turbidite formations and the great majority of other types of deposit. In the former there is a monotonous alternation of two kinds of beds: ( I ) the turbidites, in some cases with plenty of variation in grain size or in thickness, but always coarser than (2) the interstratified fine (hemi-)pelagic sediment of constant composition but variable thickness. In other types of deposit there may be either one, two, or more kinds of sediment, but if there are two or more, then the beds, as a rule, follow each other in arbitrary succession, or else cyclothems are developed with three or more types in a given sequence.

In the second place, in some turbidite formations beds may be intercalated that are obviously of quite different origin, such as aphanitic (precipitated ?) limestones. Moreover, most turbidite formations contain occasional beds that differ from the usual run and are of uncertain origin. In some formations there are two source areas that produce different turbidites.

In addition, there are a few rhythmic successions of non-turbidite nature, especially limestone-marl and shale-chert sequences, presumably both of bathyal depths. They are readily distinguishable from turbidites by the lack of graded bedding and of terrigenous or shallow-water material coarser than clay.

A major difficulty is caused by the occurrence of beds that appear to have been


formed by a mechanism related both to turbidity flow and to sliding. These beds are called fluxo-turbidites (DZULYNSKI et al., 1959). The characteristics usually shown are the absence of clear sole markings and of grading; greater and less regular thickness, and also coarser grain than neighbouring beds; and many shale pebbles. All transitions exist towards normal turbidites on the one hand, and towards obvious slumps on the other. Some instances are also known of normal graded beds containing a central part that is a pure slump with contorted slump balls and large boulders (see KUENEN et al., 1957). It is not improbable that certain graywacke formations lacking sole markings and grading but otherwise flysch-like, belong entirely in this category.

Now that field geologists, in recent years have become aware of the significance of sedimentary structures, more and more attention is being given to these features. What was first considered to be more or less typical of turbidite formations is now known to be less distinctive. In fact, shallow-water and continental deposits can show practically all the features that are typical of turbidites. Drag marks, flute casts, convolute lamination, graded bedding, current ripple mark, smooth stratification, alternation of shales and muddy sandstones, have all been observed separately or combined in red beds, shallow-water limestones, and other types of deposit (see e.g., DOEGLAS, 1962).

This renders the recognition of true turbidites more difficult. However, in the majority of cases showing some feature indicative of shallow water or emergence, there is more evidence pointing in the same direction. Then one is obviously dealing with a very shallow environment and it is unlikely that turbidites can have formed in these circumstances (except by diving flash floods). Convincing evidence for turbidites is only obtained if a sufficient number of positive structures is combined with the absence of the shallow-water features.

Turning next to deposits of a few specific types of environment, the obvious differences with turbidite formations can be emphasized. River-channel deposits, apart from lacking marine organisms, tend to be irregularly bedded, with channel scour and conspicuous cross-bedding. Flood plain deposits can contain plant remains in situ, desiccation cracks, weathered surfaces, blown sand, etc. and they lack marine fossils, while delicate lamination is destroyed by roots and burrowers.

Although there are apparently molasse formations with turbidites (KUENEN, 1959), the vast bulk consists of shallow water deposits, fresh brackish or marine, full of coarse current bedding, channel scour, wave ripple-mark etc. and lacking the regular alternation of coarse and fine typical of flysch. More obvious still is the contrast between flysch and coal formations, although the inorganic components are again sand and clay as in molasse and flysch.

Tidal flat and lagoon deposits usually show some of the following features: they are furrowed by channels, may show plenty of wave ripple-marks and megaripples. One encounters regularly alternating tidal current structures with opposing current directions, shell beds, conspicuous cross-bedding, well sorted sands. There is a lack of graded bedding and any coarse particles are restricted to channel bottoms. Fresh- and brackish-water organisms can be expected.

Delta deposits are stratified irregularly with a mixture of fresh, brackish and marine

22 PH. H. KUENEN

elements in arbitrary sequence as to grain size. They tend to contain well sorted beach or dune deposits, wave ripple-marks, swamp lignites, channel fills, strata with primary dip, and variable current directions. The foreset beds can resemble turbidites and may gradually merge into basin-floor turbidites.

Shelf deposits have several features in common with turbidite formations, such as a wide range in grain size and great horizontal extent. But on the shelf there is absence of vertical alternation of two contrasting sediment types, and there can be winnowed coarse beds, current indications of variable direction, ripple-marks of dune size, bioherms and biostromes, plenty of neritic and no bathyal organisms, and conspicuous cross bedding.

This brief review is not an exhaustive comparison between turbidites and other types of deposits. But the examples given show that after careful examination there can usually be little doubt whether a well-exposed formation belongs in the category of turbidites or not.

ACKNOWLEDGEMENTS

The author wishes to thank B. C. Heezen for advice and J. F. M. de Raaf for information concerning the Pyrenean flysch in which Mangin discovered bird tracks. L. M. J. U. van Straaten kindly provided information on a turbidite from the Adriatic. D. J. Doeglas made the mechanical analyses on which is based Fig.1 from material furnished by D. B. Ericson.

APPENDJX

A few side-lines and special aspects are treated in the following notes. The pages of the text to which they refer are indicated.

1 (p .7) . Pelagic sediments do not smooth topography

There is a slight tendency for pelagic sediments to be winnowed and thinned on elevations and to thicken in depressions, but in general, an even blanket is being spread over the deep-sea floor. As the smooth plains are due to drowning of rough topography in sediment and not to blanketing, this levelling must be attributed to the emplacement of deep-sea sands and not to the rain of pelagic matter from above onto a mountainous topography.

The combined thickness of the sands must add to several hundreds of metres at the least. Seismic prospecting indicates much thicker deposits in some basins and trenches. It should also be noted that seismic methods have revealed marked stratification below abyssal plains, but an unstratified cover on slopes and hills.


2 ( p . 7 ) . Sedimentation balance

The continental shelf off southern California is narrow. A number of rivers carry out t o sea large quantities of sandy sediment that is first dumped close inshore, and then the dominantly southerly currents and southerly beach drift carry this material along the coast. There is no direct loss off the shelf, no progressive up- or out-building of the shore, no retreat of the coastline, and no significant volume increase of coastal dunes. In other words, the supply is accurately balanced by yet some other kind of loss (INMAN and CHAMBERLAIN, 1960).

The nature of this drain was established several years ago by Shepard (see SHEPARD and EMERY, 1941). Accurate surveys of a few canyon heads that approach the beach to within a stone's throw were repeated at short intervals. This method revealed that rapid but gradual accumulation of sediment tends to be followed by sudden deepenings of the canyon heads. The intervals between losses vary but may be less than a year, in some cases several years. These data are amplified by observations and soundings at jetties reaching the heads of canyons; here, also, sudden deepenings have been observed. Calculation shows that in a very short time the canyons would be entirely choked if the contents were not passed on regularly right out into the basin beyond.

The nature of the transporting mechanism is not directly obvious, and might be slumping or creep alone. Sampling in these canyons shows sandy or even gravelly beds, some with grading, also in places where the slope is only a few per cent.

This favours the surmise that turbidity currents have been involved, because experimental turbidity currents produce graded beds of similar, slightly muddy sands and because no case is known of a slide having produced a bed of such nature without the intervention of a turbidity current.

In contrast, the bottom of canyons heading far out from the beach, where there is at present no supply of sand, are covered with fine sediment. For the sand carried out beyond the canyon on the flat basin floor, sliding is obviously not possible.

3 (p.9) . Creep

DILL (1961) has made the interesting discovery that the sediment in some, shallow submarine canyon heads is undergoing a slow, steady creep. The sudden deepening, found by Shepard, is proof that a much more catastrophic mechanism is also at work on the fill of canyon heads. On slopes of over 25" the sand can flow like a trickle of water. The longitudinal slope in the localities of creep is considerable, 10" or more (Dill, personal communication, 1963) and it cannot be likened to the slope of sub-sea fans or abyssal plains. Hence, these findings cannot be applied directly to the problem of deep-sea sands on basin floors. Most deep-sea sands are laminated and have current ripple structures, which obviously cannot be explained by creep any more than by slump.

Recently, OULIANOFF (1960a, 1960b) has called attention to the constant vibration of the sea floor by microseisms. He claims that this should cause sandy deposits to

24 PH. H. KUENEN

creep down-slope and spread out on the deep-sea floor, thus producing the deep-sea sands. Creep by experimental vibration of a sedimentation tank is invoked as support- ing evidence. Several objections can be brought forward: (I) The artificial vibration is much too powerful to simulate natural microseisms. That the latter are insufficient to cause creep is abundantly proved by the steep fronts of lake deltas and smaller marine deltas. (2) If the sands could creep across abyssal plains they should not be found buried long ago on the sub-sea fans with a slope ten times as great. (3) Globi- gerina ooze and other pelagic sediments are not subject to transportation down slopes less than 5” and no reason can be given why the deep-sea sands should be so much more mobile. (4) The upper part of a pelagic ooze is in a semi-liquid condition. It is entirely inconceivable that a layer of sand could creep across such a foundation without getting bogged down and without even showing any mixing. (5) The lamination of deep-sea sands disproves a creeping displacement.

4 (p.9) . Liquefaction

There is a close correlation between a number of submarine cable breaks on the one hand, and earth-quakes or river floods on the other (HEEZEN, 1959). “Liquefaction” followed by sliding have been invoked (TERZAGHI, 1956) in the case of earthquakes accompanied by delayed breaks (up to 14 hours later), but cables far out on the abyssal plain have been broken where sliding is impossible. The sudden softening of the sediment assumed to occur when liquefaction is thought to have taken place, would not be able to cause sufficient tension in a cable for it to snap, because cables are laid down with slack. In the case of a river flood leading to a cable break in the submarine canyon or beyond, liquefaction cannot be involved. (For further arguments see KUENEN, 1960, p.8). It is obvious that liquefaction cannot produce a deep-sea sand without the intervention of a transporting mechanism, because of the material in these sands that is foreign to the environment. Hence, liquefaction does not appear to give a satisfactory explanation for submarine cable breaks or deep-sea sands. On the other hand this mechanism could constitute a plausible cause for the take-off of those turbidity currents that are linked with an earthquake. Other mechanisms can also be invoked to start a slide, such as oversteepening (tectonic or depositional), quicksand formation, wave action, and river floods.

5 (p.9) . Bufington’s experiments

In a recent paper, BUFFINGTON (1961) has challenged the reality of high-density, high-velocity turbidity currents and has remarked in passing that normal marine currents are competent to carry sand across the deep-sea floor.

It is not the author’s intention to treat at length the velocities and densities of oceanic turbidity currents (the interested reader is referred to HEEZEN, 1959). However, a few remarks on Buffington’s paper are needed, because acceptance of his conclusions might cause doubts as to the importance of turbidity flow in the present oceans.

DEEP-SEA SANDS AND ANCIENT TURBJDITES 25

Buffington concedes the occurrence of low-density, low-velocity turbidity currents. But from his failure to produce a high-density turbidity current artificially by cascading a box-load of sludge onto a steep submarine slope, he concludes that high-density currents probably do not occur in nature. Since he also failed to set up a low-density current one might, with equal right (or lack of right), use his failure to disprove the natural development of weaker turbidity currents. These experiments have not solved the questions whether a dilute current requires a larger or a smaller volume than a concentrated one, or what the minimum size for a self-sustaining current is. Perhaps the failure of Buffington’s experiment, even if disappointing, is still understandable, because if a self-sustaining or accelerating current could be set up from so small a start as he was using, flows should be happening all the time, e.g., caused by whales. At any given locality of deposition, the interval is seldom shorter than one hundred years and usually much longer. This shows that the currents cannot be triggered easily. Whether one must jump to the opposite conclusion and follow Buffington’s claim that they must be of catastrophic size to exist at all, is doubtful.

Besides his experimental evidence, Buffington used a comparison with glowing clouds to amplify his doubt of high-velocity turbidity currents. He points to the com- paratively small distances these currents travel, but fails to appreciate the higher density and viscosity of water as compared to volcanic gases, a difference that must render an aqueous current much more efficient in holding particles in suspension. One must also consider the relatively small volume of materials below pebble size available in a volcanic cloud, and one might add in an avalanche. For these reasons possibilities as to size and persistence of a marine current must be far more favourable than for volcanic or avalanche flows.

In claiming that current velocities of one knot are competent to move coarse sand, Buffington appears to imply that marine (turbidity) currents need not exceed that speed in order to be able to deposit coarse deep-sea sand beds. But one should not overlook the fundamental difference between bottom traction, as dealt with by HjulstrGm, whom Buffington quotes, and the carrying of the same grains over a great distance in suspension. For the latter process something in the order of ten times the velocity is needed, and transport in suspension is just what a turbidity current must achieve for the hundreds of miles that it carries its load out along the Ocean bed. Any part of the load pushed along by bottom traction is lagging behind and no longer helps in propelling the current by its potential energy. Hence, a turbidity current must have carried its load of grains in suspension almost up to the point at which each particle comes to rest. This holds except for the very last stages of sand transport by turbidity currents in which lamination and ripple structures are often produced. In other words, if a coarse sand on an abyssal plain is attributed to a turbidity current, this flow must have had a velocity far in excess of that of rivers.

In the opinion of the present writer, all that Buffington’s experiments show is that, even under favourable conditions, a self-sustaining or accelerating turbidity current requires an initial volume in excess of what he was able to handle. The density (1.6) and velocity (50-80 knots) formerly claimed by the writer (KUENEN, 1952) for the

26 PH. H. KUENEN

Grand Banks turbidity current is possibly too high. However, the absence of bedding in the silty stratum found in the bottom cores taken later in this area, precludes the possibility of successive flows, and the grading is another powerful argument that all the sediment was carried and sorted in one vast body of water. The proven minimum volume of 100 km3 for the resulting turbidite, cannot reasonably be imagined as having moved down the continental slope otherwise than in a current that anyone would describs as of high density (that is, above the normal range in rivers), and of high velocity (that is, above the normal range in marine currents).

6 (p.15). Foraminifera as bio-sounders

The value of Foraminifera as evidence for depths has recently been challenged (RECH-FROLLO, 1962). The few anomalies cited cannot overthrow the evidence gained by recent studics of faunas as a whole, and in the case of flysch-like sequences there is no other explanation than difference in depth of habitat to account for the contrast between the organisms in the shales with those in the interstratified sands.

7 (p.18). Shallow-water graywackes

Mangin’s fig.2 strongly suggests that these tracks in the Basses Alpes (is this also a flysch?) are formed on a sharp-crested wave ripple-mark (MANGIN, 1962a). Rech- Frollo claims (see MANGJN, 1962b, p.36) to have seen several bird tracks in Polish flysch, but Ksiazkiewicz (personal communication, 1963) denies ever having seen or heard mention of bird tracks in Polish flysch. Such tracks are known, however, from East Carpathian Molasse. The bird tracks found to date appear to occur in sequences that are readily distinguishable from normal flysch rocks by features typically absent from the vast majority of flysch-like formations. It is here suggested as a working hypothesis that such shallow-water graded graywackes may be the deposit of sheet floods at the coast of an arid land.

Mangin’s discovery of shallow-water rocks resembling flysch is a significant contribution, but it does not affect the interpretation of the overwhelming majority of flysch-like rocks as bathyal deposits.

8 (p.19). Flysch of shallow origin?

Two recently proposed alternative hypotheses will be briefly discussed. In one, offered by MANGIN (1962b), it is first claimed that all the beds in flysch are subdivided into “unit sequences”, by which Mangin appears to refer to laminae. He even claims that the number of the units is more or less fixed at 10 or 20. Then he suggests a climatic rhythm acting in shallow water, each lamina representing a separate supply, usually annual. The grading is produced by a gradual fall-off in supply, during a climatic rhythm of several years duration. This hypothesis of Mangin offers only half an explanation, because after the sediment is supplied to the coast, presumably by


rivers with marked fluctuations, there is still some mechanism needed to carry and deposit the material in the marine environment. Because of the absence of reversing tidal-current bedding, wave ripple-marks, channels, coarse-current bedding, etc., it is hard to name a possible means of marine transportation in shallow water. Mangin does not explain why the impressive sole markings below the first coarse supply are absent below the subsequent laminae. Is there any mechanism active in shallow water that is able to spread sand in a sheet only a few millimetres thick with perfect uniformity over areas of many square kilometres? On these and many other problems (uniform direction of supply, convolute lamination, absence in flysch of build-up above the sea surface, unique types of burrowing, absence of beach features, etc.) the author of the climatic interpretation has not offered an explanation.

The chief reasons for challenging the climatic nature of the sequence in flysch-like rocks are the following:

( I ) The lamination so common in deep-sea sands cannot be attributed to a yearly rhythm, and must result from uninterrupted but short-lived flow. Hence, similar lamination in flysch is also attributable to current action. (2) The flat laminations of flysch-sandstones are in many cases seen to pass locally

into obliquely fore-set laminae of the current ripple type (Fig.2). In other words, here and there a lamina is locally split up into a dozen or more alternations that then come together again further along. Moreover, the majority of laminae are not continuous over distances of more than a few dozen centimetres or at most metres (Fig.2). Only the more conspicuous sudden changes in grain size or composition run the length of a normal exposure. In the theory of turbidity currents these major lamination planes can be attributed to more pronounced fluctuations in the current, for instance a few separate slides triggered by the same earthquake.

These characteristics of laminae form ample evidence that their development is the result of current action under more or less steady conditions of flow by local sorting in bottom traction. Variations in supply at the coast cannot be invoked to explain them. It is important to note that there is a fundamental difference with varves, which are continuous for dozens of kilometres and never split into oblique laminae.

(3) The explanation of the grading in a flysch sandstone by a climatic rhythm is based on a very unstable foundation. Hardly any meteorologists still acknowledge the existence of distinct and persistent climatic rhythms of less than a century. Neither the sun-spot cycle, Bruckner’s period or other suggested short periods have been convincingly documented. Although several authors have claimed rhythms in glacial varves (amongst others 2, 3, 6, 10, 11, and 90 years have been suggested) these are so indistinct that their existence is still a matter of doubt.

(4) If a rhythm has developed in the past, one would expect it to show a gradual increase and decrease, not a sudden maximum declining then through the years of the rhythm, such as is required to explain a graded bed. In any case, the random variations from year to year must always have been much more in evidence than the trend during a cycle. But with few exceptions the grain size within a graded bed declines regularly upwards, so that in Mangin’s explanation the yearly fluctuations are quite

28 PH. H. KUENEN

Fig.2. Two drawings from sections of turbidites illustrating the wedging shape of the laminae, as contrasted to the truly parallel laminae of glacial varves. The former are due to currents, the latter to climatic variations. A and B: Lower Ecca Sandstones, Permian; Laingsburg, South Africa. C: “Mar-

noso arenacea”, Miocene; F. Reno, Apennines.

subordinate to the trend over the years of a cycle. In this respect also the contrast with varves is most striking.

(5) A complete cycle must run from the base of a coarse bed through the covering shale to the base of the next coarse bed. If the sun-spot cycle were responsible there


should be 11 laminae in the sandstone plus shale. Actually Mangin finds about 10 or 20 in the sandstone so that during the following sun-spot cycle only fine shale has been deposited. In fact the rhythm, if it existed, would have to be much longer than the sun-spot cycle.

(6) If it is granted for the sake of argument that the supply from land showed a rhythm, why is it that the marine currents that carried and deposited the sediment showed an equivalent gradual decrease in efficiency? For the current that was strong enough to carry the coarse sand, deposited at the base of a bed, must have weakened so as to be able to drop the gradually decreasing sand sizes of a graded bed, and finally to deposit the silt at the top. A way out of this difficulty cannot be found by presuming direct deposition from the flood waters, because normal flysch is purely marine. Spreading fresh water on sea water does not carry medium or coarse sand. Abnor- mal flysch, however, may have originated from flood waters (see p. 18).

(7) Planar lamination in a graded bed can be produced experimentally by settling of a mixed load from an originally swift current set up in a circular moat and then left to die out gradually.

The other recent explanation for flysch is due to RECH-FROLLO (1962) who attributes flysch-like rocks to shallow-water sedimentation because of the muddy nature of the sandstones. She claims that muddy sandstones are produced by mixing between sandy and muddy areas on the shelf. If this suggestion is accepted, the typical flysch alternations of clay and sand must be attributed to the shifting back and forth of the zone of mixing over the place of the exposure. But only one of the two elements which are believed to mix is present, namely the mud; the other, the clean sand, has never been observed in flysch-like rocks, which rules out the hypothesis of mixing. The alternative suggestion, proposed by the same writer, that we are dealing with deltaic deposits, also meets insuperable difficulties. All shallow-water features and the wide variety of deposits and structures typical of deltas, are conspicuous by their absence from flysch-like rocks (see p.16).

9 (p.19). Composition ofjysch contrasted with deep-sea sands

Another source of misapprehension has resulted from comparisons between restricted occurrences of recent and ancient deposits. The differences thus found may be real but do not betoken a different mechanism of transport. Thus, SHEPARD (1962) has contrasted a few Alpine flysch formations that happen to be poor in Foraminifera to the Californian deep-sea basins with plentiful displaced tests. Others have quoted this remark as evidence against considering the flysch as a deep basin deposit. But there are plenty of Foraminifera in a number of flysch beds, e.g., in Poland and in the Pliocene turbidites of the South Californian oil basins. Hence the observed difference has no general significance and is not due to the environments being contrasted in any other way than biologically.

In another paper, the same author (SHEPARD, 1961) described several samples of deep-sea sands in which glauconite happens to be absent. This has also been quoted as

30 PH. H. KUENEN

evidence against a deep environment for flysch that is often rich in this mineral, but both Emery and Ericson have found deep-sea sands with plenty of glauconite.

Shepard also mentions in this paper that most of his samples were coarser at the bottom than at the top, and yet he says the description as graded sands is not accurate because of some alternations between coarse and fine or because of little change. This remark has also been used as evidence for a different origin of flysch sandstones. However, there are plenty of deep-sea sands with very marked grading, and converse- ly there are innumerable flysch beds with repeated or indistinct grading. Shepard’s description happens to be exactly what M I D D L ~ O N (1962) has found for the quartz grain of two ancient turbidites. There is “grading of size within each bed, in so far as the maximum size decreases regularly from the base to the top of the bed: the average size cannot be shown to vary regularly within beds”. Obviously, in this respect also, deepsea sands and ancient turbidites are the same.

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SHEPARD, F. P., 1951a. Transportation of sand into deep water. SOC. Econ. Paleontologists Mineralo-

221 -236.

ments. 11. Radiocarbon, 5 : 23-33.

51 : 1062-1078.

gists, Sfec. Publ., 2 : 53-65.

DEEP-SEA SANDS AND ANCJENT TURBIDJTES 33

SHEPARD, F. P., 1951b. Mass movements in submarine canyon heads. Trans. Am. Geophys. Union,

SHEPARD, F. P., 1961. Deep-sea sands. Intern. Geol. Congr., 21st, Copenhagen, 1960, Rept. Session,

SHEPARD, F. P., 1962a. Preface. In: A. H. BOUMA, Sedimentology of Some Flysch Deposits. A Graphic

SHEPARD, F. P., 1962b. Submarine valleys. J. Oceanog. SOC. Japan, 20 : 155-158. SHEPARD, F. P. and EPJSELE, G., 1962. Sedimentation in San Diego Trough and contributing sub-

SHEPARD, F. P. and EMERY, K. O., 1941. Submarine topography off the California coast. Geol. Soe.

SHOR, G. G., 1962. Determination of sediment thickness in the Gulf of Alaska using Rayleigh-wave

STANLEY, D. J., 1961. etudes skdimentologiques des gr& d’Annot et leurs 6quivalents latkraux. Rev.

STETSON, H. C . and SMTH, J. F., 1938. Behavior of suspension currents and mud slides on the con-

TEN HAAF, E., 1959. Graded Beds of the Northern Apennines. Thesis University of Groningen, Gronin-

TERZAGHI, K., 1956. Varieties of the submarine slope failures. Proc. Texas Con$ Soil. Mech. Found.

TRUMPY, R., 1960. Paleotectonic evolution of the central and ‘western Alps. Bull. Geol. SOC. Am.,

VAN STRAATEN, L. M. J. U., 1959. Littoral and submarine morphology of the Mane delta. Natl.

VAN STRAATEN, L. M. J. U., 1964. Turbidite sediments in the southeastern Adriatic Sea. In: A. H.

WINTERER, E. L. and DURHAM, D. L., 1962. Geology of southeasternVenturaBasin. U.S. Geol. Surv.,

32 : 405-418.

Norden, 23 : 26-41.

Approach to Facies Interpretation. Elsevier, Amsterdam, p. VII.

marine canyons. Sedimentology, 1 : 81-133.

Am., Spec. Papers, 31 : 171 pp.

dispersion: comments. Bull. Geol. SOC. Am., 73 : 1545-1546.

Inst. Franc. PPtrole Ann. Combust. Liquides, 16 : 1231-1254.

tinental slope. Am. J . Sci., 35 : 1-13.

gen, 102 pp.

Engr. 8th, 52 : 41 pp.

71 : 843-908.

Acad. Sci. - Natl. Res. Council, 2nd Coastal Geograph. Con$, pp. 233-264.

BOUMA and A. BROUWER (Editors), Turbidites. Elsevier, Amsterdam, pp.142-147.

Profess. Papers, 334H : 275-366.

NOTE ADDED IN PROOF

The same subject matter is treated in a somewhat different manner by W. D. NESTEROFF and B. C. HEEZEN in Revue de Gkographie Physique et de Gkologie Dyna- mique, 5 (2) : 115-127 (1962): Essais de comparaison entre les turbidites modernes et le flysch.

H. Holtedahl (personal communication) has taken a number of core-samples in Norwegian fjords. The bottom of the fjords is formed by a series of narrow abyssal plains at different levels, each fed by “pelagic” sedimentation and turbidity currents. The turbidites can be correlated from core to core. They start with conglomeratic material and grade upwards and horizontally into fine sediment. Single beds have been traced for 10 km. When fully examined this material from fjords will teach us much that can be applied to geosynclinal troughs because, in many respects, the comparison is closer than between those troughs and recent oceanic basins.

METHODOLOGY AND PALEOGEOGRAPHIC INTERPRETATION OF FLYSCH FORMATIONS: A SUMMARY OF STUDIES IN THE MARITIME

ALPS

D A N I E L J . STANLEY and A R N O L D H . B O U M A

Department of Geology, University of Ottawa, Ottawa (Canada) : Geological Institute, State University, Utrecht (The Netherlands)

SUMMARY

Reconstructing the paleogeography of flysch basins necessitates well-planned data collection programs from the start. It is recommended that information, collected conjointly in field and laboratory investigations, be recorded in a systematic manner with an eventual electronic computer program in view. Data should be easily translated into machine code for rapid selection, sequencing, grouping, calculation, and even automatic plotting on base maps. The recognition and delimitation of lateral facies variability patterns, more readily visualized when the processed data are presented in the form of isopachous, paleocurrent, and lithofacies maps, are the essential steps in interpreting conditions under which flysch sediments accumulated in basins. The results of megascopic and microscopic investigations of the Annot Sandstone flysch in the French and Italian Maritime Alps are highlighted, and solutions to both general and specific paleogeographic problems are illustrated.

METHODOLOGY

Introduction and purpose

In this epoch of geological quantification, it has become apparent that usage of abundant data is a prerequisite for reconstructing the geological history of basins. It can be shown that judicious selection and processing of logically itemized data are equally rewarding when dealing with flysch’ deposits.

Within the last decade, the number of detailed paleogeographic studies of flysch

The termflysch is used loosely in this text and follows the general definition by KUENEN (1958, p. 329): “A thick sequence of pre-paroxismal marine geosynclinal sediments, consisting of an alternation of evenly stratified shale and muddy sandstone (graywacke, etc.) and showing at least a moderate amount of graded bedding. The maximum grain size in the graded bed is 5-10 cm diameter. Coarser material is not graded and subordinate in amount. Transitions to or alterations with calcareous types also occur. Geological age is ignored.”

METHODOLOGY AND PALEOGEOGRAPHIC INTERPRETATION OF FLYSCH FORMATIONS 35

carried out in different portions of the geologic record has increased notably. Each of these studies was conducted in a somewhat different manner depending upon the purpose of the study, the particular characteristics of the flysch deposit in question, and the general geologic background and interest of the geologist carrying out the study. One of the purposes of this paper is to review some of the more basic lithologic parameters which should be taken into consideration during the investigation of any

Fig.1. Outcrop of typical flysch, the Annot Sandstone formation in the Tete de Gorgias-Vallon de 1’Estrop region above the village of Esteng in the French Maritime Alps. The photograph illustrates the thick (over 600 m in this particular locality) and monotonous nature of the formation as well as the regular alternation of distincly stratified, graded sandstone and silty shale beds which commonly

comprise flysch basin deposits.

“flysch-type” formation. Many of these variables can be measured and recorded regardless of the specific lithology of the formation or the type of study undertaken. All of the variables and the methods of measuring them mentioned in this paper are known and established in the literature. In their work with flysch in the Maritime Alps, the authors have found that the parameters most useful in determining paleocurrent trends, paleoslopes, source areas, and the like are usually among those which are simplest to measure in the field and the laboratory. These are outlined in the following text.

Methods for investigating flysch should be planned in advance so as to minimize both errors and the time while recording data in the field or in subsurface work. These

36 D. J. STANLEY A N D A. H. BOUMA

methods should also assure that the geologist obtains data which can be compared statistically from section to section or from core to core (BOUMA, 1959).

Furthermore, data collection should be planned with an eventual computer program in mind. The advent of high-speed digital computers and other electronic processing equipment now available to the geologic profession means that a whole new field of data processing must be considered. Data collected in an organized manner can be readily transferable onto punch cards for permanent filing, rapid retrieval, and machine processing.

One of the primary reasons for collecting all of this information in the first place is to select or sort out the important mappable variables and plot them on isopachous, isolith, lithofacies (usually in the form of percentage and ratio maps), and paleocurrent maps. Maps such as these are essential tools used not only in defining lithofacies and recognizing their position in the paleobasin but also in predicting lithologic trends and variations within these same basins. It is believed that paleogeographic interpretations of flysch deposits should be attempted only after these lithofacies have been rigorously delimited laterally and vertically.

Recording3eld and subsurface data

Selecting recording procedures While the authors were studying the thick, monotonous sections of repetitive sand-

stones and shales (see Fig.l), it became readily apparent that the preparation of note- books prior to a trip to the field would be invaluable. Much time-consuming writing will be spared the geologist as he critically examines hundred or even thousands of repetitious sequences of alternating sandstone and shale beds1 (or limestone and marl, siltstone and mudstone, or other repetitious sequence of evenly bedded, graded rocks comprizing a flysch). Careful preparation will allow more sections or cores to be

Fig.2. Schematized drawing to show the difference between the terms “bed” and “layer”, as used by the authors in their field work.

In this paper, the term bed is differentiated from the term Iuyer for practical purposes only. A layer is a stratified sedimentary unit in which the maximum grain size decreases from the bottom to the top of the unit. The layer theoretical shown in Fig.2 includes sediments grading upward from coarse sand to silt and mud. Beds are recognized within the thicker layer as units which have distinct or nearly distinct stratification limits or breaks, usually due to a change in grain size and differential weathering of the layer. In the example above, both the sand and silt-mud strata making up the layer are desig-

nated as beds.


examined during the limited time available to the geologist; and, furthermore, a note- book assures that a sytematic check of all variables will be carried out. In a quantitative or semiquantitative study such as proposed here, it is as important to record the absence of a particular character as it is to record its presence.

To facilitate the selection of data obtained from the field or the subsurface, collected information can be grouped under organized headings or fields for rapid retrieval. One suggestion would be to use as a field book a hard-covered ledger with pages divided into numerous columns and square spaces so that as one proceeds upward through the section it becomes possible to record the specific characteristics of each individual bed examined. Headings for each variable to be studied may be simplified to reduce space by assigning a code designation. In this fashion data may be recorded by means of a simple check, number, letter, or symbol code, or by graphic presentation in the field book (BOUMA and NOTA, 1961; BOUMA, 1962).

A field-book log sheet actually compiled directly in the field is illustrated in Fig.3. Both graphic and symbol methods of recording data were utilized in this example. An explanatory symbol legend for this particular log sheet has been compiled in Fig.4.

The simplicity of coded or graphic symbols enables them to be translated rapidly into machine computer code. This is of major significance since there are, in the case of most electronic data cards, a total of 960 possible punching positions. Such cards, usually divided into 80 columns under which are 12 possible punching positions, are of tremendous advantage in quantitative studies where so much data are recorded from every bed examined. Information can be transferred from the field book onto these small permanent records in an orderly and meaningful fashion. Automatic processing procedures such as duplicating, machine verifying, sequencing, grouping, selecting, group printing, calculating, gang punching, etc., are momentous time savers. A code- system legend book in which all symbols used are illustrated and precisely defined, is essential. It has to be kept up-to-date.

Observations made in the field can be grouped into several suggested categories; these are briefly described below and are outlined in Tables I, 11, and 111. It should be stressed, however, that the tables included here are by no means complete nor are they intended to be. They are simply proposed as illustrations of the type of data to be considered in flysch studies. As every geologist knows, no two identical lithostratigraphic problems are expected to be encountered and each worker will find a system most practical for his own specific purposes.

General information grouping Digital data can be recorded on cards, tape, or on magnetic recording media. For

convenience, primarily easier visual presentation, the following discussion will be limited to the punch-card method of data processing.

Several data-processing cards may be prepared for every bed examined in the field. The minimum information of a general and diverse nature required for the permanent record is punched on a master card. The reader is referred to Table I and F i g 5

Each card must have an identification field for rapid retrieval. On the master card

SIfRVEVOII' A. H. Souma DATE: 6-/'-6U STRATIGRAPHIC U N I T W Pe/h-&H&dd LOCATION OF SECTION iOR BORING): Pe)*-&c. (A-MJ COD1 OF SECTION: 6 (FJ

7

Fig.3. Example of a field-book log sheet on which both graphic and symbol methods of data recording have been utilized (modified after BQIJMA and NOTA, 1961; BOUMA, 1962).


shown, each bed examined receives a double number designation comprising a section or boring log code followed by a bed number. The numbering of beds would custom-

FIELD-BOOK LOG COLUMN HEADING

THICKNESS

N U M B E R O F B E D

LITHOLOGY

STRATI FlCATlON

BEDDING PLANE CONTACT

SEDIMENTARY STRUCTURES AND OTHER PROPERTIES

CURRENT DIRECTION

INDURATION

REMARKS

EXPLANATORY SYMBOLCODELEGEND

INTERVAL 92- 2 s CM ABOVE BASE O F SECTION

BEDS NO. 6 THROUGH 17 ARE ILLUSTRATED I N F I G 3

1 7 1 SANDSTONE .. .. 1-1 L.

SANDY TO SILTY SHALE .. . SHALE

VERY SHARP, F L A T CONTACT

DISTINCT, .FLAT CONTACT

GRADUAL TRANSITION (RANGE OF TRANSI- TION (0.1 CM)

GRADUAL TRANSITION (RANGE OF TRANSI- TION 0.5-1.0 CM)

GRADUAL TRANSITION, BARELY VISIBLE

IRREGULAR CONTACT

UPPER BEDDING PLANE NOT EXPOSED

UPPER AND LOWER BEDDING PLANES NOT EXPOSED

GROOVE CASTS

STRIATION (VERY THIN GROOVE CASTS)

LOAD CAST

BURROW

GENERAL ORIENTATION OF SEDIMENT TRANS- PORT (NNE-SSW) EXTENDED I N TWO COMPASS QUADRANTS: SPECIFIC DIRECTION OF PALEOCURRENT DOUBTFUL

INDURATION TYPE 4: GRAINS CANNOT BE

t SEPARATED WITH KNIFE; PRESENCE O F CaCO, CEMENT INDICATED BY HACHURES

~~~~

w SCOUR AND F I L L STRUCTURE; FILL LAMINA- TIONS ARE P A R A L L E L T O BASE OF BED

7205L POSITION AND NUMBER OF SAMPLE

3 PH. 2-15 HORIZON PHOTOGRAPHED AND PHOTO RECORD NUMBER

Fig.4. Explanatory legend to accompany Fig.3 (modified af€er BOUMA and NOTA, 1961; BOUMA, 1962).

40 D. 1. STANLEY AND A. H. BOUMA

TABLE I

INFORMATION OF A GENERAL NATURE TO BE PUNCHED ON THE MASTER DATA CARD^ ~~~~~ .

Field data categories Card column -

Identification number of bed section or boring log code bed number sequence number of data card

Geographic location of bed quadrangle letter and number designation X-axis coordinate Y-axis coordinate

Date surveyed

month year

Attitude of bed strike reading (example N 30" W) dip reading (example 45" NE)

day

Bed plane contact Degree of exposure Thickness of bed

in meters in centimeters

faulted folded jointed boudinated vein filled

General shape of bed channel fill wedge blanket finger other

Sample record thickness of interval sampled at base of bed thickness of interval samples in mid-portion of bed thickness of interval sampled at top of bed

total number of photographs taken permanent record of photos

total number of sketches made permanent record number of sketches

Deformation affecting bed

Photo record

Field sketch record

Other information to be added to master data card

(1-9) 1-4 5-8 9

(10-23) 10-15 16-19 20-23

(24-29) 24-25 26-27 28-29

(30-37) 30-33 34-37 (38) (39)

(40-43) 40-41 42-43

(44-48) 44 45 46 47 48

49 50 51 52 53

(54-56) 54 55 56

(57-61) 57

58-61 (62-66)

62

(49-53)

63-66 (67-80)

See text and Fig.5. -

arily start from the base of the section. As an example, let us assume that a card bearing the number 12-42 under card column heading 1-9 in the identification field had dropped out of the file accidently. These numbers indicate that this card represents

METHODOLOGY AND PALEOGEOGRAPHIC INTERPRETATION OF FLYSCH FORMATIONS 4 1

the forty-second bed observed above the base of section bearing code number 12. It can be replaced either mechanically or automatically in the correct stratigraphic sequence between cards 1 2 4 1 and 1243. A numbering system must be flexible enough to take into account the portions of the section covered by debris or vegetation or portions missing or repeated because of structural displacement.

A sequence number column added to the identification field permits the machines to recognize the type of data punched on any card. Position 1 under column 9, for instance, could represent the master card containing information of a general nature (see Fig.5). Other punch positions under column 9 are reserved for other types of data pertaining to the same bed (position 2 representing detailed megascopic observations collected in the field, position 3 representing microscopic data obtained in the laboratory, etc.).

The date and geographic location data on the master card are also available for identification purposes.

The strike and dip of a bed are essential information for general mapping as well as for determining the original direction of paleoccurrents. Vectorial information obtained from sedimentary structures, when measured on a tilted bed, must be corrected by rotating the bedding plane back to its original near-horizontal position.

A problem as yet unsolved is whether the shale sediments lying above a graded sandstone were deposited from the "tail" of a turbidity current or were deposited independently from the normal pelagic rain of sediments after deposition of the turbidite. For this reason, data referring to the type and form of bedding plane and contact between beds may be of importance in genetic interpretations. Punched codes under this column could designate sharp contact, rapid transition, gradual transition, irregular contact, etc. (see Fig.3,4).

For most statistical computations it is necessary to select information which has been recorded most reliably. This could imply, for instance, data extracted from those beds in a section which are most completely exposed. For this reason, a column should be reserved for coding the degree of bed exposure.

The bed thickness field is broken down into meter and centimeter columns for greater manipulation.

The degree of bed deformation is the type of megascopic information which can be related with microscopic analysis of samples (degree of metasomatism, presence of certain authigenic minerals and cements, etc.).

Statistical studies of bed shape variability are basic to any regional lithofacies analysis and must also be included in this category. Special columns should also be reserved for sample, photographic, and field sketch records for they have a tendency to accumulate rapidly and become confused. Coded information concerning the stratigraphic interval sampled or photographed should also be punched under these columns. Samples should be oriented when at all possible.

Megascopic properties of beds Numerous sedimentary structures and stratification properties associated with

Fig.5. Example of a layout for a master data card (see text).


flysch formations have been recognized and defined. Although the geologist may be on “speaking terms” with flysch terminology and associated structures, he is faced with the problem of recording the wealth of data that can be extracted from each bed. Since a great deal of paleogeographic interpretation is to be made from such megascopic data, it is necessary to prepare sufficient columns both in the field book and on data cards (Table 11, Fig.3, 6).

The information collected in this category is too extensive to be reproduced in toto on the master card; additional punched cards are required. The identification field of every card pertaining to the same bed will be identical for rapid retrieval. Only the punched sequence number of the additional detailed cards (2, 3, 4, . . . n) will vary from the master card sequence number (punched in the 1 key punch zone, as described earlier).

Readily observable factors, such as the degree of weathering, color, and structures, may be recorded without difficulty. On the other hand, data pertaining to grain size or mineralogical composition are at best tenuous in cursory field work. However it i s still recommended that such data be recorded as the collecting samples from every bed is virtually impossible. Because of the difficulties involved in describing and quantifying grain size and composition in the field, each term employed must be carefully defined and utilized consistently from the start.

It is possible to anticipate certain structures almost always invariably associated with flysch and provide column headings for them on the retrieval forms (see Fig.6). This does not imply, however, that every flysch facies is characterized by identical sedimentary properties. Each flysch deposit is distinguished by a distinct “association” of sedimentary characteristics. Nor should it be assumed that these sedimentary structures are limited to flysch deposits. They are not, for the most part.

Additional punching positions should be provided on the data cards for the number- ous other structures not listed here but which have been recognized in various paleocurrent investigations. The reader is referred to a more complete list of symbols for sedimentary properties, including structures, compiled by BOUMA (1962, pp.5-22).

Directional properties from sedimentary structures Linear and planar sedimentary structures, easily measured by compass, are among

the best tools for reconstructing the historical events of a basin. If time allowed for only one method of determining the direction of sediment transport and of predicting the size, shape, and location of beds within a basin, the authors would unhesitatingly choose the numerous linear primary directional structures found at the base, at the top, and within individual stratum.

Numerous structures associated with flysch units have been described within the last decade (KUENEN, 1953, 1957; CROWELL, 1955; BIRKENMAJER, 1958; DZULYNSKI and SLACZKA, 1958; TEN HAAF, 1959; DZULYNSKI and SANDERS, 1962; DZULYNSKI, 1963). The majority of structures described in these and other papers are associated with flysch regardless of age or geographic location. The linear and planar tendency of many such structures records the orientation of paleocurrents as well as the orientation

44 D. J. STANLEY AND A. H. BOUMA

TABLE I1

EXAMPLES OF DATA COLLECTED IN THE FIELD OR FROM BORINGS WHICH COULD BE PUNCHED ON

ADDITIONAL DATA CARDS]

Field data categories Card column

Identification numbers of bed section or boring log code bed number sequence number of data card

Degree of weathering Color Approximate grain size (in Q units)

boulder cobble pebble coarse sand medium sand fine sand silt clay

nonclay clay

Field classification conglomerate sandstone siltstone shale limestone dolomite chert evaporite coal

graded bedding lamination channel fill

internal load casts sole markings sand dikes

inclusions concretions fossils lignite other

Maximum pebble or grain size (in mm units)

Structures and other properties

slump

stylolites

(1-9) 1-4 5-8

9 (1 0) (1 1)

(12-19) 12 13 14 15 16 17 18 19

20 21

(22-30) 22 23 24 25 26 27 28 29 30

(31-43) 31 32 33 34 35 36 37 38 39 40 41 42 43

(20-21)

See text and Fig.5.

of the paleoslope or basin floor at a specific geographic location. When possible, both symmetric and asymmetric sedimentary structures should be measured conjointly. The general orientation of slides, suspension flows, or traction currents may be determined

Fig.6. Example of a layout for a detailed data card to accompany the master card (see Fig.5).

46 D. J. STANLEY A N D A. H. BOUMA

Fig.7 (upper) and Fig.8 (lower). Legends see p.47.


from lineation patterns of groove casts, striations, elongate pebbles, or symmetric ripple marks (Fig.7). Common asymmetric structures such as flute casts (Fig.8), prod casts, forset laminations, and cross-bedding inclinations can be used to obtain the actual directions of current movement.

The sedimentary structures most often encountered are listed in Table 111 where they are subdivided into three general groupings (modified after CROWELL, 1955).

TABLE 111

DIRECTIONAL DATA TO BE COLLECTED FROM SEDIMENTARY STRUCTURES'

Field data catgyories

Structures on base of bed (sole markings) flute casts groove casts lineation microchannel structures oriented inclusions or pebbles

Structures within beds cross-bedding foreset lamination convolute lamination oriented inclusions, pebbles, fossils, etc.

asymmetric ripple marks symmetric ripple marks oriented inclusions, pebbles, fossils, etc.

Structures on top of bed

Card column

(44-58) 44-46 47-49 50-52 53-55 56-58 (59-70) 59-61 62-64 65-67 68-70 (71-79) 71-73 7476 77-79

See text and Fig.5.

These groupings are based upon the position of the structures in the beds and are listed in the respective order: those on the base of beds (known as sole markings in flysch literature), those within beds, and those on top of beds. Recording the direction of the structures on data cards Sould be handled as shown in Fig.6. Three columns have been allotted for the azimhh direction. under every sedimentary structul;e field. Every time a direction is recorded, either the number 11 or the number 12 positions in the zone punch area must also be perforated. When the orientation given represents the downcurrent direction (on the basis of foreset lamination, flute casts, or other asymmetric structure), the number 11 punch position could be perforated. Punching position number 12 could, in turn, represent a general orientation direction which must be

Fig.7. Groove casts on the sole of a broken Annot Sandstone block. The general orientation of paleocurrents can be obtained from this type of linear structure (the direction must be extended in opposite

compass quadrants).

Fig. 8. Linear asymmetric structures, such as flute casts on soles of graded beds, are useful paleocurrent indicators. The flutings in this photograph indicate that clastic materials were transported from

the lower left to the upper right of the broken Annot Sandstone block.


extended in opposite compass quadrants (on the basis of elongate pebbles, groove casts, etc.).

Additional punching positions on data cards would most likely be required to record the range of direction variation obtained on any one bed, the total number of markings observed, the dimension of the structures, the degree of visibility, and the like.

Laboratory and microfacies investigations

Sampling and recording procedures Laboratory sample analyses should, whenever possible, supplement data collected

in the field or in subsurface work. Critical lithologic changes along the depositional strike and dip are often missed when laboratory observations are neglected. Microli- thologic studies are used to interpret more precisely the source areas and associated parent rocks which gave rise to the sediments transported into a flysch basin. Investiga- tions of this kind are used to obtain a better understanding of the transport mechanisms as well as to determine the physiochemical conditions which affected the depositional environment during and after sediment accumulation. Microscopic studies become particularly invaluable in subsurface work where fewer parameters are available for lithofacies mapping.

Important microscopic variability is to be expected within most graded beds regardless of thickness. There is a direct relationship between position of the sample in the bed, grain size, sorting, and mineralogy (GUBLER, 1959; STANLEY, 1963,1964). Random sampling must therefore be avoided if coherent results are to be obtained. Samples should be oriented and collected in a consistent manner (such as from the base, mid- portion, and top of the bed). The position of the bed from which the sample is collected should be recorded on the data card (see Table I, Fig.3 and 5).

The authors have found it useful to subdivide the laboratory schedule into four major categories: granulometry, fabric, mineralogical composition, and fossil determination. Variables most commonly examined are listed in Table IV. In most cases, samples can ordinarily be examined with standard laboratory equipment and techniques. More specialized procedures, including X-ray diffraction, electron microscopy, and chemical analysis, are at times necessary to supplement petrographic examinations of critical samples or cores.

The relztive importance of each parameter is again dependent upon the scope of the problem, nature of the flysch, and availability of time and equipment. Data collection in the laboratory should again be planned systematically so that the information recorded can eventually be electronically processed. The identification fields of laboratory data cards must be identical to the master punched data card so that all of the information pertaining to one bed can be selected, sequenced, and grouped.

Flysch and displaced faunas A special word of caution should be added with reference to the fossils occasionally


TABLE IV

SCHEDULE OF LABORATORY SAMPLE ANALYSIS

Granulometry Grain size distribution

maximum grain sue weighed mean, median, modal grain size first and third quartile, percentiles other size parameters

roundness index sphericity index

Grain shape

Surface texture

Orientation of elongate grains Grain imbrication Grain-to-grain relationship

Mineralogical composition Light mineral identification Heavy mineral identification Cement (or matrix) Disseminated organic matter Chemical analysis X-ray diffraction

Taxonomic determinations of microfossils Degree of abrasive wear (or other indications of reworking) Age determination (if not reworked) Palynological examination

Fabric

Microfossils and other organic remains

encountered in graded and slumped beds. Fossils found in the sandstone or conglomeratic layers, never common, generally show some degree of wear and abrasion (see Fig.9) and generally can be related either to shallow or nearshore environments or to

Fig.9. Poorly preserved Eocene Nummulites test reworked with other grains in a sample of coarse h o t Sandstone, uppermost Eocene in age in the vicinity of Annot, Basses-Alp, France; thin-

section magnification approximately x 8.


faunal associations in older underlying formations. There is much evidence that fossils in coarse sandstone “turbidites” are accidental, that is to say, either displaced from other depositional environments or reworked from older horizons (NATLAND and KUENEN, 1951; F’HLEGER, 1951; STANLEY, 1961a; BOUMA, 1962; SHEPARD and EINSELE, 1962). This is to be expected in a situation where shelf or nearshore clastic sediments have been transferred toward the deeper portion of the trough by gravity transport mechanisms such as suspension flows and slides.

The fossils found in the finer nongraded siltstones and shales are perhaps more significant indicators of time and depositional environment. Organisms present in the finer-grained lithologies usually indicate more open and deeper marine environments than do the fossils embedded in the coarser-graded horizons. It is believed that such forms settle out of suspension along with other pelagic sediments as a continuous rain over the basin floor. For this reason it is presently believed that more reliable information is to be extracted from microfossils embedded in pelagic sediments than from those found in the coarser graded beds. Furthermore, it is expected that detailed palynological investigations of finer flysch sediments would also provide rewarding results.

PALEOGEOGRAPHIC INTERPRETATION OF FLYSCH BASINS

Processing raw data

The type of data described in the preceding text is collected so that the lateral (geographic) and vertical (time) positions of the interfingering facies’ within the flysch unit under study can be delineated. Recognizing these facies is the principal step in reconstructing the geologic history of a paleobasin.

A carefully planned computer program can be used in the selection and evaluation of the more significant mappable variables. By using punch card machines, it is possible to perform addition, subtraction, multiplication, and division computations rapidly with the data recorded in the field and laboratory. Elevation points, total thicknesses, averages, percentages, and ratios may be computed rapidly and transferred automatically onto base maps. Processed data are then prepared for visual presentation, usually in the form of lithofacies maps on which contoured isolines connect data points of equal value. It then becomes the responsibility of the geologist to interpret the lateral variability and trends of the flysch deposits from the contour patterns.

In general, parameters are mapped individually on the base map. To do this, it is necessary to obtain a single numerical value for each datum point. This generally implies that all of the data pertaining to a specific parameter in a stratigraphic section or boring log are to be reduced to a single value by calculating averages, percentages, ratios, and the like.

exhibits ch2racters significantly different from t h x e of other parts of the unit” (MOORE, 1949). A facies can be defined as “any areally restricted part of a designated stratigraphic unit which


The following are typical examples of parameters which may be averaged: thickness of sandstone or shale beds; mean paleocurrent direction from primary sedimentary structures; mean orientation of elongate grain alignment; average size of pebbles in conglomerate samples; mean or modal grain size in sandstone samples; values of average grain shape or roundness.

Percentages, such as the following, are also easily plotted: graded beds; conglomerate-containing beds; channel-fill beds; slumped beds; sandstone beds exhibiting sole markings; relative percentages of either light or heavy minerals; relative percentages of matrix or cementing material; relative percentages of organic carbon and CaCO,.

Ratios can be handled in similar fashion. Ratio values commonly plotted are: clastic ratio; sand/shale ratio; sandstone/conglomerate ratio; graded bed/nongraded bed ratio; sedimentary pebbles/plutonic-metamorphic pebbles ratio; quartz/feldspar ratio; resistant heavy minerals/nonresistant heavy minerals.

Computation of quartile and moment measures can also be handled automatically using the grain size data collected in the laboratory and recorded on sample data cards. This includes the solving of dispersion (or sorting), standard deviation, dissym- metry (or skewness), peakedness (or kurtosis), and similar formulae (INMAN, 1952).

It is often necessary to determine the degree of relationship existing between different parameters. Several examples may be cited: thickness of sandstone bed and degree of graded bedding; thickness of sandstone bed and grain size; degree of coarseness and type of sole markings; grain size distribution and mineralogical composition; grain size distribution and carbonate cement content.

There is almost no limit to the work that can be programed to obtain data for con- touring maps. Electronic plotting equipment can be used to interpolate points automatically and directly print contoured structural, isopachous, and lithofacies maps, greatly reducing both error and time.l Fortunately the number of published articles treating data processing, and the selection of mappable variables by regression procedures and factor analysis are rapidly increasing. Papers of direct application along these lines are available (KRUMBEIN and SLOSS, 1958; FORGOTSON, 1960; AAPG RESEARCH COMMITTEE SYMPOSIUM, 1962; KRUMBEIN, 1962a, b).

The Annot Sandstone: an example of paleogeographic reconstruction

The former geography of a basin becomes apparent when selected isopachous and lithofacies maps, just described, are compared and superimposed on each other. Cer- tain patterns and trends will appear to stand out clearly on many of these maps. It becomes essential to critically evaluate these laterally varying lithological patterns

“Computer-automatic plotter systems can accept locations and data values for large numbers of points and produce contoured maps based on the input values.

For a map containing 1,ooO irregularly spaced data points, several months would be required to perform the computations on a desk calculator to sepsrate the observed data into regional and local components. These calculations are performed on the IBM 650 in one hour and on the IBM 704 in two minutes.” (FORGOTSON, 1962, p.42.)


when interpreting such factors as the direction of paleocurrents, the geographic positions of shorelines, paleoslopes, uplifted source areas, and depositional environments, the bathymetry and topography of the basin, the mechanisms by which sediments are transported, the zones where sediments of different provenance mix, and the like.

Two investigations of the Annot Sandstone flysch formation, Upper Eocene- lowermost Oligocene in age, were conducted independently in adjoining regions of the French and Italian Maritime A1ps.l One of these studies (STANLEY, 1961a) dealt with the regional lithostratigraphic characteristics and paleogeography of the formation in an area covering approximately 5,000 square kilometers in a region west, northwest, and north of the Argentera-Mercantour Massif on the Franco-Italian border (area A, Fig.10). The Annot Sandstone east of the Tin& River and south of the

Fig.10. Map showing the location of the Annot Sandstone Formation (in stippled pattern) and adjacent crystalline massifs (delineated by hachures).

Argentera-Mercantour Massif were examined by BOUMA (1962). This latter area is delimited in area B of Fig. 10.

These two studies were prepared as doctoral theses and defended in June 1961 before the geologic faculties at the University of Grenoble, France (Stanley) and at the State University at Utrecht, The Netherlands (Ebuma). Both theses have been published (STANLEY, 1961a; Bourn, 1962).


This sequence of alternating sandstones and shales lends itself particularly well to paleogeographic studies: these rocks are unusually well exposed, thick (100-650 m), quite continuous laterally, and less tectonically disturbed than most similar flysch units in this part of the Alps (see Fig.1). Classic regional geologic studies (BOUSSAC, 1912; GOGUEL, 1936; DE LAPPARENT, 1938; FAURE-MURET, 1955) established the stratigraphic and structural framework of the region in question. The availability of these

Fig.11. Highlights of results obtained from the megascopic field examination of t h e h o t Sandstone Formation (modified after STANLEY, 1961a; Bourn, 1962).

Diagram 1. The Annot Sandstone outcrops are shown by stippling. The location of the Argentera- Mercantour Massif (A) the Barrot Dome (E), and the Esterel Massif (C), is shown by hachures. Smaller structural domes, Remollon and Saint Etienne d'AvanWn (0) and Barles (E), were exposed to the west and are represented by triangles.

Diagram 2. The arrows indicate the direction of sediment transport as inferred from sedimentary structures. Three major directions are involved. Sediments were brought in from south to north, from west and northwest to southeast, and from east toward the west and northwest, away from the Argen- tera Massif.

Diagram 3. This diagram shows thevariation of the sand-shale ratio. The arrows indicate that the ratios decrease from south to north, from west-northwest to east, and from east to west and northwest.

Diagram 4. The arrows indicate the general directions in which sandstone beds thin. Diagram 5. The arrows point in those directions where the number of conglomerates and conglo-

meratscontaining beds decreases. Diagram 6. Dots represent the position of conglomeratescontaining pebbles with diametersexceed-

ing 10 cm. Diagram 7. Dots spot the locations of the slumped beds in the basin. These submarine slumped

layers, unlike turbidites, are poorly stratified, nongraded, contorted, dark argillaceous deposits which often enclose large rounded pebbles and reworked sandstone and shale fragments.

Diagram 8. This sketch indicates the location of sandstones deposited by traction currents. These sands exhibit prevalent cross- and forset bedding and lack the graded bedding, parallel stratification, and other characteristics of the typical flysch deposits to the north.


Fig.12. Highlights of results obtained from the microscopic investigation of Annot Sandstone samples (modified after STANLEY, 1961a; FJOUMA, 1962).

Diagram 1. The Annot Sandstone outcrops are shown by stippling. The location of the Argentera- Mercantour Massif (A ) , the Barrot Dome (B), and the Esterel Massif (C) are shown by hachures. Smaller structural domes, Remollon and Saint Etienne d’Avancon ( D ) and Barles (E), were exposed to the west and are represented by triangles. Diagram 2. Petrographic analyses of conglomerate pebbles reveal that three pebble associations occupy different geographic positions in the basin. Type I is found only in the western part of the basin, association 2 surrounds the northwestern half of the Argentera Massif (A), and association 3 is restricted to the south. Association 3 contains rhyolite and mica schist pebbles similar to rock types found only in the Esterel Massif (C) to the south.

Diagram 3. Heavy minerals, grouped into three major associations, have distribution patterns similar to the conglomerate pebble associations in diagram 2. The S-K-G association is found only in the south and includes staurolite, kyanite, and garnet in large proportions. The heavy minerals to the north, the G-R-A and R-A associations, are primarily comprised of resistant mineral suites (zircon, rutile, and tourmaline). These were derived by reworking of the partially exposed Permian and Lower Triassic sandstones and quartzite cover of the Argentera and Pelvoux Massifs.

Diagram 4. The arrows indicate a decrease in relatibe percentage of stauiolite and kyanite toward the north. Neither crystalline rocks of the mmif basement nor sedimentary cover of the Argentera (A) or Pelvoux Massifs contain significant quantities of staurolite and kyanite. These minerals, on the other hand, are present in crystalline rocks and sedimentary cover of the Esterel Massif (C) to the south. A southern origin is implied for Annot Sandstones containing these two critical minerals.

Diagram 5. Arrows show a general decrease in relative percentage of garnet away from the south, west-northwest, and east.

Diagram 6. Dots represent the locations of the highest percentages of feldspar (in sandstone) recorded in the formation.

Diagram 7. Dots indicate the geographic position of the sands containing the highest percentages of CaCO,.

Diagram 8. The sands containing the highest percentages of glauconite and nonreworked microfossils are of the nonflysch type. These sands are the same as those shown in diagram 7.


works, as well as geologic and topographic maps, enabled the authors to select rapidly the locations of the most complete stratigraphic sections and to concentrate their investigations on the lithologic aspects of the rock.

The lateral variability of lithology and sedimentary structures is illustrated in Fig. 1 1 and 12 and is explained in the accompanying legends. The data used in these diagrams have been simplified and modified from contour and other detailed lithofacies maps (STANLEY, 1961a; BOUMA, 1962). The same general trends and patterns can be found in most of these diagrams. Both field and laboratory investigations indicate that sediments were brought into the marine basin from the south, from the west-northwest, and from what is now the northwest portion of the Argentera-Mercantour Massif.

The stratigraphic and structural framework of this same region at the end of the Eocene and in earliest Oligocene time is generalized on four diagrams in Fig. 13. These simplified interpretations are explained in the accompanying legend.

Paleogeographic conclusions, which are based partially upon combined stratigraphic, sedimentological and structural considerations, are illustrated on Fig. 14.

In diagram 1 of this last figure, the paleoslopes, represented by hairlines, are shown dipping into the basin away from the south, east, and west. Relatively steep dips of 1"-3" were probable in these areas.

In diagram 2, the Annot Sandstones have been divided into two contrasting types: those which show nonflysch characteristics and which were deposited on narrow, shallow shelves are located in areas labeled Roman numeral 11; the sandstones which show true flysch characteristics and which were deposited in the relatively deeper part of the basin are found in the area labeled Roman numeral I. Detrital sediments were brought onto the narrow shelves by fluviatile and shallow marine traction currents. The rapidly accumulating sands were then periodically transferred and redeposited by slides and suspension currents into the deeper parts of the basin. Numerous faults which are known to have been active during accumulation of the formation (such as faults a and b in diagram 3, Fig.13) could well have triggered such slides and turbidity cur rents.

Diagram 3 shows hachures becoming progressively lighter toward the north. This is to indicate that the graded sandstone beds in this region become thinner and less coarse from south to north. Arrows, representing vectorial properties of linear sedimentary structures, also indicate that sediments were transported northward.

Diagram 4 is a composite picture based upon all of the field and laboratory observations. Not one, as was originally proposed, but at least four major source areas gave rise to the Annot Sandstone by the end of Eocene time. These are located in the northwestern half of the Argentera Massif (A), in the region east of the Argentera Massif (D), in a region to the west-northwest (C), and in an area to the south (B). Sediments from sources A and B mixed in the zone delineated by the hachures. Area D was uplifted at the end of Eocene time, and the subsequent tectonic displacement of nappes toward the west so completely covered this region that it is not possible at this time to determine the history of the eastern portion of the basin with any certainty. Source area B to the south was most likely the Esterel-Thyrrenide chain which extended eastward

56 D. J . STANLEY AND A. H. BOUMA

Fig.13. Generalized stratigraphic and tectonic interpretations of the region covered by the sea at the end of Eocene and earliest Oligocene time (modified after Bovss~c, 1912; Gooun, 1936; DE LAPPA-

Diagram 1. Geographic position of the marine flysch formation (A) and the lateral interfingering timeequivalent nearshore non-flysch facies (B, C, D). A = Annot Sandstone, sl., thick accumulations of alternating sandstones and shales in the restricted Nummulitic Sea; B = “Grks en plaquettes,” thin marine sands at Senez-Clumanc; C = Calcareous sands of shallow marine origin at Faucon-Gigors; D = Lagunal-lacustrian clastic facies at Taulanne-Castellane.

Diagram 2. Shallow-water mollassic conglomerates accumdated near Clumanc (E) and Saint Antonin (F) after deposition of flysch in Early Oligocene time.

Diagram 3. The fold axes related to the Provencal tectonic phase are shown as solid lines; fold axes

RENT, 1938; GUBLER, 1959; STANLEY, 1961a).


Fig.14. Palmgeographic interpretations based on combined stratigraphic, sedimentological, and structural considerations (see text for explanation of diagrams).

of the Alpine tectonic phases are represented by small crosses. Northeast-southwest trending faults a and b were active during deposition of the Annot flysch.

Diagram 4. During this period, the mobile pre-Triassic substratum was warped into a north-south trending ridge (axis in hachured area) and somewhat uplifted zones (shown by the dotted patterns).


in an area now beneath the Mediterranean Sea south of Nice and Menton (KUENEN et al., 1957; KUENEN, 1958; STANLEY, 1961a,b; BOUMA, 1962).

Solving spxific problems

Selective data collection can be used to solve paleogeographic problems of a more specific nature. One example of such problem solving in conjunction with flysch studies can be demonstrated. An attempt was made by one of the authors (STANLEY, 1961b) to explain the nonflysch nature and extremely rapid lateral facies variability of the Annot Sandstones in the vicinity of Annot (Basses-Alpes, France).

As is often the case, the lithology of the formstion in its type locality is not truly representative of the formation as a whole. If one stands at the southern end of the Coulomp Valley and looks toward the north, one cannot be but amazed by the contrasting lithology of the formation on the opposite banks of the river (see Fig. 16). On the west of the valley, in a locality known as Chambre du Roi, the formation is approximately 200 m thick and consists of very thick and poorly stratified nonflysch-like sandstone beds lying above the underlying Eocene (Priabonian) “Marnes bleues” Formation (see section 5 on cross, section A-B in Fig.16). As one looks to the east,

Fig.15. The Annot Sandstone in its type locality near Annot (Basses-Alps). This view toward the north along the Coulomp River shows the thick, coarse, poorly stratified, and poorly graded beds of sandstone lying upon the older Priabonian “Marnes bleues” formation. Not visible are the thin, well-

stratified alternating graded sandstone and shale strata just to the right of the photograph.


Fig. 16. Geologic cross sections (vertical scale exaggerated) of the Annot Sandstone in the vicinity of the type-locality in the Basses-Alps (see text and Fig.17).

one sees that the formation, less than 100 m thick, also lies upon the older “Marnes bleues”. But here the formation exhibits the typical flysch characteristics and is composed of much thinner, well stratified, regularly alternating graded sandstones and shales (see section 6 on cross section A-B in Fig. 16). Since only about 500 m separates these two outcrops, it was at first thought that a tectonic accident had displaced the rocks on the opposite banks of the Coulomp River. Detailed field work, however, revealed that no fault parallels the valley along this stretch of the river. It was then postu- .lated that variability of depositional environments and of mechanisms of sediment transport was directly responsible for the rapid lithologic changes observed in this small area.

Stratigraphic sections were selected, and a critical examination was made of the rocks both in the field and the laboratory. It was found that sandstone beds are thickest in the vicinity of stratigraphic section 5 and thin rapidly east and west (cross section A-B) and toward sections 7 and 9 in the north (cross section C-D). The relative proportion of sandstones in each section, determined by means of the sand-shale ratio, decreases in these same directions; the interbedded shales on the other hand not only become more numerous but also are thicker away from section 5. Grain size

SEC SEC 1

? x

s TURBl DI TES $

LEGEND T

ANNOT SANDSTONE (UPPERMOST EOCENE-LOWER OLIGOCENE) FT FLUXO~URBIDITES

MARNES BLEUES (PRIABONIAN) S SUBMARINE SLUMP DEPOSITS

CALCAIRE MARNEUX INTERMEDIAIRE (PRIABONIAN) T R TRACTION MOVED SEDIMENTS

CALCA I R E N UMMUL IT1 QUE - DIRECTION O F SEDIMENT TRANSPORT

CALCAI RE SENONI EN

Fig.17. Legend see p.61.


decreases and graded bedding becomes more pronounced away from sections 5 and 7 toward sections 6 and 11. The coarsest conglomerate lenses are also concentrated in the area between sections 1 and 7 along profile C-D. Petrographic analyses, however, have revealed beyond a question of a doubt that the clastic materials in all of these localities are related as far as source is concerned.

The geometry of the sandstone bodies indicates that a north-south trending depression must have acted as a sand “trap” in this locality at the end of Eocene time. This depression, probably a downwarping within the underlying “Marnes bleues” Forma- tion, had the form of a submarine valley or channel (the term canyon with its con- notations of high steep sides, probably not the case here, is avoided). This depression developed within the paleoslope as the land mass to the south became uplifted. Tectonic movements, pronounced during this period of Alpine orogeny, could well have triggered the movement of the rapidly accumulating sediments away from shore into the deeper basin to the north.

The interaction of sediment transport processes, depositional environment, and tectonic activity is illustrated diagrammatically in Fig. 17. In the block diagram the basal sands are shown as wedge- and fan-shaped accumulations thinning laterally away from the channel at the base of the paleoslope. All of the pre-requisites normally associated with flysch deposition are present: an abundant and readily available supply of coarse to fine sediments rapidly accumulating nearshore, a paleoslope with sufficient dip enabling gravity transported sediments to be shifted into the basin, and structural instability.

Poorly sorted, lithic and feldspar-rich sands containing mineral suites of metamorphic origin accumulated onto the narrow and shallow shelf. Both fluviatile and shallow marine traction currents shifted these sediments into littoral and neritic environments. The sands were again transported, this time below wave-base, down the paleoslope into the basin by suspension flows (turbidity currents), by traction, sliding, and slumping, and by mechanisms transitional between suspension and slumping (“fluxoturbidite” sediment transport described by DZULYNSKI et al., 1959). The coarser sand and pebble fractions which became entrapped and channelized in the submarine depression were not able to develop the typical “turbidite” characteristics. These deposits, wedge-shaped and poorly stratified, appear as coalescing cone- or fan-shaped units at the base of the slope and mouth of the channel.

On the other hand, the sand and silt-sized sediments which were shifted down the less deformed more regular slopes adjacent to the depression accumulated as thinner, more distinctly stratified deposits on the basin floor. They were spread over a wider area in sheet-like deposits and were able to develop characteristics typically associated with flysch: marked graded bedding, numerous sole markings, parallel stratification

Fig.17. Interpretations of the depositional origin of the Annot Sandstone Formation in thevicinity of Annot (Basses-Alp). The block diagram (vertical scale exaggerated) attempts to show the interrela- tion between lithologic variability, depositional environment, mechanisms of sediment transport, and

structural mobility.


between alternating sandstones and shales. The continuous rain of pelagic sediments are believed to have given rise to most of the muds between the graded sand turbidites. These shales and silty shales are evidently more numerous and continuous on the basin floor than they are in the channel.

Petrographic examination of the formation in this area reveals the presence of light and heavy minerals, pebbles, fossils, and other inclusions reworked from older underlying formations. Priabonian, Mesozoic, and even Paleozoic rocks were uplifted and exposed to erosion and weathering south of the basin. Uplift and erosion also affected the upper parts of the submarine slope during deposition of the Annot Sandstones, which would help to explain the presence of “Marnes bleues” and basal Annot Sand- stone fragments reworked in the younger sands deposited to the north in the deeper basin.

CONCLUSIONS

There are several fundamental reasons why methodology and flysch paleogeography are certain to interest a growing number of sedimentologists during the next few years (PETTIJOHN, 1962).

In the first place, all of the answers pertaining to the mechanisms of sediment transport, depositional environments, and the role of related tectonism have not, as yet, been provided from studies of the ancient record alone. Geologists, by necessity, are actively seeking explanations of these problems in present-day marine basins where sediments are accumulating under somewhat similar conditions. It is interesting to note, for instance, the striking sedimentological analogies between the once submerged basin area adjacent to Annot, outlined in the preceding section, and certain present- day basins such as the San Diego Trough (described by SHEPARD and EINSELE, 1962) off the coast of southern California. It is quite likely that flysch-like deposits are even now being laid down. In comparing recent to ancient rocks, the manner in which data are collected and processed becomes critical. In the case of flysch, therefore, methodology has a role of primary importance in determining whether the present can be used as a key to the past.

Methodology and paleogeography have also been given added impetus as more and more rock units exhibiting typical flysch characteristics are recognized in the geologic record. It is admitted that such sequences are not restricted to the Cretaceous and Lower Tertiary basins of the Alps, and many portions of the geologic record are now actually being “rediscovered” and reinterpreted as “flysch-type” deposits.

Furthermore, the fact that there exists an astonishingly large volume of basin rocks comprising potential source and reservoir horizons should impress those in charge of petroleum exploration programs. Flysch formations have already been described in areas adjacent to and within prolific petroleum provinces such as the Los Angeles Basin in California and the Delaware Mountain Group in Texas and New Mexico (in SULLWOLD, 1961). Quantitative and semiquantitative results obtained from studies of


recent and ancient flysch formations are certain to become invaluable to those carrying out subsurface investigations. In working with flysch-type stratigraphic traps where lateral observations are limited but where rapid lateral lithofacies variability can be expected, a judicious choice of methods and a clear understanding of paleogeography are basic requisites.

In summary, the following fundamental points may be recommended: ( I ) Those who intend to carry out quantitative investigations must familiarize

themselves with the capabilities of electronic equipment and data processing so as to be able to extract rapidly the maximum amount of usable information with the least margin of error.

(2) Data collecting should be planned and information recorded with an eventual computer program in mind.

(3) Abundant available data may be accumulated logically and systematically in the field and in the laboratory.

(4) Selected data can then be processed for translation onto base maps in the form of structural, isopachous, isolith, paleocurrent, and lithofacies maps.

(5) By comparing and superposing these maps it is possible, in most cases, to observe significant lithologic variability and facies patterns within a mappable unit.

(6) The recognition of these time and geographically controlled variations is the key step in understanding the over-all history of a flysch basin.

The multiple-parameter methods outlined above were tested with success in the Maritime Alps, and it is expected that similar lines of reasoning employed with other “flysch-type” formations will provide fruitful results.

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37 : 1044-1066.

1468-1493.

pp. 388-398.

63-8 1.

102 pp.

EVOLUTION DE LA SEDIMENTATION ET OROGENESE, VALLeE DU SANTERNO, APENNIN SEPTENTRIONAL

A. R I Z Z I N I et R. PASSEGA

AGlP Mineraria, S. Donato Milanese, Milan (Italie) ; GJologue Conseil, Bartlesville, Okla. ( U S A . )

SUMMARY

Evolution of the sedimentation and orogenesis, Santerno valley, northern Apennines

A sedimentological study of the Marnoso-Arenacea formation (northern Apennines, Italy), of miocene age, was carried out by means of the granulometric method of CM-diagrams and normal sedimentological techniques. It is possible to reconstruct the evolution of the sedimentation of this formation. This evolution appears to be closely related to orogenesis. Three phases of sedimentation can be distinguished: ( I ) preorogenetic phase, with flysch deposition; (2) orogenetic phase, during which the lowering of sea-level is marked by the appearance of “undaturbidites”; (3) postoro- genetic phase, with the filling up of the basin and a gradual disappearance of turbidites, which are replaced by pelagic sediments.

La mkthode granulomktrique des diagrammes CM, ainsi que les techniques skdimentologiques habituelles, nous ont permis de reconstruire l’kvolution de la sedimentation de la formation Marnoso-Arenacea (Apennin septentrional, Italie).

INTRODUCTION

L‘Ctude ddimentologique de la formation Marnoso-Arenacea, d‘lge miockne, a Cte conduite A l’aide des diagrammes granulometriques CM (PASSEGA, 1957) completks par d’autres tlhments, tels que caractiristiques des structures skdimentaires et en particulier direction des flute casts, composition des mineraux lourds, rapport sable/ argile, etc.

La skrie choisie est situee le long de la vallee de la rivihre Santerno, 30 km au sudest

66 A. RIZZINI ET R. PASSEGA

de Bologne (Fig. 1) oil la tectonique est particulihrement tranquille et l’exposition continue (MERLA, 1951, pp.210-212).

DESCRIPTION DE LA SERIE

Dans la vallte du Santerno la Marnoso-Arenacea peut se diviser de bas en haut en trois membres lithologiques (Fig. 1).

Alternances de Castel del Rio

Ce membre-ci a une Cpaisseur dCpassant les 2.250 m que nous avons CtudiCs. I1 est constituk par des turbidites alternant assez regulikement avec des couches d’argile. Les turbidites, dCcrites en ditail par TEN HAAF (1959), prksentent toutes les caractki- stiques de ces dtpBts, a savoir graded-bedding, flute casts, groove casts, load casts,

Ces stdiments se sont dtposCs dans une fosle d’axe nordouest-sudest. Les flute casts indiquent que, dans la fosse, les courants de turbidit6 se sont CcoulCs longitudinalement vers le sudest et non dans la direction des plus grandes pentes, laquelle Ctait trans- versale. Le facteur principal de la formation des courants de turbidit6 Ctait probablement le volume des sables qui pouvaient les former et ne s’accumulaient qu’en amont de la VallCe du Santerno sur les plateformes marginales de la fosse.

traces de limivores, convolute bedding, etc. _ _ j l L , *’ , : f

Sables de Fontanelice

Le passage des Alternances aux Sables est graduel et se produit sur quelque 150 m de s6rie. I1 est marquC par la diminution progressive de l’tpaisseur des couches argileuses. Ce membre n’est pas trhs uniforme du point de vue lithologique. En fait on peut distinguer deux zones grCseuses sCparCes par une zone plus argileuse. L‘Cpaisseur totale du membre est de 250 m environ.

Les sables sont faiblement cimentks, moins argileux que ceux des Alternances et dispods en bancs d’une Cpaisseur trts variable, qui peut aussi dtpasser les 7-8 m. Les sables de la zone grbseuse infkrieure sont souvent sillonnCs de chenaux d’Crosion dont la profondeur varie de quelques centimktres a plusieurs mbtres. Les chenaux sont toujours remplis par le matBrie1 le plus grossier ( 2 4 mm), qui forme un graded- bedding trks Cvident dans la partie infdrieure du banc.

Les argiles sont rares. Elles sont trks souvent silteuses et forment des couches peu Cpaisses, gtnbralement lenticulaires.

Les silts et les sables fins des bancs grCseux prksentent des stratifications obliques a trks petite Cchelle et des convolute beds partiellement tronquks.

Les flute casts sont plut6t rares et apparaissent dans les bancs a graded-bedding mais sont absents a la base des sables qui remplissent les chenaux d’drosion. Les load casts et les traces d’animaux sont plus frkquents. Les bancs grCseux contiennent

PATTERN CM I a l3 I 1

FORMATION

AGE

I 1 P x N

ARGILES DE TOSSIGNANO $:'$&:; A L T E R N A N C E S D E C A S T E L D E L R I O MEMBRE (650rn) (25om) (2250m)

zrF, M A R N 0 S 0 - A R E N A C E A

K S ' N I E N T 0 R T 0 N I E N H E L V E T I E N - L A N G H I E N

Fig. 1 . Coupe lithologique de la Serie de la Val& du Santerno (Apennin septentrional, Italie).

Lithological section of the Santerno Valley Series (northern Apennines, Italy). The age of the series, formation name, formation members, scale, general lithology, sand/clay ratio, and the CM pattern

are given.


souvent des fragments intraformationnels, anguleux, de marne ayant un diamktre maximum qui varie de quelques centimttres a quelques dkimttres.

Argiles de Tossignano.

Les Sables de Fontanelice passent vers le haut presque brusquement a des nouvelles alternances de turbidites et d’argiles, qui forment le troisitme membre dont l’kpaisseur est de 650 m.

Les turbidites sont reprtsentkes par des sables faiblement cimentks avec graded- bedding parfois meme repktk.

Les turbidites se rarkfient peu ii peu vers la partie supkrieure du membre, qui finalement devient entierement argileux. En meme temps l’kpaisseur des couches gr6- seuses et les dimensions des grains diminuent aussi.

Aucune empreinte n’apparait ii la base des bancs grkseux, peut-etre ii cause de leur faible cimentation. La portion silteuse des bancs grkseux montre par endroits des convolute beds.

Dans la partie moyenne de ce membre se trouvent trois gros blocs exotiques t r h rapprochks, formks par des bancs de “Sable de Fontanelice”, qui s’ktendent sur quelque 0,5 km2, avec une puissance de 20 m, en position de nette discordance angulaire, sur les Argiles de Tossignano.

Le cycle de stdimentation miockne s’achtve avec le dkpp8t de couches de gypse d’une Cpaisseur d’environ 30 m.

VARIATION DES CARACTBRISTIQUES ~BDIMENTOLOGIQUES

Les flute casts ont une direction constante, E30°S, dans tous les membres des Alternan- ces tandis que les quelques empreintes de ce genre, qu’on trouve dans les Sables de Fontanelice, sont dirigkes vers l’est.

Les minkraux lourds des Alternances ont une composition uniforme et sont reprk- sentks presque exclusivement par des grenats et des kpidotes-zofsites. Cette association change peu a peu au passage des Alternances aux Sables de Fontanelice. Ces deniers ainsi que les Argiles de Tossignano sont caractkrisks par l’apparition de disthtne, glaucophane et hornblende verte.

L‘Ctude des minkraux lourds a CtC exkutCe selon la mkthode adoptke par l’Institut Francais du Pktrole (STANLEY, 1961, p.83).

Fig. 1 reprCsente les variations du rapport sable/argile dkfini, pour un intervalle, comme le rapport entre l’kpaisseur totale des couches de sable et de celles d’argile.

Les autres caractkristiques sCdimentologiques seront discutks pour chaque membre skparkment.

S~DIMENTATION ET OROGEN~SE, VALLBE DU SANTERNO 69

M~THODE GRANULOMBTRIQUE CM

Cette mtthode met en tvidence les relations existant entre la texture des sediments et l’agent de dtp6t (PASSEGA, 1957).

Les Cchantillons d’un skdiment donnt sont reprtsentts par deux paramktres: C, une valeur approchte du grain maximum et M , le mtdian. Si un dtp6t est reprtsentt par une trentaine d‘tkhantillons sur un diagrarnme CM, les points correspondants forment un “pattern” dont la forme dtpend des caracttristiques de l’agent de transport.

Le pattern typique des dtp6ts de courants tractifs (Fig.2), qui transportent une partie du stdiment par roulement (partie N - 0 - P - Q) et une partie par suspension

Fig. 2. Exemple de diagramme CMcomplet de dtpat de courants tractifs.

Example of a complete CM pattern of deposits from traction currents. The grain size (M) is given in microns on the absciss; the maximum grain size (C) on the left ordinate.

(Q - R), a une forme arqute; celle des dip& des courants de turbiditt qui transportent tout le rnattriel en suspension, a une forme lintaire parallde la droite C = M (Fig. 3 F) .

INTERPR~TATION DES CARACT~RISTIQUES S~DIMENTOLOGIQUES - RELATION

AVEC LA TECTONIQUE

Le pattern F de la Fig.3 est typique des Alternances de Caste1 del Rio, et a la forrne


E

B

D

F

~BDIMENTATION ET OROGEN~E, VALLBE DU SANTERNO 71

lineaire caracteristique des turbidites. Deux autres patterns, de ce membre, qui ont BtC construits, sont identiques au pattern F. La constance de la forme des patterns et de la direction des flute casts dans les plus de 2.000 m d’epaisseur de ce membre, indiquent que la sedimentation a eu lieu dans une pkriode de subsidence forte m a i s graduelle, qui a maintenu la mCme topographie de fosse pendant toute la sedimentation de ce membre. I1 s’agit probablement d’une periode prCorogCnique.

Le pattern E de la Fig.3 reprksente la zone inferieure des Sables de Fontanelice. Sa forme fait penser a un dkp8t de courants tractifs. Cependant, on p u t faire valoir quelques arguments qui s’opposent 21 cette interpretation. Les bancs sablew sont partiellement ?t graded-bedding, les flute casts, quoique rares, sont assez typiques, les load casts et les convolute beds sont communs. Le diagramme CM indique une forte turbulence, qui pour un dCpBt de courant tractif impliquerait une trks faible profondeur d’eau (PASSEGA, 1960). D’autre part, tous les autres membres de la Mar- noso-Arenacea etant constitues par des turbidites, il semble peu probable de trouver au milieu d’eux un episode de sables de trks faible profondeur.

Les Sables de Fontanelice ont des caractkristiques trbs proches de celles des dCp8ts que DZULYNSKI et al. (1959) ont appelb fluxoturbidites. Selon ces auteurs des glissements sous-marins seraient B l’origine des courants de turbidit6 et les fluxoturbidites seraient un dBp8t intermediaire entre le mud flow et la turbidite.

Comme les fluxoturbidites dkrites par Dzulynski et al., les Sables de Fontanelice, forment, eux aussi, des bancs irrbguliers, separks par des niveaux d’argile discontinus. Les Sables sont moins argileux et plus grossiers que les turbidites des Alternances, et les argiles sont plus silteuses que celles des Alternances. Le graded-bedding vertical est assez rare, sauf vers la base du remplissage des chenaux &erosion. Les flutes casts sont plus rares mais les load casts et les stratifications obliques sont plus abondants que dans les turbidites. Ces caracteristiques sont citCes par Dzulynski et al. comme Ctant typiques des fluxoturbidites. I1 semble donc que les Sables de Fontanelice puissent Stre un d6p8t de ce genre. I1 faut, toutefois, faire une restriction.

Comme il semble que les courants de turbidit6 de la Marnoso-Arenacea n’aient pas eu comme origine des glissements sous-marins comme ceux imaginCs par Dzulynski et al., mais plut8t des suspensions formCes par de violentes tempCtes (PASSEGA, 1962), les Sables de Fontanelice seraient plut8t un dBp8t intermediaire entre les depbts de vagues et les turbidites. Peut-&re vaudrait-il donc mieux parler, tout au moins pour les skdiments des Sables de Fontanelice, d”‘undaturbidites” que de “flwoturbidite”. L‘absence absolue de glissements dans les Sables de Fontanelice vient A l’appui de cette hypothkse.

Fig.3. Diagrammes CM de la Sr ie de la Vallk du Santerno. Patterns A, B, C: Membre “Argiles de Tossignano”; patterns D, E: Membre “Sables de Fontanelice”; pattern F: Membre “Alternances de

Castel del Rio”.

CM patterns of the Santerno Valley Series. Patterns A, B, C are from the “Argiles de Tossignano” Member; patterns D, E from the “Sables de Fontanelice” Member; pattern F from the “Alternances

de Castel del Rio” Member (see Fig.1).

72 A. RIZZlNl ET R. PASSEGA

La ressemblance avec les Sables de Fontanelice fait penser qu’au moins une partie des ”fluxoturbidites” dkrites par Dzulynski et al. pourraient Stre des “undaturbidites”. Cette hypothbse expliquerait l’observation de ces auteurs, qui ont not6 que les fluxoturbidites Ctaient moins argileuses que les vkritables turbidites. Ces sCdiments moins argileux semblent peu compatibles avec une origine des courants de turbidit6 comme une coulCe vaseuse. I1 semble en tous cas que les Sables de Fontanelice se soient form& dans un milieu assez semblable a celui suggCrC par Dzulynski et al. pour les fluxoturbidites. L‘apport du matCriel n’6tait plus parallble a I’axe du bassin, comme il l’ktait pendant le dCpbt des Alternances, mais les flute casts indiquent qu’il avait son origine ti l’ouest. Le changement de la composition des mineraux lourds con- firme le changement de la provenance des stdiments.

Ces skdiments ont dQ Ctre dCposCs assez prbs de leur lieu d’origine car vers l’ouest la cbte n’6tait qu’a quelques kilomktres de la VallCe du Santerno.

La variation du rapport sable/argile (Figl), le changement dans la direction des flute-casts, la variation des minCraux lourds et l’apparition d’undaturbidites correspondent probablement A une phase orogtnique qui a dB soulever considkrablement le fond de la fosse et son bord sudoccidental.

La diminution de profondeur de la mer a probablement dCterminC sur ce bord la formation des dipbts sableux de vagues. Ces dkpbts ont CtC resCdimentCs dans la VallCe du Santerno sous forme d’undaturbidites A une profondeur qui devait dkpasser celle de l’action des vagues vu l’absence dans cette IocalitC de dtpbts attribuables uniquement aux vagues.

Le pattern D de la zone sableuse superieure des Sables de Fontanelice ressemble a un pattern de turbidite et marque probablement le passage entre les undaturbidites des Sables de Fontanelice et les turbidites des Argiles de Tossignano.

Les patterns suivants, C - B - A (Fig.3), des bancs de sables qui font partie des Argiles de Tossignano, sont des patterns de turbidite. A mesure que l’on s’tlkve dans ce membre, les turbidites deviennent de plus en plus rares, leur Cpaisseur diminue, et leur texture devient plus fine.

Durant la pCriode de dtpbt des derniers courants de turbiditt le fond du bassin recoit par glissement des blocs exotiques formCs par des bancs de Sable de Fontanelice. L‘absence d’krosion au contact entre ces blocs et les Argiles de Tossignano, qui est clairement marquCe par une discordance angulaire, montre que ce glissement a 6tC trbs doux. La pente sur laquelle il s’est produit Ctait presque horizontale puisqu’elle recevait les dtpbts des courants de turbidit6 les plus faibles de la Marnoso-Arenacea.

Le fait que l’on trouve ces blocs dans la partie moyenne des Argiles de Tossignano, indique que la phase d’orogtnbse s’est peut-Stre prolongte pendant une partie de la skdimentation de ce membre.

La sddimentation de la partie supdrieure des Argiles de Tossignano pourrait corres- pondre a une phase postoroginique durant laquelle, par suite d‘une faible subsidence, la fosse se comblait. Les pentes devenaient de plus en plus faibles et rendaient 1’Ccoule- ment possible seulement aux courants de turbidit6 qui transportaient des silts, qu’une faible turbulence suffisait A maintenir en suspension.

S~DIMENTATION ET O R O G E N ~ E , V A L L ~ E DU SANTERNO 13

Les dernikes couches de ce membre, entikrement argileuses, correspondent probablement a une profondeur du bassin encore trop forte pour le transport par vagues, mais avec des pentes trop faibles pour l'koulement de courants de turbiditk.

Les Argdes de Tossignano sont recouvertes par des couches de gypse, qui indiquent une restriction du bassin.

CONCLUSIONS

L'kvolution des skdiments de la Marnoso-Arenacea est Ctroitement like A l'orogknbe. Ce rapport a ktk m i s en kvidence par la reconstruction du mkcanisme de leur dkp6t.

Ce rapport a permis de distinguer trois phases de skdimentation. La phase prkoro- gknique, qui correspond au dkp8t du flysch; la phase orogknique, pendant laquelle la diminution considkrable de la profondeur de la mer est marquke, dans la vallk du Santerno, par l'apparition d'undaturbidites et probablement, dans le voisinage, par des sables peu profonds; enfin la phase postorogknique correspondant au comblement du bassin et A la disparition graduelle des turbidites remplackes par des skdiments pklagiques.

NOTE

Aprts la prksentation de cet expos6 de nombreuses undaturbidites semblables, tant par leurs caracttres lithologiques que par leurs patterns CM, celles de la vallke du Santerno ont kt6 dkouvertes dans les sondages de la vallke du P6. Elles remplissent le fond d'ktroits bassins de plusieurs centaines de kilombtres de longueur du Tortonien et du Plioctne moyen. Elles ont kt6 dkposkes dans des mers dont la profondeur deter- minke par palkokcologie des foraminiftres (M. A. Chierici, communication person- nelle) ktait de plusieurs centaines de mbtres. Ces undaturbidites correspondent a des pkriodes de soulbvement du bord des bassins.

La dispersion des points du diagramme CM qui reprksentent la partie la plus gros- sitre, basale des dkp8ts est attribuk A un kcoulement trts rapide et trts variable des courants de turbiditk qui causait, surtout prts de leur base, des variations dbordon- nkes de la turbulence.

REMERCIEMENTS

Nous adressons les remerciements les plus vifs a la Direction Gknkrale de la Societa AGIP Mineraria, qui a bien voulu nous permettre la publication de ce rapport.

Nous devons remercier aussi M.G. Long pour la collaboration que les laboratoires gkochimiques nous ont offerte dans l'exkution de ce travail; M. M. Pieri, qui nous a guidks dans le choix des skries a ktudier; M. D. Tedeschi pour l'ktude palkontologique et M. G. Livraga qui a fait la coupe de terrain.

74 A. RIZZINl ET R. PASSEGA

BIBLIOGRAPHIE

DZULYNSKI, S., KSIAZKIEWICZ, M. and KUENEN, PH. H., 1959. Turbidites in flysch of the polishcarpa-

MERLA, G., 1951. Geologia dell’Appennino Settentrionale Bull. SOC. Geol. Ital., 70 : 95-382. PASSEGA, R., 1957. Texture as characteristic of clastic deposition. Bull. Am. Assoc. Petrol. Geologists,

PASSEGA, R., 1960. Skdimentologie et recherche de phole . Rev. Inst. Franc. Pitrole Ann. Combust.

PASSEGA, R., 1962. Problem of comparing ancientwith recent sedimentary deposit. Bull. Am. Assoc.

STANLEY, D. Y. , 1961. Etuaks sidimentologiques des Gr&s d’Annot et de Ieurs Equivalents latiraux.

TEN HAAF, E., 1959. GrudedBeAofthe Northern Apennines. Thesis, Univ. of Groningen, Groningen,

thian Mountains. Bull. Geol. SOC. Am., 7.0 : 1089-1 118.

41 : 1952-1984.

Liquides, 15 : 1731-1740.


Thbe, Univ. de Grenoble, Grenoble, 158 pp.

102 pp.

THE TURBIDITE CONCEPT IN BRITAIN

GILBERT KELLING

Geology Department, University College of Swansea, Wales (Great Britain)

SUMMARY

The location in time and space of British formations recognised as turbidites is reviewed. The basis and results of directional studies of British turbidites are discussed and it is shown that although several cases are known of simple longitudinal derivation there also exist significant departures from this ideal scheme. The problem of transverse depositional flow is emphasized and the possibility of reworking by indigenous currents or the influence of reflected surge-waves is examined. Lateral relationships of some British turbidite sequences are analysed and some conclusions are offered on the environmental significance of the observed facies changes. Similarly the sequential position and vertical relationships of some turbidite formations are outlined and their possible meaning in terms of basin development is discussed briefly. Finally it is demonstrated that the intimate connection between the trend and location of structural elements and the sedimentary attributes and stratigraphic position of turbidite formations is explicable on the basis of contemporaneous and continuing tectonism on both a basin-wide and a local scale.

INTRODUCTION

The past decade has seen the concept of turbidity flow widely applied to British rocks and the implications of the general theory with its corollary aspects have prompted considerable reappraisal of existing interpretations of palaeogeography, sedimentary and tectonic history in the British geosynclines.

The present account is concerned solely with some sedimentological attributes of turbidites. It constitutes an attempt to summarise the main results which have accrued through the application of the resedimentation hypothesis to British rocks and to assess the possible future development of the turbidite concept in Britain..

STRATIGRAPHICAL DISTRIBUTION

Table I and Fig.1 illustrate the distribution in time and space of those British forma-

76 G. KELLING

tions currently described as turbidites in published accounts. Only marine geosynclinal sediments have been considered here although several British formations display turbidite characteristics combined with other features which indicate deposition in a variety of marine and continental environments (CUMMINS, 1958; DINELEY and ALLEN, 1960; CROWELL, 1960).

Most British turbidites occur in the Lower Palaeozoic formations within the Cale- donian orogen or in the Upper Palaeozoic sediments of the Variscan fold-belt, but Precambrian examples are also coming to light. Graded greywackes and slide- breccias of presumed Cambrian age occur in the Isle of Man but have not yet been designated turbidites (GILLOTT, 1956; SIMPSON, 1962).

Well documented turbidite formations occur in the Cambrian and Silurian rocks of Wales but as yet none have been described from the Ordovician. Widespread unconformities and thick volcanic successions may in part account for this absence and the dearth of detailed sedimentological data from the Ordovician rocks is an important contributory factor. Nevertheless available information suggests that, with the probable exception of the Bala greywackes, the Welsh Ordovician contains no thick, widespread turbidite formations.

TRANSPORT CRITERIA AND DIRECTIONS

Regional studies of transport directions in British turbidites have made use of a variety of oriented features but erosional sole-structures such as flute and tool marks have furnished most of the directional data. It is unfortunate that in many instances no distinction has been drawn between the orientation of such structures and others, such as ripple mark or convolute lamination, of depositional or deformational origin. An increasing body of evidence suggests that variations in the orientation and relative abundance of these groups of structures reflect differences in the hydraulic properties of the currents responsible for their formation (cf. DZULYNSKI and SANDERS, 1962).

Directional studies have shown that the longitudinal transport of material parallel to the length of the trough envisaged by KUENEN (1957) is dominant in most British turbidite formations (Fig. 1). Turbidites derived from one end of the geosynclinal basin have been described by WOOD and SMITH (1959) from the Valentian rocks of western Wales and by CUMMINS (1957) from Wenlock greywackes in northeastern Wales. However directional structures from the Upper Ordovician rocks of southwestern Scotland reveal a more complex transport scheme (KELLING, 1962, pp. 132-1 36). The dominant direction of turbidity flow is parallel to the caledonoid trend of the depositional trough but there is evidence of a,double sense of derivation, from both northeast and southwest. The petrographic uniformity of these turbidites shows that such oscillation was probably controlled by local bathymetric conditions and is not to be ascribed to periodic changes in the ultimate source of the sediment. There is evidence that as time went on unidirectional transport from the northeast became progressively established further and further south (KELLING, 1962, p. 136). A com-

TABLE I'

TURBIDITE FORMATIONS RECOGNISED IN BRITAIN

Code n a 2 Reference LocaIity Formation

1 2 3 4 5 6 7 8 9

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

STEWART (1 962a, 1962b) Colonsay and Islay, Innei Hebrides, Scotland KNILL (1959, 1960a) Loch Awe, western Scottish Highlands S ~ N and WATSON (1954,1955) Banffshire Coast, northeastern Scotland STURT (1961) Perthshire, Scottish Highlands B m m and WALTON (1960) Lleyn peninsula, northern Wales KOPSTEIN (1954) Harlech Dome, northern Wales DEWEY (1962) Central Murrisk, Mayo, western Ireland STANTON (1 960) Southwestern Murrisk, Mayo, western Ireland JACKSON (1961) Lake District, northwestern England WILLIAMS (1 962) W a n , southwestern Scotland KELLING (1 962) Rhinns of Galloway, southwestern Scotland WOOD and SMITH (1959) Cardigan coast, western Wales CUMMINS (1957) Denbighshire-Montgomeryshiie, northern Wales CWNS (1959a, 1959b) Denbighshire-Montgomeryshire, northern Wales HOLLAND (1958,1959) Radnorshire, Wales WALTON (1 955) Peeblesshire, southeastern Scotland CRAIG and WALTON (1 962) Kirkcudbrightshire, southwestern Scotland ROLFE (1961) Lanarkshire, mid Scotland MCKERROW and CAMPBELL (1960) Killary Harbour, western Ireland COPE (1959) WEIR (1960,1962) GILL (1961) County Dublin, Ireland PRENTICE (1960,1962) ALLEN (1 960)

Devilsbit Mountain, central Ireland County Clare, central Ireland

Devon and Cornwall, southwestern England Derbyshiie, northern England

Basal Tomdonian (Precambrian) Upper Dalradian (? Cambiian) Upper Dalradian ( ? Cambrian) Lower-Upper Dalradian (Eocambrian- ? Cambrian) Lower Cambrian Lower Cambrian Lower Ordovician Lower Ordovician CI

Lower Ordovician er

8 Upper Ordovician Llandoverian (Silurian) z Wenlockian (Siurian) G Ludlovian (Silurian) z Ludlovian (Silurian) 2

Fi s

Upper Ordovician 5 W

E Lower Silurian Middle Silurian Valentian (Silurian) Wenlockian (Silurian) Salopian (Silurian) Salopian (Siurian) Visean (Carboniferous) Namurian-Westphalian (Carboniferous) Namurian (Carboniferous)

-

This table lists only those formations for which detailed published accounts are available and which are explicitly stated to be marine turbidites. More

The code number has been used to define the locality of a particular formation on the general map, Fig.1. general accounts, such as those of KUENEN (1953, 1957) have been omitted from this list.

4 4

78 G. KELLING

Fig.1. Index map of Britain to show location of formations described as turbidites in accounts published up to June, 1963. Code numbers refer to formations listed in Table I. The associated current directions have been obtained from the appropriate account except in the case of the open arrow near Harlech which is based on KNILL (1959, p.318). For the present purpose depositional structures are taken to include crossbedding and ripple mark in addition to deformational features such as flow

marks, convolute and slump structures.

parable situation exist in the Silurian greywackes of Kirkcudbrightshire (CRAIG and WALTON, 1962, p. 118). Similarly opposed directions of transport appear to occur in the Dalradian turbidites of Loch Awe and Kilmory Bay (KNILL, 1960a, pp.279, 283) while the apparent discrepancy in current directions obtained from the Cambrian Harlech Grits of northern Wales by KOPSTEIN (1954) and BASSETT and WALTON (1960) may be explicable in this way (KNILL, 1960b, p.107).

THE TURBIDITE CONCEPT IN BRITAIN 79

KNILL (1959, 1960a), recognises two principal current-defined facies within the sediments of the Caledonian geosyncline in Britain. His axial’ facies is derived longitudinally and comprises turbidite units; the marginal facies is derived from the sides of the trough and includes the thick shale sequences and fine-grained interbeds within the turbidite formations.

However, recent studies have shown that both longitudinal and lateral supply may be inferred from the same sequence of turbidites. In the Girvan district of southwestern Scotland WILLIAMS (1 962, pp.62-68) has described slide-conglomerates and greywackes derived laterally, from the north and northwest, which interfinger southwards with graded greywackes in which evidence of longitudinal transport, from east and northeast, is dominant. Nearby, in the Rhinns of Galloway, the Caradocian succession commences with flaggy greywackes and conglomerates which were transported by currents flowing from the north or northwest. These rocks are replaced to the south by greywackes derived longitudinally from the northeast or southwest.

Recently DEWEY (1962) has demonstrated comparable interdigitation in the Areni- gian greywackes of Murrisk, County Mayo. He describes axial turbidite units which are relatively coarse with complex grading and carry erosional sole-structures which indicate transport along the length of the trough from an eastern source. These are interbedded with the lateral turbidites which are less coarse, graded, with flow-casts, convolute lamination and other deformational structures generated by turbidity flow down a relatively steep north-facing lateral slope. DEWEY (1962, p.250) states that wherever the axial and lateral turbidites are interbedded “the direction of current flow is distinctly at right angles with no intermediate directions”. He therefore rejects the hypothesis that the currents entered the basin laterally, subsequently turning to flow along the bathymetric axis and proposes instead that turbidity currents of differing source with contrasted hydraulic properties were responsible for the axial and lateral units.

Directional divergence of another type has been emphasized by PRENTICE (1 960, 1962) who maintains that depositional structures (ripple marks, cross-lamination and flow casts) in the Carboniferous turbidites of northern Devon were formed by flow in directions approximately normal to the east-west trend of the turbidity currents responsible for the formation of the associated erosional sole-structures (see below, p.81).

In the Silurian turbidites of Kirkcudbrightshire, southwestern Scotland, erosional sole-marks indicate longitudinal transport, mainly from the northeast, whereas ripple marks in the silty tops of graded greywackes and within the fine-grained interbeds were formed by currents flowing from southeast or northwest, transverse to the geosynclinal axis (CRAIG and WALTON, 1962, p.118). A similar situation obtains in the Kirkcolm Group turbidites of Caradocian age in the Rhinns of Galloway (Fig.2) where evidence of lateral supply from the north and northwest is almost entirely

* This use of the term axial to some extent conflicts with the usage of previous workers (e.g., JONES, 1938, p.lxvi). The axial black shales of Jones’ definition would form part of Knill’s marginal facie.

80 G. KELLING

i TOTAL KIRKCOLM SOLE STRUCTURES 115 obsarvations of currant sansa

N

TOTAL KIRKCOLM TRANSVERSE RIPPLE

56 obsarvations of currant sense

*I. FREQUENCY

Fig.2. Directions of current derivation deduced from (A) sole structures (mainly flute and groove casts), and ( E ) transverse ripple mark. From Kirkcolm Group turbidites (Ordovician), Rhinns of

Galloway, Scotland. Assigned to semi-octant classes.

derived from transverse ripple mark, the sole-structures indicating longitudinal transport (Fig.2; cf. KELLING, 1962, fig.17).

An analogous combination of longitudinal sole-structures and laterally derived ripple mark may be inferred from the Lower Silurian turbidites of Peeblesshire (WALTON, 1955, pp.329-332) and inadequate data suggest a comparable relationship in the Salopian rocks of central Ireland (COPE, 1959, fig.4, p.229). In the Lower Cam- brian turbidites of the Harlech Dome the principal current trend in the grits is almost north-south but small-scale current bedding in the siltstones is derived from the southeast (KNILL, 1960b, p.107).

Available evidence thus suggests that although in some sequences the trends of all the directional structures are mutually compatible, near-perpendicular divergence of erosional and depositional structures is of relatively widespread occurrence in British turbidites. Moreover, a similar anomalous relationship may be seen within an individual turbidite unit as PRENTICE (1960, pp.220-221) has demonstrated. Personal observations in the Ordovician rocks of southwestern Scotland and in the Valentian turbidites of Wales (see below, p.82) bear out this conclusion. Sixteen silty greywacke units in a randomly chosen 100 ft. sequence of the Aberystwyth Grits (cliff exposures a quarter mile south of Aberayron, sixteen miles south of Aberystwyth, western Wales) exhibit flute casts on the base and transverse ripple marks or measureable ripple lamination on the upper surface. Of these, nine units show ripple crests approximately parallel to the sole-structures, four have ripples trending at right angles to the flute casts and the ripple marks in the remaining three are either complex or too indistinct to relate accurately to the erosional features.

If we except cases of interbedding, such as DEWEY (1962) describes, divergence in the current directions given by erosional and depositional structures within individual turbidite units or sequences may be explained in three main ways:

(a) Erosion and deposition were caused by successive turbidity currents of differing source and character.


(b) Erosion and initial deposition were achieved by a single turbidity flow but the fine-grained fraction of the resulting bed was subsequently reworked by transverse, indigenous bottom currents.

(c) Erosional and depositional structures were both formed by the same turbidity current but external factors influenced the formation of structures during the depositional phase of the current.

The possibility of erosion by one turbidity current and deposition from another, later flow has been invoked from time to time (e.g., CROWELL, 1958, p.333; CUMMINS,

1959b, p.176) but it is unlikely to be of general significance since such a mechanism implies not only that erosional hollows remain unfilled for some time but that the depositional currents were derived consistently from the sides of the trough. In the Upper Ordovician turbidites of southwestern Scotland some units bear depositional structures compatible with the current-trend of associated erosional features whereas other beds carry ripple mark of anomalous trend; yet the petrographic similarity of these rocks is evidence that they shared the same source (KELLING, 1962, p.134).

Reworking of the silty upper part of the graded turbidite by weak bottom currents flowing transverse to the length of the trough offers a feasible explanation in some cases, especially where the silty interbeds reveal signs of weak current-action (CRAIG and WALTON, 1962, p. 118; KELLING, 1962, p.135). Such an explanation also accounts for the common association of divergent depositional trends with fine-grained and silty sediments. The existence of aligned graptolite stipes in mudstones from turbidite sequences (WILLIAMS, 1962, p.66) furnishes additional evidence for some current movement in the intervals between turbidity flows. Moreover, the argument that bottom currents of sufficient strength to form ripple mark do not exist at the considerable depths usually implied for turbidite deposition has been invalidated by recent work on the deep sea floor (SWALLOW and WORTHINGTON, 1957, p.1183; HEEZEN,

1959, p.714). However, subsequent reworking cannot account for the frequent occurrence of ripple mark and convolute lamination of anomalous trend in the upper portions of well-graded turbidites, with no internal sign of a break in deposition (see Fig. 3).

The third alternative is the most difficult to assess if only because the nature of the external factors influencing deposition is virtually unknown. PRENTICE (1962, p. 106) contends that basal scour-structures in the Culm turbidites of Devon record the direction of turbidity flow during an early, high velocity stage whereas basal flow casts and ripple marks of anomalous trend indicate adjustment to the slope of the seabed during the depositional phase of the current (cf. BIRKENMAJER, 1958, p.146). The plausibility of this hypothesis is somewhat impaired by the nearly perpendicular relation of the two trends (erosional and depositional) which carries the implication that turbidity currents initially flowed along rather than down the lateral slopes of the trough. It is unlikely that such a situation could persist for long periods over a wide area.

The principal difficulty encountered in determining the trend and character of the depositional current regime of turbidites is that normally “the greater part of each greywacke post. . . throws no light on the direction of the depositional currents”

82

i G. KELLING

ssw NNE

A MICROLAVER

0 4

2

ESE WN MICROLAYER C

- 0 1 2 3 4 5 SCALE IN CM

Fig. 3. Left: Sketch, partly diagrammatic, of the base of a silty greywacke with flute casts, Valentian, Afon Camddwr, Rhayader, Wales. Right: Internal structure of the greywacke revealed on two mutually perpendicular faces to illustrate the method of sequential current analysis detailed in Table 11. Note overall grading upwards from microlayer 2. From specimen S/4/7200 in University College of

Swansea Geology Department Rock Collection.

(CRAIG and WALTON, 1962, p. 118). Occasionally, however, it is possible to decipher the entire erosional and depositional history of a single, usually thin, turbidite unit.

An example of this type, illustrated in Fig.3, is a silty greywacke of Valentian age from the river Camddwr, southwest of Rhayader, mid Wales. This thin (4.5 cm) bed carries prominent flute casts on the base with parallel trending asymmetrical ripple marks on the upper surface. The unit is graded overall, from fine sand within the flutes to very fine silt at the top and ripple-lamination is present throughout. Seven distinct microlayers may be distinguished within the turbidite, separated by junctions which may be erosional or non-depositional. Three-dimensional analysis of the attitude of laminae within successive microlayers enables the sequence of events shown in Table I1 to be constructed.

Consideration of the current-data in Table I1 shows that flute-erosion was accom- plished by flow from south-southwest and the variation in thickness of individual layers suggests that dominant supply was from the same direction. However, superimposed upon this main trend there was a complex and periodic interplay of transverse depositional (tractional) currents which commenced at the base of microlayer 2. Nevertheless the overall grading from microlayer 2 upwards shows that the bed represents essentially a single phase of deposition rather than a concatenation of distinct depositional events. Clearly, too, a time-interval, probably of some duration, inter- vened between the two episodes of flute-erosion.

TABLE I1

SEQUENTIAL ANALYSIS OF STRUCTURES WITHIN GREYWACKE SPECIMEN S/4/7200'

Level in Form and dimensions unit' of structure Nature and orientation of current Remarks

layer 7

layer 6

layer 5

layer 4

layer 3

layer 2

layer 1

layer 0

asymmetrical T-ripple marks X=70mm; h = 1 2 m m

asymmetrical T-ripple marks h=60+mm; h = 1 0 m m

? longitudinal dunes h.=50+mm; h = ?

longitudinal dune-like forms h=55mm; h = 1 6 m m

asymmetrical T-ripple marks h = 6 5 m m ; h = 1 4 m m

isolated T-ripple mnrks h= ?55mm; h = 18mm

group I1 flutes, corkscrew with lateral indentation

ripple-drift bedding with minor contortions

group I flutes, "whale back type"

black mudstone

depositional, from E20"S

depositional, from ? S5"E

depositional, from S20"W


depositional, from E1O"S

depositional, from W20"N or ? E20"S

erosional, from S25"W


erosional, from S25"W

continuous, slight basal erosion; cuts down to layer 4

discontinuous, depositional base

thin, discontinuous; occurs in troughs of layer 4 ripples

continuous, thins towards north-northeast; slight basal erosion

discontinuous, strong basal erosion

coarsest layer in unit; fills group I1 flutes

cut down to layer 0 in places

precise form of structure doubtful

cut through layer 0, max. depth 9.5 mm

-

SeeFig.3.

QQ w

84 G. KELLING

c

This example records the operation of some factor, other than the forward pro- gression of the turbidity current, which influenced the deposition of materials of fine sand and silt size from the flow. The absence of genuine slope-criteria (slump structures, flow casts, etc.) from this sequence is regarded as evidence that deposition did not occur actually on the marginal slope of the Welsh trough. On the other hand the periodicity of the transverse flow recorded in Table I1 suggests quasi-oscillatory currents while the principal direction of transverse currents (from between east and southeast) may be related most plausibly to the west-facing slope which in Valentian times may be assumed to have existed some distance to the east of Rhayader (cf. KNILL, 1959, Fig.4, 5).

Consideration of the hydraulic properties of turbidity currents suggests a possible explanation of the facts outlined above.

The arrival of the dense, high velocity, wedgeshaped nose of a turbidity current produces nearly instantaneous displacement of a large body of water. Some of this displacement occurs upwards or in the direction of flow but most of the water must be transferred laterally. The energy involved in this transference may be dissipated side-

Cd. v Ab Ld. D -

I ,I1 .* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I . - . . - - - * _ - - - _ _ . . . . . . .

Fig. 4. Approximately transverse (A-B) and longitudinal (C-D) sections of the main Welsh trough at the end of Valentian times to illustrate postulated relationships of turbidite formations and adjacent facies, on the assumption of longitudinal filling from the southwest. Only differential isostatic subsidence is allowed for. Vertical scale and slopes are greatly exaggerated. Inset shows outline map of Wales with location of lines of section. Lithofacies: a = limestone, shelly sandstone, calcareous siltstone; 6 = barren blocky mudstone; c = conglomerate and pebbly greywacke; d = black shale; e = greywacke turbidite. Localities: Fg. = Fishguard; Lp. = Lampeter; Lv. = Llandovery; Cd = Car- digan; s. F. = Strata Florida; A6. = Aberystwyth; Ld. = Llanidloes; Td. = Talerddig. Formations: I = Caradocian; 2 = Ashgillian; 3 = Strata Florida Grits (Middle Valentian); 4 = Aberystwyth Grits (UpEr Valentian).


ways in the form of surges comparable to the bow-waves of a fast ship. The existence of sea-bed features of sufficient size, such as the marginal slopes of the trough, may give rise to reflection and regeneration of the surge-waves which will return with trends approximating to the strike of the feature or slope. The energy and velocity of the reflected waves will be relatively small and will decrease with distance from the reflecting feature.

For any point in the path of a turbidity current there occurs a time-lag between the moment of displacement (the passage of the nose of the current) and the return of the reflected surge-waves. During this time turbidity flow continues and the slower, rearward portions of the current may have reached the point in question so that deposition may have commenced. While the turbidity current maintains velocities and turbulence sufficiently high to keep material finer than, say, medium sand in suspension it is doubtful whether the weak transverse movements will be able to exert any influence but during the later stages of deposition when fine sand and silt is being laid down the velocity of the transverse flow may match or even exceed the forward motion of the weakening turbidity current and transverse depositional structures may be produced.

Whether any of the mechanisms postulated above is in fact responsible for the formation of transverse structures it is evident that in many cases it is no longer possible to maintain the concept of a turbidite sequence as the product of spasmodic incursions of unidirectional, high-energy, density currents into an otherwise stagnant environment (cf. Dorr, 1963, p.127).

FACIES RELATIONSHIPS

Lateral relationships

The concept of turbidity flow carries implications of bathymetric significance. For example, turbidity currents are governed by gravity; consequently, axially derived turbidites' must occupy the bathymetric axis of any basin in which they occur (CUM- MINS, 1959b, p. 176) whereas uninterrupted pelagic sequences will accumulate either on more elevated portions of the sea-bed or in regions where turbidity flow is not active. This interpretation of relative bathymetry further implies that where thick turbidite sequences are axially derived the adjacent formations (in the cross-current sense) were deposited on surfaces sloping inwards towards the trough axis.

The mode of this lateral passage from the axial turbidite facies is of great environmental interest. In the Girvan district WILLIAMS (1962) has demonstrated very rapid changes in thickness and lithology as the Upper Ordovician neritic sediments are

Laterally derived turbidites, particularly fluxoturbidites (DZULYNSKI et al., 1959) under certain circumstances may have originated from turbidity currents which possessed insufficient energy to carry the load as far as the axis of the trough but this is probably a rare situation and no authentic British example is known to the writer.

86 G. KELLING

traced southwards through a transition group of slide conglomerates and laterally derived greywackes which interlinger marginally with thick axial turbidite formations (see p.79). Less complete evidence of a comparable passage occurs in rocks of similar age in the Rhinns of Galloway (see p.79). Moreover in the latter area the correspond- ing transition on the southern side of the turbidite belt may be discerned.

Here the main turbidite formation is at least 6,000 ft. thick with numerous thin bands of graptolitic black shale. The thickness decreases rapidly southwards and within twelve miles the greywackes are replaced by about 100 ft. of black shales and cherts (KELLING, 1961, p.55). This passage is achieved by an increase in the thickness of the lutite interbeds and a decrease in the number of greywacke beds. The turbidites, although thinner in the south, show a less marked decrease in median grain-size. The greywackes are mainly derived from the northeast so that this north-south section is approximately parallel to the depositional strike. The relationships described above therefore suggest that in Upper Ordovician times this part of the Scottish trough was asymmetrical in section with a bathymetric axis near the present Southern Uplands fault, flanked to the north by conglomeratic apron-sediments and passing south into a more elevated region of black shale accumulation. The rate of thinning of the turbidites indicates that this north-facing slope had a maximum inclination of 6".

A broadly similar situation can be inferred for mid Wales throughout much of the Bala-Valentian succession (Fig.4). Shelly and sandy mudstones and limestones domi- nate a shelf region lying mainly to the east of an arcuate line running from St. Davids through Rhayader. Westwards these sediments are replaced rapidly by unfossiliferous mudstones and siltstones, then by thin black shales with thick wedging bodies of conglomerate and coarse, pebbly greywackes (JONES, 1938, p. lxxxiii). This transition facies passes westwards into the graptolitic black shales (with or without turbidite intercalations) of central Wales which probably represent the bathymetric axis of the main Welsh trough at this period. The distal, northwestern margin of the basin can be readily defined through the occurrence of thick sequences of slumped shales and grits around Corris and Plynlimon (northeast of Aberystwyth). These sediments appear to have been shed from a shallower region lying to the north and northeast (Berwyns- Bala arch), or possibly from the postulated land mass in the Irish Sea (JONES, 1938, p. lxxviii).

Much interest attaches to the occurrence of conglomerates in the transition facies on the southeastern flank of the Welsh trough. These conglomerates do not mark faunal breaks (DAVIES and PLATT, 1933, p.203) but represent brief incursions of coarse material into an environment otherwise dominated by deposition of black shales. The lenticular bodies of conglomerate are elongate in a roughly strikewise (southwest- northeast) direction and some become appreciably coarser towards the southwest. Preliminary observations by the writer suggest that the rudites occupy several channels of variable size and some bodies show evidence of slide-origin. Signs of slumping are also widespread. Associated sedimentary structures are mainly deformational although tool and scour marks occur. Derivation is complex but most of the rudites appear to be laterally derived, from the south-southeast. These coarser bands may


represent a rudite apron formed at the base of the eastern slope of the Welsh trough. SMITH and RAST (1958) describe an Upper Dalradian sequence of pebbly arenites,

limestones and pelites from Argyll, southwest Scottish Highlands, with features highly reminiscent of the transition facies described above.

Stratigraphical relationships

The Ordovician turbidites of southern Scotland and western Ireland succeed thin sequences of graptolitic black shales, radiolarian cherts and spilitic effusives. A similar euxinic-volcanic suite characterises much of the Ordovician of central and western Wales, preceding the main turbidite phase in the Welsh trough. In Devon and Cornwall black shales and cherts precede the Namurian turbidite flood (GOLDRING, 1962, p.87).

Significantly, the marked lithological change from pelagic deposition to sedimentation of coarse clastics is seldom accompanied by a tectonic or faunal break. Moreover pelagic sediments occur between individual turbidite units. However, black shales and cherts often have wider lateral extent than associated turbidites presumably because the former, as products of vertical settling from suspension, are not subject to the restrictions imposed by bottom topography on gravity controlled turbidity flows.

The absolute bathymetric position of geosynclinal euxinic sequences is still in dispute but the basin-wide extent of the precursor ewinic phase indicates that the controlling factor was probably not depth per se but lack of coarse terrigenous detritus - a concept embodied in AUBOUIN’S (1959) phrase “pkriode de vacuitk” but without the connotation of initial deepening. Therefore the appearance of turbidites need not imply drastic diastrophic changes within the basin but rather may reflect an increase in the supply of coarse detritus at a particular point. Such an increase may be controlled ultimately by tectonic events in the source area relative to the rate of basin subsidence. This tectonism can produce widespread and important breaks in the shelf- areas but effects may be muted or entirely suppressed in the deeper region of the trough (CROOK, 1959, p.338). Where longitudinal transport is dominant the phase of vacuity and the phase of filling may exist simultaneously, euxinic sediments accumulating in distal parts of the trough beyond the reach of the coarse detritus which is being deposited in regions nearer to the source.

The Bala-Valentian rocks of central and western Wales furnish one example of this mode of trough filling. Throughout Late Ordovician and Early Silurian times the zone of transition marking the eastern limit of the trough was almost static along the line of the mobile, northeast trending Towy anticline in east central Wales. To the west, deposition of graptolitic black shale was virtually continuous but thick diachronous greywackes of probable southwesterly source (WOOD and SMITH, 1959) which appeared first in the Caradocian near Fishguard spread progressively north and eastwards throughout the succeeding periods (JONES, 1938, fig.1; KNILL, 1959, p.322). The later Valentian greywackes thus appear to overlap the transition facies to the east (Fig.4) as axially supplied turbidites began to fill the trough. There is virtually no evidence in

88 G. KELLING

these trough-sediments of the important unconformities which occur in the equivalent shelf-sequence to the east (apart from a local break at the base of the Upper Valentian in the country east of Aberystwyth).

Direct current evidence is not yet available from the uppermost Silurian of the Welsh trough but a study of Ludlovian facies indicates that the final stages of infilling were marked by lateral encroachment of shelf sediments from the east across the failing zone of axial turbidites (HOLLAND and LAWSON, 1963; CUMMINS, 1959b). Moreover facies changes within the Ludlovian are broadly synchronous in directions parallel to the length of the Welsh trough (HOLLAND and LAWSON, 1963, fig.17). These facts suggest that although this basin received most of its turbidite fill longitudinally from the southwest, the final phase was dominated by lateral supply of relatively fine- grained material.’

TECTONIC CONTROL OF TURBIDITE DEPOSITION

In his classic studies of the British Lower Palaeozoic geosyncline JONES (1938, 1955) drew attention to the close parallelism which exists between the distribution pattern of facies within the developing trough and the orientation of subsequent major tectonic structures. Recent studies of transport directions in Precambrian, Lower and Upper Palaeozoic turbidite sequences have emphasized this congruence of sedimentary and tectonic trends (see p.76). It has even been suggested that not only the trend but the sense of axial transport is related to the direction of plunge of later fold-axes (KNILL, 1960a; CUMMINS, 1959b, p.177) although this is not an invariable rule (cf. DEWEY, 1962, p.250; KELLING, 1962, p. 136).

Local variations in fold trend may be duplicated precisely by the directions of turbidite transport. Thus CUMMINS (1959b) describes the longitudinal filling in Salopian times of two mutually perpendicular troughs which lay across Denbighshire and Montgomeryshire, northeastern Wales. The respective east-west and north-south trends of these basins, deduced from facies distribution and transport directions, closely reflect the orientation of Caledonian structures in each area. JACKSON (1961) points out that the south-southwesterly source-direction of the turbidite Loweswater Flags (Lower Ordovician) of the Lake District is oblique to the east-west trend of the main Caledonian folds of Late Silurian age but is parallel to the local trend of pre- Caradocian structures.

Contemporaneous faulting as a factor in the production and distribution of turbidites has acquired new significance in recent studies. For example WILLIAMS (1962) ascribes the production of Caradocian slide conglomerates and associated greywackes in the Girvan region to slip along contemporaneous submarine fault-scarps. GILL

’ On empirical grounds it is highly improbable that a geosynclinal basin can be filled entirely by axial flow. The shallowing (and constriction) of the basin which must follow cessation of subsidence or active elevation will eventually bring even the central parts of the trough within reach of “normal” m-irine currents. In such an event currents generated on the relstively steeper lateral slopes will obviously be more effective than those travelling along the axis of the trough.


(1961) has reinterpreted the Visean Rush conglomerates and graded calcarenites of County Dublin in a similar manner. A more tenuous connection between faulting and turbidites is provided by WHITAKER (1962, pp.339, 350) who suggests that the site and trend of submarine channels in Ludlovian shelf-edge sediments in the Welsh Border- land were controlled by contemporaneous movement along normal cross-faults. Such channels may have provided routes of access enabling near-shore sediments to reach deeper parts of the basin as turbidites. The diversity in thickness and lithology of the shelf-edge sediments of Bala and Valentian age in the southern part of the Welsh Borderland has been explained in terms of pre-Wenlock movements along caledonoid structures such as the Towy anticline, and also on east-west cross-folds and faults (JONES, 1925; DAVIES and PLATT, 1933; WILLIAMS, 1953).

Tectonic events controlling geosynclinal sedimentation may be of two orders of magnitude. First there are basin-wide events which may be tensional or compression- al. Compression may produce constriction and perhaps separation of troughs and concurrent elevation of borderlands or even portions of the existing basin (MAC- GILLAVRY, 1961, pp.144145) and thus may provide conditions leading to sedimentation of turbidites. Such constriction is reflected in the common occurrence in the turbidites of fragments derived from older geosynclinal sediments and volcanics, while basin-wide submergence resulting in transgression across the shelf-areas appears to be correlated with the initiation of turbidite phases (see CUMMINS, 1961, p.77).

Second order events are of relatively local importance and comprise the contemporaneous movements on folds and faults detailed above. Such effects maintain local instability along the trough-margins and furnish one means (perhaps the most important) of initiating turbidity flow through periodic seismicity.

CONCLUSIONS

The first decade of the turbidite concept in Britain has seen the achievement of the following principal results:

(I) An exclusively shallow water origin for sandy sediments is no longer a tenable hypothesis. Greywackes of turbidite character may represent relatively deep milieus of deposition.

(2) Recognition of the dominant role of longitudinal transport in geosynclinal sequences (compared with the traditional concept of lateral derivation) has revolu- tionised views on provenance (cf. CUMMINS’ Wenlock greywackes, 1957, p.442). As a consequence the role of cordilleran sources such as the postulated land-ridge of Silu- rian times in the Irish Sea (JONES, 1938, p.cvi) may be somewhat diminished in importance.

(3) Longitudinal transport can also explain certain puzzling facies relationships, such as the “by-passing” of thin sequences of fine-grained rocks by thick, coarse turbidites of equivalent age and similar general source (e.g., Lower Silurian of southern Scotland, JONES, 1938, p.xciii).

90 G. KELLING

(4) The relative bathymetry of greywacke turbidites and black shales has been virtually reversed (see p.85-86).

(5) Studies of lithological variation and of transport directions in British turbidites have re-emphasized the interdependence of sedimentary pattern and tectonic framework in the developing geosyncline.

Despite the substantial progress which has been made many British geosynclinal arenites and rudites still await re-examination. Outstanding specific problems include the following:

( I ) The relative importance of flank supply (from cordilleras?) versus supply from tectonic welts athwart the trough. Both sources may subsequently give rise to longitudinal transport. To resolve this problem more petrologic data are required.

(2) The precise mode of transition from shelf to turbidite facies is in many cases unknown or imperfectly understood and awaits detailed sedimentological investigation.

(3) No two turbidite sequences are identical. In addition to the characters common to all turbidites each sequence possesses some distinctive features which reflect differences not only in provenance but also in hydraulic regime, basin topography and bathymetry. Careful documentation of such features may enable general or specific conclusions to be drawn as to the environmental status of particular sequences. As an example, it is clear that in some turbidite formations the role of indigenous or reworking bottom currents may be greater than is commonly supposed (see pp.81-85). It is obviously desirable to ascertain the extent of such influences.

Many of the opinions and conclusions expressed in earlier sections of this paper are founded on hypothesis or on empirical reasoning. Some will almost certainly prove to be inadequate or incorrect. However they are offered in the expectation that they will stimulate further effort in what has so far proved to be a very fruitful field of research.

REFERENCES

ALLEN, J. R. L., 1960. The Mam Tor Sandstones: a “turbidite” facies of the Namurian deltas of Derbyshire, England. J. Sediment. Petrol., 30 : 193-208.

AUBOIN, J., 1959. A propos d’un centenaire: les aventures de la notion de g6osynclinal. Rev. Gkogrqh. Phys. Gkol. Dyn., 2 : 135-188.

BASSETT, D. A. and WALTON, E. K., 1960. The Hell’s Mouth Grits: Cambrian greywackes in St. Tudwal’s Peninsula, North Wales. Quart. J. Geol. Soc. London, 116 : 85-110.

BIRKENMAJER, K., 1958. Oriented flowage casts and marks in the Carpathian flysch and their relation to flute and groove casts. Actu Geol. Polon., 8 : 117-148.

COPE, R. N., 1959. The Silurian rocks of the Devilsbit Mountain district, County Tipperary. Proc. Roy. Irish Acad., Sect. E, 60 (6) : 217-242.

CRAIG, G. Y. and WALTON, E. K., 1962. Sedimentary structures and palaeocurrent directions from the Silurian rocks of Kircudbrightshire. Trans. Eiiinburgh Geol. SOC., 19 : 100-119.

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REVIEW OF TURBIDITE STUDIES IN THE UNITED STATES

E A R L E F . M C B R l D E

Department of Geology, University of Texas, Austin, Texas (U. S. A . )

SUMMARY

Although the study of turbidites in the United States is increasing at a fast pace, most references to turbidites to date are short articles that describe the presence of alleged turbidites or treat one aspect of them. Many of the more detailed studies are unpublished theses or dissertations that receive little circulation.

Most studies have been limited to outcrop features with emphasis on the description of sedimentary structures. A few detailed studies include thin section petrography and the mapping of directional current structures.

The flysch-type formations of the Appalachian and Ouachita geosynclines, and the Tertiary Basin deposits of southern California have received the most study. These areas have totally different tectonic frameworks and enable comparisons to be made between turbidites of linear geosynclines and turbidites of small, steep-walled basins. The depositional history of turbidites in these is summarized.

INTRODUCTION

Turbidites are significant sedimentary rocks; not only do they yield information on the physical properties of a fascinating and important agent of erosion, transportation, and deposition, but they yield some of the most detailed clues to the geologic history of sedimentary basins that contain them. Study of turbidites in the United States is proceeding at an increasing rate. About half the references on turbidites that have appeared since 1950 have appeared in the last three years. However, most of these references are abstracts or short articles in which the presence of supposed turbidites is merely noted or a particular aspect of turbidites is described. Additional brief comments appear in lengthy geologic reports of areas in which turbidites are present. Although detailed sedimentological reports exist, many are unpublished Master’s theses or Doctoral dissertations that are available, once one becomes aware of their existence, only through library loan or purchase of a microfilm copy. To ignore unpublished works in a review of United States turbidites would be to omit important information; to attempt to discover, obtain, and review all such work in a short time

94 E. F. McBRIDE

is impractical. However, in order that this article may be as broad as possible, unpublished works that the writer is familiar with are included in the review.

In Table I turbidite references are summarized as to the rock unit studied and its locality, the kind of article, and the subject matter covered; this table presents the major review data. Complete references to the works cited are given at the end of the article. Localities of turbidites studied to date are shown in Fig. 1. The writer is aware

Fig. 1 . Map of localities of turbidites mentioned in Table I.

of additional localities where turbidites have been recognized and studied, but the results have not yet appeared in print. Undoubtedly new localities of turbidites will be found in the future, particularly in the western United States where many areas have received only reconnaissance study.

The term turbidites was introduced by KUENEN (1957, p. 231) for all deposits of turbidity currents. In this paper turbidite will be used for the deposit of individual turbidity currents; that is, a turbidity current deposits one turbidite bed (sedimentation unit). Turbidites will be used for a group of such beds. Although turbidity current deposits have been recognized in non-marine deposits, such as those in Pleistocene Lake Bonneville, Utah (FETH, 1954), and modern Lake Mead (GOULD, 1951), the term turbidite has by usage acquired the connotation of maring deposit and is used as such in this review. Use offresh water turbidite or non-marine turbidite should serve to distinguish these other rare deposits.

This review is restricted to studies of ancient turbidites of the continental United States exclusive of Alaska and does not treat the many important contributions that

TABLE 1

SUMMARY OF TURBIDITE REFERENCES _ _ _ _ _ _ _ _ ~

I_ --

Type of Subject matter2 Paleocurrent map Reference Rock unit Locality article’

Appalachians

BIRD (1961)

FRAKE~ (1961)

KUENEN ( 1956)

LOWMAN (1961)

MCBRDE (1 96h)

MCIVER (1961)

MELLEN ( I 956)

Renssalaer (C.) New York

(DeV.1 Pennsylvania

“Portage” (Dev.) New York

Deepkill (Ord.) New Yolk

Martinsburg (Ord.) Virginia to New York

“Portage” (Dev.) New York, Pennsyl- vania, Maryland

(Pre-C.) Georgia

SMOOR (1960) Normnnskill (Ord.) New York

A Geologic history; turbidites comprise much of the section.

S; describes varicolored and non-red turbidites

S; argues for turbidity current origin in deep water.

Describes presence of sedimentary flow breccias and turbidites.

T, S, M; general sedimentology of a flysch unit along a 400 mile distance.

P

P

A

P

U T, S, M; general sedimentology of turbidites and partially equivalent non-turbidites.

P S, M; argues for turbidity current deposition.

Mapped 32 sole marks.

Mapped over 700 sole marks; transverse, oblique and lateral transport.

Mapped over 2,400 sole marks. Very uniform transverse orientation over entire area.

Mapped 18 cross-beds. Longitudinal transport.

U T; grain orientation study; grains oriented parallel and imbricate upcurrent.

Measured flute casts and grain orientation at 7 localities. Longitudinal transport.

A = abstract, U = unpublished thesis or dissertation, N = note, P = published article, M = map. 9 T = textwe, S = sedimentary structures, M = mineralogy, P = paleontology, Sy = stratigraphy.

W v,

TABLE I (continued) ~~~~ -~

Reference Rock unit Locality

S ~ O N (1959) Naples (“Portage”; New York DeV.)

SUTTON (1960) Naples (“Portage”; New York

VAN HOUTEN (1954) Martinsburg (Ord.) New Jersey

WEBER (1961) Normanskill and New York and Charney (Ord.) Canada

WEBER and MIDDLE- Normanskill and New Yolk and TON (1961) Charney (Ord.) Canada

DeV.)

Delaware Basin

HULL (1957) Delaware Mountain Texas, New Mexico (Permian)

NEWELL et al. (1953) Permian formations Texas, New Mexico

RIGBY (1953) Permian formations Texas

RIGBY (1958) Permian formations Texas

Basins of Calijornia

BALDWIN (1959) Pic0 and Repetto Ventura Basin (Pliocene)

Type of article Subject matter Paleocurrent map

N S, Sy; uses flute cast orientation to aid in correlation.

Mapped drag marks and flute casts a t over 50 localities.

P Chiefly stratigraphy; S; concludes turbidities are clinothem and fondothem deposits.

S; argues for turbidity current deposition. N

N Geochemistry of presumed turbidites.

P Geochemistry of presumed turbidites.

P S, M; general sedimentology; sands brought into deep basin by turbidity currents and later reworked.

S, M; treats a reef complex; describes turbidites and submarine slide and slump deposits.

Notes occurrence of subaqueous landslides and associated turbidites.

Brief mention of turbidites associated with mass submarine movements.

P

A

P

U T, S, M; general sedimentology of unindurated turbidites.

? a

Paleocurrent map Reference Rock unit Type of

Locality article Subject matter

Topanga (Miocene) Pic0 (Pliocene) Knox- ville (Jurassic)

P Brief description ofturbidites; emphasis on submarine slide and mudflow deposits.

CROWELL (1957)

S, P; argues for transportation and deposition by turbidity currents; deep water indicated by Foraminifera.

T; grain orientation study; many beds have orientations athwart sole marks.

T, S, M, Sy, P; general sedimentology of ancient submarine “fan”.

NATLAND and KUENEN (1951)

(Pliocene) Ventura Basin P

not stated A Sporrs (1962)

5 8

Mapped over 300 cross- beds and a few other structures; radial “fan” CI

dispersion. 2:

SULLWOLD (1960) Modelo (Miocene) Ventura Basin P

SULLWOLD (1961)

WINTERER (1954)

Several Tertiary format ions

Tertiary formations

P

Ventura Basin U

S, Sy; emphasis on geometry of turbidites.

T, S, Sy; part of an areal geologic report.

Ouaclrita foldbelr

BOKMAN (1953) Stanley (Carbon.) Oklahoma

Oklahoma

P

A

General sedimentology with emphasis on T and M; concluded sandstones were deposited by “turbidity flows”.

Concludes units are typical black-shale flysch facies with many turbidites and some depositional erratic boulders.

S; Brief depositional history of flysch units as part of geologic report.

CLINE (1959) Stanley, Jackfork and Johns Valley (Carbon.)

CLINE (1960) Stanley, Jackfork and Oklahoma Johns Valley (Carbon.)

P

v)

TABLE I fcontinued)

Subject matter Paleocurrent map Type ?t Locality article Referznce Rock unit

COTERA (1962) Tesnus (Carbon.) Texas

JOHNSON (1962) Tesnus (Carbon.) Texas

KIMBERLY (1961) Smithwick (Penn.) Texas

MCBRIDE f1962b) Haymond (Penn.) Texas

RHNEMUND and (Carboniferous) Arkansas DANILCHIK (1957)

SHELBURNE (1960) Stanley, Jackfork, Oklahoma Johns Valley (Carbon.)

Other localities

Don (1961) Squantum (Middle Mascachiisetts

FETH (1954) Pleistocene Utah

Pal.)

U T, S, M; General sedimentology; concludes some Mapped 40 sole marks; but not all sandstones of the formation are chiefly transverse trans- turbidites. port.

S; paleocurrent study of sandstones possibly Mapped several beds at deposited by turbidity currents. each of 47 localities;

chiefly transverse transport.

Mapped over 100 directional features, chiefly

Longitudinal transport.

U

U T, S, M; general sedimentology of a thin (450 ft. thick) unit of turbidites and slumpfolds.

groove and flute casts. I”

E : r 0

A Concludes unit is typical flysch with many turbidites and some submarine slide deposits.

Data on directional structures are given in explanation accompanying geologic map.

S; brief dspositional history as part of geologic report; sole marks indicate longitudinal current transport.

M Turbidity current origin not claimed by authors. Longitudinal transport shown by sole marks. Non-turbidites probably included in study.

P

P S, Sv; brief description of turbidites; emphasis on pebbly to bouldery mudstones.

Sedimentary structures suggest turbidites in Pleistocene lake deposits.

A

TABLE I (continued)

Reference

FAG AN (1 962)

Hovr (1 959)

PaSSEGA (1 954)

PHINNEY (1961)

WILSON (1950)

~

Rock unit

Carboniferous

Wilcox (Eocene)

Dakota (Cret.) Pottsville (Penn.)

Meguma (Pte-C. or Ord.)

Vanceburg (Miss.)

Type of Subject matter Paleocurrent map Locality article

Nevada

Texas

Wyoming Tennessee

P S, M, Sy; turbidites associated with chert and volcanic rock in eugeosynclinal deposits.

Sy; large channel (3,000 ft. deep) attributed to erosion by turbidity currents: study of subsurface data.

T, S; emphasis on importance of turbidites to oil exploration; gives examples of alleged turbidites.

P

P

Nova Scotia, Canada A Features suggest turbidites

Ohio, Kentucky U S, Sy; thesis on “flow makings” as current Mapped 39 readings in indicators; concluded sandstones probably deposited by “density currents”

a small area.

C 2 rl m U

100 E. F. McBRIDE

describe Pleistocene and Recent turbidites of the continental borderland or ocean basins.

AREAS OF STUDY

In the United States turbidites have been identified in rocks ranging from Precambrian to Pliocene in age and from a wide range of geologic settings. The bulk of turbidite studies has been in the Paleozoic foldbelts (the Appalachian Mountains of eastern United States, the Ouachita Mountains in Arkansas and Oklahoma and structural extension in Texas) and in the Tertiary Coast Ranges and adjacent areas in southern California. Turbidites of the Appalachians and Ouachita system are chiefly typical flysch sandstone of Precambrian and Paleozoic age that were deposited in linear geosynclines. In contrast, the Tertiary turbidites in California were deposited in relatively small, steep-sided basins such as exist today offshore (GORSLINE and EMERY, 1959; EMERY, 1960). Turbidites have been described in yet another geologic setting - the Permian Reef complex of Texas and New Mexico. Here turbidites were deposited in a deep basin rimmed much of the time by reefs. Other areas where alleged turbidites have been identified are listed in Table I and are shown in Fig. 1. With the exception of FAGAN’S (1962) paper on Carboniferous eugeosynclinal rocks of Nevada, most references of the ,,other localities” merely note the presence of turbidites in the particular area studied.

TECHNIQUES AND TOPICS OF STUDY

Although turbidites have been studied by most techniques common in sedimentology, most studies have been largely limited to field descriptions of gross lithology, bedding characteristics, and the sedimentary structures that are characteristic of turbidite sequences. Quantitative data on the abundance of various internal bedding structures (graded bedding, convolute bedding, and the like) have been recorded only by KIMBERLY (1 96 l ) , MCIVER (1 961) and MCBRIDE (1 962a). McIver was able to compare the abundance of various structures in a distal marine turbidite facies with partially time equivalent proximal marine (mostly non-turbidites) and fluvial beds.

In most studies beyond those of reconnaissance nature paleocurrent information was obtained, and numerous workers have compiled paleocurrent maps (see Table I). Sole marks, chiefly flute casts and groove casts (drag-mark variety) are the most commonly used directional structure both because of their prevalence and ease of measurement. Cross-bedding has also been used by some workers, but generally in formations where sole marks are not exposed. Of minor importance as directional structures used in mapping are other types of sole marks, parting lineation, and clast or fossil orientation. The general practice has been to record only one ,,current” reading per bed, but to get as many readings as possible at each outcrop and summarize them in

TURBIDITE STUDIES IN THE UNITED STATES 101

some form of rose diagram. The form of the rose diagram has not been standardized, but one similar to the concentric circle diagram introduced by CROWELL (1955) is the most popular.

The compilation of detailed (bed by bed) measured sections as a means of correla- ting individual beds by either petrographic features or bed thickness has not yet been attempted. SUTTON (1960), however, has been able to make approximate correlation of sections separated tens of miles by making and comparing “logs” on which are plotted the azimuth of flute casts at their particular stratigraphic position.

Various laboratory techniques have been applied to study the texture and composition of turbidite samples. Grain size studies have been made by mechanical analyses of unconsolidated samples by BALDWIN (1959), NATLAND and KUENEN (1951), and SULLWOLD (1960); and on consolidated samples by using thin sections by COTERA (1 962) and MCBRIDE (1 962a). Brief descriptions on the mineralogy of turbidites are given by numerous writers, but the most comprehensive works are those by BOKMAN (1953), KIMBERLY (1961), WEBER and MIDDLETON (1961), COTERA (1962) and MCBRIDE (1962a). A geochemical study of the concentration of metallic elements in turbidite beds by WEBER and MIDDLETON (1961) found the variation between successive beds and between sections to be greater than within beds and between formations probably as a result of the relative distance a turbidite had traveled from its source.

Grain orientation from thin sections have been studied by SMOOR (1960), COTERA (1962), MCBRIDE (1962a), and SPOTTS (1962). Cotera’s study .includes some non- turbidites and he did not specify which of his samples he considered to b: turbidites. McBride found a highly preferrred orientation and upcurrent imbrication but was unable to determine whether the orientation was chiefly a depositional fabric or the result of tectonic deformation. Smoor found a consistent parallelism between flute casts and grains in folded beds but did not consider effects of deformation. Spotts worked on undeformed Tertiary turbidites and found a pronounced deviation (average of 47 degrees) between sole marks and associated grain orientation that he attributed to a change in the direction of current flow between the time of flute eiosion and grain deposition. Spotts and Smoor also noted a distinct upcurrent imbrication of grains. MCIVER (1961) reported a high degree of parallelism between sole marks and “grain orientation” in both unfolded and steeply dipping beds. The “grain orientation” was determined indirectly by measuring dielectric anisotropy with a device operated by the Shell Development Company.

Information about the areal dimension and shape in plan view of turbidites is meager. The importance of this information to the petroleum industry and the difficulties of determining it from subsurface techniques was emphasized by SULLWOLD (1961). From knowledge of turbitites in the Tertiary basins of California, Sullwold proposed three regions in which characteristic geometry of turbidites might develop: channel or submarine canyon, fan, and basin floor. He also described possible ancient deposits of each environment. An example of a submarine canyon that existed at the edge of the continental shelf in Texas during Eocene time was described by HOYT (l959), who mapped the extent of the channel in the subsurface using electric logs. The

102 E. F. McBRIDE

channel at its largest is 10 miles wide, 3,000 ft. deep, and 50 miles long, and was presumably cut and filled largely by turbidity currents.

PASSEGA (1954) has maintained that the geometry and texture of turbidites deposited in basins differ markedly from those deposited on shelves. Passega describes the Dakota and New Castle-Muddy Formations of Cretaceous age in the Powder River Basin, Wyoming, as examples of shelf turbidites. The evidences cited for a turbidity current origin of these deposits, however, is not wholly convincing to the writer.

SUMMARY OF DEPOSITIONAL HlSTORY OF MAJOR TURBIDlTE BASlNS

Although the study of turbidites in North America is still in the infant stages, work to date reveals interesting paleocurrent patterns and inferences about paleogeography. A brief summary is given below for several areas where our knowledge is most complete.

Appalachians

In the southern part of the Appalachian geosyncline turbidites showing longitudinal transport (parallel to the tectonic strike) were deposited during Cambrian time (MELLEN, 1956). During Ordovician time turbidites showing transverse, oblique, and longitudinal transport and derived from a source to the east were deposited in the central Appalachians (MCBRIDE, 1962a); whereas farther north, a similarly complex paleocurrent pattern developed from turbidites derived chiefly from borderlands to the west of the geosyncline (SMMOOR, 1960; BIRD, 1961). Turbidites were again deposited during the Devonian in the Central Appalachians and New York. These turbidites show a remarkably uniform paleocurrent pattern from east to west over several thousand square miles (SUTTON, 1959; MCTVER, 1961). The lateral extent of the turbidites and paleocurrent patterns .show that the geosyncline during Ordovician time had the shape of a long doubly plunging trough oriented parallel to the bordering sourceland; whereas during Devonian time the basin was broader and had only a slope away from the sourceland and perpendicular to the geosynclinal axis.

Ouachita foldbelt

Geosynclinal deposits of the Ouachita system extend a distance of 1,300 miles, largely in the subsurface, along the southern edge of the Central Stable Region of North America (FLAWN et al., 196 1). Turbidites of Mississippian and Pennsylvanian flysch- type deposits are exposed in the Ouachita Mountains in Arkansas and Oklahoma; and at the edge of the Llano uplift and in the Marathon Basin, Texas. Turbidites in the Ouachita Mountains and the Llano uplift show chiefly longitudinal transport and were derived from inferred source lands to the east (REINEMUND and DANILCHIK,

TURBIDITE STUDIES IN THE UNITED STATES 103

1957l; SHELBURNE, 1960; KIMBERLY, 1961). The Marathon Basin has at least two distinct turbidite-bearing units, both with sources to the east. The older formation (Tesnus) shows predominantly transverse transport (JOHNSON, 1962; COTERA, 1962), whereas the younger (Haymond) formation shows chiefly longitudinal but important transverse transport in addition (MCBRIDE, 1962b).

Southern California

Turbidites of the Tertiary Basins of southern California show important differences from those of the long geosynclinal belts because of their different tectonic setting. These turbidites were deposited in narrow, steep-walled basins that were filled generally by sediment derived from local source areas (WINTERER, 1954; BALDWIN, 1959; SULLWOLD, 1960), similar to conditions that can be studied today in offshore basins along the Continental Borderland (GORSLINE and EMERY, 1959). Turbidites of the Modelo Formation show a semi-radial dispersal pattern that indicates deposition as a fan off the mouth of a submarine canyon (SULLWOLD, 1960). The great abundance of slump structures and conglomerate beds in the Tertiary formations undoubtedly also reflects the steep slopes of the basin walls (WINTERER, 1954; BALDWIN, 1959). The Tertiary turbidites are unique among those in North America for additional reasons. Paleoecologic studies of the Foraminifera of the pelagic clays interbedded with turbidites have produced strong documentation for water depths of several thousand feet for much of the time of turbidity current deposition (NATLAND and KUENEN, 195 1 ; NATLAND, 1957). Furthermore, the Tertiary turbidites are economi- cally important inasmuch as they have already yielded billions of barrels of oil (SULLWOLD, 196 l), a feature not characteristic of turbidites of the geosynclines.

The study of turbidites has led to a revision of our concept of geosynclinal sedimentation. In nearly all studies the evidence points to deposition of turbidites below wave base in fairly deep water. The recognition of turbidites in the flysch units of most linear geosynclines has destroyed the age-old concept that geosynclines are filled only by shallow water deposits; but at the same time this recognition has opened the way to re-evaluating our ideas concerning the sedimentary and tectonic history of basins of deposition.

NOTE

Additional published works dealing with turbidites that have appeared since this manuscript was submitted include a discussion of subaqueous gravity depositional processes by DOTT (1963), a study of quartz grain sizes and shapes in turbidites by MIDDLETON (1962), and an abstract describing features of a carbonate flysch unit by THOMASSON and THOMSON (1962).

Paleocurrent data only were given by Reinemund and Danilchik.

104 E. F. McBRlDE

ACKNOWLEDGEMENTS

The writer would like to acknowledge helpful comments by R. L. Folk and F. J. Pettijohn. Errors of omission are solely those of the writer.

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BALDWIN, E. J., 1959. Pliocene Turbidity Current Deposits in Ventura Basin, California. M. Sc. thesis,

BIRD, J. M., 1961. Age and origin of the Rensselaer Graywackes, Nassau Quadrangle, south-central

BOKMAN, J., 1953. Lithology and petrology of the Stanley and Jackfork formations. J. Geol., 61 :

CLINE, L. M., 1959. Black-shale flysch facies of the Ouachita Mountains, southeastern Oklahoma

CLINE, L. M., 1960. Late Paleozoic rocks of the Ouachita Mountains. Oklahoma, Geol. Surv. Bull.,

COTERA, A. S., 1962. Petrology and Petrography of Mississippian-Pennsylvanian Tesnus Formation,

CROWELL, J. C., 1955. Directionalcurrent structures from the prealpine flysch, Switzerland. Bull.

CROWELL, J. C., 1957. Origin of pebbly mudstones. Bull. Geol. SOC. Am., 68 : 993-1010. Don JR., R. H., 1961. Squantum “tillite”, Massachusetts - evidence of glaciation or subaqueous

mass movements? Bull. Geol. SOC. Am., 72 : 1289-1306. Don JR., R. H., 1963. Dynamics of subaqueous gravity depositional processes. Bull. Am. Assoc.

Petrol. Geologists., 47 : 104-128. EMERY, K. O., 1960. The Sea off Southern California; a Modern Habitat of Petroleum. Wiley, New

York, 366 pp. FAGAN, J. J., 1962. Carboniferous cherts, turbidites, and volcanic rocks in northern Independence

Range, Nevada. Bull. Geol. Soc. Am., 73 : 595-612. FETH, J. H., 1954. Convoluted bedding suggests turbidity-current deposition in Pleistocene Lake

Bonneville, Utah (Abstract). Bull. Geol. SOC. Am., 65 : 1251. FLAWN, P. T., GOLDSTEIN JR., J., KING, P. B. and WEAVER, C. E., 1961. The Ouachita system, Texas,

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Penn. Acad. Sci., 35 : 116-123. GORSLINE, D. S. and EMERY, K. O., 1959. Turbiditycurrent deposits in San Pedro and Santa Monica

Basins off southern California. Bull. Geol. SOC. Am., 70 : 279-290. COULD, H. R., 1951. Some quantitative aspects of Lake Mead turbidity currents. In: J. L. HOUGH

(Editor), Turbidity Currents and the Transportation of Coarse Sediments to Deep Water, a Symposium - SOC. Econ. Paleontologists Mineralogists Spec. Publ., 2 : 34-52.

Hour, W. V., 1959. Erosional channel in the middle Wilcox near Yoakum, Lavaca County, Texas. Trans. GuIfCoast Assoc. Geol. SOC., 9 : 41-50.

HULL JR., J. P. D., 1957. Petrogenesis of Permian Delaware Mountain Sandstone, Texas and New Mexico. Bull. Am. Assoc. Petrol. Geologists, 41 : 278-307.

JOHNSON, K. E., 1962. Paleocurrent study of the Tesnus Formation, Marathon Basin, Texas. J. Sediment. Petrol., 32 : 781-792.

KIMBERLY, J. E., 1961. Sedimentology of the Smithwick Formation, Burnet County, Texas. M. A. thesis, Univ. of Texas, 95 pp.

KUENEN, Ph. H., 1956. Problematic origin of the Naples rocks around Ithaca, New York. Geol. Mijnbouw, 18 : 277-283.

KUENEN, PH. H., 1957. Sole markings of graded graywacke beds. J. Geol., 65 : 241-258. LOWMAN, S. W., 1961. Sedimentary environment of the Deepkill “Black Shale” (Ordovician Beek-

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TURBlDITE STUDIES IN THE UNITED STATES 105

MCBRIDE, E. F., 1962a. Flysch and associated beds of the Martinsburg Formation (Ordovician), central Appalachians. J. Sediment. Petrol., 32 : 39-91.

MCBRIDE, E. F., 1962b. Sedimentology of the Haymond Formation (Pennsylvanian flysch), Marathon Basin, Texas (Abstract). Geol. SOC. Am., Spec. Papers, 73 : 204 pp.

MCIVER, N. L., 1961. Upper Devonian Marine Sedimentation in the Central Appalachians. Ph. D. dissertation, Johns Hopkins Univ., 530 pp.

MELLEN, J., 1956. Precambrian sedimentation in the northheast part of Cohutta Mountain Qua- drangle, Georgia. Georgia Mineral Newsletter, 9 : 46-61.

MIDDLETON, G. V., 1962. Size and sphericity of quartz grains in two turbidite formations. J. Sediment. Petrol., 32 : 725-742.

NATLAND, M. L., 1957. Paleoecology of west coast Tertiary sediments. In: H. S. LADD (Editor). Treatise on Marine Ecology and Paleoecology - Geol. SOC. Am., Mem., 67 ; 543-572.

NATLAND, M. L. and KUENEN, PH. H., 1951. Sedimentary history of the Ventura Basin, California, and the action of turbidity currents. In: J. L. HOUGH (Editor), Turbidity Currents and the Transporta- tion of Coarse Sediments to Deep Water, a Symposium - SOC. Eon. Paleontologists Mineralogists, Spec. Publ., 2 : 76-107.

NEWELL, N. D., RIGBY, J. K., FISCHER, A. G., WHITEMAN, A. J., HICKOX, J. E. and BRADLEY, J. S., 1953. The Permian Reef Complex of the Guadalupe Mountains Region, Texas and New Mexico. Freeman, San Francisco, 236 pp.

PASSEGA, R., 1954. Turbidity currents and petroleum exploration, Bull. Am. Assoc. Petrol. Geologists,

F'HJNNEY, W. C., 1961. Possible turbidity-current deposit in Nova Scotia (Abstract). Bull. Geol. SOC. Am., 72 : 1453-1454.

REINEMUND, J. A. and DANILCHIK, W., 1957. Preliminary Geologic Map of the Waldron Quadrangle and Adjacent Areas, Scotr County, Arkansas. Oil and Gas Investigation, Map OM 192, U. S. Geol. SUN., Washington.

RIGBY, J. K.. 1953. Subaqueous landslides and turbidity currents in the Permian of West Texas. (Abstract). J. Sediment. Petrol., 23 : 134.

RIGBY, J. K., 1958. Mass movements in Permian rocks of Trans-Pecos, Texas. J . Sediment. Petrol.,

SHELBURNE JR., 0. B., 1960. Geology of the Boktukola syncline, southeastern Oklahoma. Oklahoma,

SMOOR, P. B., 1960. Dimensional Grain Orientation Studies of Turbidite Graywackes. M. Sc. thesis,

Spom, J. H., 1962. Sand-grain orientation and imbrication in turbidity-current sandstones (Ab-

SULLWOLD JR., H. H., 1960. Tarzana fan, deep submarine fan of late Miocene age, Los Angeles

SULLWOLD JR., H. H., 1961. Turbidites in oil exploration. In: J. A. PETERSON, and J. C. O s m ,

SUTTON, R. G., 1959. Use of flute casts in stratigraphic correlation. Bull. Am. Assoc. Petrol. Geologists,

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THOMASSON, M. R. and THOMSON, A., 1962. Dimple limestone - a turbidite sequence (Abstract).

VAN HOUTEN, F. B., 1954. Sedimentary features of Martinsburg slate, northwestern New Jersey.

WEBER, J. N., 1961. Geochemistry of graywackes and shales. Science, 131 : 664-665. WEBER, J. N. and MIDDLETON, G. V., 1961. Geochemistry of turbidites of the Normanskill and

Charny formations. 1. Effect of turbidity currents on the chemical differentiation of turbidites. 2. Distribution of trace elements. Geochim. Cosntochim. Acta, 22 : 200-288.

WILSON, W. J., 1950. Subaqueous Flow-markings in the Lower Mississippian Strata of South-central Ohio and Adjacant Parts of Kentucky. M. Sc. thesis, Univ. of Cincinnati, Cincinnati.

WINTERER, J. L., 1954. Geology of Southeastern Ventura Basin, Los Angeles County, California. Ph. D. dissertation, Univ. of California, Los Angeles, 141 pp.

38 : 1871-1887.

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Bull. Geol. SOC. Am., 65 ; 813-818.

SEDIMENTARY STRUCTURES AND PALEOCURRENTS IN THE MARGINAL LITHOFACIES OF THE CENTRAL-CARPATHIAN FLYSCH

ROBERT M A R S C H A L K O

Geological Institute of D. &ur, Bratislava (Czechoslovakia)

SUMMARY

Marginal lithofacies have been formed immediately below the active source zone. They consist predominantly of coarse clastics. In direction to the basin axis, granulometric composition and thickness of beds decrease and transition from irregular bedding into graded bedding may be observed there. In this same direction, thickness of diagonal bedding - torrentional type - and magnitude of channels indicating direction of progressing currents with great strength are lessening too. The changes take place down the current.

Criterii concerning the direction of sedimentary transport are analyzed separately in the individual lithofacies. They are based upon the analysis of primary sedimentary structures - current lineations, sole markings, pebble orientation, grain orientation, diagonal bedding orientation - which are formed by the current and which determine the direction of the current. It has been found by means of the mapping of sedimentary structures in marginal lithofacies, that currents keep their constant direction during the Upper Eocene and Lower Oligocene. This fact, and the character of bedding and its spacial distribution, indicate the gravitation transport mediated by turbidite currents and slides.

On the ground of the investigations of paleocurrents and of the study of sedimentary slump folds, the primary and secondary slopes of marginal lithofacies deposition have been constructed.

INTRODUCTION

Sedimentological investigations in the Central-Carpathian flysch are important mainly because of its being carried on in the flysch lithofacies non-affected by tectonics. While the flysch lithofacies of many geosynclines were folded and broken in the paroxysm stage, especially those in marginal (near-cordillera) segments, the Central-Carpathinan flysch has not been affected by the folding. Therefore it is possible to define in detail the source-area and to study lithofacies formed in its immediate vicinity, socalled marginal lithofacies.

SEDIMENTARY STRUCTURES IN THE CENTRAL-CARPATHIAN FLYSCH 107

It has been proved - by means of analyses and comparison of structures in beds of the marginal lithofacies with those of the basal transgressive lithofacies - that the beds, although having morphologically similar form and thickness, did not originate by equal transport mechanisms. The majority of characteristics, found in the shallow- water transgressive lithofacies, are missing in the marginal lithofacies. Based on these comparisons a conclusion can be arrived at, viz. that marginal flysch lithofacies originated in a different sedimentation environment, where the influence of gravitational transport accompanied by the origin of slides and turbidity currents had been applied.

The gravitational transport, coming from differently situated centres, influenced the different velocities of sedimentation in the basin and has been the main cause of lateral changes in lithofacies. It can be followed mainly in sections perpendicular to the direction of the deposition of clastics. Gravitational transport had determined not only the irregular growth of lithofacies, but - in places of maximum supply - even bcal erosion phenomena, which may be overestimated in incomplete geological investigations and erroneously be considered as disconformities accompanied by inter- ruption of sedimentation.

It has been proved by sedimentological research, that the filling of this part of the basin in the Upper Eocene and Lower Oligocene had not taken place only laterally from the lateral source but also proceeded independently in a longitudinal direction from distant sources, which are not available for study at the present.

LOCATION

The Central-Carpathian flysch is situated in the West-Carpathians, where it forms mountain units and the filling in of tectonic depressions between the so-called core mountain-ranges. It is of Upper Eocene and Lower Oligocene age.

The marginal lithofacies studied form a component-part of a larger mountain-range of SariLkC Hory Mountains situated in the east. North of the core of the Cierna Hora Mountains and Spigsko-GemerskC Rudohorie Ore-Mountains the flysch reaches the valley of the Torysa River. In the west it is tectonically separated from the Branisko massif, and in the east from the Miocene and neo-volcanite formations.

ROUGH SPACE RELATIONS AND CRITERIA FOR THE MAPPING AND CLASSIFICATION OF

LITHOFACIES

It has been shown by geological mapping and stratigraphic investigations, that the flysch lithofacies have been differenciated between the underground of the Cierna Hora-Gemer source-area and the margin to the axis of the basin. While near the margin the lithofacies consist predominantly of thick conglomerate beds, in a direction from the margin to the axis it gradually decreases in thickness, grain size, erosion results and other characteristics, while the sorting improves. Beds in the form of flat elongated

108 R. MARSCHALKO

tongues reach 15-20 km and more towards the axis of the basin, but it is difficult to follow them. In the case of periodic alternations of beds, series of remarkable thickness have been formed, characterized by predominating complexes of clastics, available for mapping, i.e., the conglomeratic flysch. The ratio conglomerate/sandstone and claystone changes quickly basinward towards sandstones and claystones.

In the mapping of marginal lithofacies at various distances from the margin of the source-area in normal flysch sequences, isolated beds of large extent and thickness have been found, differentiated from the adjacent flysch series by a striking change of granulometric composition and by a development of characteristic internal slump structures, indicating the origin of submarine sliding. The flysch sequences are characterized by mass occurrences and maximums in the distribution of slide beds of great thickness - to such an extent that the mapping and correlation in three dimensions, and the classification of the wild flysch lithofacies, analogous to those of the Alps (Kaufmann, as quoted in TRUMPY, 1960) and of the Caucasus (VASSOEVICH, 1948) have been continued.

The mapping of characteristic structural and vector properties of the flysch clastics - agreeing strikingly in material and morphology, has brought results that are helpful in the classification of the separate lithofacies, and in the understanding of their development relations in the basin.

By means of micropaleontological investigation, the age of the beds has been determined as Upper Eocene and Lower Oligocene (MARSCHALKO, 1961), and the stratigraphic interval - on account of the younger Oligocene microfauna. Micropaleonto- logical investigation proved that the separated lithofacies, unstable in space, formed immense, finger-like bodies (WELLER, 1958), disappearing, without stratigraphic correlation value. Therefore it is only possible to use them for correlation in wider territory to a limited extent.

Macropaleontological dates from the basal transgressive lithofacies, and associations of planctonic and bentonic Foraminifera from the marginal lithofacies, indicate the exclusively marine environment of the source, without the smallest indications of brackish character. The abundance of plant detritus in the marginal lithofacies represents the resedimented remains.

In stratigraphical investigations we kept partly to the division of flysch according to

Fig.1. Lithofacial map of the Central-Carpathian flysch north of the Cierna Hora Mountains and northeast of the Branisko Mountains. I = The Mesozoic and Paleozoic underlier in the whole. 2 =

Basal transgressive lithofacies. 3 = Claystone lithofacies. 4 = Subflysch. 5 = Intermediate flysch. 6 = Wildflysch. 7 = Conglomeratic and microconglomeratic flysch. 2-7 = Upper Eocene to Lower Oligocene. 8 = Andesite bodies. 9 = Tortonian conglomerates (?). 10 = Alluvium. I1 = Actual border of lithofacies. I 2 = Supposed border of lithofacies: tectonic lines of greater importance; tectonic lines of lesser importance. 13 = Strike and slope of beds. 14 = Flute casts. 15 = Prod casts. 16 = Groove casts (the outer circle); brush casts (the inner circle). 17 = Orientation of long axes of pebbles (50 pieces). 18 = Current bedding. 19 = Oriented load casts. 20 = Sense of the movement of slump folds (marked by long line) perpendicular to the axis (short line). 21 = Subtracted direction of

the movement of giant ripples.

110 R. MARSCHALKO

VASSOEVICH (1948), and thus the following main lithofacies have been determined: (I) basal transgressive lithofacies, (2) claystone lithofacies and subflysch, (3) conglomeratic and microconglomeratic flysch, (4) typical and non-typical wild flysch, (5) intermediate flysch.

Their distribution is given in the lithofacial map (Fig.1). Lateral relations are presented by stratigraphic-facial schemes (Fig.2).

I I1 111 S N S N

,= b::t+:.a. 2 0 4 p q 5 m *L.".l Fig.2. Stratigraphic-facial schemes of marginal flysch lithofacies. Stratigraphical interval Upper Eocene-Lower Oligocene marked by full line. Cross-sections: I = JAKuboviany-Rozkoviany. I1 =

KvaFany-Sabinov. I11 = Kendice-Pregov. 1 = Basal transgressive lithofacies. 2 = Claystone lithofacies. 3 = Subflysch. 4 = Intermediate flysch. 5 = Wild flysch with slides. 6 = Conglomeratic and

microconglomeratic flysch.

TYPES OF BEDDING AND THEIR THREE DIMENSIONAL DISTRlBUTION IN LITHOFACIES

Basal transgressive lithofacies

In the West-Carpathians, the transgressive lithofacies were formed after the period of Cretaceous folding. There is a distinctive angular nonconformity with the underlying rocks of the crystalline, and with the Mesozoic of the Cierna Hora Mountains along the northern margin where the latter crops out. It represents a cycle, consisting essentially of two main lithotypes in strict sequence.

In the lower part are basal conglomerates and breccias, in the upper part subgraywackes and siltstones with sporadic slides which have macrofauna of different composition to those in the basal series.

Conglomerates and breccias completely reflect the composition of the local underlying sediments over which the transgression proceeded. In the majority of cases the material consists of homogenous dolomitic limestone breccias and conglomerates with a sandstone matrix. Well developed carst relief moderated the activity of traction currents. Therefore neither orientation of long axes of pebbles nor imbrication has been observed. The sorting is bad and stratification is not developed distinctly.

Different development has been observed in well-sorted heterogenous conglomerates alternating in beds of lens-like shape. Extension of beds of 20-30 cm in thickness hardly exceed 250 m. The lower surface of beds with abundant erosion channels, often

SEDIMENTARY STRUCTURES I N THE CENTRAL-CARPATHIAN FLYSCH 111

with a depth of 150-200 cm and a width of 4-10 m, are very irregular. In beds containing small pebbles, or more frequently in coarse-grained sandstones, cross-bedding is very common. This structure is very frequent in two to three open series which may reach the thickness of 10-80 cm. If outcrops cut the cross-laminated bodies perpendicularly to the current direction, arcuate laminae and so-called cross-bedding (“Kreuz- schichtung”, NIEHOFF 1958) appear in these cross-sections. In sections parallel to the current-direction, shovel-like concave laminae occur. According to NIEHOFF’S (1 958) classification, the cross-bedding of the arcuate type originates by means of movement of giant ripples and the simultaneous activity of rhythmically pulsating tidal currents.

From the study of the direction and slope of cross-bedded laminae in embankment bodies, it can be seen that the direction of traction currents (rose diagram Stefanska Huta, Fig.1) was first to east-northeast, northeast and northwest with small pole changes and crossing of current systems. According to NIEHOFF (1958), the maximum current direction indicates the slope, since in this direction the optimal slumping of beds has been found. The opinion may be proved by extensive slides of coarse clastics with macrofauna in fine-grained siltstones in the upper part of the transgressive lithofacies north of the ripple field.

Currents, transporting and sorting the coarse-clastic material from the southeast, south and southwest, did fade away in a northerly direction due to bathymetric conditions. In connection with this, the lithological changes of transgressive lithofacies in the vertical direction should be studied in all cross-sections known. In a vertical direction the medium diameter changes too. By the change in medium diameter thicknesses of series of the cross-bedding morphological distinctnessch ange as well (SCHWARZ- ACHER, 1953). In a vertical direction more abundant occurrence of horizontal lamination may be observed, interrupted by the growth of pyrite concretions and slump activity in some places. In upper parts, morphological characteristics of stratification disappear completely, and slow transition into claystones takes place. The disappearing of the transgressive cycle ends by slow vertical granulometric refinement of grains. The pelagic biotope appears with the Foraminifera association, whilst the macrofauna disappears completely.

Claystone lithofacies and subfIysch

Claystone lithofacies and subflysch develop slowly from the upper part of the transgressive lithofacies. They are characterized by marly claystones of light grey-blue colour with slight lamination of lighter colours. In some places concentrations of laminae of carbonates with high contents of Mn-carbonates may be observed.

In the upper part of the lithofacies, sedimentation of claystones has been perma- nently interrupted by deposition of 0.7-8 cm thick successions of laminae and beds of glauconitic sandstones with graded bedding (KUENEN and MIGLIORINI, 1950). In the southwestern part of the territory, predominance of horizontal lamination has been observed, while in the northern part current bedding of approximately 1 cm in size has developed, which serves in the study of current directions.

112 R. MARSCHALKO

The share of graded bedding in the composition of claystone lithofacies and subflysch is very small; the sorting of the coarse fraction is sometimes somewhat regular. Subgraywackes with graded bedding have distinct lower surfaces with sole markings and slightly laminated transitions overlying claystones.

Slump structures are only characteristic for certain areas. They are more abundant in the south and southwest than in the north. Whole successions of siltstone laminae with claystones have been affected by slumps. All stages of transition, from elongation, pressing, to tearing and migration have been observed in very complicated forms.

The present-day distribution of the claystone lithofacies of the subflysch, and the comparison with equivalent lithofacies in the adjacent territory, prove that the growing thickness in a northerly direction (300 m), in a northwesterly direction (200-300 m), indicate quick subsidence of the zone under the condition of slow sedimentation of claystones in the Upper Eocene. In a southeasterly direction, along the margin of the cierna Hora Mountains, lithofacies gradually lose their thickness and disappear. This phenomenon may be caused by: (Z) non-sedimentation of clay in the southern area, (2) lateral transition with the upper part of transgressive lithofacies and with the typical wild flysch, (3) erosive activity of extensive slides, especially in the place of their maximum entrance into the basin during deposition of the conglomeratic flysch and wild flysch.

All the alternations require an uplifted zone in the south.

Conglomeratic and microconglomeratic yysch

During geologic mapping, coarse-clastic beds of the conglomeratic flysch of the tongue-like shape forming three layered series, some even 80 m thick, deposited in the non-typical wild flysch have been found. They disappear in finger-like shapes in this wild flysch in northwesterly direction. In the north-northeasterly direction, the contact of the conglomeratic flysch with typical wild flysch is facial, the former wedges into the latter in several reasonably thick beds.

Conglomeratic and microconglomeratic flysch are characterized by several basic types of bedding with spacial distribution in lithofacies.

(I) The basic type is the graded bedding, in which a division of coarse-clastic from the bottom to the top has been found in several varieties. In the slow sorting of coarse fraction from the bottom to the top characteristic simple graded bedding arises (KUENEN, 1953; KSIAZKIEWICZ, 1954) with a characteristic asymmetrical shape. The average size of the coarse fraction does not exceed 6 cm, but the size of individual boulders reaches 1 x 2 m. Thickness of beds in claystone differ from 1-10.5 m.

In the repeated sorting of the coarse fraction in one bed, the recurrent graded bedding occurred (KUENEN, 1953; KSIAZKIEWICZ, 1954). This can be formed when a new turbidity current eroded - after some time - part of the claystones or the upper part of graded-bedded strata, and reduced its thickness. With respect to the fact that between beds with recurrent bedding no claystones have been developed (though their occurrence has been abundant in fragments in various segments of the bed), it may be


supposed that turbidity currents cause plain erosion and are the origin of seemingly recurrent bedding. This recurrent bedding is rather frequent in the conglomeratic flysch, though having such a different origin that it is necessary to differenciate it. Unusual types of bedding with sudden stops to the sorting of the coarse fraction and sharp separation from the fine-grained fraction, have also been found. Also in the upper strata there is a bed which ends sharply. Mutual ratio of thicknesses of both fractions is changing. The beds reach 0.5-8 m in thickness.

Graded bedding of described types is not equally developed as in the plain. The maximum concentration (60-70 %) has been observed in places, in the northwest- west-northwest, 10 km away from the present-day margin of the conglomeratic flysch in the southeast.

(2) A different type of bedding is represented by irregular bedding (mixed bedding, BIRKENMAJER, 1959) without horizontal sorting of fraction and without distinct inner orientation of the components. There are frequent claystone and sandstone fragments and slump overfolds with the same composition as the beds of the underlying series. Shapes of fragments, slump balls and slump overfolds indicate that claystones were plastic at the time of the movement. On the surface of many unconsolidated rounded claystone fragments pebbles have been stuck, armouring the fragments. Lower and upper surfaces of beds with irregular bedding are always strikingly smooth. Some beds are even 8.5 m thick. They do not differ from the graded beds in thickness, yet their inner structure indicates their origin by means of submarine sliding.

Claystone fragments and slump overfolds, as well as rounded blocks of the same composition as the bed itself, have also been observed in beds with graded bedding, especially in microconglomerates and coarse-grained sandstones. Therefore it may be supposed that there exist transitions from irregularly bedded strata to graded-bedded ones. Spacial distribution of irregular bedding with the conglomeratic flysch and microconglomeratic flysch proves the supposition. Irregular bedding forms 60-70 % of the coarse conglomerate beds in the area Klenov-KvaEany-Such6 Dolina, south and southeast of permanent occurrence of typical graded bedding.

Apart from slump overfolds (CROWELL, 1957) and claystone fragments, many of the irregularly bedded conglomerates have sandstone fragments identical with the underlying beds, siltstone and sandstone chunks, blocks of large size (1 x 1 x 1.5 m) and irregular, more or less angular shape. They are often quite sharp-edged, coming from the basal transgressive lithofacies, and have also frequently been found. Since the transgressive lithofacies were only connected with the base of the formation, they merge under the conglomeratic flysch in the north. The finger-like contact of the basal lithofacies with the conglomeratic flysch has not been observed, and the origin of slump claystone overfolds together with blocks of the basal lithofacies cannot be explained by slumping of beds in the basin, but rather by the abrasion of abruptly inclined slopes of the continental terrace built by claystone and basal lithofacies, and uplifted in the south of the basin in the period of the origin of extensive slides of the conglomeratic flysch. A sharp erosion contact of the conglomeratic flysch with the basal and claystone lithofacies mapped in the south, in the zone Klenov-Such&

114 R. MARSCHALKO

Dolina, 6-8 km wide, testifies to the cutting-in and erosive force of the passing slides. A low degree of roundness of blocks and fragments from the basal transgressive

lithofacies as far as 10 km from the southeastern margin of the conglomeratic flysch proves that transport in slides has taken place quickly and that the material deposited has not undergone any further washing-through.

If the proceeding slide reached the zone of unconsolidated sequence of sandstone and claystone, it tumbled down the underlying beds, compressed them, kneaded them and deformed them into slump forms as slump overfolds, slump balls, slump rolls, folded lumps, and transferred them in the moving slide mass farther from the place of their original deposition. The structures originated as a consequence of sinking, grooving and dragging of the passing masses along the sea-floor (CROWELL, 1957) and not by later slumping of beds already formed. The latter possibility of origin is indicated by various structures of thickening of beds, pull-apart structures and slump folds.

Decrease of the erosive force of slides and of turbidity currents from the place of the maximum entering into the basin, have been proved by the investigation of channels on the base of beds of the conglomeratic flysch. On the base of irregularly bedded strata 0.5-2 m deep channels have been found, filled by clastics with irregular sorting of pebbles and by fragments and slump overfolds of claystones, and plainly truncated by the current passing further without deposition, or - in the majority of cases - depositing a bed with finer grained material. Rare are the cases of preservation of channels of this type, in most cases straight and sharp lower surfaces of beds have been found.

Another very frequent type of channel is formed by a current depositing material. Channels of this type are found together with graded bedding of smaller thickness, occurring northwest of the former. Also with decreasing thickness of beds the depth of channels has been decreasing, and thus the channels have acquired smaller erosive forms described as flute casts. The phenomenon has been observed in a southeast- northwesterly direction together with other phenomena, e.g., refinement of granulometric composition, better sorting of particles and increasing thickness of claystone.

Reliable proof of the one-direction activity of turbidity currents in conglomeratic flysch has been offered by current bedding. It has been found in the upper surface of beds, always in one series only. By its straight laminae it looks most like the type of torrential bedding (SHROCK, 1948), but many observations have shown that in one series, in a section parallel to the plane of symmetry sigmoid, shovel-like forms in the margin, and straight laminae in the axial part, may occur. Less frequent is the presence of one series in an isolated bed of table-like form in claystones.

On the ground of quantitative observation of the thickness of torrential bedding and the thickness of beds in which it occurrs, a relation has been found (Fig.3), viz. that with the decreasing bed thickness the thickness of diagonal bedding also decreases. Since it has been observed in a southeast-northwesterly direction, the entering of currents, gradual decrease of traction force and gradual disappearing of currents, have been presumed in this direction as well.

In no case has the degree of alternation of many series of diagonal bedding been

SEDIMENTARY STRUCTURES IN THE CENTRAL-CARPATHJAN FLYSCH 115

found to be typical for alluvial sediments (BOTVINKINA, et al. 1954; TIMOFEEV, 1954), nor the “herring-bone” type of bedding (the diagonal one), originating in consequence of migration of currents in various directions, as found on beaches (SHROCK, 1948). Neither has the cross-bedding, abundant in basal lithofacies, been found there. One series is bound to one bed by graded bedding, all structures of the bed (long axes of pebbles, channels) have the same orientation, therefore the origin of the described torrential bedding may be presumed only in the case of uninterrupted wide progress of turbidity currents.

Fig.3. Relation between the thickness of torrential bedding and the thickness of the conglomeratic flysch beds. Thickness of torrential bedding is indicated at the horizontal axis.

All the above mentioned studies show that the conglomeratic flysch differentiation of clastics from the source-area situated south of the present-day distribution of the conglomeratic flysch is predominant. By means of material composition of pebbles, the direction of currents with the position of the source-area from which the pebble- material came, has been confronted. Compared to the basal facies, the composition of the conglomeratic flysch only contains heterogenous conglomerates with mixed associations of rocks of the Gierna Hora Mountains crystalline, of the Spigsko-GemerskB Ore Mountains and of younger mantle rocks of the Jurassic and Lower Cretaceous of the West-Carpathian and Kriina developments.

The amount of unstable rock fragments (limestones, basics, granites) is rather high and reaches 40-50 % on the average. PETTIJOHN (1957) classifies such rocks as immature lithic conglomerates. Immature conglomerates with non-disintegrated fresh rocks may have originated in a source-area with high topographic relief, and with heavy rains which have effectively supported mechanical erosion accompanied by immediate transportation.

116 R. MARSCHALKO

Typical and non-typical wildjysch

The lithofacies of the wild flysch represents the connection between three main series of the conglomeratic and microconglomeratic flysch fading out here, and the stratigraphic matrix for the extensive slide bodies. With regard to the abundance of the slide bodies, typical wild flysch with a high occurrence and non-typical wild flysch with low occurrence of slide bodies can be distinguished. Flysch series of typical wild flysch developed northeast of the line Sucha Doha-OndraBovce, differ from non-typical wild flysch developed west of this line, especially in the sense that their composition is that of homogenous-bedded medium grained-sandstones, coarse-grained siltstones in beds with thicknesses of 0.20-5 m, with abundant claystone fragments and inclusions, irregularly distributed in various parts of the bed and oriented differently to the lower surface. Homogenous bedding represents 70 % of all types of bedding known.

The amount of interrupted, recurrent bedding with sharp-edged claystone fragments horizontally laminated or current-bedded in the top, is very small (10-22%). The maximum size of the fraction does not exceed that of medium-grained sandstone. The amount of irregular bedding in the typical wild flysch is very small. No slumping of beds and pull-apart structures have been developed. Interlayer claystones (1-4 cm, maximum 30 cm thick) are calcareous to marly with pelagic biotope of planctonic Foraminifera.

In sequences of the typical wild flysch, giant slide bodies occur with a composition in striking contradiction to the flysch sequences described. Thickness of bodies may sometimes reach 12-15 m. The extension of bodies, followed by mapping, exceed 30 km2. Striking separation of bodies at the bottom and concordant deposition has been observed in the majority of slides.

In the composition of bodies, the matrix consists of a mixture of sand, silt and clay. Pebbles and blocks of rocks are irregularly, chaotically placed in standing position in the matrix, together with soft components and synsedimentary chunks, which are deformed into typical forms of slump overfolds (CROWELL, 1957), and slumped sheets (KSIAZKIEWICZ, 1958a). Some blocks of limestone, measuring 1.5 x 2 x 3 m, bored through by organisms, originate from tidal zones. Sharp-edged chunks and blocks, measuring 2 x 6.3 x 4.5 m, composed of rocks of the claystone lithofacies and siltstones of the upper part of the basal lithofacies, represent the tumbled-down sequences. Unconsolidated sediments, rapidly deposited in the littoral zone, have not remained there for various reasons. They cut deeply into the underlying sediments as the masses slid and tumbled down. The origin of slump fragments and slump overfolds of identical composition - as with underlying flysch sequences - may be explained in the same way as those in the irregular bedding of the conglomeratic flysch.

From the studies of the composition of pebbles in slide bodies, it follows that pebbles have come from the dispersion centre situated south of the longitudinal northwest-southeast course of the basin. Similarly to the conglomeratic flysch, the crystalline cores of the (Sierna Hora Mountains and SpiBsko-GemerskC Ore Mountains, and their sedimentary mantle have served as the source. Since the slides took the


shortest route to the basin, the supposed direction of sliding is south-north. A slightly different development of sedimentary structures has been observed in the

non-typical wild flysch. The amount of graded bedding and irregular bedding with minor slump balls, blocks and claystone fragments is 60-80 %, and the importance of homogenous bedding is decreasing. The maximum grain-size in graded bedding is exceeding that of coarse-grained sandstones, and, locally, that of microconglomerates.

In the irregular bedding, the arrangement of coarse grains is without any regulari- ties. The bed thickness, 0.2-5 m, is similar to other types of bedding. In some places occurrence of claystone fragments and minor slump sheets and balls is so abundant that in more detailed mapping it was possible to make horizons with claystone breccias. Although there are often pull-apart structures and slump deformed beds in the sequences, the explanation of the origin of claystone breccias by slumping and creeping of beds in the basin (LOMBARD, 1956) seems highly improbable. The presence of claystone breccias is frequent, even systematic. The origin of claystone breccias would presume quick changes in the slope of the floor after deposition of each bed, and systematic slumping should leave slide casts (KUENEN, 1956), but no slide casts have been observed. Flute casts on the base of these beds show, that the moving currents were characterized by internal turbidity. It may be assumed that breccias represent depositions of slides, deposited below steep slopes. The slide, which has eroded various consolidated claystones on the steep slope, could not acquire, in a short time, the character of a typical turbidity current. After the passing of the critical angle of the slope, quick deposition of a part of the slide has taken place in the form of a flat fan. The beds formed are characterized by irregular bedding, bad sorting, development of chaotically “flowing” claystone fragments and slump sheets, and balls in the matrix. Also the initial stages of slumping in the form of “swollen” and thickened beds, pull- apart structures and slump folds have been found. Beds with convolute laminations have not been observed.

Intermediate jlyscli

The intermediate flysch forms the equivalent of the wild flysch and conglomeratic flysch in the basin. It contains 75-90% of graded-bedded sandstones and siltstones with convolute laminations. The maximum size of the coarse fraction reaches the limit of gravels. Thickness of beds is 60-80 cm on the average, 350 cm at a maximum. Convolute laminations occupy the middle, less frequently the upper, strata of beds. It may be observed in unchanged thickness in the bed. Continuity of laminae has been preserved. Twisted inclusions of claystone lamines have not been found. There are no load casts and slide casts on the lower bed surface, since convolution has no relation to gravitational slumping. It is connected to the origin of one bed only and is a result of primary synsedimentary processes.

118 R. MARSCHALKO

CURRENT DIRECTION AND DEPOSITIONAL SLOPE

The analysis of stratification, granulonietry and bedding gives no complete picture of processes active during the transport of clastic material from the source to the basin. In order to determine the real direction of transport of clastics in three dimensions, the growth of flysch lithofacies and their relations to the source-area, methods analyzing vector properties of clastics have been used. The problem is first to investigate all sedimentary structures with linear orientation in the direction of current activities, which enables the determination of the force and the current direction, and the slope of the floor along which the currents moved.

Due to work by KUENEN (1952, 1953, 1957a), VASSOEVICH (1953), KOPSTEJN (1954), KSIAZKIEWICZ (1954, 1958b), CROWELL (1955, 1957), DZULYNSKI and RADOMSKJ (1955), BIRKENMAJER (1958), TEN HAAF (1959) and others, many properties are known determining the progress of currents, and the force and deposits formed by them. Therefore it is not necessary to analyze the separate structures.

In analyzing current directions in the separate lithofacies, sedimentary structures of the same type cannot be used. In the conglomeratic flysch, long axes of pebbles, torrential bedding and axes of channels have been measured and all values for one bed have been controlled. In the wild flysch, intermediate flysch and subflysch, mainly the sole markings have been used, i.e., flute casts, drag marks, impact casts, oriented load casts, current bedding, grain lineations, plant remnants lineations. The study of oriented slump folds has been found to be of special importance.

Studies on oriented sedimentary structures in lithofacies have been applied to solve ( I ) the direction of currents forming subflysch and intermediate flysch, (2) the direction of currents forming typical and non-typical wild flysch, inserted between beds of conglomeratic flysch and giant slides and their relationship to the source-area, (3) the lateral entering of coarse clastics, which becomes very clear in the origin of the conglomeratic flysch, (4) the depositional slope, especially in the marginal parts of the basin near the source-area.

All lithofacies have been covered by mapping of current lineations but the data are incomplete, especially concerning claystone lithofacies and subflysch, due to the lack of natural outcrops and the overlaying of younger lithofacies. Poor dates of distribution of current directions in the subflysch are represented by two rose diagrams representing lower, middle and upper parts of the subflysch.

In the lower part two more distinct crossed current systems predominate. The first runs southeast-northwest, the second southwest-northeast with an indication of pole alternation. In the upper part of the subflysch, southwest of MoEidlany, strong dispersion of currents has been observed. In the contact series of the subflysch with intermediate flysch a stronger influence of currents from the south to the north and north- northwest has been observed, as well as a gradual charge southeast-northwest, especially in younger series of the intermediate flysch. The fan-like shape of the current distribution in the upper part of the subflysch and in the intermediate flysch is very striking. qlthough its direction to the south could not be followed due to the lithofacies


being overlaid by younger beds, it can be presumed - according to the diameter of the fan (dispersion) - that currents entered the basin from the south.

The direction the middle and upper parts of the intermediate flysch current system have been measured, which is in agreement with younger systems, and its direction is southeast-northwest (rose diagram, Rogkoviany, Fig. 1). Pole change of current direction has been observed from northwest to south-southeast. In some sequences directions have been found which are distinctly different to the former, with an oblique angle from northeast to southwest. Orientation of this system is rather anomalous with respect to predominating systems from south to north, 'southeast and northwest. It indicates that in the intermediate flysch the entering of clastics into the basin has been from the source situated in the north and northeast (MARSCHALKO and RADOMSKI, 1960) for a certain time. The analysis shows that for the filling of the basin by clastics the southern cierna Hora-Gemer source-area has been most important. Abrupt entering of great amounts of coarse clastics from the southern source to the north has been observed, especially in the origin of the conglomeratic flysch and extensive slide bodies of the wild flysch. There a question arises: what is the relation between predo- minately fine-grained homogenous-bedded sandstones of typical wild flysch and the southern source-area, producing clastics with high gravel contents ?

In the study of current systems in flysch sequences in which slides alternate, surprising stability of current direction has been determined on an extensive surface (200 km2) running without change from southeast to northwest. Since the southeast-northwest current system has also been measured in the southernmost part of the wild flysch on its contact with the cierna Hora Mountains, and in the southwest of it (rose diagram, Ondrdovce, Fig.l), one may assume that it continues to the southeast in sequences of typical wild flysch separated by tectonic line of the Hornhd River and covered by sediments and volcanites of the Miocene. The remarkably constant current system represents longitudinal filling of the basin (KUENEN, 1957b), passing in agreement with the position of the axis of the basin and independently of the lateral filling. Therefore fine-grained homogenous-bedded siltstones and sandstones, inserted between slide bodies, have no genetic relation to the southern source-area and are transported by turbidity currents from another source-area. For this reason they cannot be called marginal lithofacies.

Typical lateral filling of clastics in the basin (DZULYNSKI, et al., 1959) has been proved by petrographical and sedimentological investigations of the conglomeratic and microconglomeratic flysch. Orientation of long axes of pebbles, torrential bedding and orientation of axes of channels in the conglomerate beds point to the uniform direction of transporting slides and currents from the south-southeast to the north in older constituents (KvaEany, Suchh Doha) , and to northwest and west-northwest in younger constituents of the conglomeratic flysch (Chminianske Jakuboviany).

Since current directions in the conglomeratic flysch areas, about 15-20 km from the southeast margin (Chminianske Jakuboviany), show coincidence with primary longitudinal filling of the typical wild flysch, a detailed investigation of two independent sequences of the non-typical wild flysch alternating with two sequences of the con-

Fig.4. Legend see p. 12 I


glomeratic flysch (over a surface of 15 x 10 km) has been carried out to differentiate the lateral filling from the longitudinal fllling of the typical wild flysch.

It has been observed that current directions in the lowermost conglomerate sequence I (Fig.4) and in its overlying non-typical wild flysch I’ are in agreement according to oriented structures. Besides that, internal structures of the conglomeratic flysch are oriented in agreement with lineations of the non-typical wild flysch. Characteristic lateral filling of clastics from the south-southeast is certain and might have been followed by many sequences of the non-typical wild flysch along the margin of the (llierna Hora Mountains (rose diagrams OvEie, Zipov, Fig. 1).

In the conglomerate sequence ZZ and in the overlying non-typical wild flysch ZZ’ slight change of current direction (Fig.4) to the west-northwest has been shown by measurements. It may be observed again in both lithofacies quoted. In the non-typical wild flysch there is an increasing amount of coarse fraction, graded bedding and irregular bedding with horizons of claystone breccias and sliding. Here, these phenomena are very frequent compared to the typical wild flysch.

Generally it may be stressed that current directions in the non-typical wild flysch, 15-20 km from the present-day southeast margin, have approximately the same directional values as the primary longitudinal filling in the typical wild flysch. This is in agreement with the axis of the basin and with the course of large tectonic structures, yet lithological proofs undoubtedly affirm differences conditioned by abrupt lateral entering of clastics from the southern source-area. Transporting currents, forming conglomerate beds and the non-typical wild flysch, change direction in the basin and acquire a course parallel with the position of the axis in this segment of the basin (Fig.5).

From the general regional pattern of current distributions, it appears that the predominating uniform current direction observed over a long time represents a strong argument for the turbidity current hypothesis concerning the origin of the marginal flysch lithofacies.

For the origin of turbidity currents a slope is necessary. Therefore uniform current directions, measured in separate lithofacies, indicate the slope along which the turbidity currents were moving. The majority of oriented load casts (Fig.1) is really in agreement with the predominating current direction, i.e., the filling by clastics has been the first main factor determining the so-called primary depositional slope of the basin (TEN HAAF, 1959).

The analysis of current directions in the basin show that the primary depositional slope of the basin had been developed during the formation of separate lithofacies in two main directions: (1) in the axis of the basin the depositional slope gradually decreased from the southeast to the northwest; (2) near the margin of the southern source-area the slope ran perpendicularly and transversely to the axis in the north- northeast and northwest.

Fig.4. Current-rose diagrams of two sequences of conglomeratic flysch I and II, alternating with two sequences of the non-typical wild flysch I‘ and II’. Marking as in Fig.1.

122 R. MARSCHALKO

From the analysis of distribution and frequency of slump folds and pull-apart structures in the typical wild flysch, it appears that the primary depositional slope which was formed during the deposition of clastics by turbidity currents and longitudinal filling from one centre, could not have been very steep, since periodic slumping of deposited beds has not taken place at all.

n Fig.5. Map of current directions in marginal lithofacies during Upper Eocene and Lower Oligocene. I = Epimetamorphosed crystalline of the Spiii-Gemer Ore Mountains. 2 = Mesocatazonally metamorphosed crystalline of the Cierna Hora Mountains. 3 = Line of overthrust of the Spiii-Gemer Ore Mountains crystalline on the Cierna Hora Mountains crystalline. 4 = Main current directions during Upper Eocene. 5 = Main current directions during Lower Oligocene. 6 = Extensive slides in Upper

Eocene. 7 = Extensive slides in Lower Oligocene.

The situation is different in the conglomeratic flysch and the non-typical wild flysch deposited near the southern margin of the basin, where, in some cases, axes of slump folds have been oriented primarily perpendicularly (Fig.1, 4) to the course of the axis of the basin, and less frequently transversely or parallel to it. Several deformed beds, occurring together, show that slump folds have been caused by forces long after the deposition of beds. Therefore it may be supposed that they originated by more rapid supply of the primary slope by the clastics and in consequence of tectonic bending of the depositional slope. In the non-yypical wild flysch, the direction of


slumping has been mainly from the south to the north, northwest an east-northeast, in connection with increasing tectonic pressure, with the uplifting of the southern source-area and with the origin of steep slopes on one hand, and axial depression on the other.

Certain specific data, e.g., the origin of horizons with claystone fragments and slump rolls, origin of extensive submarine slides with blocks of basal and transgressive lithofacies in the wild flysch, and especially the high amount of irregular bedding in the conglomeratic flysch, distribution and distance of slides, and the irregular and graded beddings from the margin of the source-area, show that the uplifting of the source-area together with older basal lithofacies took place in a short time. They were accompanied by the origin of sufficient inclination of the slope along which the sliding of gravel masses, abrasion of uplifted beds and transport far into the basin, could take place.

Based on these results, it may be supposed that the origin of large slide bodies, conglomeratic and non-typical wild flysch, depends upon the so-called secondary slope, the function and influence of which will be explained in more detail.

The given values for the inclination of the slope on which the slides originated and on which the sliding took place, differ between various scientists. According to some sedimentologists (KUENEN, 1953; KUENEN and CAROZZI, 1953) the slope must have been concave and with such a dip that it was possible for rolling particles to descend freely into the basin under the influence of gravity. Others (Vassoevich as quoted in RUCMN, 1959) suppose that the inclination from the source-area to the axial part of the basin has been moderate and they prove it by the distribution of slides at the marginal side of the source-area only.

In the analysis of the three dimensional distribution of submarine slide bodies in this area, it may be seen that extensive slides accumulate in the zone of the typical wild flysch from its southernmost margin over distances of 7-10 km and in the zone of the conglomeratic flysch and the non-typical wild flysch from its margin (KvaEany, Sedlice) 15-20 km and more to the centre of the basin. Since all the slides in the zone have not been washed-through, they are deposited below the level of wave action and strong currents, so it may be assumed that this zone occurred at greater depths and near the steep slope of the continental terrace.

From the analysis of the lithological composition of slide bodies and irregular bedding it may be seen that steep slopes of continental terraces consisted of uplifted older lithofacies as upper constituents of basal transgressive lithofacies, claystone lithofacies and partly those of the subflysch. Extensive sliding masses composed of gravels, tumbling down the slope of continental terrace to the north, cut into the slopes and grooved submarine valleys into them. Erosion relief of such a valley has been preserved in a zone, 6-8 km wide, in the area Klenov-Such6 Dolina. Sharp truncations of the upper constituents of the basal lithofacies and claystone lithofacies, preserved only in fragments by bodies of the conglomeratic flysch may be observed. The truncations have low angle (3"-5", ROSING, 1947) and show wedging out of irregularly bedded conglomeratic sequences on contact with the lithofacies. The depth of the

124 R. MARSCHALK0

cutting-in, determined by the mapping, is 150-200 m in the zone of Klenov-Such6 D o h a and does not correspond to the real depth of the erosion of a submarine valley, since it represents only the lower part of the cross-section, leading into the bottom of the basin. Based on these observations it may be considered that: (1) slopes of continental terraces represent secondary slopes, cut-through by submarine valleys in this case, (2) the slope of the continental terrace must have been so steep that no deposition could take place, but only erosion by sliding masses, (3) the slope must have been curved in certain stages during the formation of the conglomeratic and wild flysch in the lower part of the cross-section leading to the bottom of the basin.

Coarse clastic material periodically sliding from the edge of the continental terrace and moving quickly downward to the bottom of the basin had been deposited at the foot of the continental terrace in the form of a flat fan (KUENEN and MIGLIORINI, 1950; SULLWOLD, 1960) and has formed the primary depositional slope.

The uplifting of the source-area caused high relief. The velocities of the periodic supply of clastics increased and an immense amount of coarse clastics moved into the basin and therefore the primary slope increased abruptly. In such cases, slides descend- ing from the edge of the continental terrace rest only partly on the depositional slope. Usually they pass as heavy watery slides, tumbling down the unconsolidated overlying series forming slump overfolds and chunks of claystones with irregular bedding. On a suitable slope and at the necessary distance from the place of the origin of slides (20-30 km) they become somewhat turbulent and the resulting deposits are at a transition between fluxoturbidites and turbidites. High amounts of irregular bedding at the margin of the source-area with the occurrence of claystone slump overfolds and armoured fragments, sharp changes of the sorting of coarse fraction in the conglomeratic flysch, horizons with claystone fragments and slump rolls in the non-typical wild flysch are typical.

Less common is where the primary slope was increasing slowly. There was an abrupt uplift of the source-area and the origin of steep secondary slope, which was curved at the contact with the basin lithofacies. Slides were suddenly retarded, sinking in underlying unconsolidated series. They did not pass far into the basin, but concentrated at a short distance from the foot of the slope. Such a development took place in the beginning of the formation of the typical wild flysch and non-typical wild flysch. This is the stage which preceded the origin of the conglomeratic flysch.

If the primary slope was increased near its margin by the supply of clastics, by tectonic uplift and by the leaning-out of continental terraces, then slumping, origin of slump folds, and pull-apart structures in the depositional slope of the basin may have taken place.

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handel. Koninkl. Ned. Akad, Wetenschap., Afdel. Natuurk., Sect. I, 20 (3) : 147.

Geol. Mijnbouwk. Genoot., Geol. Ser., 18 : 189-195.

Alps. J. Geol., 61 : 363-373.

58 : 91-127.

then). Z . Deut. Geol. Ges., 99 : 8-39.

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126 R. MARSCHALKO

TRWY, R., 1960. Paleotectonic evolution of the central and western Alps. Bull. Geol. SOC. Am.,

VASSOEWCH, N. B., 1948. Hysh i Metodkujevo Zzuchenijz. Vses. Neft. Geol. Razved. Nauchn. Issled.

VA~SOEVICH, N. B., 1953. 0 nekotorych flyshevych texturach (znakach). Tr. Lvovsk. Geol. Obdl&sto.

WE-, J. M., 1958. Stratigraphic facies differentiation and nomenclature. Bull. Am. Ass. Petrol.

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Geologists, 42 (3) : 609-639.

FLYSCH FORMATIONS OF THE NORTHERN APENNINES

ERNST TEN HAAF

Geological Institute, State University, Utrecht (The Netherlam&)

SUMMARY

At least a dozen distinct types of flysch occur in the northern Apennines. Two differential processes - resedimentation and tectonic sliding - are invoked to account for their distribution in space and time, and to trace some genetic connections.

INTRODUCTION

From Genoa to Lake Trasimene, various flysch formations make up the major part of the Apennine chain. Their location and succession reflect the orogenic history, while their diversity has been instrumental in shaping, not only the present landscape, but even its tectonic structure.

Mountain building in the northern Apennines has been characterized by two pecul- iar and decisive features. Firstly, folding and consequent sliding did not affect the entire area at once, but progressed from west to east during the Oligocene and Miocene (MERLA, 1951). An even earlier, Cretaceous-Eocene phase of orogeny must be postulated in a “Palaeoapennine” zone, now foundered, west of the present peninsula. Secondly, the successive structures emerged very late, so that the upper part of the sedimentary pile - the flysch formations - remained largely unlithified during orogeny. This prolonged “hapalotectonic phase” (TEN HAAF, 1961a) gave an unpre- d e n t e d opportunity for differential displacements, both by resedimentation and by gravitational sliding.

In reviewing the various flysch formations’ involved, we shall follow the natural threefold division of the northern Apennines (Fig. 1):

(I) The autochton of Toscana, Romagna, and Umbria (southern half of our map, and beyond).

(2) The allochton that chaotically overlies the former, and reigns supreme on the slopes of Emilia between the watershed and the Po valley.

(3) The rocks of eastern Liguriu (between Genoa and La Spezia) and farther north; in part similar, and passing into, the formations of the Emilian allochton, but structur- ally an imbricated thrust-pile rather than a promiscuous flow.

.

Named “formations”, in Italian usage, may represent mere mapping units (cf. MAXWELL, 1959b).

Fig.1. Simplified map of the major flyxh formations of the northern Apemines.

LlGURlAN SERIES ALLOCHTON - I AUTOCHTON

garenarie wperioriY

passing E into the

'scisti gal-trini" (with ophiolites,

"argille scagliose")

\ , ,J"" "3" --I ....-..- -,

Sr k

(older sediments) "alberese' (Eocene)

' (Cretaceous)

FLYSCH FORMATIONS OF UNCERTAIN AGE AND AFFINITY

4 sedimentary contact

* autochton

-----) minor tectonic

I imit allochton-

contact

direction of -b turbid* currents

FACES

post - orogentic 0

chiefly chiefly d- argillaceous careau~ flysch

("alberesi ''1

pelit- and limestones

flysch

Legend to Fig. I .

130 E. TEN HAAF

AUTOCHTONOUS FLYSCH FORMATIONS

In the watershed area, the pre-orogenic series (mainly carbonates, topped by the shaly “scisti policromi” or “scaglia”) is overlain concordantly by the well-known Oligocene “macigno”. This was the first formation to be explained by the hypothesis of turbidity currents (MIGLIORINI, 1943; KUENEN and MIGLIORINI, 1950). “Resedimentation” accounted not only for the facies of alternating shales and graded graywacke beds, and for the presence of (reworked) Eocene Foraminifera, but also for the obvious lack of a near-by source area for the enormous quantity of sand involved. Originally, turbidity currents were still supposed to have run transversely off the nascent chain, fed by detritus from the hypothetical Palaeoapennine land mass to the southwest; but investigation of the current directions has revealed a longitudinal supply from the northwest, out of Liguria or adjacent regions (TEN HAAF, 1958, 1959). We shall concern ourselves presently with the origin of the sand in the macigno.

Below the macigno there occur, in some places, beds of nummulitic “brecciola”, considered by KUENEN and MIGLIORINI (1950) as turbidites of local origin. Upward, the macigno passes into the more marly “macigno B” or “Vicchio series” near its eastern margin; but elsewhere, a top is lacking and typical macigno is covered directly by allochton, or unconformably by Villafranchian or marine Pliocene. The thickness must be several kilometres.

With the progress of orogeny, the trough of turbiditic sedimentation was evidently shifted eastward: the top of the autochton on the outermost fold ridges is constituted, not by macigno, but by the ‘yormazione marnoso-arenacea” of Lower-Middle Miocene age. Mechanically, it is very similar to the macigno, deposited likewise by turbidity currents from the northwest, and of great thickness, but slightly more calcareous and fossiliferous. The “marnoso-arenacea” is overlain by the shallow-water sandstones, marls, and evaporites of the Po valley border. Its base is exposed only in Umbria, where the underlying Oligocene - a thin pelitic “scaglia cinerea” - must be the lateral equivalent of the macigno. Apparently this part of the sea floor was at first too high to be reached by turbidity currents following the axis of the macigno trough.

A formation very much resembling the marnoso-arenacea, but slightly younger again - Upper Miocene - extends north of the Gran Sasso massif (outside the map of Fig.1). Its resedimentation by turbidity currents from the north makes it seem likely that, genetically, this “Picenejysch” is still connected with the flysch of the northern Apennines (TEN HAAF, 1959).

Thus, successive autochtonous sandy flysch formations have been deposited in an elongated foredeep that migrated east and south with the advance of orogeny, during the Oligocene and Miocene. The large masses of sand contained in these vast and thick formations have been transported longitudinally by turbidity currents from the northwest. Lateral supply from adjacent rising ridges was presumably restricted to pelitic material, after the initial resedimentation of patches of “brecciole”.

.

FLYSCH FORMATIONS OF THE NORTHERN APENNINES 131

ALLOCHTONOUS FLYSCH FORMATIONS

The allochton consists of the notorious “argille scagliose” or slickensided clays, mixed up with ophiolite masses and with various slabs and fragments of recognizable sedimentary formations. On the margins of Eastern Liguria, argille scagliose are seen to develop, by increasing tectonization, out of the “scisti galestrini“; farther on, their volume has probably been supplemented by the incorporation of other shaly formations, such as “scaglia”, wherever these had been exposed - by the sliding off or resedimentation of overlying formations, or by diapirism. The emplacement of the allochton must have been a gradual process, keeping pace with the eastward progress of orogeny. It is envisaged as a series of submarine gravity slides, among partly unconsolidated sediments, toward the retreating foredeep (MERLA, 1951 ; SIGNORINI, 1956).

The “argille scagliose” themselves are not properly a flysch formation. Although in part derived from flyschoid sediments, they have been too thoroughly tectonized and contaminated. But among the embedded slabs of distinctive formations, there are several types to interest us.

These allochtonous units are of two kinds: those that have their counterparts in the autochtonous series, from which they have apparently been detached, and “exotic” formations that must have travelled far, since they are quite foreign to the autochton and can be matched, if at all, only in Liguria.

Among the former are the numerous outcrops of allochtonous macigno and marnoso-arenacea surrounded by argrlle scagliose. Most of these slabs have gyrated variously while sliding away, as can be shown by comparison of the apparent direction of turbidity flow, in each of them, with the very constant orientation northwest-southeast in the autochton (TEN HAAF, 1957). Others have been turned upside down, as on M. Cimone.

Recurrent exotic flysch types are the “pietraforte” and “alberese”. The “pietraforte”, much used as a building stone, is a turbiditic series of fine-grained calcareous sandstone beds alternating with dark shales, of Upper Cretaceous age. It only occurs in the Tuscan allochton, and has probably been deposited originally as a Palaeoapen- nine flysch.

The Eocene “alberese”, on the contrary, is extremely widespread as great and small slabs all through the allochton as well as in eastern Liguria. Its white-weathered outcrops consist of well-stratified alternations of marls, turbiditic calcareous sandstones, and limestone beds - dense marly limestones as well as calcarenitic turbidites.

Some of the Tuscan alberesi seem to be in stratigraphic contact with underlying pietraforte, while in the Emilian allochton alberese is overlain unconformably by various, but largely molassic, younger sandstone series. These allochtonous Upper Oligocene-Miocene formations (blank on our map) have not been crumbled very much and can be reconstructed (PIERI, 1961) into a sequence comparable to the post-orogenic series north of Liguria and the autochton of the Salsomaggiore anticline. Accord- ing to MERLA (1957) they have been deposited on top of the still-moving allochton.

132 E. TEN HAAF

The “Monhidoro sandstone” is a very curious exotic, a sandy flysch forming a single huge overturned sheet with upended edges (SIGNORINI, 1938; MAXWELL, 1959a). It only corresponds, in general aspect, turbiditic character, coloured feldspar content, and presumable age (Lower Eocene?) to the “arenaria superiore” of distant Liguria.

EASTERN LIGURIAN FLYSCH FORMATIONS

Various attempts have been made (e.g., TREVISAN, 1956; REUITER, 1961) to fit the sedimentary rocks of eastern Liguria into a single stratigraphic column. But as ages are in part uncertain and seem to overlap largely, and since, moreover, several sequences occur only as separate tectonic units, it seems preferable to consider merely the sedimentary superpositions visible in the field -which are not many (cf. BONI, 1961a). In the present writer’s opinion, there probably existed a “trough axis facies” (which need not have remained stationary) of shales and sandy turbidites, contemporary with a more marginal sedimentation of the “alberese” type.

The Eocene alberese has already been met with in the allochton. In Eastern Liguria it is not rooted in place either, but occurs as “thrust” sheets, generally rather low in the stack of tectonic units, between slices of scisti galestrini or directly overriding the so-called Ligurian “macigno”. Apparently, from lying on top of the initial sedimentary pile, the Eocene alberesi started early on their sliding career.

On the contrary, the impressive series of Cretaceous “alberese” or “ji‘ysch d helmin- thotdes” rides tectonically high as a vast, warped and faulted plate north and east of Genoa. There is much difference of opinion as to whether this is a parautochtonous mass related to, and thrust only slightly over, the adjacent galestrini (MERLA, 1957; BONI, 1961a), or part of a great nappe (ELTER, 1960) - perhaps extending, even, into the Maritime Alps (e.g., LANTEAUME, 1958). Turbidite supply from southerly directions suggests a (Palaeoapennine?) source of sediment in common with the coeval, and not too dissimilar, pietraforte, and very distinct from the later supply, from the northwest, of macigno-type sandstones.

The age and attribution of several of the slabs of “alberese” in the north are still doubtful (BONI, 1961a).

The “scisti galestrini” are the formation most characteristic of eastern Liguria. The thick series is mainly shaly, but interstratified in varying proportions with limestones (“palombino”) and thin beds of turbiditic sandstone, giving it a flysch character at least in part. The age is mostly Upper Jurassic and Cretaceous.

Tectonically, the “galestrini” are imbricated in thick folded slices, separated by curiously tectonized “comminute” zones that show all transitions to the argille sag- liose farther east, even to the association with ophiolite masses that probably belonged to the base of the galestrini complex (TREVISAN, 1956, TEN HAAF, 1961a). The galestrini override the macigno of the northernmost Tuscan autochton, and envelop outcrops of Eocene alberese.

On top of this pile of galestrini, and at least partly in stratigraphic continuity, lie

FLYSCH FORMATIONS OF THE NORTHERN APENNINES 133

the “arenarie superiori” or “uppermost sandstones”, a turbiditic graywacke-and-shale series similar to the macigno, though slightly more variegated, and locally containing more coarse fragments and pink feldspar (ELTER and SCHWAB, 1957). Its position above the galestrini makes a (Lower) Eocene age most likely; but this is as yet unproved by good fossils, and current assignations range from Upper Cretaceous to Oligocene. The top of the formation is lacking everywhere, but a thickness of at least a kilometre has been preserved in some places.

The situation of the arenarie superiori is very suggestive. Except near the present coastline, where a few slivers have been folded into the galestrini, they only occur in subhorizontal and gently warped tracts on top of the uppermost units of galestrini, and are lacking over wide areas where folding and thrusting prevail. It seems likely that the arenarie superiori were still unconsolidated during orogeny and could not withstand much tilting, but disappeared by resedimentation into the macigno trough (TEN HAAF, 1961a).

Finally, in a few tectonic windows below all the mentioned units, there are some outcrops of sandy formations that are generally considered autochtonous or “Tosca- nide”, and equated to the macigno in spite of conspicuous differences and ill-known, but probably senior, ages. In the window of Bobbio there is a series of turbiditic sandstones similar to the macigno, with supply from the northwest, but fossil finds in the overlying marls seem to indicate an Upper Eocene age’. The adjoining Val d’dvero series has been much disputed; its massive green sandstones and conglomerates, alternating with turbidites and red shales, cannot be matched anywhere; and from tectonic considerations as well, it appears likely that the entire Val d’Aveto sequence does not belong to the window of Bobbio at all, but constitutes an exotic mass (TEN HAAF, 196 1 b).

The window of Bedoniu (half-way between Bobbio and La Spezia) shows something else again: an anticline of curiously interstratified sandstone-and-shale, apparently non-turbiditic, but similar to the macigno in composition. An Upper Eocene age has been suggested here also (REUTTER, 1960).

What lies below these sandstone series can only be surmised. According to those who stress the supposed “Toscanide” affinity, it should be the equivalent of the Tuscan “scaglia” or “scisti policromi”, and then Mesozoic limestones. The present author has recently proposed (TEN HAAF, 1961a) that the windows expose the top of the Ligurian sandy series, missing - by resedimentation and denudation - from the higher tectonic units, and that, therefore, the Ligurian “macignos” would pass downward into arenaria superiore.

An Oligocene age, more recently re-advocated by BONI (1961b) and MUTTI (1963) would make the Bobbio sandstones - but not the others - truly an extension of the Tuscan macigno. However, at present data are not from the Bobbio sandstone itself, but from adjacent formations of uncertain relevance.

134 E. TEN HAAF

RELATIONSHIPS OF THE VARIOUS FLYSCH FORMATIONS

The envisaged relations are of two kinds: derivation by tectonic displacement, and derivation by resedimentation. In the northern Apennines both of these processes seem to have been active on a large scale, thanks to the retarded lithification of the submerged argdlaceous and arenaceous flysch.

Only limestones can consolidate soon after deposition; accordingly we find the alberesi, stiffened by numerous calcareous beds, uprooted and scattered as completent slabs. Graviational sliding of the more argillaceous series produced thick comminute shear zones that increased and multiplied until all stratification was lost in the chaotic flow of argille scagliose.

Of the unconsolidated sandy flysches disturbed by approaching orogeny, large parts must have spilled downslope and departed along the successive foredeeps in turbidity currents, to be re-deposited as Similar, but younger and more “mature”, formations elsewhere. A whole “cannibalistic” series can thus be imagined, strung out en khelon from northwest to southeast, and from Eocene to Miocene in time: arenaria superiore and Ligurian “macigno” -+ macigno, macigno and Emilian sands +

mamoso-arenacea, mamoso-arenacea + Picene flysch. The primordial source of all this arenaceous material is still unknown, since the oldest sandy flysch (arenaria superiore) is already re-sedimented. Speculation about its ancestry may range unchecked from the Gulf of Genoa up to the inner Alps.

Any attempt at “unscrambling” the northern Apennine flysch must further reckon with two different directions of transport, both actuated by gravity. The turbidity currents that re-deposited the sandy formations followed, along the strike, the axes of successive troughs, but the subsequent tectonic slides (Ligurian “nappes”, argille scagliose, exotics, and uprooted autochton) must have moved mainly down the direction of steepest slope, that is, down the front of the nascent chain -transversely to the strike (cf. MAXWELL, 1959b).

The relations suggested by all these considerations are represented in the diagram of Fig.2. Much of it is mere hypothesis, and the responsibility is entirely that of the present author. Probably, each of the cited geologists, who have recently worked among the flysch formations of the northern Apennines, would have placed differently a few of the arrows. Yet most of them would agree that progressive early orogeny has spilt out, differentially, tKe contents of an ancestral Palaeoapennine-Ligurian flysch trough, and that the flysches of the northern Apennines were emplaced by individual participation in either, or both, of the vast gravity-impelled migrations: longitudinal resedimentation and transversal sliding.

ACKNOWLEDGEMENT

Part of the field work has been made possible by grants from the Netherlands Organi- zation for Pure Scientific Research (Z.W.O.).

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FLYSCH FORMATIONS OF THE NORTHERN APENNlNES 135

REFERENCES

BONI, A, 196Ia. Per la geologia dell'Appennino settentrionale a W. della linea La Spezia-Piacenza.

BONI, A., 1961b. Messa a punto e considerazioni sul confront0 stratigrafico tra i flysch della Liguria

ELTER. P., 1960. I lineamenti tettonici dell'Appennino a nordovest delle Apuane. Boll. Soc. Geol.

Atti Zst. Geol. Univ. Pavia, 12 : 63-196.

Occidentale e dell'Appennino settentrionale. Boll. SOC. Geol. Zrd., 80 (4) : 103-128.

I t d , 79 273-312.

136 E. TEN HAAF

ELTER, P. and SCHWAB, K., 1957. Gedogia della regione tra Vara e Magra. Boll. SOC. Geol. Ital.,

KUENEN, PH. H. and MIGLIORINI, C. I., 1950. Turbidity curients as a cause of graded bedding. J. Geol.,

LANTEAUME, M., 1958. Schema structure1 des Alps marithes franco-italiennes. Bull. SOC. GPol.

MAXWELL, J. C., 1959a. Orogeny, gravity tectonics and turbidites in the Monghidoro area. Trans. N.Y.

MAXWELL, J. C., 1959b. Turbidite, tectonic and gravity transport, northern Apennine Mountains,

MERLA, G., 1951. Geologia dell’Appennino settentrionale. Boll. SOC. Geol. Ital., 70 : 95-382. MERLA, G., 1957. Essay on the Geology of the Northern Apennines. A.G.I.P. Mineraria, Milano, 30 pp. MIGLIORINI, C. I., 1943. Sul mod0 di formdone dei complessi tipo macigno. Boll. SOC. Geol. Ital.,

M m , E., 1963. Direzioni d’apporto dei clastici entro il macigno e il “Tongriano” dell’ A p e ~ i n o di

PIERI, M., 1961. Nota introduttiva a1 rilevamento del versante appenninico padano eseguito nel

REUTTER, K. J., 1960. Geologische Wntersuchungen im Gebiet zwischen Bedonia und Varese Ligure im

REUTTER, K. J., 1961. Zur Stratigraphie des Flysches im Ligurischen Apennin. NeuesJahrb. Geol.

SIGNORINI, R., 1938. Una msta zona a strati rovesciati tra l’Idice e il Setta nell’Appennino bolognese.

SIGNORINI, R., 1956. Tipi strutturali di scendimento e argille scagliose. Boll. SOC. Geol. Ital., 75 : 69-95. TEN HAAF, E., 1957. Tectonic utility of oriented resedimentation structures. Geol. Mijnbouw,

TEN HAAF, E., 1958. Les directions d’apport dans le flysch arena& des Apennins. Eclogue Geol. He Iv..

TEN HAAF, E., 1959. Graded Beds of the Northern Apennines. Thesis, Univ. of Groningen, Groningen.

TEN HAAF, E., 1961a. Differenciation tectonique des skdiments dans l’Apennin ligure. Boll. SOC. Geol.

TEN HAAF, E., 1961 b. La structure de la fenetre de Bobbio. Boll. SOC. Geol. Ital., 80 (3) : 95-100. TREVISAN, L., 1956. Aspetti e problemi del cornplesso delle “argille scagliose ofiolitifere” nei suoi

affioramenti occidentali uoscana marittima e Liguria). Boll. SOC. Geol. Ital., 75 : 23-40.

76 : 137-1 72.

58 : 91-127.

France, 6e SPr., 8 : 651-656.

Acad. Sci., Ser. 2, 21 : 269-280.

Italy. Bull. Am. Assoc. Petrol. Geologists, 43 : 2701-2719.

62 : 48-49.

Piacenza. Riv. Ital. Paleontol., 69 : 235-258.

1955-59 dai geologi dell’A.G.1.P. Mineraria. Boll. SOC. Geol. Ital., 80 : 3-34.

Nord-Apennin. Thesis, Universitat von Berlin, Berlin, 83 pp.

Palaontol., 11 : 563-588.

Boll. SOC. Geol. I td , , 57 : 139-154.

19 : 33-35.

51 : 977-980.

102 pp.

Ital., 80 (3) : 87-94.

TURBIDITE IN DER RECHTSRHElNISCHEN GEOSYNKLINE

W . P L E S S M A N N

Geologiseh-Palaontologisehes Institut der Georg-Awust- Universitat, Gottingen (Deutschland)

SUMMARY

Turbidites in the geosyncline east of the river Rhine

An attempt is made to show the part played by sedimentation from turbidity currents in the development of the geosyncline east of the river Rhine. Following on from the Eifel Stage to the deeper Upper Carboniferous, turbidite formations appear again and again in the deep parts of the basin far from the continent. Each of the various source areas delivers different material. Sand-, greywacke-, and limestone-turbidites can be fixed in space and time.

ZUSAMMENFASSUNG

Es wurde der Versuch gemacht, den Anteil der Sedimentation aus Suspensionsstrbmen im Laufe der rechtsrheinischen Geosynklinalentwicklung aufzuzeigen. Von der Eifel- Stufe durchgehend bis zum tieferen Ober-Karbon kommt es jeweils in den festland- fernen und tiefen Beckenteilen zur Bildung von Turbiditen. Verschiedene Lieferge- biete bringen dabei verschiedenes Material. Sand-, Grauwacken- und Kalkturbidite lassen sich raumlich und zeitlich klar fixieren.

EINLEITUNG

Es war bisher ein Hauptziel der Turbidit-Forschung, die Einzelmerkmale dieses Sedi- mentationstypus zu beschreiben und zu deuten. Ein weiterer Schritt war die ubertra- gung und Auswertung der Merkmale auf grbssere horizontale Erstreckung und weitere Zeitabschnitte. Es SOU hier in einer kurzen Skizze versucht werden, die neuen Erkennt- nisse uber diese Sedimentationsart einmal bei der Betrachtung der Fullung eines ganzen Geosynklinal-Sektors anzuwenden. Sicher kommt dieser Aufsatz zu fruh, noch sehr vie1 Gelandearbeit muss geleistet werden, um endgultigeres aussagen zu konnen. Trotzdem sol1 der Versuch hier gemacht werden, um Anregungen zu geben, Widerspriiche herauszufordern und um damit die Forschung vielleicht weiter zu treiben.

138 W. PLESSMANN

DIE RECHTSRHEINISCHE GEOSYNKLINE

Ein Gebiet, das sich fur die Betrachtung der Sedimentation aus “turbidity currents” in Raum und Zeit geradezu anbietet, ist das astliche und besonders das nordastliche Rheinische Schiefergebirge. Auf relativ kleinem Raum haben wir hier einen Geosyn- klinal-Querschnitt, in dem die verschiedensten Sedimente verschiedensten Alters und verschiedenster Fazies mehr oder weniger gut aufgeschlossen sind. Versuchen wir nun, hier in einer schematischen ubersicht den Ablauf der Geosynklinalfullung zu skiz- zieren.

Devon

Die eigentliche Senkung im Kern des rechtsrheinischen Schiefergebirges (Ebbesattel) beginnt im Unter-Gedinne. Das Ober-Gedinne mit seinen roten Schiefern und Sand- steinen zeigt hier wie in weiteren Teilen des Gebirges den bedeutendsten festlandnahen Einfluss. Spuren von Turbiditen aus dem Gedinne sind bisher nicht bekannt, anschei- nend blieb wie auch in der folgenden Siegen-Zeit der Trog so flach, dass sich Suspen- sionsstrome nicht entwickeln konnten.

Das Unter-Ems wurde ebenso wie die Siegenschichten im nardlichen Bereich des rechtsrheinischen Schiefergebirges uberhaupt nicht ausgebildet. Erst das Ober-Ems transgrediert nach Norden und bezieht das Gebiet nardlich des heutigen Siegener Sattels erneut und verstarkt in die Absenkung ein. Turbidite aus dem hachsten Unter- Devon sind mir nicht bekannt. Sie waren erst ganz weit im Sudosten, im Nordland- fernsten Bezirk zu erwarten.

Im Mittel-Devon, beginnend mit der Eifel-Stufe, erhalten wir eine verstarkte Gliederung des betrachteten Sektors. Die Nordkuste ruckt weiter nach Norden und Nordwesten vor, sodass in den landferneren Geosynklinalbezirken im Sudosten Bedingungen erreicht werden, um Suspensionsstramen den Abfluss zu errnaglichen. Wir kennen im Norden, in landnahen Gebieten, machtige Ablagerungen mit reichem Benthos, unruhiger Sand-Ton Sedimentation (rheinische Fazies), wahrend im Suden, im landferneren Gebiet, abgesehen von Wurmspuren nur nektonische und planktonische Lebewesen in dunklen Schiefern gefunden werden (herzynische Fazies, Typ Wissenbacher Schiefer). Unvermittelt schalten sich nun in diese dunklen, unter Still- wasserbedingungen sedimentierten Schiefer glimmerreiche Sandsteine in zahlreichen Horizonten ein. Schane Beispiele sind die unteren und oberen Raumlander Quarzite von je etwa 100 m Machtigkeit auf dem Messtischblatt Berleburg, die alle Merkmale von Turbiditen zeigen. Nach Ubersichtsmessungen kommt die Stramung generell von Norden, z.T. von Nordosten bzw. von Nordwesten. In einzelnen Banken, die sedimentaren Breccien ahneln, ist zu sehen, dass haufig zerbrochenes rheinisches Benthos vorliegt, das hier uberhaupt nicht bodenstandig sein konnte und einen raschen und weiten Transport von Norden her bezeugt. Ganz ahnlich liegen die Verhaltnisse im Eisenbergquarzit an der Diemel-Talsperre.

Im unteren und mittleren Givet blieben die Faziesbezirke im Grossen und Ganzen

TURBIDITE IN DER RECHTSRHEINISCHEN GEOSYNKLINE 139

gesehen in ahnlicher Lage. Im Nordwesten haben wir machtige, bis zu 3.000 m erreichende sandige und kalkige Sedimente, im Suden finden wir dunkle Schiefer von kaum 100 m Machtigkeit, die sowohl in der Berleburger Umgebung (Schiittung generell von Nord) als auch im Diemelgebiet durch glimmerreiche Sandsteine mit allen Merkmalen von Turbiditen aufgegliedert werden.

Im hoheren Givet riickt die Grenze herzynische und rheinische Fazies noch weiter nach Nordosten vor. Machtige Riffkalke (bis zu 800 m machtig) deuten darauf hin, dass in isolierten einzelnen Bezirken die verstarkte Senkung durch das Korallen- wachstum lange Zeit kompensiert wurde. In den zwischen den Riffkorpern liegenden tieferen Beckenteilen kamen feinkornige Tone zum Absatz (Typ Nuttlarer Dach- schiefer), denen ein Benthos praktisch fehlt. Diese Tone werden nun mit scharfen Grenzen aufgegliedert durch bis zu 1 m Machtigkeit erreichende Kalkbanke, die eine deutliche Gradierung zeigen. An der Basis schon makroskopisch sichtbar, enthalten diese Kalkbanke in Massen meistens zerbrochene Korallen, Stromatoporen, Brachio- poden usw. Wir haben hier deutliche Kalkturbidite vor uns, die seit der aufschluss- reichen Arbeit von MEISCHNER (1962) als besonders gute Stiitzen fur die Richtigkeit der “turbidity current”-Theorie gelten miissen. Ursprungsorte des Materials werden die Riffrander gewesen sein, von denen episodisch Riffschutt in die tieferen Becken- teile glitt.

Im Ober-Devon konnen wir aus der Faziesverteilung ersehen, dass der Nordrand der Geosynkline sich noch weiter nach Nordwesten verlagerte und gleichzeitig die schon im Givet begonnene Spezialgliederung der landfernen, tieferen Trogteile sich weiter verstarkte. Schwellen- und Beckenbezirke sind klar erkennbar.

In der Adorf-Stufe setzt sich in einzelnen Bezirken die Kalk-Turbiditbildung wie im oberen Givet weiter fort. Seit der Nehdenstufe gleiten generell gesehen von Norden glimmerreiche Feinsande rnit Suspensionsstromen in die StillwasserbezirKe. Die Schwellen mit Cephalopodenkalk-Sedimenten werden von den Strbmen urnflossen. Ganz im Siiden scheint ein Festland, die Mitteldeutsche Schwelle, steil aufzusteigen und Grauwacken, vielleicht zum Teil mit Suspensionsstromen nach Norden ins Becken zu liefern.

Karbon

Mit Beginn des Karbons waren zumindest die nordostlichen Geosynklinalteile weit vom Landeinfluss abgeschirmt. Es schieden sich sehr eintonige und uber weite Bezirke nachweisbare Alaun- und Kieselschiefer ab. Turbidite aus diesen Serien sind mir im Nordosten nicht bekannt, lediglich einige sedimentare Breccienlagen in den Kiesel- schiefern (z.B., auf Blatt Laasphe) mit zerbrochenen Faunenresten mogen auf die Existenz von “turbidity currents” hinweisen. Ganz im Suden geht vom weiter aufstei- genden Festland die im Ober-Devon begonnene Lieferung mit Grauwacken weiter.

Erst im hoheren Unter-Karbon finden wir wieder Turbidite in verschiedendsten Bezirken und in zahlreichen Fallen. Von Siiden und Sudosten kommen Grauwacken ins Becken. iiber diese Grauwacken nach Nordwesten hinaus reichend auch von

140 W. PLESSMANN

Meischner beschriebene Kalkturbidite. Im Nordwesten scheinen die Kulm-Platten- kalke ebenfalls zum Teil Absatze aus Suspensionsstromen, diesmal von Nordwesten bzw. Norden her zu sein.

Im Ober-Karbon verlagerte sich das siidliche Festland (bzw. dis siidliche Insel), von wo seit der Nehden-Zeit Grauwacken nach Norden geschuttet wurden, weiter nach Nordwesten. Wie WACHENDORF (1962) zeigte, wurde das Becken des Flozleeren von Siiden her mit Grauwacken-Suspensionsstromen aufgefiillt. Im hbheren Namur ver- flachte sich das verbliebene nordliche Restbecken und nahm bei weiter andauernder Senkung die rund 3.000 m machtigen flbzfiihrenden Schichten auf.

Dieser kurze Riickblick zeigt, dass wir im Laufe der Entwicklung der Geosynkline Schichtfolgen mit Turbiditen immer an denjenigen Stellen finden, wo wir aus faziellen Griinden (Fazies = Summe der primaren petrographischen und palaontologischen Merkmale einer Ablagerung) festlandferne und tiefere Beckenteile annehmen mussen. Das sind die Gebiete mit herzynischer Fazies. Die Turbidit-Bildung geschieht im allgemeinen unabhangig von orogenetischen Bewegungen.

Liefergebiete

Als Liefergebiete kommen von der Eifel- uber die Givet-Stufe bis zum hohen Ober- Devon zunachst das Nordland in Frage, genauer der nordische Scheltbereich, denn alle diese Schichtserien bestehen aus glimmer- und kalkreichen Sandsteinen, die sicher im Flachseebezirk schon vorher aufbereitet waren. Die langsam sich generell nach Nordwesten verschiebende Grenze rheinische-herzynische Fazies (mit einem Uber- gangsgebiet) bedeutet gleichzeitig eine fortschreitende Eintiefung. Denkbar ist als Auslosungsort von Suspensionsstromen dann der sich eintiefende Schelf.

Im Gegensatz dazu bestehen die aus dem Siiden bzw. Sudosten gelieferten Sedimente des Ober-Devons, Unter- und Ober-Karbons vorwiegend aus Grauwacken, die auf eine rasche zeitliche Folge von fortschreitender Hebung, Abtragung, Transport und Ablagerung hindeuten. Damit sol1 nicht gesagt sein, dass alle Grauwacken auch Turbidite sind.

Sonderfalle von Turbiditen sind die Kalkturbidite, die einmal von Riffrandern (oberes Givet und Adorf), dann von sudlichen und nordlichen kalkigen Flachwasser- Sedimentationsbezirken (Unter-Karbon) ins tiefere Becken gelangten. Alle diese Typen sind flachenhaft verbreitet ; Ausnahme ist die “Packelmann’sche Querzone” (siehe SCHMIDT, 1962, Abb.4).

Neben diesen drei angefuhrten Typen gibt es vielleicht einen vierten, aber von sehr untergeordneter Bedeutung, namlich Tuff-Turbidite. Zum Beispiel liegen am Diemel- stausee in der Eifel-Schichtenfolge bis 1 m machtige, gut gradierte Keratophyrtuffe, die an der Basis zahlreiche, meist zerbrochene Fossilien mit “rheinischem Charakter” fuhren, die in den ubrigen Sedimenten fehlen.

TURBIDITE IN DER RECHTSRHEINISCHEN GEOSYNKLINE 141

SCHLUSSBETRACHTUNG

Wie bereits erwahnt, ist diese Skizze nur ein erster Versuch, die Bedeutung der Tur- bidite bei einer Geosynklinalfullung aufzuzeigen. Angeharige des Gottinger Geolo- gisch-Palaontologischen Institutes arbeiten seit einiger Zeit an diesem Objekt. Weitere Untersuchungen werden in Kiirze in Angriff genommen.

LITERATUR

KULICK, J., 1960. Zur Stratigraphie und Palaogeographie der Kulm-Sedimente im Eder-Gebiet des nordostlichen Rheinischen Schiefergebirges. Fortschr. Geol. Rheidand Westfolen, 3 (1) : 243-288.

MEISCHNER, K.-D., 1962. Rhenaer Kalk und Posidonienkalk im Kulm des nordostlichen Rheinischen Schiefergebirges und der Kohlenkalk von SchreufaIEder. Abhandl. Hess. Lundesamtes Bodenforsch. 39 : 47 s.

PLESSMANN, W., 1961. Stromungsmarken in klastischen Sedimenten und ihre geologische Auswertung. Geol. Jahrb., 78 : 503-566.

PLESSMANN, W., 1962. uber Stromungsmarken in Ober-Devon-Sandsteinen des Sauerlandes. Geol. Jahrb., 79 : 387-398.

RABIEN, A., 1956. Zur Stratigraphie und Fazies des Ober-Devons in der Waldecker Hauptmulde. Abhandl. Hess. Landesamtes Bodenforsch., 16 : 83 S.

RABIEN, A., 1959. Stratigraphische und fazielle Probleme im Palaozoikum der nordwestlichen Dill- mulde. Z. Deut. Geol. Ges., 110 : 629-633.

SCHMIDT, H., 1962. Uber die Faziesbereiche im Devon Deutschlands. In: H. K. ERBEN (Redakteur), Symposium Silur-Devon Grenze, 1960. Schweizerbart, Stuttgart, S. 224-230.

SEILACHER, A., 1958. Zur okologischen Charakteristik von Flysch und Molasse. Eclogae Geol. Helv.,

WACHENDORF, H., 1962. Wesen und Herkunft der Sedimente des westfalischen Flozleeren. Thesis, Univ. 51 : 1062-1078.

Gottingen, Gottingen, 61 S.

TURBIDITE SEDIMENTS IN THE SOUTHEASTERN ADRIATIC SEA

L. M . J . U . VAN STRAATEN

Geological Institute, State University at Groningen, Groningen (The Netherlands)

SUMMARY

A sand-silt layer in acore from a depth of 1,198 m in the southeastern Adriatic Sea, is interpreted as having been deposited by a turbidity current on account of the following properties: ( I ) a sharp base, (2) muddiness of the sand in parts, (3) grading of grain sizes, (4) the characteristic sequence of parallel laminations in the lower part, then ripple laminations, then convolutions, and finally, fine parallel laminations in the top part, and (5) the presence of numerous tests of shallow water forminifera. The cores from this region generally show sand and silt layers, intercalated in the fine pelagic muds. The topography of the area below a depth of about 1,200 m is typically that of an abyssal plain.

INTRODUCTION

The Adriatic Sea is, on the whole, rather shallow; depths exceeding 1,OOO m exist only

Fig.1. Southeastern Adriatic Sea, with location of the sections given in Fig.2 and 3, and of station 293.

L. M. J. U. VAN STRAATEN 143

in the southeastern part (Fig. 1). During a sedimentological expedition in the summer of 1962 it was found that the sea floor in most of this southeastern part has a marked relief. However, beyond a depth of 1,200 m, the bottom is quite flat and slopes gradually to the deepest places, which are approximately 1,216 m below sea level'. The latter lie east of the centre of the flat area, which itself lies east of the axis of the Adriatic Sea.

STRATIFICATION AND STRUCTURES

Subsurface reflections of the precision depth recorder used during this part of the expedition showed that everywhere in the flat area the bottom sediments are well stratified, at least down to some 12 m below the surface2. This stratification has a striking lateral continuity, separate layers being traceable over distances of several dozens of kilometres (see Fig.2, 3). On the edges of the flat area, the stratified series is seen to thin out suddenly in some places. Yet, southwest of station 350-A, a series of about the same thickness was found which may have been deposited synchronously with the series in the flat area.

Cores taken from the sediments in this general region all contain one or more layers of sand and silt, intercalated between fine pelagic mud. In long cores, several such layers were encountered, e.g., in the 330 cm core of station 293 (depth 1,198 m, position N 41"45,3' E 18"9,0', X on Fig.1) at 46, 58, 160, 199, 239 a'nd 289 cm from the top3. These layers are mostly from one to a few centimetres thick. At station 353 (depth 1207 m, position N 42"07,2' E 17'38,O') a much thicker layer of some 12 cm was found at a depth of 461 cm (in the core), and the layer at 289 cm in the core from station 293 has a thickness of 17 cm. Probably the reflections registered by the precision depth recorder took place on relatively coarse-grained layers of such thicknesses of 10 cm or more.

It seems likely that these sands at stations 353 and 293 belong to the same layer; their differences in depth below the surface could then be due to the thinning out of the series over the edge of the flat area. In this connection it may be remarked that the depths, as measured in the cores, may be somewhat smaller than the real depths of the layers below the sea floor, owing to shortcomings of the coring method.

While many of the thinner sand and silt layers have lost their original depositional structures, evidently as a result of burrowing by benthonic animals, the thicker ones usually show laminations and grading of the grain sizes. Cross-sections of the thick layer in the core from station 293 are given in Fig.4. The sections have the same

No indications whatever were found of the presence of low transverse ridges and troughs, as given on the Carta Batimetrica del Mediterraneo Centrale, Mare Adriatico, 1 : 750,000, published by the Istituto Idrografico della Marina, Genoa, 1960.

In Fig.2 and 3 the depths of the layers below the surface have been presented as they would be if there were no difference in velocity of the ultrasound waves in the sediment and in the water. * These figures refer to the base of each layer.

144 T

UR

BID

ITE

SED

IME

NT

S IN T

HE

AD

RIA

TIC

SEA

Fig.2. Section dong line A-A' of

Fig.1.

Fig.3. -ion along linc B-B of

Fs.1.


Fig.4. Turbidite layer (almost natural size) from 289-272 cm below surface in core from station 293 (Xon Fig.1).

146 TURBIDITE SEDIMENTS IN THE ADRIATIC SEA

orientation and are about 1% cm apart. They display features which together are typical of turbidites, viz. (a) a sharp base, (6) muddiness of part of the sand, especially in the lower laminae, (c) a rough grading of grain sizes, and ( d ) the characteristic sequence of parallel laminations in the lower part, then ripple laminations, then convolutions and finally, fine parallel laminations in the top part. After the photographs were taken further drying out of the sediment rendered the latter laminations still much more distinct. In the 55 cm thick top part, more than 90 sets of a darker and a lighter lamina were counted, some of them having a thickness of only 200 p. As far as the author is aware, no such complete analogy in structures to ancient turbidites described by Kuenen and others (including well-developed convolutions) has hitherto been recorded from deep-sea sands from the recent sea floor.

COMPOSITION AND TEXTURES

The bulk of the sand consists of quartz grains and grains of calcium carbonate, in approximately equal proportions. Glauconite grains are common. Furthermor, the sand contains numerous tests of shallow water Foraminifera including Asteriginata mamilla (WILLIAMSON), Gibicides lobatulus (WALKER and JACOB), Elphidium advena (CUSHMAN), Elphidium granosum (D‘ORBIGNY), Rosalina globularis (D’ORB~GNY), Spiroplectammina wrightii (SILVESTRI), Streblus beccarii (LINNB), cf. CHIERICI et al. (1962), and also spines of echinoids.

The coarsest grains, up to some 160 p, are found in the muddy sand laminae (dark coloured on the photographs). Most of the grain sizes in these dark laminae lie between 80 and 120 p; the light coloured laminae are better sorted, and practically free of clayey material. In the lower part their texture is, on the whole, a little finer than that of the muddy sand laminae. In the middle part, with the convolutions, they have grain sizes mainly from 40-80 p; above the zone with convolutions, many very thin laminae are also practically free of lutite admixtures, and consist mostly of grains of 10-40 p.

The layer described above was most probably formed during the Pleistocene period as is indicated by the presence of large numbers of tests of Globigerina pachydermu (EHRENBERG) and Globorotalia scitula (BRADY), while remains of Orbulina universa (D’ORBIGNY) are lacking. These features point to deposition under cooler climatic conditions than those of the present day (PARKER, 1958).

ACKNOWLEDGEMENTS

The author gratefully acknowledges the help of the Koninklijke/Shell Exploratie en Productie Laboratorium at Rijswijk, the Nederlandse Organisatie voor Zuiver Weten- schappelijk Onderzoek at The Hague, the State University at Groningen and the Na- tional Science Foundation at Washington. The ship used for this part of the expedition (planned ip cooperation with Dr. Tj. H. van Andel) was the “Horizon” of Scripps


Institution of Oceanography at La Jolla. The Foraminifera of the section, discussed in this paper, were kindly identified, and their distribution interpreted, by the Konink- lijke Shell Laboratory at fijswijk.

REFERENCES

CHIERICI, M. A., Busr, M. T. et @A, M. B., 1962. Contribution B unebtude kcologique des Foramhi- f&res dans la mer Adriatique. Rev. Micropaliontol., 5 : 123-142.

PARKER, F. L., 1958. Eastern Mediterranean Foraminifera. In: H. P E ~ R S O N (Editor), Rept. Swed. Deep-sea Expedition. 8. Sediment Cores from the Mediterranean Sea and the Red Sea, 4 : 217-283.

LES SABLES PROFONDS DE LA MBDITERRANGE OCCIDENTALE

JACQUES BOURCART

Lnboratoire a‘e Gkologie Dynamique. Universitk de Paris, Paris (France)

SUMMARY

The deep sands of the western Mediterranean

The morphology of the western Mediterranean is the same as that of the Atlantic, as described by HEEZEN and EWING (1957), at the borders of the basin: continental shelf and continental slope, sculptured with submarine canyons, continental rise, totally flat abyssal plain.

Until now, it was thought that except for the littoral sands and those at the end of the continental shelf, the totality of this sea was occupied by muds. Drilling-operations in the continental rise have disclosed coarse- and fine-grained sands, silts and cobbles (- 2,400 m), which can only be provided by coastal currents.

At the continental rise, on the abyssal plain, we have gathered stratified cores, consisting of sands and muds with bands coloured by manganese, and some horizonts that are formed only by planktonic pteropods and foraminifers.

The study of the western Mediterranean will surely permit us to resolve the problem of turbidity currents in the future, thanks to the relief in submarine canyons and to the new apparatuses of Captain Cousteau: diving saucer and “Trolka”.

RBSUMB

La morphologie de la Miditerran&. occidentale est identique a celle de l’Atlantique, dkrite par HEEZEN et EWING (1959), sur les bords de la cuvette: plateau continental et pente continentale sculptks par des gorges sous-marines, glacis pri-continental (“continental rise”), plaine abyssale tout a fait plate.

Jusqu’a prbent, en dehors des sables littoraux et de ceux de la fin du Plateau continental (sables du large), on pensait que la totaliti de cette mer itait occupie par des vases. Des carottages faits dans le glacis y ont dicouvert des sables, sablons, silts et galets (- 2.400 m), qui ne peuvent provenir initialement que des fleuves c6tiers.

Au large du glacis, nous avons rCcoltC, en plaine abyssale, des carottes stratifikes faites de sables et de vases avec des bandes colorks par le manganhse et quelques niveaux uniquement faits de ptiropodes et de foraminifhres planktoniques.

LES SABLES PROFONDS DE LA MBDITERRANNBE OCCIDENTALE 149

L’Ctude de la MCditerrank occidentale, particulitrement facile, permettra surement, dans l’avenir, de rdsoudre le probltme des Ccoulements turbides, grlce au relief en canyons sous-marins et aux nouveaux engins du Cdt. Cousteau: Soucoupe plongeante et “Troika”.

INTRODUCTION

Dans les derniers cent ans, deux probltmes encore irr6solus intkressent a la fois la morphologie et la ddimentation sous-marine: celui des canyons sous-marins et celui des sables profonds. L‘un et l’autre ont CtC traitb dans les oceans profondset dans des zones assez eloignees, ne permettant pas une Ctude approfondie et, de ce fait, ont CtC l’objet de controverses surtout thtoriques.

AussitBt libCrC de mes obligations militaires, j’ai entrepris l’ktude des premiers canyons dkouverts en MBditerranCe, prts de la frontitre espagnole, par mon Maitre Georges Pruvot, Directeur du Laboratoire de Banyuls sur Mer (PRUVOT, 1894). Grace a la proximitk du canyon, aux moyens nautiques mis a ma disposition par le Directeur actuel du Laboratoire: Georges Petit, puis surtout a la possibilite de travailler avec de petites unites de la Marine Nationale: dragueurs de mines ou chasseurs et surtout ceux fournis par le Cdt. Cousteau: batiment de recherches scientifiques “Calypso” et soucoupe plongeante, j’ai pu reprendre et j’esptre poursuivre ce travail.

Dans la suite, j’ai pu entreprendre une Ctude compltte du nord de la MCditerranCe occidentale (BOURCART, 1955; BOURCART et al;, 1961 ; BOURCART et ROS-V~CENT, 1962). Cette Ctude a CtC effectuke grace a la “Calypso”, il en est rCsultC une carte au 1 /1.000.000t de cette mer.

LA PENTE CONTINENTALE DE LA MER LIGURE

Aprts la construction d’un carottier a piston, dCrivC du carottier KULLENBERG (1947), une sCrie de prdltvements a Ct6 obtenue, notamment au pied de la pente continentale, entre Nice et le Haut-Fond de Santa-Lucia, qui joint la Spezzia au Cap Corse.

Le long de cette pente, A peu prts ouest-est, nous avons pu rkolter, jusqu’a Bor- dighiera, des carottes de sables grossiers intercalks de bandes de vase. Les sables contiennent les mCmes ClCments que le cordon de galets qui va de Nice a Antibes, c’est a dire de ceux du Massif du Mercantour-Argentera, notamment de son m u r granitique et de sa premiere enveloppe de pklites rouges et de g r b triasiques. A hauteur de Vinti- mille, la ligne de sonde a coupC, au deli de la frontitre italienne, la rivitre de la Roya, qui descend de la face a l’est du Massif du Mercantour-Argentera. A -2.410 m, la sonde a ramen6 du sable fluvial granoclasd qui recouvre une couche de galets de 6 cm. Ces galets surmontts de sables se poursuivent tout le long de la vallCe de la Roya, jusqu’h -2.600 m, devant Vintimille.

La bande de sables profonds dCbute devant Nice, en Baie des Anges, a -1.900 m,

150 J. BOURCART

contre I’A-pic du Cap Ferrat oh sa direction est celle de cette falaise sous-marine soit nord-nordouest-sud-sudest et devient ensuite parallele au fond de la pente continentale a peu p r b ouest-est. Cette bande sableuse a a peu prts 3 milles de large et est doucement inclinte vers le sud, diviske, suivant la pente, en bandes 6troites ressem- blant a des dunes dont le versant raide est tournt vers le large. En utilisant le sondeur P.D.R. de la “Calypso”, le Cdt. Cousteau a reconnu la m&me disposition qui semble donc exister des deux c8tes du Golfe de Gsnes.

REPARTITION DES SEDIMENTS TERRIGBNES

Les carottes obtenues ont atteint une moyenne de 2 m. Elles descendent a peu pres a la base du dtp6t, ce que dkmontrent des lits plus grossiers comme grains avec m&me des granules et des graviers. L’ensemble est stratifie et coup6 de vases surtout quartzeuses, contenant des lits de matieres organiques: surtout feuilles de Phragmites et oogones de Chara avec des fragments d’drundo Donax a la partie inftrieure. Les bandes de vase se terminent vers le haut de deux facons difftrentes:

(1) par augmentation progressive du calibre des Bltments et passage aux sablons (silt); les grains de ceux-ci passent ensuite aux sables qui redeviennent des sablons dans la partie suptrieure de la stquence;

(2) la bande de vase est brutalement interrompue par une coulte de sable avec parfois de petits galets a la base; sa surface est strite et souvent de petits galets de vase existent a la base de la s6rie sableuse. I1 semble que cette disposition soit due a un courant torrentiel de sable ou A une chute en cascade analogue A celle photographik par SHEPARD (1960, Fig.9).

Ce type de courant, fait de sable et d’eau, a 6t6 observ6 lors du percement du tunnel de Meudon sur la ligne de chemin de fer de Paris (Invalides) a Versailles et a causi d’6normes difficult&; ou lors du percement de “sables boulants” dans les chantiers et aussi dans les galeries creusies dans les Alpes a travers les “quarzites” triasiques. Sans que I’on ait ce propos employ6 le mot de “courants turbides”, il est certain que les sables fins plus ou moins aquiftres coulent comme un liquide. La composition de ces sables, presque pas calcaires et presque sans foraminiftres, est la m&me que celle des roches des galets du cordon de la Promenade des Anglais a Nice, qui proviennent tous du Var, notamment de psammites rouges du Permien qui, trts reconnaissable au microscope binoculaire, peuvent servir d’indicateurs. I1 en est de m&me de ceux de la Roya, en face de Vintimille. La bande de sables dtbute ti -1.900 m. Elle parait continuer la direction d’une bande caillouteuse qui, d’aprts la carte lev& par GENNES- SEAUX (1962), poursuit le cours du Paillon a partir du cours commun avec le Var.

Rappellons que la Baie des Anges n’est pas une portion du plateau continental, mais que, du Cap d’Antibes au Cap de Nice, c’est un cane en creux tail16 dans des marnes pliocenes qui sur le continent remontent jusqu’a la chaine des Baous (Gattitres, 224 m; Carros, 376 m) et sur la rive gauche du Var: La Roquette, 360 m; Aspremont, 400 m et dans la vallte du Paillon: la Trinitt Victor, 175 m.

LES SABLES PROFONDS DE LA M~DITERRANN~~E OCCIDENTALE 151

Dans cette baie, les diffkrents fleuves c8tiers: Brague, Loup, Cagne, Var, Magnan, Paillon, se sont creusks des cours sous-marins qui sont remplis de sablons, sables et graviers, ou de sables et galets qui aboutissent tous B la cuvette de -1.800 m et, finalement, sont continues par la trainke de sables stratifiks dont nous venons de parler. Le reste de la baie est occupk par de la vase c6titre et de la vase bleue, dure, avec foraminiftres plioctnes en gknkral en saillie entre deux coulkes de galets avec un peu de sable.

MODE DE TRANSPORT ET S~DIMENTATION

En prolongement des cours d’eau subakriens, on trouve en gkndral un mklange de vase, sables et galets. Gennesseaux a suivi ces coulkes de tout venant en exkutant une skrie de films avec la “Troika” du Cdt. Cousteau (GENNESSEAUX, 1962b; GENNE~SEAUX et LE CALVEZ, 1960). Ces photographies montrent une skrie de faits t r b caractkristiques: (I) les galets sont disposks parallklement aux berges trts raides des chenaux et non dans le sens des courants; (2) des microfalaises, de 1 m environ de hauteur, courant sur la berge. Ces observations conduisent B penser que le transport des galets, graviers et sables se fait par kboulement, latkralement de l’ouest vers I’est et semble arretk par un relief rocheux du a des failles. Puis les dlkments amends ainsi vers l’est sont trids et en meme temps descendent vers le fond de la baie.

En dehors de ces coulkes de matkriaux relativement meubles, la pente continentale formke de vase trts dure et en gknkral plaisancienne, est presque toujours revEtue de vase trts riche en eau et trts mobile (“slumping”) en formant des microfalaises ou parfois des cirques. Les dragages ramtnent du bas de la pente des galets de vase, que I’on retrouve souvent par dragages dans les sables du glacis au pied de la pente vers - 2.600 m. Les vases qui s’accumulent dans les rades, c o m e celle de Villefranche, sont kgalement trts riches en eau, mais elles viennent du large et contiennent des foraminiftres planktoniques et beaucoup de dkbris vkgktaux, notamment de poils de rhizones de posidonies ou de feuilles de ces naiadacks. I1 en rksulte une vase trts riche en humus (ktudik par Ros-Vicent, voir BOURCART et ROS-VICENT, 1962) et en sulfate de fer qui forme une tache dam le fond de la rade.

Ce type de vase, a partir de Toulon, remplit la partie sup6rieure des gorges SOUS-

marines oh cette vase est associke avec des galets fluviatiles et de grandes coquilles de la faune a Cyprina islandica qui avait ktk dkcouverte dans la rkgion de Banyuls, soit dans le canyon, soit sur la plateforme du Cap Creus par PRWOT (1894). Cette faune est citke dans tous les traitds classiques et y est considkrk comme sicilienne. J’ai montrk, du point de vue stratigraphique, et MARS (1960), du point de vue palkontologique, qu’elle date de la fin du dernier glaciaire. Les dix-huits canyons qui dkcoupent la pente continentale du Var a I’Aude, sont

combles par cette vase, en gknkral jusqu’i 100 m, la partie supkrieure seule, ce qui est le cas pour le Grand Rh6ne, par des sables coquilliers du plateau continental qui paraissent comme aspirks dans la gorge; on y retrouve des galets a partir du canyon

152 J. BOURCART

qui prolonge la Durance, sous la Camargue et a partir du canyon de Narbonne, c’est B dire des Pyrtnks.

LES CANYONS ET LA S~DDIMENTATION PROFONDE

Les missions effectukes avec la soucoupe plongeante de Cousteau dans les canyons au voisinage de Port Vendres, ainsi d’ailleurs que les forages de la Socittt des PBtroles MMiterrankns en Camargue, ont montrB que les canyons du Golfe du Lion ont BtB creuds A la fin du Miodne par des fleuves et envahis par la mer au dCbut du Plioctne.

La gorge actuelle est, comme l’ont montrB nos carottages, incomplttement remplie d’un mBlange pdteux: vase, coquilles de la faune atlantique, cailloutis fluvial pyrenkns, qui la moule en affectant une forme semi-cylindrique, remplissage dont une prochaine mission dkterminera l’ktendu.

En rBsumB il existe trois proc6dBs de remplissage des canyons: sables stratifib, vase, cailloutis, apr&s melange avec du bBton de vase.

L‘hypothbe ayant BtB Bmise, notamment par 1’Ccole de Lamont, que les plaines abyssales doivent leur horizontalit6 B des sables ou limons apportCs par les canyons sous-marins, une carotte no.124 a BtC prBlevCe A la sortie de la rivikre de Nice, juste avant sa jonction avec la Rivikre de Genes (Fig. 1). Elle a ramenCe (a partir de -2.500 m) une sBrie trts Bpaisse, finement stratifik, de sables fins, de sablons et de vase grise. La composition minkralogique est la mbme que celle du Var et de la Vallk de Nice soit: quartz, micas, feldspaths, psammites du Permien du Mercantour.

I1 ne s’agit plus d’koulement turbulent, mais de stratification plus ou moins rCgu- litre, sans Brosion a la base et sans galets, au moins sur les buttes rocheuses qui apparaissent parfois au milieu des sables.

En 1960, la zone centrale de la plaine abyssale du Golfe de G h e s a BtB Btudik A l’ouest de la Corse et au nord de la Sardaigne. Du point de vue de son remplissage rien n’Ctait connu et elle Btait considBrk comme entitrement faite de vase grise. Toutes ces carottes sont analogues A la carotte no. 124, c’est B dire composkes d’alternances de sables fins quartzeux et de sablons micads avec des intercalations de vases, sans turbulence ou Brosion.

La fraction > 40 p est infkrieure B 5 %. Des strates uniquement faites de globigCri- nes, orbulines et ptkropodes, interrompent la succession; certains lits sont entitrement composds de ces organismes. D a p r b une suggestion de TrBgouboff (communication orale), il pourrait s’agir d’une thanatocoenose succt3dant a une mort subite du plankton B la suite, soit d’une variation hydrologique, soit d’une Bpizootie (p6ridi- nien?). Cette observation a BtB faite au large de Villefranche.

Fig.1 (p.153). Profil en long de la vallk sous-marine de Nice et de ses affluents.

Longitudinal profile of the submarine valley of Nice and its affluents. Vase jaune = yellow mud. Vase grise = gray mud. Zone oxydke = oxydated zone. Sable fin = fine-grained sand. Sablon = very fine- grained sand. Sable grossier = coarse-grainedsand. Galets de vase = mud-cobbles. Galets = cobbles.

LES SA

BL

ES P

RO

FO

ND

S DE

LA

MI~D

ITE

RR

AN

N~E

O

CC

IDE

NT

AL

E

153

154 J. BOURCART

En 1962, une croisibre de huit jours a ktk faite en direction de Minorque. Quatre longues carottes et trois carottes Alinat de gros diambtre ont ktk prklevkes sur l’aligne- ment Minorque - axe du Golfe de GCnes (Fig.2). Toutes ces carottes sont en vase jaune oxydke et vase grise, parfois noire, avec des niveaux rouges et bandes de sables fins ou de sablons et meme la carotte no.16 prts de l’emplacement du carottage 0.18 de PETTERSSON (1961), contient 0,52 m de sable a sa base, sans vase. Ces sables sont toujours quartzeux avec feldspaths, zircons, micas, un peu de calcaire crayeux (23 % de la fraction > 40 p) et quelques grains de rikbeckite.

Fig.2. Carte de la Mtditerrank occidentale avec localisation des carottages. + = Carottages mission H. Pettersson (1947-1948). 0 = Carottages sdrie Golfe du Lion (1960), en cours d‘etude. = Carot- tages drieRivi6re de Nice (1958-1961), en cours de publication. 0 = Carottages drie plaine abyssale

(1961), en cows d’etude. A = Carottages sbie plaine abyssale (1962), en cows d‘Ctude.

Map of the western Mediterranean with core locations. + = Corings by H. Petterson (1947-1948). 0 = Core-series Gulf of Lions (1960), in study. 0 = Core-series Riviera of Nice (1958-1961), in press. 0 = Core-series abyssal plain (1961). in study. = Core-series abyssal plain (1962), in study.

A un niveau comparable, des bandes de vases, colorkes par le manganbse, se trouvent dans les carottes, ainsi que des niveaux de ptkropodes analogues a ceux de la rivibre de Nice. La vase par endroits est en bandes de teintes diffdrentes, variant entre le brun et parfois m&me le gris vert clair.

L’origine des premibres coulees du mtlange vase-galets dans la Baie des Anges est a chercher dans la microfalaise limite de la terrasse ou plateforme limite du littoral, qui est entaillke soit en forme de rebord, soit faconnk en cordons par les vagues.

Les photographies, presque continues, obtenues avec la “Trolka”, en remontant le Paillon, montrent plusieurs microfalaises successives limitant 1’6boulement, le chenal ttant caractdrisk, ce qui est absolument remarquable, par des ripples longitudinaux.

Ces diffkrents traits morphologiques doivent permettre dans la suite une kvaluation

LES SABLES PROFONDS DE LA M~DJTERRANN~E OCCIDENTALE 155

de la vitesse d’koulement des galets et peut h e , par cinimatographie, de la nature de leurs mouvements. I1 est probable que souvent il s’agit du pivotement des galets.

La transformation du mtlange initial plus ou moins uniforme en sable a peu pr&s pur, a partir de la cote -1.800 m, pourra Ctre ainsi observe. L’Ctude systimatique de la Baie des Anges, que M. Gennesseaux a entrepris sur mon conseil, peut, grace a ces multiples faits favorables et a l’emploi de la “soucoupe plongeante”, permettre de rtsoudre le problkme encore ma1 connu des “icoulements turbides”.

BIBLIOGRAPHIE

BOURCART, J., 1955. Les sables profonds de la Mtditerrantk. Arch. Sci. (Geneva), 8 (1) : 5-13. BOURCART, J., 1960. Sur la repartition des ddiments observb en Mbditerrantk occidentale. Intern.

BOURCART, J. et ROS-VICENT, J., 1962. Sur le remplissage ddimentaire de la partie centrale de la

BOURCART, J., GENNESSEAUX, M. et KLIMEK, E., 1961. Sur le remplissage descanyons sous-marins de la

GENNESSEAUX, M., 1962a. Une cause probable des Coulements turbides profonds dam le canyon

GENNESSEAUX, M., 1962b. Les canyons de la Baie des Anges, leur remplissage ddimentaire et leur

GENNESSEAUX, M. et LE CALVEZ, Y., 1960. Meurements sous-marins de vases pliocknes dans la Baie

HEEZEN, B., THARP, M. and EWING, M., 1959. The floors of the oceans. 1. The North Atlantic. Geol.

KULLENBERG, B., 1947. The piston core sampler. Svenska HydrograJ Biol. Komm. Skrijter, Ser. 3:

MARS, P., 1960. Note sur les gisements sous-marins B faune celtique en Mkditerrantk. Ruppt. ProcPs-

P ~ R S S O N , H. (Editor), 1961. Rept. Swed. Deep-sea Expedition, 1947-1948,8 (4) : 335-391. PRWOT, G., 1899. Essai sur la topographie et la constitution des fonds sous-marins de la region de

SHEPARD, F. P., 1960. Deep sea sands. Intern. Geol. Congr., 21st, Copenhagen, 1960, Rept. Session.

Geol. Congr., 2lst, Copenhagen, 1960, Rept. Session, Norden, 23 : 7-18.

Mediterrantk occidentale. Compt. Rend., 254 (16) : 2897-2901.

Mediterrantk francaise. Compt. Rend., 252 : 3693-3698.

sous-marin du Var. Compt. Rend., 254 : 2038-2040.

rale dans la ddimentation profonde. Compt. Rend., 254 : 2409-241 1.

des Anges. Compt. Rend., 251 : 2064-2066.

SOC. Am., Spec. Papers, 65 : 122 pp.

HydrograJ 1 (2) : 46 pp.

Verbaux Rkunions Comm. Intern. l?tude Sei. Mer Mkditerranie, 15 (3) : 325-330.

Banyuls, de la plaine du Roussillon au Golfe de Rosas. Arch. Zool. Exptl. Gen., 3 (2) : 599-672.

Norden, 23 : 26-42.

ALLODAPISCHE KALKE, TURBIDITE IN RIFF-NAHEN SEDIMENTATIONS-BECKEN

K . - D . M E I S C H N E R

Geologisch-Palaontologisches Institut der Georg-August- Universitat, Gottingen (Deutschland)

SUMMARY

Allodapic limestones, turbidites in near reef sedimentary basins

Allodapic limestones have the following characteristics: (1) Type of sequence. Interstratification of pelitic layers with clastic limestones.

Regular beds which can be traced over long distances without considerable change in thickness. Absence of features indicating shallow water.

Decrease, in a given series, of individual and overall limestone thickness in the same direction as grain size decreases (horizontal grading).

(2) Sedimentary features of individual limestone beds (Fig. 1). Lower contact sharp, sometimes with flute and groove casts; graded bedding, upper contact mostly indistinct.

Larger pebbles near lower contact, sometimes imbricated. Planar bedding becomes gradually thinner towards the top of the bed, grading into lamination. Sometimes current ripple lamination and convolute bedding.

Sorting includes fossils and is poor in coarse basal part of bed. Grains are very poorly rounded.

(3) Geometry. Each of the detrital limestone beds forms a lenticular body. The coarser basal layers attain their maximum thicknesses upstream, while the finer grained upper parts have their maxima further downcurrent in the order of grain size (Fig.2).

(4) Bio-facies. The pelitic intercalations are formed in pelagic “Stillwasser”. Both nectonic and planctonic fossils occur statistically scattered, benthos absent.

In contrast, detrital limestones consist predominantly of fragments of shallow marine benthos, mostly reef-dwellers, with an admixture of pelagic fossils, which are rare in contemporaneous reef-complexes. Benthonic fossils are never in living position, but sorted according to grain size. Ooids are common.

It is concluded that the calcareous detritus was derived from reefs. This material was shed episodically into near by basins through turbidity currents. A model for transportation and sedimentation is presented in order to relate certain sedimentologic features to particular sedimentary. processes.

ALLODAPISCHE KALKE 157

Allodapic limestones must be distinguished from sediments accumulated by slumping and sliding, from autochthoneous limestone/clay series of pelagic “Schwel1en”- facies, and from calcitic arenites of shallow water.

Allodapic limestones are very useful tools for environmental and paleogeographical reconstruction of sedimentary basins. But they were so far neglected and often misinterpreted.

Examples of allodapic limestones are described from the Devonian and Carboni- ferous of the rhenish geosyncline, the Malm of the Swabian Alb, and the west hellenic flysch trough of Greece. Several examples previously published are mentioned.

ZUS AMMENFASSUNG

Allodapische Kalke haben folgende Merkmale: (I) Gesteinsverband. Pelite wechsellagern in vielfacher Wiederholung mit klasti-

schen Kalken. Die einzelnen Banke sind regelmiissig aufgebaut. Sie lassen sich ohne grossere Veranderung in Machtigkeit und Zusammensetzung uber weite Entfernungen verfolgen. Es fehlen alle Merkmale, die auf Ablagerung in flachem Wasser deuten.

Innerhalb desselben Schuttungs-Korpers nehmen durchschnittliche Bank-Machtig- keit und Gesamt-Machtigkeit des Kalkes gleichsinnig mit der Korngrosse von einem Zentrum aus nach allen Seiten ab (horizontale Gradation).

(2) Sedimentare Strukturen innerhalb einer Kalkbank (Fig. 1). Die Unterflache ist vollig scharf. Sie kann Ausgiisse von Stromungsmarken tragen. Die mittlere Korn- grosse nimmt von unten nach oben ab (Gradation). Die Obergrenze ist mi s t unscharf.

Grossere Gerolle liegen nahe der Unterflache, mitunter in Dachziegel-Lagerung (Imbrication). Im oberen Teil stellt sich eine zunehmend engstandig werdende ebene Feinschichtung ein, die in eine Lamination ubergeht. Mitunter kommen Stromungs- Rippeln und Convolution vor.

Die Sortierung umfast auch die Fossilien. Sie ist in dem basalen Teil der Bank schlecht und wird nach oben besser. Die Zurundung ist sehr gering.

(3) Verteilung im h u m . Jede detritische Kalkbank bildet einen linsenfonnigen Kbrper. Die grobkornigen basalen Partien erreichen ihre grosste Machtigkeit im stromauf liegenden Teil, w&rend die Maxima der feinen oberen Bankteile stromabwarts versetzt sind (oblique Gradation, vgl. Fig.2).

(4) Biofazielle Kriterien. Der pelitische Anteil der Wechsellagerung ist ein Sediment der pelagischen Stillwasser-Fazies. Nektonische und planktonische Fossilien sind in statistischer Verteilung eingestreut und oft bemerkenswert gut erhalten, Benthos fehlt.

Die detritischen Kalke dagegen bestehen uberwiegend aus Trummern benthonischer Flachwasser-Bewohner - meist aus Riff-Biotopen - mit einer Einmengung pelagischer Fossilien, die in Riffen gleichen Alters fehlen. Benthonische Fossilien sind nie in Lebendstellung, sondern nach der Korngrosse sortiert. Ooide sind haufig.

Der Kalk-Detritus wird von Riffen hergeleitet, deren Schut durch “turbidity currents” episodisch in benachbarte Stillwasser-Becken eingebracht wurde. Es wird ein

158 K.-D. MEISCHNER

Model1 gegeben, anhand dessen sich die einzelnen sedimentologischen Strukturen auf bestimmte Vorgange beim Transport und der Ablagerung des Detritus zuruckfiihren lassen.

Allodapische Kalke mussen abgegrenzt werden gegen Gesteine, die durch Sediment- gleitung (“slumping and sliding”) gebildet wurden, autochthone Kalk-Ton-Wechsel- lagerung z.B. der pelagischen Schwellenfazies und Kalksande des Flachwassers.

Allodapische Kalke sind wertvolle Hilfsmittel fur palaogeographische Rekonstruk- tionen und die Analyse fossiler Sedimentations-Becken. Sie werden aber bisher meist ubersehen oder falsch gedeutet.

Beispiele fur allodapische Kalke werden beschrieben aus Devon und Karbon der rheinischen Geosynkline, dem Malm der Schwabischen Alb und dem westhellenischen Flyschtrog Griechenlands. Einige Beispiele aus der Literatur werden angefuhrt.

EINLEITUNG

Die folgende Arbeit behandelt Sedimente, die in mehreren Formationen, raumlich weit voneinander getrennt und unter verschiedenen geologischen Verhaltnissen vorkommen. Ein Teil dieser Gesteine ist Iangst bekannt. Sie werden aber hier von einem Standpunkt her betrachtet, von dem aus sie als einheitlicher Typus mit charakteristischen Merkmalen erscheinen. Dieser Standpunkt ist der sedimentologische, wobei unter Sedimentologie mit BROUWER (1 962) nicht eine spezielle Arbeits-Richtung ver- standen wird, sondern eine Wissenschaft, die sich bemuht, alle - organische und anor- ganische - Aspekte der Sedimentation in angemessener Weise zu berucksichtigen.

Es sol1 hier ausdrucklich betont werden, dass die sedimentologische Deutung der allodapischen Kalke ohne die vorbildliche Arbeit, die zuvor an Flysch-Gesteinen geleistet worden ist, sicher nicht maglich gewesen ware. Die Beschreibung der allodapischen Kalke ist daher auch weniger ein Beitrag zur Sedimentologie der Kalke als eine Fortsetzung der Turbidit-Sedimentologie in anderem Milieu.

Die Beobachtung allodapischer Kalke ist nicht neu. KUENEN und TEN HAAF (1956) haben gradierte Kalke mit Stromungsmarken aus den Abruzzen und dem Apennin beschrieben. Sie fuhren mehrere Autoren an, die jlhnliches beobachtet haben, darunter CAROZZI (1952), der‘sich auch um die fazielle Analyse solcher Sedimente im Malm der Nappe de Morcles der Westalpen bemuht hat (CAROZZI, 1955).

Die sedimentologischen Merkmale allodapischer Kalke sind aber noch wenig bekannt, fazielle und palaogeographische Aspekte kaum untersucht. Die folgenden Beschreibungen, die angesichts der Fulle des Materials und der auftauchenden Fragen nur den Charakter einer ersten Obersicht haben ki)nnen, sollen zu einer besseren Beachtung solcher Gesteine und zu weiteren Beobachtungen anregen.

I Umfangreiche Schriften-Verzeinchisse findet man bei BOUMA (1962), KUENEN und HUMBERT (1964), und PLBSMANN (1961).

Den Herren Prof. H. Schmidt, Prof. Seilacher und Dr. Plessmann (Gbttingen) danke ich fur Rat und Hilfe.


DIE SEDIMENTOLOGISCHEN MERKMALE ALLODAPISCHER KALKE

Gesteins- Verband

Profile in allodapischen Kalken haben ein sehr charakteristisches Aussehen. Es sind immer Wechsel-Lagerungen harter, detritischer Kalkbanke mit tonigen und merge- ligen Zwischenmitteln oder pelitischen Kalken. Dieser Wechsel vollzieht sich haufig - hundert- und tausendfach -, er ist schroff und oft auffallig regelmassig. Die Machtig- keiten und Strukturen der mitunter weithin verfolgbaren Einzel-Banke sind sehr konstant. Innerhalb eines begrenzten Profils uberschreiten die Kalkbanke selten einen Grenzwert der Machtigkeit. Dichte, Korngrosse und Struktur der Kalkbanke, Mach- tigkeit der Zwischenmittel, das Mengen-Verhaltnis von Kalk zu Ton kiinnen von Profil zu Profil stark schwanken. Dennoch ist der Habitus einer allodapischen Kalk- Serie so typisch, dass man sie im allgemeinen auf den ersten Blick ansprechen kann. Die Ahnlichkeit mit einigen Grauwacken-Serien und bestimmten Flysch-Sedimenten ist gross.

Innerhalb einer alters-gleichen Serie allodapischer Kalke nehmen die Gesamt-

1 1 PELITES containing necton and Dlancton

I

plant remains convolute bedding

diagenetic fault adjacent to hornstone lens

I current ripple lamination

lutite spots

hornstone lutite balls

silicified parts

im br icat ion

MAIN PHASE

4 PRE -PHASE

t PELITES containing necton _ - . - and plancton

Fig.]. Ideal-Bank mit allen in allodapischen Kalken vorkommenden Strukturen. Machtigkeit ca. 1 m.

Ideal bed with all structures occurring in allodapic limestones. Thickness of bed about 1 m.

160 K.-D. MEISCHNER

Machtigkeit der Kalke, ihre Korngrosse und die durchschnit tliche Bank-Machtig- keit, von einem Zentrum ausgehend, gleichsinnig ab.

Die einzelne Bank

Der Aufbau der Einzel-Bank ist statistisch abhangig von ihrer Machtigkeit. Die einzelnen Struktur-Zonen sind am vollstandigsten in dicken Banken vertreten, dunne Banke sind meist unvollstandig. Die beste Ausbildung zeigen etwa 1 m machtige Banke. Der Aufbau einer idealen allodapischen Kalkbank ist etwa folgender (vgl. Fig. 1).

Korngrossen und Schichtung Die Untergrenze ist fast immer messerscharf. Kalk-Detritus uberlagert ohne Uber-

gang feinkornige Ton-Gesteine.. (0)l Uber der scharfen Unterflache liegt Kalk-Detritus von einer Korngrosse, die

oft kleiner ist als das Maximum, das in der Bank erreicht wird. Einzelne grobere Gerolle, meist Eisenkarbonat-Scherben, konnen vorkommen.

(I) Daruber folgt mit mehr oder weniger scharfer, oft welliger Grenze grober Detritus, vermengt mit grossen Gerollen von Fremd-Gesteinen, meist feinkornigen Kalken oder Fossil-Schalen. Dieser Bank-Abschnitt ist nieist am machtigsten. Er ist gradiert. der Detritus wird nach oben immer feiner, die Ton-Beimengung wird starker.

Die grobsten Korngrossen liegen oft nicht an der Basis von 1, sondern in einer hoheren Schicht. Die Gerollfuhrung kann an einer oberen Grenze scharf absetzen. Plattige und stengelige Gerolle konnen dachziegelartig gegen die Stromung geneigt sein (“imbrication”).

Im oberen Teil von I stellen sich bei Erreichen einer bestimmten Korngrosse eigenartige Einschlusse ein. Es sind mehrere Millimeter grosse Tonpartikel, die, wenn sie einen hohen Kalkgehalt besitzen, kugelig sein konnen, meist aber sind es platte, runde Tonschmitzen. Im Querbruch erscheint das Gestein dann parallel zur Schichtung gestrichelt, die Schichtflachen sind gefleckt.

(2u) Uber dem kompakten gradierten Bankteil folgen ebene Schicht-Fugen, die nach oben immer dichter aufeinander folgen und in eine primar ebene Feinschkhtung (“lamination”) ubergehen. Die Schicht-Fugen sind in bituminbsen Kalken mit Ton- Hauten belegt, die vorwiegend aus organischem Material bestehen. Sie trennen Teil- Banke, die ihrerseits wieder gradiert sein konnen. Die allgemeine Korngrosse nimmt aber stetig ab.

(2b) Tm oberen Teil von 2 kann vereinzelt eine primare Winkelschichtung auftreten (“current ripple lamination”). Schliesslich erreichen Korngrosse und Menge des Kalk-Materials die Grossenordnung der pelitischen Beimengung. Die Fein- schichtung wird sehr engstandig. Dieses Sediment neigt zu convoluten Strukturen.

Die Ziffern beziehen sich auf Fig. 1.


(3) Die hangendsten Teile der Bank sind oft sehr feinschichtige Mergel, die durch

Die Bank geht so ganz allmahlich in das pelitische Zwischenmittel uber. Der Uber- diagenetische Entmischung flaserig und schuppig werden konnen.

gang kann rasch vorgehen, ist aber immer fliessend.

Sortierung und Zurundung Der Sortierungsgrad des Detritus-Materials ist mit der Korngrosse korreliert. In

den groben Bank-Teilen ist das Korngrossen-Spektrum sehr breit. Zwischen dicken Gerollen und feinkorniger Grundmasse sind alle Obergange vorhanden. Je mehr die maximale Korngrosse abnimmt, desto besser wird die Sortierung. Feinkornige Bank- Teile haben meist ein enges Kornspektrum. Grundmasse ist in der ganzen Bank in feiner Verteilung vorhanden, sie tritt aber in groberen Partien stark zuriick.

Die einzelnen Korner des Fossil-Detritus sind kaum gerundet. Selbst sehr empfind- liche Schalen von Foraminiferen, Brachiopoden sowie Schwamm-Nadeln, verzweigte Korallen- und Bryozoen-Skelette und zierliche Conodonten sind tadellos erhalten. Vieles ist zerbrochen, aber nur selten etwas korrodiert. Dagegen konnen grossere Gesteins-Gerolle, besonders in den Konglomeraten, stark zugerundet sein.

Stof Bestand Die Kalke bestehen ganz uberwiegend aus Calcitkornern, die als Bruchstucke der

kalkigen Hart-Teile von Fossilien zu erkennen sind. Stucke von Brachiopoden- und Mollusken-Schalen oder Korallen sind nur anzusprechen, wenn sie eine ausreichende Grosse besitzen. Dagegen verrat sich der Detritus von Echinodermen-Skeletten und Bryozoen-Stocken durch seinen regelmassigen Feinbau auch noch bei kleineren Korngrossen.

Foraminiferen sind in einigen Banken ausserordentlich haufig. Ostracoden und Klein-Fossilien konnen ebenfalls zum Aufbau der Banke beitragen.

Auch Fossil-Reste, die entweder aus einem lockeren Kalk-Gerust aufgebaut werden wie die Echinodermen-Skelette, oder aus hohlen Schalen bestehen, unterliegen der gleichen Korngrossen-Sortierung wie kompakte Korner. Nur sind sie im Durchschnitt grosser als die Korngrosse der umgebenden Bank, weil fur den Sortierungs-Mecha- nismus nur Dichte und Grosse des gesamten Kornes Bedeutung haben.

Haufig fuhren allodapische Kalke Ooide. Sie sind aber nur untergeordnet neben Detritus vorhanden und werden nicht gesteinsbildend.

Neben dem Kalk-Detritus kommen in einigen Kalk-Serien Quarz-Korner, Feldspate und Gesteins-Bruchstiicke vor. Besonders Quarz ist fast immer vorhanden und kann einen betrachtlichen Prozentsatz der Bank-Masse stellen.

Diagenetische Veranderungen Verqiretschung von Gerollen. Einige der Gerolle aus pelitischem Kalk haben sehr

unregelmassige Umrisse. Benachbarte Korner haben sich oft tief eingedriickt. Mitunter fullen sie auch nur als einheitlich feinkornige Grundmasse die Liicken zwischen groben Gerollen. Es handelt sich hier eindeutig um Gerolle, die zur Zeit

162 K.-D. MElSCHNER

ihrer Einbettung noch weich gewesen sind und dann bei der Setzung des Sediments zerquetscht wurden. Besitzen solche Gerolle ein internes Gefiige, so ist es mit deformiert.

Convolution. Die feinkornigen, feinschichtigen Bank-Teile neigen bei einer bestimmten Korngrosse dazu, sich zu Wulst-Strukturen, im Querschnitt girlandenformigen Bogen und schliesslich liegenden Falten-Strukturen zu deformieren. Das sind die gleichen Strukturen, die in sandigen Sedimenten “convolute lamination” genannt werden. Sie entstehen durch diagenetische Verformung des noch weichen Sediments, vielleicht verbunden mit einem thixotropie-artigen Zusammenbruch des Gefiiges.

Convolution, Winkelschichtung und Setzungs-Figuren um Hornstein-Linsen konnen leicht miteinander venvechselt werden. Es ist also immer eine genaue Analyse notig.

Verkieselungen. Fast alle allodapischen Kalke sind etwas verkieselt. Im allgemeinen sind einzelne Kbrner oder Teile der Grundmasse durch Quarz oder Chalcedon crsetzt. Aus vielen Banken konnen daher Mikro-Fossilien durch k z e n mit Sauren gewonnen werden.

Regelrechte Hornsteine sind in Form flacher Linsen oder Bander an bestimmte Korngrossen gebunden. Sie liegen parallel zur Schichtung in den Bank-Teilen, welche die beste Sortierung aufweisen. In dicken, grobkornigen Banken ist das im oberen Teil der Fall, in diinneren feineren kann es nahe oder ganz an der Basis sein. Solche Hornstein-Linsen fehlen in keinem Profil.

Die Verkieselungen sind friihdiagenetisch, denn sie haben die Setzung des Sediments nicht mehr mitgemacht. Die dadurch bedingten Machtigkeits-Schwankungen auf engem Raum fuhren oft zur Deformation der Feinschichtung. Neben flachen Horn- stein-Linsen treten in den schichtungslos gradierten Bank-Teilen (Zone Zb) annahernd kugelformige Zonen starkerer Einkieselung auf. Sie sind aber vie1 seltener.

Sekundares Korn- Wachstum, Neubildungen. Nach der Ablagerung der Banke traten noch umfangreiche Stoff-Verlagerungen ein. So sind Quarzkorner oft calcitisiert worden, Calcit wurde verkieselt. Aber Calcit- und Quarzkorner sind auch weiterge- wachsen. Die Calcite durchdringen dann einander und bilden luckenlos verzahnte

Fig.2.A. Profil durch die Ideal-Bank in Stromungsrichtung. Die maximale Machtigkeit der verschiedenen Korngrossen-Klassen verschiebt sich mit abnehmender mittlerer Korngrosse beckenwarts (oblique Gradation). Gesamtechtigkeit der Bank ca. 1 m, L h g e 15-20 km.

B. Profile in allodapischen Kalken, nach ihren sedimentologischen Merkmalen in das Schiittungs- Schema (Fig.2A) eingeordnet. Masstab 1 : 100.

C. Beispiele fiir allodapische Kalke. Die Profile sind nach dem Schema (Fig.2A) geordnet. Die schraffierten Bereiche sind nicht bekannt. Nicht eingeklammerte Ortsnamen bezeichnen die Profile, die in Fig.2B dargestellt sind, die eingeklammerten sind nur im Text erwahnt.

A. Section through an ideal bed in current direction. Note downstream sequence of maximum thicknesses for different fractions. Whole thickness reaches more than 1 m, length up to 15-20 km.

B. Comparison of the general character of beds in actual profiles with the model bed (Fig.2A). C. Examples of allodapic limestone sequences in relation to the ideal profile. Hatched parts not

known. Those not in parentheses are represented among the profiles of Fig.ZB, others in text only.

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164 K.-D. MEISCHNER

Strukturen. Weitergewachsene Quarze werden oft idiomorph. Sie konnen zonar ver- unreinigt sein oder einen kataklastischen Kern haben. In einigen Kalken sind auch Neubildungen von Pyrit in Form hochidiomorpher Wurfel und Pentagondodekaeder und von idiomorphem Baryt haufig.

Rekonstruktion des Schuttungs-Korpers

Abweichungen von dem Ideal-Bild einer allodapischen Kalkbank sind haufig. So kann die Gradierung sich wiederholen, die maximale Korngrosse kann erst weit oben in der Bank oder auch schon unmittelbar an der Basis erreicht werden. Am haufigsten ist aber sozusagen die Bank von unten her gekappt. Je dunner die Bank, desto mehr Struktur-Zonen fallen von unten her aus. Kalk-Serien, die keine grosseren Bank- Machtigkeiten erreichen, zeigen uberhaupt nur Strukturen, die den oberen Teilen der idealen Bank entsprechen.

Mitunter kann man eine einzelne Bank in der Schuttungs-Richtung uber einen Auf- schluss hinaus verfolgen. Man ist aber weitgehend auf statistische Auswertung der Beobachtungen angewiesen, wenn man die Veranderung der Ideal-Bank im Raum feststellen will. Man kommt zu etwa folgendem Bild (Fig.2).

Sowohl in Schuttungs-Richtung stromabwarts wie stromauf nimmt die Machtigkeit der Bank gleichzeitig mit der Korngrosse ab (“horizontal grading”). Diese Abnahme geht vorwiegend zu Lasten der unteren Bank-Teile, die von unten her abgebaut werden. Die Bank wird stromaufwarts rascher reduziert als abwarts. Der stromauf gelegene Abschnitt fuhrt aber besonders haufig grobe Korner, die weit uber der allgemeinen Korngrosse liegen, haufig auch grosse Fossil-Schalen. In stromab von der Ideal-Bank gelegenen Teilen sind solche Gerolle selten, die Sortierung ist einheitlicher.

Die Machtigkeits-Maxima der einzelnen Bank-Zonen liegen nicht an einem Ort iibereinander. Das Maximum der nachst hangenden, feineren Zone ist gegenuber der liegenden, groberen jeweils beckenwarts verschoben.

Profile, die in der Nahe der maximalen Bank-Machtigkeiten liegen, enthalten haufig Banke mit kompletten Zonen-Folgen.

Weiter stromauf gelegene Profile sind unregelmassiger. Schon in einem begrenzten Abschnitt kommen alle Zonen der Ideal-Bank vor, aber meist in gering-machtigen Banken mit verstummelter Abfolge. Grosse Fossil-Schalen und Gerolle sind lagenweise haufig. Spuren starkerer Erosion sind festzustellen.

In stromab gelegenen Profilen nehmen die Kalkbanke eine regelmassige, der jewei- ligen Entfernung vom Zentrum entsprechende Struktur an. Ausnahmen sind selten, grossere Gerolle kommen kaum noch vor.

Stromungs- Marken

KUENEN und TEN HAAF (1956) beschreiben Kalke mit deutlichen Stromungs-Wulsten (“flute casts”), GWINNER (1961) bildet “groove casts” aus dem Malm von Zainin- gen ab. In den mir bekannten Vorkommen sind solche Wulste selten. Einige Banke im


Rhenaer Kalk zeigen deutliche “flute casts”. Etwas haufiger sind Schleifmarken (“drag marks”) und Stossmarken (“impact casts”).

Stromungs-Marken sind in allodapischen Kalken sehr vie1 seltener als in Flysch- Sedimenten gleicher Struktur. Sie kommen iiberhaupt nur unter Banken nicht zu f’einer Korngrosse vor. Fur eine Rekonstruktion der allgemeinen Schiittungsrichtung reichen sie nicht aus.

ZUR ENTSTEHUNG DER ALLODAPISCHEN KALKE

Allodapische Kalke werden als Sedimente von Suspensionsstromen gedeutet. Diese Deutung ist nach unserer heutigen Kenntnis zwingend und widerspruchlos. Sie beruht nicht nur auf oberflachlichen Analogien oder einer Zeitmode. Auch ohne Kenntnis rezenter “turbidity currents” oder der Experimente Kuenen’s fuhrt die Analyse der sedimentaren Strukturen und der faziellen Merkmale zu solchen Anforderungen an das gesuchte Schuttungs-Modell, dass man entweder auf einen Mechanismus in der Art der “turbidity currents” gefiihrt wird oder nicht zu einer widerspruchlosen Deutung kommt. Die Annahme, dass Suspensionsstrome den Kalk-Detritus in ein tiefes Stillwasser-Becken gebracht haben, erfullt die Forderung nach der einfachsten, d.h. die wenigsten Hilfs-Hypothesen oder anaktualistische Verhaltnisse vorausset- zende Deutung. Das sol1 im folgenden noch einmal kurz demonstriert werden.

Sedimentologische Kriterien

Der Schuttungs-Mechanismus allodapischer Kalke muss einige sedimentare Vorgange erklaren, deren Spuren im Sediment in den vorhergehenden Kapiteln beschrieben wurden.

(a) Die Schuttung setzt schlagartig in weiten Gebieten praktisch gleichzeitig ein. Das folgt aus der schroffen Uberlagerung feinstkorniger Pelite durch groben Detritus. Einzelne dieser Grenzflachen lassen sich teilweise sehr weit (17 km Luftlinie) verfolgen.

(6) Das Materal wird mit einer deutlichen tangentialen Komponente geschuttet. Gefolgert aus Kornregelung (“imbrication”) und dem Vorkommen von Stromungs- marken.

(c) Das Transport-Medium erodiert den Untergrund nur in ganz eigentiimlicher Weise. Es besitzt eine hohe Stromungs-Geschwindigkeit.

Mir ist kein Fall bekannt, in dem eine jiingere Bank durch altere hindurchgreift. Ebenso fehlen alle Priele, sedimentaren Diskordanzen und grossstilige Winkel- schichtung. Die Schichtung ist vollig konkordant.

Dagegen findet man unter einigen Banken Stromungsmarken, Zeugen fur Auskol- kungen und Abschleifungen, die aber unter derselben Bank eine bestimmte, im Ver- haltnis zur Bank-Machtigkeit geringe Erosionstiefe nicht iiberschreiten und weit verbreitet und statistisch verteilt sind. Das bedeutet eine ganz spezifische, flachenhafte

166 K.-D. MEISCHNER

Erosion. Trotz der geringen Erosionstiefe muss die Stromungs-Geschwindigkeit sehr hoch gewesen sein, weil feinkornige, fest gelagerte Pelite erodiert werden konnten (vgl. das Diagramm von HJULSTROM, 1934-1935, S.298; hier Fig.3). Die feste Lage- rung der Pelite geht wiederum daraus hervor, dass sie Stromungsmarken mit steilen, teilweise unterschnittenen Randern konservieren konnten.

Size of particles, mm

Fig.3. Beziehungen zwischen Stromungs-Geschwindigkeit, Transport und Ablagerung von Sedimen- ten einheitlicher Korngrosse in einem FIuss.

Diagram showing relationship between current velocity, erosion, transportation, and deposition of uniform sediments in a river (after Hjulstrom in KUENEN, 1950, p.259).

Alles deutet auf ein Medium mit starker, flachenhaft gleichartiger Stromung mit

(d) Die Sedimentation folgt in jedem Fall der Erosion unmittelbar nach. Die Erosionsformen sind stets an die Unterseiten detritischer Kalkbanke gebunden;

sie kommen nicht isoliert im Pelit vor (ungestorte Feinschichtung). Niemals schiebt sich zwischen die Phasen der Erosion und der Sedimentation ein anderes Ereignis ein. Es besteht eine (allerdings nur grobe) statistische Beziehung zwischen der Starke der Erosion und der Sedimentation. Stromungs-Wiilste konnen groberes Material als die Umgebung enthalten (vgl. hierzu PLESSMANN, 1961, S.523).

Das bedeutet aber einen plotzlichen Umschwung von flachenhafter Untersattigung des stromenden Mediums (Erosion) zu ebenso flachenhafter starker Obersattigung (Sedimentation).

(e) Das Transportmedium ist fur ein breites Kornspektrum gleichzeitig iibersattigt. Der Sortierungsgrad ist mit der Korngrosse korreliert.

eigenartigen, statistisch verteilten Inhomogenitaten (Wirbel).


Gradation (“graded bedding”) ist das auffalligste und haufigste Merkmal der Sedi- mente von Suspensionsstromen (“turbidity currents”). Das bedeutet jedoch nicht, dass Gradierung in jedem Fall auf Ablagerung aus Suspensionen schliessen lasst. Sie ist nur das Ergebnis stetig abwandelnder Sedimentations-Bedingungen und kann daher in Sedimenten verschiedenster Entstehung auftreten.

Charakteristisch ist dagegen die Verknupfung von Gradation und Sortierung. In Ablagerungen von Suspensions-Stromen finden wir in der Regel alle Korngrossen, also auch feine Grundmasse, in der gesamten Bank. Die maximale Korngrosse nimmt von unten nach oben ab. Der Sortierungsgrad nimmt dagegen deutlich zu.

Eigenartig is, dass Einschlusse von Ton-Gestein relativ grober Korngrosse sich noch einmal gehauft in feinkornigen Bank-Teilen finden (Zone Zc). Bei genauer Betrach- tung stellt sich heraus, dass es sich hier um dunne Haute von seifigem, feinkornigem Ton handelt, die vollig flach gepresst sind und das Chagrin der Detrituskbrner abfor- men. Die einfachste Deutung ist folgende.

In dem turbulent stromenden Transportmedium werden feine Tonflocken (vielleicht zusammen mit organischem Material) zu wasserreichen Kugein zusammengerollt. Ihre Sinkgeschwindigkeit entspricht derjenigen der sie umgebenden kompakten Korner. Eine Bestatigung scheinen die kugelformigen Einschliisse in bestimmten Flinzkalken zu bringen.

Pflanzenreste, die haufig bereits vor der Sedimentation in der Kalkbank mazeriert gewesen sein durften, haben - auch wenn sie mit Wasser gesattigt sind - nur eine Dichte, die nahe uber der des Wassers liegt. Sie werden nach oben aus der Suspension herausgedruckt und sinken nur sehr langsam wieder ab. Sie reichern sich daher in den Schluff-Korngrdssen an der Oberkante der Banke an. cf> Die Sedimentations-Bedingungen andern sich mit nachlassender Heftigkeit ganz

allmahlich wieder zu denen des pelagischen Stillwassers. Der Ubergang von der detritischen Bank in den Pelit nach oben ist meist vBllig fliessend. Feinkbrniges Material der Suspensions-Schiittung vermengt sich allmahlich mit den “normalen” Beckensedimenten. Die regelmassige, immer engstandiger werdende Feinschichtung deutet auf rhythmisches Auspendeln der Wasserunruhe. Rippel- Schichtung in diesem Stadium bezeugt eine tangentiale Komponente und bodennahen rollenden Transport.

(9) Die Korner sind ungewohnlich wenig abgerollt. Die tadellose Erhaltung zerbrechlichster Fossil-Reste konnte auf einen nur kurzen

Transport deuten. Da aber ein weiter Transportweg aus faziellen Grunden bewiesen ist, muss der Schluss anders lauten: Die Korner sind auf sehr schonende Weise transportiert worden. Rollender oder schleifender Transport scheiden daher aus. Der Erhaltungs-Zustand der Detrituskorner deutet auf ganz iiberwiegend schwebenden Transport, wie er fur Suspensionen charakteristisch ist.

Die gut gerundeten Gerolle der Konglomerate scheinen dagegen zu sprechen. Doch ist zu berucksichtigen, dass es sich um Gesteine handeln kann, die im Brandungs- bereich zugerundet wurden, bevor sie in die Suspension gerieten. Ferner sind die Gesteine zum Teil noch wenig verfestigt gewesen und konnten auch bei schonendstem

168 K.-D. MEISCHNER

Transport obefiachlich abgewaschen werden. Gerade das Vorkommen grosser, bei der Sedimentation noch weicher Gesteinsstucke spricht gegen einen Transport durch Bodendrift.

(h) Das transportierende Medium besitzt eine extrem hohe Transportkraft, die unter den gegebenen geologischen Bedingungen nicht von reinem Wasser erreicht werden kann. Die Schuttungen treten episodisch, aber iiber lange Zeit gleichsinnig auf.

Nach der Kurve von Hjulstrom (Fig.3) miisste das Material der grobkornigen Banke allodapischer Kalke von Stromungen mit Geschwindigkeiten von mindestens 2 mlsec transportiert worden sein. Zwar werden so hohe Geschwindigkeiten von Meeres-Stromungen erreicht, doch nur in grossen, stetig fliessenden Konvektions- stromen oder durch Drangung von Gezeitenstromung in Engstellen. Beides kommt fur allodapische Kalke nicht in Frage. Wir finden keine Anzeichen stetiger oder wenigstens langere Zeit andauernder starker Stromungen. Im Gegenteil deuten die tonigen Zwischenmittel auf stromungsarmes oder -freies Stillwasser. Fur periodische Schuttungen findet sich ebenfalls kein Anhaltspunkt. Es fehlt jeder Hinweis auf Wel- lenbewegung, die an sich zur Verlagerung von Kornern dieser Grosse imstande ist (Strandkonglomerate). Das Transportmedium kann daher nicht eine normale Kon- vektions- oder Gezeitenstromung oder Brandung sein.

Allodapische Kalke treten im Profil episodisch auf, wenn auch oft mit einer gewissen Regelmassigkeit, sie sind in verschiedensten Formationen in Becken unterschiedlicher geologischer Lage verbreitet. Innerhalb einer Kalk-Serie, die mehrere biostratigraphi- sche Zonen umfassen kann, folgen die Banke einer polaren linearen Anordnung, d.h. sie sind iiber lange Zeit von einer Seite her episodisch eingeschiittet worden. Kata- strophale Ereignisse und abnorme Bedingungen konnen wir daher ebenfalls aus- schliessen. Der Schiittungs-Mechanismus besitzt Regelmassigkeit und Stabilitat.

Fassen wir diese sedimentaren Erscheinungen zusammen, denen das Schuttungs- Modell geniigen muss!

In einem ruhigen Becken wird das bodennahe Wasser innerhalb kurzer Zeit iiber grosse Entfernungen stark beschleunigt, das Transportmedium ist untersattigt und erodiert flachenhaft. Unmittelbar anschliessend ist es stark iibersattigt. Sediment aller Korngrossen fallt aus und fullt die gerade geschaffenen Erosionsformen uber weite Gebiete fast gleichzeitig mit starker tangentialer Komponente und einem sehr regelmassigen Sedimentations-Verlauf.

Das Sediment-Material stammt aus Gebieten, die ausserhalb der naheren Umge- bung liegen. Es muss folglich im Zusammenhang mit den Stromungs-Vorgangen in kurzer Zeit weither transportiert sein. Dabei miissen hohe Geschwindigkeiten ge- herrscht haben, die sonst in dem Sedimentations-Becken nicht auftreten. Solche Schiittungen ereignen sich iiber lange Zeit mit einer gewissen Regelmassigkeit in Starke und Richtung.

Bereits diese aus den sedimentaren Strukturen abgeleiteten Bedingungen engen den Kreis der in Frage kommenden Mechanismen so weit ein, dass nur der Schluss auf Suspensionsstrome ubrig bleibt. Die fazielle Analyse der Sedimente liefert weitere Argumente.

ALWDAPISCHE KALKE 169

Biofazielle Kriteried

Allodapische Kalke zeigen Fazies-Merkmale, die von denen der zwischengeschalteten Pelite abweichen, oft sogar ganz gegensatzlich sind. Der “Fazies-Wechsel” vollzieht sich mit Beginn jeder Kalkbank von neuem plotzlich und pendelt an ihrer Oberkante langsam zuruck. Mit dem schroffen Wechsel der Korngrossen und sedimentaren Strukturen, aus dem wir einen krassen Wechsel der stromungs-dynamischen Verhalt- nisse ableiten, vollzieht sich auch scheinbar ein biologischer Wechsel. 6kologisch stark gegensatzliche Faunen losen einander ab.

Die Existenz-Moglichkeit mariner Tiere wird entscheidend bestimmt durch die Sauerstoff-Versorgung, die eine Funktion der Wasserbewegung ist, das Nahrungs- angebot, den Salzgehalt des Wassers, die Temperatur, die Lichteinstrahlung und (in nur abhangiger Beziehung) die Tiefe (vgl. SCHMIDT, 1935). Autochthone pflanzliche Fossilien diirfen wir uberhaupt nur in durchlichteten Tiefen erwarten. Das gilt auch fur die Kalkalgen, die einen wesentlichen Anteil am Aufbau von Riffen haben.

Die Zwischenmittel sind oft ausserst feinkornige, sehr fein geschichtete Pelite, namlich Tonschiefer, Alaunschiefer oder pelitische Kalke, die keinerlei Anzeichen von Wasserbewegung aufweisen. Die innerhalb bekannter biostratigraphischer Einheiten sedimentierten Machtigkeiten sind auffallig gering. Die Gesteine enthalten lagenweise haufig Fossilien aller Grossen, die auf den Schichtflachen in regelloser Streuung ohne jede Sortierung liegen. Es sind fast ausnahmslos Vertreter des Nekton, Plankton und Pseudoplankton. Es fehlen alle fur Flachwassersedimente typischen Erscheinungen sowie Anzeichen reichen Bodenlebens.

Die hin und wieder vorkommenden Lebensspuren zeigen nur, dass O2 zu bestimmten Zeiten nicht ganz fehlte. Ihre Erzeuger stellen ausserst bescheidene Anspruche an den Beluftungszustand des Bodenwassers. Die vereinzelten Brachiopoden und Lamel- libranchiaten sind ausschliesslich solche, die SCHMIDT (1935) als “Pseudo-Benthos” bezeichnet. Sie werden als Epizoen des Plankton gedeutet.

Die Fauna der Zwischenmittel ist eindeutig die des pelagischen Stillwassers. Fehlen von Benthos, ungestorte, sehr feine Schichtung und haufig dunkle Farbung (durch Pyrit und Bitumen), deuten auf lebensfeindliche, sauerstoffarme, lichtlose Tiefen mit mehr oder weniger unbewohnbaren Boden. Organische Substanz wird nur unvollstandig abgebaut. Der resultierende CO,-uberschuss fuhrt haufig zur Auflosung der Fossil-Schalen, es entstehen dunkle, pyritreiche oder bituminose Sedimente mit meist ungestorter Feinschichtung. Es sind die Bodentypen 4-6 der Einteilung von SCHMIDT (1935, S.21).

Die Kalkbanke dagegen werden von Fossil-Detritus aufgebaut, der uberwiegend von benthonischen Organismen des flachen Bewegt-Wassers stammt. Reste von Brachio- poden, grossen Muscheln, Schnecken, Korallen, Bryozoen und Crinoiden sind so

Die folgende Fkweisfiihrung kann nicht als vollsthdige Fazies-Analyse gelten. Es sei fur die pelitische Komponente auf die ausgezeichnete Darstellung von RABIEN (1956), fiir die Kalke auf J u x (1960) verwiesen.

170 K.-D. MEISCHNER

haufig, dass sie oft das Bild der Banke ganz bestimmen und mehrere Autoren veran- lassten, die Kalke als “Riffschutt” anzusehen.’

Fur die Kalke hatten wir ein Meer anzunehmen, in dem Kalk produzierende Orga- nismen gunstige Lebensbedingungen fanden. Das bedeutet: Oberangebot an Sauer- stoff infolge starker Wasser-Bewegung, warmes Wasser (Sattigung mit CaCO, gunstig fur Produktion und besonders Erhaltung von Kalkschalen); das heisst aber auch flaches Wasser.

Der beobachtete Wechsel in der Fossilfuhrung von detritischen Kalken und Peliten ware also nicht nur ein Wechsel der artlichen Zusammensetzung der Fauna, sondern ebenso eine standig wiederholte Anderung der erwahnten chemischen und physikali- schen Daten.

Dieser krasse Fazies-Gegensatz lasst sich rein schematisch verschieden deuten. Man konnte an Schwankungen des Meeres-Spiegels denken, indem der Beckenboden episodisch immer wieder in den Bereich bewegten, durchlufteten Wassers gehoben bzw. hin und wieder in lebensfeindliche Tiefen versenkt wird. Der Wechsel hiitte dann tektonische Ursachen.

Andererseits ware eine Art “Klima-Wechsel” denkbar, dergestalt dass entweder tatsachlich das Klima ganzer Erdzonen schwankt oder aber ein abgeteiltes Meeres- becken episodisch mit wannem Wasser gespeist wird, wobei die Wasserbewegung zunimmt bzw. ein warmes Meeresbecken zeitweilig vom Frischwasser abgeschnurt wird und biologisch verodet.

Tatsachlich sind solche Deutungen fur allodapische Kalke wiederholt bis in neueste Zeit gegeben worden. Es besteht hier eine auffallige Parallele zur Deutung von Flysch- Gesteinen, deren Rhythmik von einigen Autoren zum Teil auch heute noch auf tektonische oder klimatische Schwankungen zuruckgefuhrt wird, obwohl das I)ber- gewicht der sedimentologischen und palaontologischen Argumente fur die Theorie der “turbidity currents” inzwischen geradezu erdriickend geworden ist.

Auch im Falle der allodapischen Kalke fuhrt ein einfacherer Weg zum Ziel. Wir konnen mit guten Grunden annehmen, dass die feinkornigen, langsam sedimentierten Gesteine, die nektonische und planktonische Fossilien einschliessen, die normalen bionomischen Bedingungen am Meeresboden wiederspiegeln. Die Substanz der detritischen Kalkbanke ist dagegen episodisch aus Bereichen anderer Fazies herantransportiert und im Stillwasserbecken sedimentiert worden. Mit anderen Worten: Die Tiere, deren Detritus wir in den Kalkbanken finden, waren am 01% ihrer Ein- bettung nicht lebensfahig, das Material der Kalkbanke liegt ortsfremd im Bereich anderer Fazies. Dieser Schluss ist deshalb berechtigt, weil die Fossilien der Kalkbanke keinen normalen biologischen Verband bilden.

Benthonische Flachwasser-Organismen, deren Reste wir in den Kalkbanken vor

In einemeigenartigen Gegensatz hierzu steht die Tatsache, dass Serien allodapischer Kalke wiederholt als “fossilleer” bezeichnet wurden. Der Widerspruch erklart sich leicht. Alle Fossil-Reste sind in der beschriebenen Weise sortiert. Grosse Fossilien sind also nur in grobkornigen W e n zu erwarten, die aber meist selten sind. Der feine Detritus ist im frischen Gestein nicht erkennbar und nur auf angewitterten Flachen verkieselter Banke mit einiger Aufmerksamkeit zu entdecken.


uns haben, bilden im Leben bestimmte Siedlungsformen aus. Viele von ihnen leben angeheftet oder in bestimmter Orientierung flach dem Boden aufliegend, sie umkrusten einander, wachsen aufeinander auf und bilden feste Kolonien und Stocke mit gemein- schaftlichem Skelett oder dichte Rasen. Die Ausbildung dieser Organisationsformen richtet sich hauptsachlich nach der Wasserbewegung. Von der Brandungszone abwarts lasst sich eine zonare Anordnung der Wuchsformen und Vergesellschaftungen erkennen, die mit Ausdriicken wie Bank-, Block-, Knollen-, Rasen-Riff bezeichnet werden (WEDEKIND, 1924; BIRENHEIDE, 1962; STRUVE, 1963).

Solche Strukturen sind im fossilen Sediment erkennbar, sofern sie an Ort und Stelle uberdeckt werden, auch wenn Vorgange der Auflosung oder Abschwemmung eine gewisse Auslese treffen. Ein grosser Teil der Schalen kann zerstort und als Detritus verfrachtet werden. Er wechsellagert dann mit Riff-Rasen oder -Stotzen.

In allen allodapischen Kalken lasst sich aber keinerlei Anzeichen einer solchen Besiedlung an Ort und Stelle finden. Wir haben es stets mit vollig isoliertem Detritus zu tun, dessen einziges Ordnungs-Prinzip sedimentologische Merkmale sind. Dariiber hinaus lasst sich zeigen, dass Organismen, die im Siedlungsbereich des Flachwasser- Benthos nicht oder nur sparlich vorkommen, in allodapischen Kalken regelmassig vertreten sind. Das sind, z.B., im Devon und Karbon Goniatiten und Conodonten, im Malm Belemniten und planktonische Foraminiferen. Es ist anzunehmen, dass solche Reste beim Uberrollen des Becken-Bodens von der Suspension aufgenommen wurden. Ihre zahlenmassige Verteilung und Auslese gibt Hinweise darauf (MEISCHNER, 1962, S.40). D.h. die allodapischen Kalke enthalten eine Taphocoenose mit Bestandteilen benthonischer und nektonischer Organismen verschiedener Lebens- bereiche. Die Reste benthonischer Flachwasserbewohner uberwiegen bei weitem. Die fazielle Analyse fiihrt damit ebenfalls zu der Vorstellung, dass das Material der detritischen Kalkbanke aus entfernten Gebieten anderer Fazies herantransportiert worden ist.l

Der Schiittungs-Mechanismus

Der Schuttungs-Vorgang ist etwa folgender: Der Schutt grosserer Riff-Korper2 hauft sich am Rande von Stillwasserbecken unterhalb der Reichweite normaler Brandungs- Turbulenz an. Entweder bei Uberschreitung der Stabilitats-Grenze durch Anlagerung oder Relief-Ubersteilung oder bei aussergewohnlichen Beanspruchungen wie Erdbe- ben, Stiirmen, Verlagerung von Stromungen, extremen Gezeiten, gerat eine grossere Sedimentmasse unter dem Einfluss der Schwerkraft in Bewegung. Sie gleitet mit zunehmender Geschwindigkeit hangab und lost sich dabei vollig in eine hochturbu-

Dieser Schluss wurde fur den Rhenaer Kak schon von SCHMIDT (1942) gezogen. Schmidt sprach von “Driftkalken”, die durch “Bodendrift” in Stillwasserbecken gekommen sein sollten. a Der Begriff “Riff” wird hier im weitesten Sinne gebraucht fiir ein Gebiet, in dem eine Lebens- gemeinschaft skelett-bauender Tiere schneller aufwachst als das umgebende Sediment und dadurch eine Erhebung formt, auf der auch die okologischen Bedingungen sich von denen der Umgebung unterscheiden.

172 K.-D. MEISCHNER

lente Suspension hoher Dichte auf, die mit grosser Geschwindigkeit iiber den Becken- boden schiesst und dabei etwas Sediment von der Oberflache aufnimmt. Die Erosion geschieht einmal durch die vor der Front liegenden Wasser-Massen, die schon vor Ankunft der Trubungswalze selbst stark beschleunigt werden und stark untersattigte, gleichformige Stromungen hoher Geschwindigkeit bilden. Sie heben flachenhaft die unverfestigten Beckentone ab und bringen sie in Schwebe. Da jedes grobere Material fehlt, ist dieser Vorgang sehr schonend (“erosion of an unusual type” SEILACHER’S, 1962). Zum anderen durfte die Suspension selbst noch die Beckensedimente kurz- fristig erodieren und unter Beteiligung groben Materials Stromungsmarken (“flute casts” und “groove casts”) schaffen.

Schliesslich wird der Strom durch Nachlassen der Hang-Neigung langsam gebremst, er kann stark iibersattigt werden, die Sedimente fallen rasch und grob nach der Sink- geschwindigkeit geordnet aus (“graded bedding”).

Die feinen Partikel sinken vie1 langsamer ab. Sie werden daher von schwankenden Boden-Stromungen erfasst, die entweder “Nachwehen” des “turbidity current” selbst sind oder 2.B. Gezeitenstrome. Die Sedimentation des feinen Materials wird dadurch rhythmisch oder periodisch gestort (Feinschichtung, Lamination).l Bei starkem Ober- wiegen der tangentialen Komponente konnen Stromungs-Rippel-Strukturen auftreten (“current ripple lamination”).

Die feinste Trube des Suspensionsstromes vermischt sich mit der autochthonen pelitischen Sedimentation. 1st diese silikatisch, so entstehen Merge1 als Oberkante der Banke.

Nach Ablagerung der Banke konnen sich die feinkornigen, feinschichtigen oberen Partien, die moglicherweise wegen ihres hohen Gehaltes an Ton und organischem Material einen unverfestigten Sedimentbrei bilden, zu faltenartigen Strukturen ver- biegen (“convolute lamination”).

Das Sediment enthalt Bestandteile, die leicht mobilisierbar sind und wahrend der Diagenese wandern.

(I) Amorphe Kieselsaure der Skelette mit eingeschlossenen Organismen ist leicht loslich. Sie wandert offenbar nach dem Prinzip der besten Wegbarkeit und scheidet sich daher in den gut sortierten, ziemlich feinkornigen, aber noch tonarmen Niveaus der Kalkbanke in Form von Hornstein-Lagen und flachen Knollen wieder aus.

Ausserdem kommt es zu mannigfaltigen Wechsel-Wirkungen zwischen karbonati- schen Losungen und Si02, die sich in mehreren Generationen von Verkieselungen und Calcitisierungen aussern.

(2) Die organische Substanz lebend oder vor Abschluss der Verwesung eingebet- teter Fossilien kann unter den herrschenden Stillwasser-Bedingungen nicht vollstandig abgebaut werden. Das verbleibende Bitumen impragniert Fossil-Schalen und Hohl-

Es ist nicht einzusehen, wieso diese laminierten Bank-Teile aus einem laminar stromenden Medium sedimentiert sein sollen. Eine laminare Stromung bedeutet fur den Sedimentations-Vorgang nur eine inhomogene Translation parallel zur Sedimentobefiache. Eine Feinschichtung ist so nicht zu erkliiren. Ein besonderer Name (“Laminite”, LOMBARD, 1963) ist meines Erachtens ubefiussig.


Raume (Stinkkalke). Anreicherungen von Schwer-Metallen konnten in einem Fall nachgewiesen werden (BOTTKE, 1962).

ZUR NOMENKLATUR, DEFINITION UND ABGRENZUNG ALLODAPISCHER KALKE

Allodapische Kalke konnen im einzelnen sehr verschieden aussehen. Das gemeinsame Merkmal aller Vorkommen ist aber, dass Material aus Gebieten flachen, bewegten Wassers den autochthonen Sedimenten pelagischer Stillwasser-Fazies unter ganz charakteristischen sedimentaren Erscheinungen eingeschichtet ist. Diese Art des Vor- kommens wird auf einen einheitlichen Schuttungs-Vorgang zuriickgefuhrt, der nach unserer heutigen Kenntnis nur der von “turbidity currents” sein kann. So betrachtet, sind allodapische Kalke “Turbidite”. Diese Bezeichnung ist aber nicht mehr als eine Kurz-Fassung der sedimentologischen Deutung (Turbidit = Ablagerung eines “turbidity current”). Sie stellt unsere Kalke in eine Reihe mit Gesteinen, fiir die wir einen gleichen Sedimentations-Mechanismus annehmen.l Mit der Gultigkeit dieser Theorie fallt auch der Begriff. Fur jemanden, der diese Deutung nicht akzeptiert, gibt es auch keine “Turbidite”.

Es ist daher ein Name vorzuziehen, der die Kalke unabhangig von ihrer sedimentologischen Deutung kennzeichnet : Allodupischer Kulk2 (MEISCHNER, 1962). Der Begriff “Turbidit” wird dadurch nicht beriihrt und kann als Ober-Begriff gelten, solange wir keinen Grund haben zu bezweifeln, dass allodapische Kalke durch “turbidity currents” sedimentiert worden sind.

Die Definition allodapischer Kalke wurde also lauten: Allodapische Kalke sind Einschaltungen detritischer Kalke in Ton-Gesteine. Sie sind Sedimente der pelagischen Stillwasser-Fazies und bestehen aus Material, das iiberwiegend aus entfernten Gebieten anderer Fazies herantransportiert wurde.

Gedeutet werden allodapische Kalke als Ablagerungen von “turbidity currents”. Selbstverstandlich konnen sich in der Praxis Schwierigkeiten mit der Abgrenzung

dieses Begriffs ergeben. Das liegt in der Natur eines Begriffes, der ja eine subjektive Abstraktion aus dem Natur-Zusammenhang ist. Von personlichen Missverstandnissen abgesehen, ware es 2.B. moglich, dass sich definitions-gerechte allodapische Kalke in Richtung auf das Liefergebiet mit mehr oder weniger autochthonen detritischen Kalken, Riffschutt u.a. verzahnen, dass die sedimentologischen und faziellen Beson- derheiten an Pragnanz verlieren usw. Indessen kann es nicht Aufgabe des definieren- den Autors sein, die Entwicklung eines Wissens-Gebietes in allen Einzelheiten vorher- zusehen. In diesem Falle sind, dem Wissens-Stande folgend, vorhandene Begriffe neu zu definieren oder neue zu bilden.

Nach drei Seiten kann der Begriff allodapische Kalke aber schon jetzt abgegrenzt werden.

( I ) In der Umgebung von Tiefschwellen (vgl. RAESIEN, 1956, S.67) finden sich oft

Diese Amahme trifft sicher fur einen Teil der in der Literatur beschriebenen “Turbidite” nicht zu. Von griechisch: drhho6anoc = anderswoher stammend, fremd.

174 K.-D. MEISCHNER

Wechsel-Lagerungen dichter Kalkbanke mit pelagischen Tonschiefern, die eine gewisse Regelmassigkeit erreichen konnen. Solche Kalke haben aber nicht die sedimentologischen und faziellen Merkmale allodapischer Kalke. Haufig stehen sie im Verband mit Kalkknollen, Flaserkalken oder Kramenzelkalken. Es sind Obergange von der Fazies der Cephalopodenkalke in die reinen Tonschiefer der Becken. Ver- breitet sind solche Gesteine z.B. im Oberdevon des Rheinischen Schiefergebirges.

(2) Aus einigen Gebieten sind “endostratische oder intraformationelle Breccien, diastratische Rutschungen” bekannt geworden, Erscheinungen, die auf Vorgange zuriickgefuhrt werden, die bei KUENEN (1950, S.240 ff.) unter dem Sammelbegriff “slumping” (etwa: Sedimentgleitung) zusammengefasst sind. Die Strukturen solcher Gleitmassen weichen von denen der allodapischen Kalke erheblich ab. Charakteris- tisch sind z.B. weitgehende Entschichtung des Sediments, Bildung von Breccien, die teilweise Gesteine des unmittelbaren Untergrundes enthalten, starke Machtigkeits- Schwankungen, Gleitfalten bis Wickel-Strukturen oder wirre Verknauelung von Sedimentpaketen, gelegentlich auch gradierte Entmischung (vgl. hierzu REMANE, 1960; GWINNER, 1961). Zwar hatten sich solche Massen zu “turbidity currents” entwickeln konnen, doch handelt es sich hier zunachst um einen anderen Vorgang. Um ein Sediment “allodapischer Kalk” nennen zu konnen, muss es die Strukturen zeigen, aus denen wir schliessen, dass es nach vollstandiger Zerstorung der ursprunglichen Struktur und freiem Transport sedimentiert worden ist.

(3) Eine Abgrenzung der allodapischen Kalke ist ferner notig gegen die Kalksande des Flachwassers. Hauptsachlich handelt es sich hier urn den Riffschutt, der lebende Riffe stets begleitet und vor ihrer Front, im “back-reef” und zwischen den Teil-Kor- pern abgelagert wird. Weiter kommen Kalksande in flachen Meeresbuchten vor wie z.B. im Ost-Teil der nardlichen Adria, wo wegen des Mangels an anderen Einschut- tungen Organismen-Reste, die durch Tiere und Wellengang zerstort wurden, grossere Sedimentkorper aufbauen konnen. Im Grunde ist das aber die gleiche Unterscheidung, die wir zwischen den Sedimenten silikatischer “turbidity currents’’ und Flachwasser- sanden treffen. Kalk-Detritus unterliegt genau den gleichen mechanischen Vorgangen wie ein silikatischer Sand. Die Abgrenzung von Schuttungs-Typen ist im kalkigen Milieu sogar leichter, weil die Verknupfung mit autochthonen Siedlungsformen einen sicheren Schluss auf die Bildungs-Bedingungen erlaubt. Dass Riffschutt oder Flachsee- Kalksande mitunter allodapischen Kalken ahneln konnen, berechtigt also nicht allein schon zu Zweifeln an deren Existenz. Wie bei silikatischen Sanden auch, ist stets eine genaue lithologische und iikologische Analyse nbtig, urn zu einem sicheren Urteil zu kommen.

MwLICHKEITEN GEOLOGISCHER AUSWERTUNG

Aus der Deutung der allodapischen Kalke als Sediment von Suspensionsstromen ergeben sich einige wichtige geologische Folgerungen.

Massen-Verlagerungen durch Suspensionen geschehen unter Einfluss der Schwer-


kraft, d.h. sie setzen ein erhebliches Gefalle zwischen Liefergebiet und Sedimentations- Raum voraus. Die allodapischen Kalke sind Sedimente tieferer Becken und bestehen aus Material des Flach-Wassers.

Daher gibt uns das Vorkommen allodapischer Kalke einen Hinweis auf Gebiete altersgleicher, kalkreicher Flachwasser-Fazies in abschatzbarer N&e, auch wenn diese erodiert sind oder unter jungerer Bedeckung liegen.

Aus den Schuttungs-Merkmalen lasst sich die Schuttungs-Richtung und damit die Becken-Neigung und die Lage der Bewegtwasser-Gebiete ermitteln. Aus statistischen Beobachtungen uber den Bank-Aufbau kann man die palaogeographische Lage von Einzel-Profilen innerhalb einer Schuttungs-Serie schatzen und Angaben uber die ursprunglichen Dimensionen der Sedimentkorper erhalten (vgl. Fig.2).

Die Tatsache, dass wahrend langerer Zeit grossere Kalkmassen geliefert wurden, die aber nur einen Bruchteil des im zugehorigen Flachmeer vorhandenen Kalkes dar- stellen, lasst auf eine kontinuierliche Produktion grosser Kalkmengen schliessen, d.h. auf Riffe oder wenigstens riffahnliche Zonen starker Besiedlung durch kalkabschei- dende Organismen. So ausgedehnte Aufwuchs-Zonen konnen aber nur zustande kommen, wenn der Zuwachs durch Absenkung des Bodens kompensiert wird. (Der Vorgang ist logischerweise eigentlich umgekehrt.)

Die Tatigkeit von “turbidity currents” bedeutet einen Vorgang, der zur Aus- gleichung des Reliefs fuhrt, wenn es nicht durch einen anderen Mechanismus standig erneuert wird. Wir nehmen an, dass dieser Mechanismus eine weitraumige Senkung ist, die zwar die Becken tiefer legt, in den Aufwuchs-Zonen aber wegen der hohen Zuwachsgeschwindigkeit der Organismen wirkungslos bleibt. Vorkommen machtiger allodapischer Kalke sind daher Indikatoren einer regionalen Senkung. Damit ist noch nichts uber die Ursachen dieser Senkung gesagt.

Die Tiefe, bis zu der eine ausreichende Kalkproduktion moglich ist, lasst sich nach rezenten Vergleichen auf 30-50 m maximal schatzen. Kann man zeigen, dass das Liefergebiet ein regelrechtes Riff oder ein anderer regelmassiger Schuttungskorper war, so l a s t sich die Tiefe des Beckens abschatzen. Sie muss wenigstens so gross gewesen sein wie die Differenz der Machtigkeiten gleichaltriger Flachsee- und Becken- sedimente.

Diese Ergebnisse konnten gering erscheinen. Fur palaogeographische Rekonstruk- tionen stehen aber meist nur ausserst sparliche Hinweise zur Verfugung, die noch dazu oft mehrdeutig sind. Allodapische Kalke liefern zwar wenige, aber eindeutige Kriterien, die fur die Einordnung weiterer Beobachtungen eine feste Grundlage bilden. Der Nachweis von allodapischen Kalken ist demnach von grossem Interesse; er lasst weitreichende palaogeographische Schlusse zu.

BEISPIELE FUR ALLODAPISCHE KALKE

Im folgenden sollen einige Serien allodapischer Kalke aus verschiedensten Gebieten kurz besprochen werden. Nicht in allen Fallen liegen eingehende Untersuchungen vor.

176 K.-D. MEISCHNER

Fig.4. Legende siehe S.177. Legend see p.177.


Es werden einige Vorkommen einbezogen, die auf Grund guter Beschreibung in der Literatur oder mundliche Mitteilung durch die Bearbeiter eine befriedigende Deutung zulassen. Viele Kalk-Serien, die den Verdacht auf allodapische Kalke erwecken, werden hier nicht angefuhrt, weil die Unterlagen zu unsicher sind. Es wird noch einmal an die Aufstellung bei KUENEN und TEN HAAF (1956) erinnert.

Rheinische Geosynkline

Die Flinz-Fazies des Devons Der alteste mir bekannte allodapische Kalk ist der Flinz-Kalk im Devon des Rhei-

nischen Schiefergebirges (Fig.4). Als Flinz wird eine wohlgeschichtete Wechsel-Lage- rung dunkler, bituminoser, meist dichter Kalke mit dunklen Tonschiefern bezeichnet. Diese Fazies ist im oberen Givetium bis zur Adorf-Stufe in weiten Gebieten verbreitet. Die geologische Stituation ist folgende.

Etwa bis zum mittleren Givetium werden im nordwestlichen Teil des rechtstrheini- schen Schiefergebirges machtige Flachwasser-Sande und -Tone sedimentiert. Gelegent- liche Einlagerungen von geringmachtigen Korallenkalken bezeugen kurzfristige Unterbrechungen der Sandschuttung. Anzeichen tieferen Wassers finden sich erst siidostlich einer Fazies-Grenze, die etwa von Koblenz nach Brilon das Gebirge quert (SCHMIDT, 1962).

Fig.4. Die Beziehungen zwischen Massenkalk- und Flinz-Fazies im Devon der rheinische Geosyn- kline.

A. Palaogeographische Karte des nordlichen Rheinischen Schiefergebirges. Die Grenzen zwischen rheinischer und herzynischer Fazies verlauft im mittleren Givetiurn etwa an der unterbrochenen Linie. Der Sparganophyllum-Kalk (mittleres Givetiurn) ist mit regelmihiger, Massenkalk-Riffe sind durch unregelmassige Punktierung angegeben. Unter Verwendung von Daten aus SCHMIDT (1962) und PLSSMANN (1 962).

B. Sedimentations-Geschichte des nordlichen Rheinischen Schiefergebirges wahrend der Bildung der Massenkalke (oberes Givetiurn bis Adorf-Stufe). In Stichworten: a. Mittleres Givetium. Im Gebiet rheinischer Fazies unreine Sande und Tone, an einzelnen Stellen AnSatze zu Riffktirpern und -rasen. Am Aussenrand des Schelfs eine Zone bevorzugten Kalk-Aufwuchses (Schelfrandkalk = Spargano- phyllum-Kalk). b. Oberes Givetium. Die Sand- und Tonschuttung hat nachgelassen, die andauernde Absenkung wird an einigen Stellen durch Riffwachstum ausgeglichen. Das Briloner Massenkalk-Riff wird im Westen durch die synsedimenthe Altenburener Storung begrenzt. Erste Einschiittungen von Riff-Detritus in benachbarte Becken durch “turbidity currents”. c. Grenze Mitteldevon/Oberdevon. Der Hohepunkt des Riffwachstums ist uberschritten, die starkere Absenkung kann nicht mehr ausgeglichen werden. d. Obere Adorf-Stufe. Das Riff-Wachstum ist erloschen, die Sedimente der Becken- Fazies greifen allrnahlich iiber die versenkten Rimorper. Vermutlich wird an einigen Stellen noch Riffdetritus aufgearbeitet und in die Becken geschuttet. e. Nehden-Stufe. Silikatische “turbidity currents” bringen grosse Sand-Mengen vom Nord-Kontinent in das Becken. Die versenkten Riffe werden urnflossen, durch sie geschutzte Teilbecken bleiben frei von Sand (vgl. PLESMANN 1962).

Relationship between “Massenkalk” and “Flinz” facies in the Devonian of the Rhenish geosyncline. A. Paleogeographic map of the northern Rheinisches Schiefergebirge. Boundary between Rhenish

and Hercynian facies until Middle Givetian times shown as a broken line; Sparganophyllum-limestone (Middle Givetian) by stippled, and “Massenkalk” reefs by grey shading.

B. The sedimentary history of the northern Rheinisches Schiefergebirge during the formation ofthe “Massenkalk” (Upper Givetian to Adorfian). Partly based on data by SCHMIDT (1962) and PLE~~MANN (1962). For further explanations see text.

178 K.-D. MEISCHNER

Im hoheren Givetium gewann auch im nordwestlichen Schiefergebirge die Senkung allmahlich die Uberhand iiber die Sedimentation, wahrscheinlich nicht durch starkere Senkung, sondern durch Nachlassen der Schuttung, wie man aus der weiten Verbrei- tung des korallenreichen Spurgunophyllum-Kalkes schliessen kann. Grosse Gebiete wurden weit unter den Meeresspiegel versenkt, das Riff-Wachstum erlosch allmahlich (Wallener Schiefer). An einigen Stellen hielt der Aufwuchs benthonischer Kalk-Orga- nismen mit der Senkung Schritt. Diese Gebiete begannen, als Riffkorper iiber ihre Umgebung herauszuragen. So entstand ein kraftiges Relief. Die sandige Sedimenta- tion erreichte die Becken zwischen den Riff-Komplexen nicht mehr, die Wasserbewe- gung ging soweit zuriick, dass die Boden der Becken zu lebensfeindlichen Stillwasser- gebieten wurden. Ihre Sedimente sind schwarze, feinschichtige Pelite (Nuttlarer Schiefer z.B.).

Allmahlich, in einzelnen Gebieten zu unterschiedlichen Zeiten, aber uberall vor Ende der Adorf-Stufe, wurden auch die Riffkorper starker versenkt, das Wachstum der Riff-Bildner erlosch, die Fazies dunkler Tone, stellenweise mit Flinzkalken, griff iiber die Massenkalkkorper. Aus der bis dahin angehauften Machtigkeit von einigen hundert Metern Iasst sich ein ebenso grosser Betrag der Absenkung ableiten, wenn man annimmt, dass das intensive Riff-Wachstum auf Tiefen bis etwa 50 m beschrankt war. Die Sedimentation in den Becken blieb dagegen zuriick, woraus sich eine zuneh- mende Verscharfung des Reliefs ergab. Wahrend der gesamten Zeit der Massenkalk- Bildung gelangten Suspensionsstrome von Riff-Detritus in die tieferen Becken- Regionen.

Die charakteristische Flinz-Fazies hat schon lange das Interesse der Geologen gefunden. Sie enthalt aber im allgemeinen nur noch die Auslaufer der Suspensions- schuttungen, dunne, feinkornige, feinschichtige oder fast dichte Kalke, die gelegentlich noch gradiert sein konnen. Dagegen blieb der Bereich grosster Bank-Machtigkeit wenig beachtet, er wurde teilweise als Riffschutt oder lokale Sonder-Fazies angesehen. Die Flinzkalke sind noch zu wenig untersucht, um eine genaue Darstellung des gesamten Sedimentations-Ablaufes geben zu konnen. Daher sollen nur einige besser bekannte Spezial-Becken betrachtet werden.

TAFEL I

A. Regelm-ige Wechsellagerung von Peliten und detritischen Kalken im Kulm-Plattenkalk. Nord- ostliche Ecke des Steinbruchs an der Edelburg bei Menden, nordliches Rheinisches Schiefergebirge.

B. Gradierte allodapische Kalkbank, hauptsachlich aus den Zonen l a und Ib bestehend. Die Mach- tigkeit der Zonen 2 und 3 ist reduziert. Kulm-Plattenkalk, Steinbruch an der use bei Menden, nordliches rheinisches Schiefergebirge. Natiirliche Grosse.

A. Type of sequence in allodapic Kulm-Plattenkak. Northeastern comer of Edelburg quarry near Menden, northern Rheinisches Schiefergebirge.

B. Graded allodapic limestone bed containing mainly zones l a and Ib, while thickness of the zones 2 and 3 is reduced. Kulm-Plattenkalk, use quarry near Menden, northern Rheinisches Schiefer- gebirge. Natural size.

TAFEL I

180 K.-D. MEISCHNER

Der Flinz des Beckens von Nuttlar-Meschede. In der Umgebung von Nuttlar und Meschede im Sauerland finden sich gute Aufschlusse in typischer Flinz-Fazies. Ge- legentlich kommen darin besonders schone, machtige allodapische Kalkbanke vor (Tafel I). Das Material 1asst sich einmal vom Briloner Massenkalk-Plateau ableiten, das sich ostlich der schon wahrend der Sedimentation des Massenkalkes als Fazies- Grenze wirksamen Altenbiirener Storung erstreckte und an dieser tektonischen Linie plotzlich abbrach. Grossere Detritus-Massen durften aber aus dem Massenkalk der Attendorner Mulde geliefert worden sein. Die Flinz-Fazies geht in Richtung auf diesen Massenkalk in die Fazies der allodapischen Kalke maximaler Bank-Machtigkeit, Gesamt-Machtigkeit, Korngrosse usw. iiber, die etwa im Beisinghauser Kalk erreicht wird. Noch weiter in Richtung auf das Liefergebiet nimmt die Machtigkeit rasch ab, die sedimentologischen Strukturen verwischen sich, grosse Fossilschalen (hier Cepha- lopoden) stellen sich ein. Die Gesteins-Ausbildung zeigt Anklange an die Cephalopo- den-Fazies der Tief-Schwellen im Sinne RABIEN’S (1956, S.67). Das Profil des Arper Kalkes zeigt etwa dieses Bild, es liegt aber nicht mehr auf derselben Verbindungslinie Riff-Flinz. Interessanterweise kommen hier auch synsedimentare Rutschungen grosseren Ausmasses vor, die auf einen steileren Hang deuten konnten. Es ist zu vermuten, dass die Riffkorper in einer gewissen Wassertiefe von Cephalopodenkalken umgeben waren. Material dieses Siedlungs-Streifens wurde von den dariiber hinweggehenden Triibungswalzen erfasst und beckenwarts verschleppt. Die Analyse dieses Flinzbeckens verspricht wertvolle Ergebnisse.

Der Flinz des ostlichen Schiefergebirges. Auch an der Sud-Flanke des Briloner Mas- senkalk-Plateaus wurde Kalk-Detritus durch “turbidity currents” uber den heutigen Ostsauerlander Hauptsattel hinweg in die anschliessenden Stillwasserbecken verfrachtet. Gradierung und andere typische Strukturen sind deutlich vorhanden. Eine interessante neue Arbeit von BOTTKE (1 962) bringt erstmals chemische Gesichtspunkte. Bottke konnte hohe Gehalte an fossilem Polybitumen mit Spuren-Gehalten an V, Co, Ni und Mo nachweisen. Er schliesst auf unvollstandigen Abbau organischer Substanz.

Bottke gibt eine bionomische Deutung der Sedimente, die von der hier vertretenen abweicht. Er versucht den Wechsel zwischen Kalk und Ton als eine zyklische Folge von Sapropel, Gyttja und bitumenarmen Anteilen zu deuten, wobei zeitweilig der Eh-Wert negativ war und der pH-Wert durch freies C02 unter 7 sank. Er schliesst aber aus dem Vorkommen kleiner (pseudo-benthonischer !) Brachiopoden und Lamelli- branchiaten in den Kalken auf Bodenleben in gut durchluftetem Wasser, ohne die Moglichkeit einer Verfrachtung zu erwagen.

Der Ooser Plattenkalk. Eines der schonsten Beispiele fur allodapische Kalke hat KREBS (1962) beschrieben. Sorgfaltige Aufnahme des Fossil-Inhaltes von Kalken und Schiefern und petrographische Daten fuhren im Ooser Plattenkalk zu den gleichen Ergebnissen wie in anderen allodapischen Kalken. Das ist umso bemerkenswerter, als Krebs seine Arbeit unter einem ganz anderen Gesichtspunkt geschrieben hat. Seine Deutung ist, dass die Kalkbanke der rheinischen (Frischwasser-), die Schiefer der herzynischen (Stillwasser-) Fazies angehoren: “Wahrend der Zeit der Ooser Platten- kalke fand ein standiger Wechsel zwischen Bildungen einesjachen, gut durchlufteten,


bewegten und eines tieferen, schlecht durchlufteten, stromungsarrnen bis stillen Was- sers statt” (Hervorhebungen vom Verfasser).

Das ist im Prinzip die gleiche Deutung, wie sie bei Flyschgesteinen versucht wurde. Wir geben der Deutung der Kalke als Sedimente von Trubungsstrbmen den Vorzug. KREBS’ (1962, S.212-213) Aufstellung von 5 Kalk-Typen, die eine bathymetrische Reihenfolge sein soll, erweist sich damit als eine sedimentare Abfolge grob-fein, die auf Sedimentation durch “turbidity currents” zuruckzufuhren ist. Typ 3, “gelb- graue Mergel, 2.T. mit knolligen Kalkalgen bzw. Kalkknollen, die Crinoiden und

TABELLE I

DEUTUNG VON GESTEINS-TYPEN IM OOSER PLATTENKALK

Gesteins-Typ in KREBS (1962, S. 212-213) Kommentar

1. Graue, dickbankige bis massige, spatige bis brecciose Riffdetrituskalke mit lagigen Stromatoporen, Korallen und Crinoiden.

2. Graue diinnbankige, feinspatige bis fein- detritische Kalke mit einigen Einzelkoral- len, Crinoiden, Brachiopoden und Schalen- bruchstiicken. Haufig geht innerhalb eher Kalkbank diesel Typ nach oben in Typ 4 iiber.

4. Graue bis dunkelgraue, plattige, dichte, bituminos riechende, splittrig brechende Kalksteine mit vereinzelten Brachiopoden (fast ausschliesslich Leiorhynchus forrnosus, ortlich Trilobiten (Asteropyge supradevo- nica), vereinzelt Goniatiten, hlufig Ortho- ceren und Ostracoden . . .

5. Braunschwarze bis schwarzgraue. feinblat- trig zerfallende, schwach kalkige Tonschie- fer. Bei starkerem Kalkgehalt enthalten sie lagenweise zerbrochene kalkschalige Bra- chiopoden (z.T. sicher Leiorhynchus formo- sus). Die kalkarmeren Schiefer sind voll von Styliolinen, seltener Tentaculiten, Anapty- chen, flachgedriickten Goniatiten, diinn- schaligen Zweiklappern und Pflanzenhack- se l . . .

Moglicherweise Riffschutt, wenn “lagig” bedeutet, dass autochthone Stromatoporen- Rasen usw. vorkoxnmen. ist Wechsel-Lagerung von Biostromen mit Schutt anzunehmen. Die Beschrankung solcher Gesteine auf den unteren Teil der Ooser Plattenkalke konnte dafur sprechen.

Sonst konnte es sich urn den gerollfiihrenden unteren Teil dicker Banke (Zone la) handeln, wo plattige Stromatoporen-Fladen vorkommen.

Folge la der Ideal-Bank (Fig.1); man beachte den Hinweis auf den Ubergang in Typ 4.

Zone Ib bis 2a der Ideal-Bank. Auffalig sind die engen Parallelen zum Rhenaer Kalk, in dem ebenfalls vereinzelt Brachiopoden und Trilo- biten auf den Schichtfugen in diesem Bank- niveau auftreten.

Zonen 2b und 3 der Ideal-Bank. Uber den ganzen Leiorhynchus zerbrochene, Einmengung von Nekton und Plankton, diinnen Schalen und Ptlanzen-Resten.

182 K.-D. MEISCHNER

Brachiopoden, vereinzelt auch Orthoceren enthalten . . . ”, gehort nicht in diese Reihe. Es handelt sich moglicherweise um autochthone Knollen-Kalke und Mergel.

Allodapische Kalke im Karbon Rhenaer Kalk und Posidonienkalkl. Im ostlichen Teil des Rheinischen Schieferge-

birges herrscht im Unterkarbon die Kulm-Fazies, eine Fazies pelagischen Stillwassers. Den geringrnachtigen autochthonen Beckensedimenten sind zwei stratigraphisch verschieden alte und aus verschiedenen Richtungen geschuttete Serien allodapischer Kalke eingelagert, der Posidonienkalk (Dinantium IIIa3-PSpi, aus Sudosten geschuttet) und der Rhenaer Kalk (Dinantium III~spi-IIIy, aus Osten geschuttet)*.

Die geologische Situation ist weit komplizierter als die der devonischen Flinzkalke. Die Kalke sind namlich dem Aussenrand von gleichaltrigen Grauwacken beckenwarts vorgelagert. Sie sind aus der gleichen Richtung geschiittet wie diese, aber weiter in das Becken vorgedrungen. Die Grauwacken ihrerseits sind synorogene Sedimente eines sich im Hinterlande auffaltenden Gebirges, der “Mitteldeutschen Schwetle”;

Mit einer langeren Beweisfuhrung lasst sich zeigen, dass die Kalke von Riffen abzu- leiten sind, die dem Aussenrand dieser Grauwackenkorper aufgesessen haben. Damit mussen wir fur einen Teil der kulmischen Grauwacken des ostlichen Rheinischen Schiefergebirges eine Ablagerung im Flachwasser-Bereich annehmen, die Riff korper trennen als “Schelfrandkalke”, Beckensedimente und Kiistenstillwasser. Das Agens der Kalkproduktion und -Schuttung war die Absenkung einer der varistischen Faltung vorgelagerten Saumtiefe, die fur eine bestandige Versteilung bzw. Erhaltung des Reliefs sorgte. Die Tatsache, dass sich dieser Ablauf in ganz gleicher Weise mit geanderter Schuttungsrichtung wiederholt hat, gibt der Deutung eine grossere Sicherheit.

DerKulm-Plattenkalk. Eines der grossartigsten Beispiele fur allodapische Kalke ist der Kulm-Plattenkalk im Norden des rechtsrheinischen Schiefergebirges. Eine im Zentrum der Sedimentation - etwa bei Herdringen bis Muschede - iiber 100 m machtige Folge von hunderten gradierter Kalkbanke ist den Beckensedimenten einge- schaltet. Alle sedimentologischen Erscheinungen lassen sich in grosser Vielfalt in guten Aufschlussen studieren. Leider ist die Korngrosse des Kulm-Plattenkalkes ziemlich fein, so dass die Zone l a der Ideal-Bank meist fehlt. Eine Ausnahme machen die naher am Schiittungs-Zentrum liegenden westlichen Teile, die teilweise grobe Konglomerate und grosse Goniatiten-Schalen enthalten (Profile zwischen Letniathe und Hagen, vgl. Fig.5).

Der Kulm-Plattenkalk beginnt im Dinantium IIIa, und reicht bis an die Grenze Unter-Karbon-Ober-Karbon hinauf. Er ist also etwa gleichzeitig mit dem Posidonien- kalk und Rhenaer Kalk abgelagert. Herkunftsgebiet ist zweifellos der Kohlenkalk, ein Brachiopoden-Korallen-Kalk stationar organogener Entstehung, der dem relativ stabilen Schelf des Brabanter Massivs aufwuchs und nach dem Osten bis in den

Eine ausfiihrliche Darstellung findet sich bei MEISCHNER (1962). Hier werden nur die Ergebnisse

Die Buchstaben und Zahlen beziehen sich auf die Feinstratigraphie nach Goniatiten (vgl. KULICK, dieser Arbeit ohne Beweisfiihrung referiert.

1960).

ALLODAPISCHE W K E 183

Velberter Sattel vorstosst. Allerdings ergibt sich eine Schwierigkeit. Die Sedimentation des Kohlenkalkes setzt im Velberter Sattel etwa an der Grenze Dinantium I11 a-p aus (B~GER, 1962). Die Hauptmasse des Plattenkalkes ist also junger als der Kohlenkalk in diesem Gebiet. Zwei Erklarungen sind moglich.

(1) In der weiteren Umgebung ging die Kohlenkalk-Sedimentation weiter. Die Ver- haltnisse am Velberter Sattel sind nur lokal gultig, sie zeigen einen langsamen Ruckzug der Riff-Zone wie in der Massenkalk-Fazies des Devons.

Fig.5. Die Beziehungen zwischen Kohlenkalk und Kulm-Kalken. A. Palaogeographische Karte des nordlichen Rheinischen Schiefergebirges m Zeit der hoheren

Vk5-Stufe. Der Rhenaer Kalk ist etwas junger als der Posidonienkalk, gleichzeitig mit beiden wurde der Kulm-Plattenkalk geschuttet.

B. Schnitt durch das Sedimentations-Becken.

Relationship between “Kohlenkalk” and Kulm-limestones. A. Palmgeographic map of the northern Rheinisches Schiefergebirge at Upper ViSean times. Note

that the Rhenaer Kalk was deposited somewhat after the Posidonienkalk, while the Plattenkalk is contemporaneous with Rhenaer Kalk plus Posidonienkalk. B. Section through the sedimentary basin.

(2) Der Plattenkalk ist im wesentlichen ein Abbauprodukt abgestorbener, aber noch unverfestigter Kohlenkalkriffe und ihrer Schuttkorper.

Die Sedimentation der Kulm-Plattenkalke steht im Zusammenhang mit einer Ver- starkung der bis dahin langsamen Absenkung, die - wie im devonischen Massenkalk - einige hundert Meter erreicht hatte. Als Folge starkerer Senkung erlischt das Riff- Wachstum, die Fazies dunkler Stillwasser-Gesteine greift uber den Kohlenkalk nach Westen vor. Moglicherweise ist die verstarkte Absenkung eine Folge des Heran- wanderns der subvaristischen Saumtiefe (PAPROTH, 1960), so dass man ausserdem eine Versteilung des Reliefs durch imosten starkeres und fruheres Einsinkenannehmen darf.

184 K.-D. MEISCHNER

Der “Schieferkalk” im Malm von Nusplingen

Der beriihmte Fossil-Fundpunkt Nusplingen im Malm Cl der Schwabischen Alb zeigt ein sedimentologisch interessantes Profil. Inmitten der pelitischen, ausserst gleichmassigen lithographischen Kalke mit ihrer vollig ungestorten Feinschichtung liegen einige grob detritische, gradierte Banke und “Geroll-Tone” mit Fliesstrukturen in Form zerscherter liegender Falten.

GWINNER (1961) gibt eine zusammenfassende Darstellung dieses Vorkommens und weiterer Lokalitaten mit gleichen Erscheinungen. Seiner Deutung der grobkornigen Banke als Resedimente ist zuzustimmen. In Einzelheiten steht Gwinner allerdings unter dem Eindruck einer vorgefassten Theorie, die ihn in den deutlich gradierten Banken “Aufwirbelungszonen” uber den Zonen “subaquatischer Gleitung” sehen las t . Die Beobachtungs-Tatsache, dass gradierte Banke nur in den seltensten Fallen Rutschungs-Horizonte direkt uberlagern, zwingt ihn zur Einfuhrung einer Hilfs- Hypothese, derzufolge das Material der “Aufwirbelungszone” durch Schwerkraft oder Stromung weiter verfrachtet wird. So lassen sich Rutsch-Horizonte ohne uberlagernde gradierte Folgen erklaren, fur isolierte gradierte Banke wird umgekehrt angenommen, dass die zugehorigen “slumping”-Zonen in der Nachbarschaft liegen.

Wir sehen in diesen Sedimenten die gleichen Erscheinungen wie sonst uberall. Die gefalteten, gewickelten Geroll-Tone sind durch Sedimentgleitung (“slumping”) zustande gekommen. Die gradierten Banke dagegen sind allodapische Kalke rnit den typischen Merkmalen dieser Sedimente.l Neben den deutlichen sedimentaren Kriterien (Gradierung, Einregelung von Fossilien, Convolution) finden sich fazielle. Benthos (Brachiopoden, Muscheln, benthonische Foraminiferen) kommt in den allodapischen Banken, nicht aber in den pelitischen Zwischenmitteln vor. Ebenfalls treten fruhdia- genetische Hornstein-Linsen und -Lagen auf.

Damit ist selbstverstandlich nicht ausgeschlossen, dass Sedimentgleitung in einen regelrechten “turbidity current” ubergehen kann.

TAFEL ll

A. Zone la einer allodapischen Kalkbank voll von aufgearbeiteten Goniatiten. Kulm-Plattenkalk, Steinbruch am Schalk bei Letmathe, nordliches Rheinisches Schiefergebirge; x 0,6.

B. Gradierte Kalkbank im “Schieferkalk” von Nusplingen (Oberer Jura der Schwabischen Alb). Natiirliche Grosse.

C. Obere Teile, Zonen 2 und 3, einer allodapischen Kalkbank rnit Hornstein-Linse. Die Lamination ist durch unterschiedliche Sackung deformiert. Kulm-Plattenkalk, Steinbruch sudlich Herdringen, nordliches Rheinisches Schiefergebirge; x 0,s.

A. Zone la of an allodapic limestone bed full of reworked goniatites. Kulm-Plattenkalk, Schalk quarry near Letmathe, northern Rheinisches Schiefergebirge; X 0.6.

B. Graded limestone intercalation in “Schieferkalk” from Nusplingen (Upper Jurassic of the Swabian Alb). Natural size.

C. Upper part, zones 2 and 3, of an allodapic limestone bed with hornstone lens. Lamination is deformed by differential settling. Kulm-Plattenkalk, Herdringen quarry, northern Rheinisches Schiefergebirge; x 0.5.

TAFEL I1

186 K.-D. MEISCHNER

Die geologische Situation des Vorkommens ist ahnlich der der devonischen Flinz- kalke. Zwischen Riffen von Kieselschwammen und Korallen, die auf langsam sinken- dem Boden aufwuchsen, bildeten sich einzelne Stillwasserbecken, in die nur wenig Sediment gelangte, so dass sich schliesslich ein starkes Relief herausbildete. Der Schutt benachbarter Riffe wurde zusammen mit benthonischen Fossilien durch “turbidity currents” in die Stillwasserbecken eingeschuttet.

Das Becken von Nusplingen ist modellhaft klein, es hat nur etwa 1.000 m Durch- messer. Trotzdem haben sich freie Suspensionen entwickeln konnen.

Der Fossil-Inhalt der pelitischen Banke ist reich und ungewdhnlich. Neben (nekto- nischen) Fischen, Ammoniten, Belemniten sind auch Flugsaurier uberliefert. Die ausgezeichnete Erhaltung dieser Reste deutet auf Bedingungen lebensfeindlichen Still- wassers, in dem jede Zerstorung durch Aasfresser unterblieb. Es bestehen erhebliche Unterschiede zu den gleichaltrigen Fossil-Vorkommen von Solnhofen und Eichstatt.

Allodapische Kalke in Griechenland

Machtige Serien allodapischer Kalke findet man in West-Griechenland. Sie liegen im Vorland der Pindos-Olonos-Tripoli- Zone im westhellenischen Flyschbeckenl. Sie lassen sich von Joannina in Epiros bis nach Messenien auf dem Peloponnes verfolgen. Inwieweit Teile des Olonos- und Tripolitzakalkes (PHILLIPSON, 189 1) mit diesem Kalk identisch sind, muss vorlaufig offen bleiben.

Hinweise auf das Alter der Kalke geben Nummuliten, die - wie die Goniatiten im Palaozoikum - in einigen Banken vorkommen. Sie sind parallel zur Schichtung ein- geregelt und deutlich gradiert. Charakteristisch und auffallig sind die Lagen und flachen Linsen von Hornsteinen, die wegen der generell feinen Korngrosse im allgemeinen nahe der Basis der Banke liegen. Das Herkunftsgebiet der allodapischen Kalke diirften Nummulitenkalke gewesen sein, die in breiter Front den Schelf der sich vor dem Orogen eintiefenden Saumsenke einnahmen.

Ein interessantes Vorkommen findet sich bei Dodona in Epiros. Theater, Tempe1 und Wohn-Bauten des altgriechischen Orakels sind aus leicht metamorphem allodapi- schem Kalk erbaut. Die sedimentaren Strukturen wurden bewusst fur Zier-Effekte oder zur Erhohung der Haltbarkeit benutzt. Ausgewahlte Banke wurden in bestimmter Orientierung eingebaut, um mit den Hornstein-Linsen ein Muster zu erzielen. So ist z.B. die umlaufende Brustung in halber Hohe der Theater-Range aus einer einzigen Bank errichtet, die invers verbaut wurde. Die Sitz-Reihen sind aus Banken mit Hornstein-Lagen gebaut, indem man die abrieb- und wetterfesten Hornsteine als Sitzflache benutzte. Bei feinkbrnigen Banken mit Hornsteinen an der Basis bedeutet das inverse Lagerung im Theater. Einige Bausteine enthalten gradiert sedimentierte und verkieselte Nummuliten.

Die Strasse von Joannina nach Arta verlauft im Lourdos-Tal bei Konklisi kilo- meterweit in allodapischen Kalk-Serien. Weitere ausgedehnte Vorkommen finden

Vgl. die Tektonische Karte bei L U ~ G (1963, Abb.1, S.l l ) .


sich an der Strasse Tripolis-Kalamai zwischen Paradisia und Dervini, stets mit tonigem dunnbankigem Flysch vergesellschaftet. Beim Abstieg in die messenische Ebene 6 km sudlich Dervini sind auch Kalke aufgeschlossen, die aus groberem Detri- tus bestehen und reichlich Mikro-Fossilien enthalten.

Doch sind allodapische Kalke nicht auf den westhellenischen Flysch beschrankt. Ahnliche Gesteine finden sich auch auf dem ostlichen Peloponnes, und in Bootien. Meine Beobachtungen sind hier aber nur obedachlich, wie uberhaupt in einem geologisch so wenig bekanntem Gebiet wie Griechenland diese Mitteilungen nur eine erste Fund-Meldung sein konnen.

Verschiedene Mitteilungen uber allodapische Kalke

In zahlreichen geologischen Arbeiten werden Sedimente in palaogeographischen Situationen und mit Strukturen beschrieben, welche die Vermutung nahelegen, dass es sich um allodapische Kalke handelt. Oft werden solche Serien als “Plattenkalke” bezeichnet, die Kalke selbst als “feinbreccios, organodetritisch, organogen-detritisch, rifforganogenodetritisch” oder “organogener Crinoidenkalk”. Aber der Verdacht kann sich nur auf grobe Beschreibungen stutzen, sichere Hinweise findet man nur selten, weil die Bearbeiter nicht auf dergleichen Strukturen geachtet haben. Daher ist es verfruht, alle oder viele solcher Vorkommen hier zu diskutieren. Drei Beispiele seien aber noch angefuhrt, die eine gewisse Bedeutung haben.

( I ) Das permische Capitan-Riff der Guadelupe Mountains in Texas und New Mexico lieferte grosse Schuttmassen in das vorgelagerte Becken. Dieses Vorkommen ist tadellos erhalten und aufgeschlossen. Es kann als Modell-Fall gelten, an dem sich die Ereignisse qualitativ und quantitativ erfassen und auf ihre Ursachen zuruckfuhren lassen (ADAMS und FRENZEL, 1950; NEWELL et al., 1953).

(2) CHLUPA~ (1962) beschreibt in einer Studie uber die Plattenkalke (Hhdy-Kalk) im Mahrischen Karst (Tschechoslowakei) Fazies-Verhaltnisse, die eine Gliederung des Sedimentations-Raumes in eine flache Schwelle und ein tieferes Becken mit Einlage- rungen oberdevonischer und unterkarbonischer allodapischer Kalke erkennen lassen.

Allerdings stimmt ChlupiE der Deutung seiner Hhdy-Kalke als allodapisch nicht zu. Sein Argument ist, dass die Kalke eine wesentlich grossere Machtigkeit besitzen als die Pelite und daher nicht Ergebnisse episodischer Sedimentations-Vorgange sein konnen (ChluphE briefliche Mitteilung, 1962).

Dagegen ist zu sagen, dass die Sedimentation einer Kalkbank aus einem Suspen- sionsstrom nur sehr kurze Zeit (Stunden bis Tage) erfordert, die Pelite dagegen in Zeitraumen sedimentiert sind, die um viele Zehner-Potenzen hoher sein konnen.

(3) Grossere Vorkommen allodapischer Kalke darf man immer dort erwarten, wo Fazies-Differenzierungen und grosse Riff-Komplexe bekannt sind. Ein solches Gebiet ist auch die Alpine Trias in der Norischen und Rhatischen Stufe. Neben dem Dach- steinkalk gibt es norische und rhatische Plattenkalke. Viele verbergen sich unter dem Namen “Kijssener Fazies.” In mehreren neuen Arbeiten l a s t sich verfolgen, dass die fazielle Deutung der detritischen Kalke noch Schwierigkeiten macht und Fehl-Deutun-

188 K.-D. MEISCHNER

gen die Regel sind. Nach miindlicher Mitteilung von Herrn Prof. A. G. Fischer (1962) gibt es auch in der Hallstatter Fazies der roten Ammonitenkalke gradierte Kalkbanke, die auf Ablagerung durch Suspensionsstrome zuruckzufuhren sind.

SCHLUSSBETRACHTUNG

Allodapische Kalke kommen unter verschiedensten geologischen Bedingungen vor. Sie stellen Gesteins-Typen dar, deren eigenartige Natur bisher meist zu Fed-Deutun- gen Anlass gab. Bei sorgfaltiger sedimentologischer und palaontologischer Analyse sind sie aber ein Werkzeug, dessen Wert fur fazielle und palaogeographische Rekonstruktionen und damit auch fur die kommerzielle Praxis nicht hoch genug ein- geschatzt werden kann.

TAFEL UI

Sedimentare Strukturen allodapischer Kalke in Schnitten quer zur Schichtung. Alle Bilder sind

A.

B.

C .

D.

E.

F.

negative fotografische Vergrosserungen von Dunnschliffen; x TO. Untergrenze einer schlecht sortierten, groben Kalkbank (Zone la). Der unterlagernde Pelit ist durch Setzung deformiert. Posidonienkalk (Dinantium IIID), Hillershausen, nordostliches Rheini- sches Schiefergebirge. Grosse Gerolle aus feinkornigem Material, die durch Sediment-Setzung deformiert sind. Sortierung sehr schlecht (Zone la) . Rhenaer Kalk (Dinantium IIIy), Steinburch am Kohlberg bei Sudeck, nordostliches Rheinisches Schiefergebirge. Zone lb, der Kalk besteht aus Fossil-Detritus und Mikrofossilien. Die Sortierung ist schlecht, aber besser als in Tafel IIIA und B. Bituminose Impragnationen von Fossil-Schalen erscheinen hell. Rhenaer Kalk (Dinantium HID), Steinbruch Rhena, nordostliches Rheinisches Schiefergebirge. Fladenforrnige Ton-Einschliisse liegen parallel zur Schichtung. Oberer Teil der Zone lb . Rhenaer Kalk (Dinantium IIIy), Bomighausen, nordostliches Rheinisches Schicfergebirge. Die feinkornige Zone 2a wird durch diinne Einschaltungen von organischen Material gebandert. Rhenaer Kalk (Dinantium My), Bomighausen, nordostliches Rheinisches Schiefergebirge. Flaser-Textur, die auf diagenetische Entmischung in der Zone 3 zuriickgefiihrt wird. Die Flasern bestehen aus Kalkspat (dunkel) und Ton (hell). Posidonienkalk (Dinantium IUD), Diidinghausen, nordostliches Rheinisches Schiefergebirge.

Sedimentary features of allodapic limestones in vertical sections. All figures are negative prints of actual slides; x 10.

A. Lower contact of poorly sorted coarse limestone bed (zone la). Pelite underneath load casted. Posidonienkalk, Hillershausen, northeastern Rheinisches Schiefergebirge.

B. Large pebbles of fine grained material deformed by settling. Sorting very poor (zone la). Rhenaer Kalk, Kohlberg quarry near Sudeck, northeastern Rheinisches Schiefergebirge.

C. Zone lb , limestone consisting of detrital fossils and of microfossils. Sorting poor, but better than in “Tafel” IIIA and IIIB. Bituminous impregnation of fossil shells in light colours. Rhenaer Kalk, Rhena quarry, northeastern Rheinisches Schiefergebirge.

D. Lenticular clay pebbles parallel to bedding. Upper part of zone 16. Rhenzer Kalk, Bomighausen, northeastern Rheinisches Schiefergebirge.

E. Fine grained zone 2a laminated by thin intercalations of organic material. Same locality as “Tafel” IIID.

F. Phacoidal structure due to diagenetic differentiation in zone 3. Lenticles consisting of calcite (dark) and clay (light colours). Posidonienkalk, Diidinghausen, northeastern Rheinisches Schiefergebirge.

A

C

E

TAFEL I11

B

D

F

190 K.-D. MEISCHNER

Allerdings sind unsere Kenntnisse von diesen Sedimenten noch gering. Die Gesteine vieler Gebiete, in denen man allodapische Kalke erwarten konnte, mussten unter diesem Gesichtspunkt untersucht werden. Vor allem fehlt noch jede quantitative Arbeit, die aber in Kalken auch grbsseren Schwierigkeiten begegnet und mehr Auf- wand erfordert als in silikatischen Sanden.

Auswertung von Stromungs-Anzeichen, genaue Aufnahme des palaontologischen Bestandes, eine gute Feinstratigraphie, Korngrbssen-Analyse, Bestimmung und Aus- wertung der silikatischen Begleit-Minerale, chemische Untersuchungen u.a. sind nbtig und versprechen interessante Ergebnisse.

Der Zweck dieser Arbeit ist erfullt, wenn sie zu solchen Untersuchungen anregt. Ob sich die hier vorgetragenen Gedanken im einzelnen bestatigen oder nicht, ist gleich- giiltig, sofern nur unsere Kenntnis verbessert wird.

LITERATUR

ADAMS, J. E. and FRENZEL, H. N., 1950. Capitan barrier reef, Texas and New Mexico. J. Geol.,

BLREWIDE, R., 1962. Siedlungs- und Wuchsformen mitteldevonischer Korallen aus der Eifel. Natur

WER, H., 1962. Zur Stratigraphie des Unterkarbons im Velberter Sattel. Decheniana, 114 : 133-170. B o r n , H., 1962. Der Roteisenstein des 6stlichen Sauerlandes und seine Beziehuugen zur Strati-

Bourn, A. H., 1962. Sedimentology of Some Flysch Deposits. Elsevier, Amsterdam, 168 pp. BROUWER, A., 1962. Past and present in sediientology. Sedimentology, 1 : 2-6. CAROZZI, A.. 1952. Tectonique, courants de turbidit6 et ddimentation. Application au Jurassique

sup6rieur des chines subalpines de HauteSavoie. Rev. G&n. Sci. Pures Appl. Bull. Assoc. Franc. Avan. Sci., 59 : 229-245.

CAROZZI, A., 1955. Nouvelles observations microscopiques sur les d6p6ts de courants de turbidit6 du Malm de la nappe de Morcles en Haute-Savoie. Bull. Znst. Natl. Genevois, 57 : 3-31.

CHLUPAE, I., 1962. Zur Biostratigraphie und Faziesentwicklung der Devon/Karbon-Grenzschichten im Mahrischen Karst. Geologie, 11 : 1001-1017.

GWINNER, M. P., 1961. Subaquatische Gleitungen und resedimentiire Breccien im Weissen Jura der Schwabischen Alb (Wiirttemberg). Z. Deut. Geol. Ges., 113 : 571-590.

HJULSTROM, F., 1934-1935. Studies of the morphological activity of rivers as illustrated by the river Fyris. Bull. Geol. Inst. Univ. Upsala, 25 : 221-527.

Jvx, U., 1960. Die devonischen M e im Rheinischen Schiefergebirge. Neues Jahrb. Geol. Paliiontol. Abhandl., 110 : 186-392.

KREBS, W., 1962. Das Ober-Devon der Priimer MuldelEifel unter Ausschluss der Dolomit-Fazies. Notizbl. Hess. Landesamtes Bodenforsch. Wiesbaden, 90 : 210-232.

KUENEN, PH. H., 1950. Marine.Geology. Wiley, New York, 568 pp. KUENEN, PH. H. and HUMBERT, F. L., 1964. Bibliography of turbidity currents and turbidites. In:

A. H. Bourn and A. BROUWER (Editors), Turbidites. Elsevier, Amsterdam, pp.222-246. KUENEN, PH. H. and TEN HAAF, E., 1956. Graded bedding in limestones. Koninkl. Ned. Akad. Weten-

schap., Proc., Ser. B., 59 : 314-317. KULICK, J., 1960. Zur Stratigraphie und Palaeogeographie der Kulm-Sedimente im Eder-Gebiet des

nordostlichen Rheinischen Schiefergebirges. Fortschr. Geol. Rheinland Wesrfalen, 3 : 243-288. LOMBARD. A., 1963. Laminites: a structure of flysch-type sediments. J. Sediment. Petrol., 33 : 14-22. LUTTIG, G., 1963. Italienkcha und griechisches Pliopleistoziia. Z. Deut. Geol. Ges., 114 : 7-31. MEISCHNER, K.-D., 1962. Rhenaer Kalk und Posidonienkalk im Kulm des nordostlichen Rheinischen

Schiefergebirges und der Kohlenkalk von Schreufa/Eder. Abhandl. Hem. Landesamtes Bodenforsch., 39 : 47 s.

58 : 289-312.

Museum, 92 : 21-28.

graphic und Fazies des oberen Givets und der Adorf-Stufe. Roemeriana, 6 : 15-96.


NEWELL, N. D., RIGBY, J. K., FISCHER, A. G., WHITEMAN, A. J., HICKOX, J. E. and BRADLEY, J. S., 1953. The Permian Reef Complex of the Guadelupe Mountains Region, Texas and New Mexico. Freeman, San Francisco, 236 pp.

PAPROTH, E., 1960. Der Kulm und die flozleere Fazies des Namurs. Stand der Untersuchungen und olTene Fragen. Fortschr. Geol. Rheidand Wesqalen, 3 : 385-422.

PHILIPPSON, A., 1891. Geologische Karte des Peloponnes, 1 : 300.000. Friedlander, Berlin. RESSMANN, W., 1961. Stromungsmarken in klastischen Sedimenten und ihre geologische Auswertung.

PLESSMANN, W., 1962. Uber Stromungsmarken in Ober-Devon-Sandsteinen des Sauerlandes. Geol.

RABIEN, A., 1956. Zur Stratigraphie und Fazies des Ober-Devons in der Waldecker Hauptmulde.

REMANE, J., 1960. Les formations brkhiques dans le Tithonique du sud-est de la France. Trav. Lab

SCHMIDT, H., 1935. Die bionomische Emteilung der fossilen Meeresboden. Fortschr. Geol. Palaeontol.,

SCHMIDT, H., 1942. Nach Goniatiten gegliederte Profile im sauerlandischen Kulm. Decheniana,

SCHMIDT, H., 1962. uber die Faziesbereiche im Devon Deutschlands. In: H. K. ERBEN (Redakteur),

SEILACHER, A., 1962. Paleontological studies on turbidite sedimentation and erosion. J. Geol.,

Smwe, W., 1963. Das Korallen-Meer der Eifel vor 300 Millionen Jahren - Funde, Deutungen.

WEDEKIND, R., 1924. Das Mittel-Devon der Eifel. I. Die Tetrakorallen des unteren Mitteldevon.

Geol. Jahrb., 78 : 503-566.

Jahrb., 79 : 387-398.

Abhandf. Hess.'Landesamtes Bodenforsch., 16 : 83 S.

GPol. Fac. Sci. Univ. Grenoble, 36 : 75-1 14.

38 (12) : 154 S.

101 : 49-63.

Symposium SilurlDevon-Grenze, 1960. Schweizerbart, Stuttgart, S. 224-230.

70 : 227-234.

Probleme. Natur Museum, 93 : 237-276.

Schriften Ges. Beforder. Ges. Naturwissenschaften, 14 : 1-93.

THE OCCURRENCE OF FLUTE CASTS AND PSEUDOMORPHS AFTER SALT CRYSTALS IN THE OLIGOCENE ‘‘GRRS A RIPPLE-MARKS” OF THE

SOUTHERN PYRENEES

J. F. M. DE R A A F

KoninklijkelSheIl Exploratie en Produktie Luboratorium, Rijswijk (The Netherlands)

SUMMARY

A short description is given of the lower part of the Oligocene sediments outcropping in the province of Navarra (Northern Spain) near the village of Liedena.

One of the salient features is the presence of graded beds bearing flute casts in a continuous section which also contains layers revealing evidence of evaporitic conditions.

The sediments in question form the basis of the huge molassic fill of the Ebro basin and should not be considered a flysch in spite of their rhythmic aspect and local grading.

INTRODUCTION

On the occasion of the Symposium held at London, February 1961, under the heading: “Some aspects of sedimentation in orogenic belts” (DE RAAF, 1961), I expressed the view that studies in the Koninklijke/Shell Exploratie en Produktie Laboratorium of microfaunas occurring in pelitic intercalations of some representative alpine flysch sequences, point to a bathyal-abyssal environment of deposition.

The sequences then mentioned, characterised by graded bedding, belong to the Alpine orthogeosynclinal belt and include Ultrahelvetic flysch deposits (Switzerland), macigno complexes (Italy) and the Peka Cava flysch (France). The graded sandstones occurring in these complexes have, in all important respects, the same characteristics. It is an easily recognisable type of sandstone described in many publications, notably by Ph. H. Kuenen and his followers (see KUENEN and HUMBERT, 1964), and its properties have recently been collated and summarized by BOUMA (1962) in his study of the Peira Cava region.

The latter author gives a series of drawings (BOUMA, 1962, pp.49-51) showing the different aspects these sandstones may assume. The whole range of variants encountered in the field can best be described by adopting a lettering system such as he uses, and by designating, for instance, a graded bed as being of the a-c type, etc.

At about the time of the above-mentioned investigations, I inspected other environ-

FLUTE CASTS AND PSEUDOMORPHS IN THE SOUTHERN PYRENEES 193

ments for the presence of graded beds characterised by sandstones of the same type, and research was not restricted to orthogeosynclines. It was considered that this would shed light on the mechanisms responsible for the formation of these sandstones. Preliminary results indicate that they occur most frequently in environments deeper than the neriticum, but that they may also occur in association with beds the nature of which points to shallower water conditions.

GRADED SANDSTONES OF THE SOUTHERN PYRENEES

Eocene sediments of the southern Pyrenees extending west of the Aragon River - an area which has been the object of an admirable study by MANGIN (1959-1960) - are very instructive in this respect. The unusual occurrence of a limited number of important neritic limestone intercalations in graded sequences is the prominent feature here. The Oligocene of the same region presents an even more remarkable case, in that there are graded arenaceous units of the type mentioned above, close to saline lagoonal deposits, in an uninterrupted sequence (MANGIN, 1962). Thus, at the base of the Oligocene molasse-like deposits outcropping in the Pamplona area, marine clastics and lagoonal gypsiferous deposits occur and the latter are locally associated with Mangin’s “grks A ripple-marks”, in which I found evidence of grading together with indications pointing to evaporitic conditions.

The Liedena Beds

Description I had an opportunity to pay two brief visits to exposures of these sandstones near

the village of Liedena (36 km southeast of Pamplona), in one instance guided by Mangin, and a short account of features observed now follows.

The cross section visited runs parallel to a roughly north-south part of an abandon- ed railway, along which poles are found at regular distances of about 20 m (MANGIN, 1962). The beds are overturned to the south and parts of the section rich in sandstone beds have an uneven rhythmic aspect (Fig.1). From north to south, the following types of beds can be observed:

(I) Beds outcropping near pole 130: red and greenish grey marls with thin intercalations of siltstone. Both the mark and the siltstones contain a certain amount of gypsum. Towards the south (i.e., towards the top) the sequence becomes gradually more arenaceous.

(2) Beds outcropping between a point about 17 m north of pole 129 and pole 127: an alternation of beds consisting of relatively fine-grained sandstone, siltstone and marl. No systematic grain-size studies have been made of the arenaceous sediments, but a cursory inspection suggests that there is a predominance of ungraded beds, which is particularly true of the thinly bedded and fine-grained units. Sandstones interrupted by discontinuous lenses or tongues of silty to pelitic material are not

194 J. F. M. DE RAAF

Fig.1. General aspect of the “grh B ripple-marks” seen at pole 129. The very noticeable bed at the extreme left is the one revealing the flute casts shown in Fig.2. Oligocene near Liedena village,

Navarra. northern Spain.

Fig.2. Overturned graded sandstone bed with flute cast sole markings. Oligocene, Liedena, Spain.


Fig.3. Overturned sandstone bed with apparently symmetrical ripple-marking on upper depositional surface. Oligocene, Liedena, Spain.

infrequent. The best examples of grading were found in the thickest sandstone beds (ca. 1 m thick).

Individual graded units of type a, a-b and a-c (see p.192) were recognised. On the sole of the graded units good flute casts (Fig.2), groove casts and other less

characteristic sole markings are occasionally present. The bird tracks described by Mangin were also found in this part of the section. Several thin beds reveal evidence of slumping. Many of the sandstones and siltstones display ripple marks on their lower or upper surfaces. The ripple marks often have directions that do not differ very much from either the strike or the dip of the beds. Good instances of apparently symmetrical ripple marks, that are generally thought to have been caused by wave action, have been observed (Fig.3). Other kinds of ripples have also been seen, and it is clear that a detailed investigation of rippling by sectioning the sandstones and determination of the directional features is needed. Another subject worth further investigation is the silty and marly pelites occurring between the sandstones and siltstones. They are generally greyish, but subordinate beds occur that are red in colour. No micropal- aeontological study of the pelites has been made as yet.

Towards the top (between poles 128 and 127) the sequence becomes richer in fine- grained material.

(3) Beds outcropping between poles 127 and 126: only very fine-grained, thinly bedded sandstones and siltstones have been developed in this part of the section (Fig.4). They often bear delicate sole markings (burrowings, etc.) and in particular some pseudomorphs after salt crystals that merit special mention (Fig.4, 5).

Some of the intercalated marly pelites have a brown reddish colour.


Interpretation The individual graded units encountered in the Liedena section have a similar

sedimentary structure to those intercalated in deep-water pelites, and also to those occurring in the above-mentioned Eocene sediments of the southern Pyrenees. However, the Liedena Beds have been deposited near or at a coast, in a belt where temporarily and locally evaporitic conditions existed.

Fig.4. Overturned sequence consisting of marly pelite with intercalations of very line sandstone and siltstone; pseudomorphs after salt crystals occur occasionally as sole markings. For assessment of

size, see sunglasses at bottom left. Oligocene, Liedena, Spain.

As regards the mode of formation of graded units lodged in different environments, KUENEN and MIGLIORIN~’S turbidity theory (1950) is, in my opinion, the best one for the explanation of widespread grading in proven deep-water deposits. The same mechanism of turbidity-current activity can possibly be invoked for the formation of a large part of similar beds associated with shallower deposits; but here each case should be considered separately, since other processes may have to be taken into account. The above-mentioned marine Eocene formations of the southern Pyrenees represent a case which demands such special scrutiny.

The origin of sole-marked sandstone bodies stemming from more continental environments has been explained in the literature in different ways. Theories put forward by, for instance, CUMMINS (1958; sheetfloods) and PRENTICE (1962; crevasse deposits) are of particular interest for sections like those of Liedena. Before any hypothesis can be confidently adopted, it is. however. considered that more observations are needed


Fig5 Pseudomorphs after salt crystals as sole markings: finegrained silty sandstone bed. Oligocene, Liedena, Spain.

to shed light on the role played by graded bedding and on the shape of individual graded units in the “gr& a ripple-marks”, as well as the latter’s relationship with other facies (WNGIN, 1959-1960, fig.92, sandstones with nummulites, conglomerates, etc.).

It may be useful to summarize the different features that, at Liedena, point to shallow or negligible aqueous cover during deposition: ( I ) red and greenish pelites associated with gypsum, (2) salt pseudomorphs, (3) bird tracks, (4) abundant ripple marks on upper as well as lower surfaces of sandstone beds with crests running in different directions, (5) occurrence of apparently symmetrical ripples (presumably wave ripple- marks), (6) a particular kind of lensing and interfingering in certain arenaceous units.

The above account shows that graded beds of the same habitus may occur in differing depositional environments and that a turbiditic origin is particularly evident for those which occur in bathyal or deeper deposits.

GENERAL REMARKS

Tn the course of my investigations, I came to the conclusion that they occur also in differing megatectonic environments, such as orthogeosynclines, postorogenic units


(GNACCOLINI~, 1960), intracratonic units M ALL EN^, 1960; GILL, 1961) etc. In the orthogeosynclines they attain their maximum development and play an important role in flysch comFlexes.

The Liedena Beds dealt with in this account form the basis of the huge molassic fill of the Ebro Basin and should not be mistaken for a flysch, in spite of their rhythmic aspect and local grading.

ACKNOWLEDGEMENTS

The author wishes to thank the directors of Shell Internationale Research Maat- schappij N.V. for permission to publish this article.

REFERENCES

ALLEN, J. R. L., 1960. The Mam Tor sandstones: A “turbidite” facies of the Namurian deltas of

BOUMA, A. H., 1962. Sedimentology of Some Flysch Deposits. A Graphic Approach to Facies Inter-

Cumms, W. A., 1958. Some sedimentary stmtures from the Lower Keuper sandstones. Liverpool

DE RAAF, J. F. M., 1961. Discussion. In: Some Aspects of Sedimentation in Orogenic Belts ( a Sympo-

GILL, W. D., 1961. Non-orogenic equivalents in Ireland. In: Some Aspects of Sedimentation in

GNACCOLINI, M., 1960. Contributi alla conoscenza della paleogeografia del Langhiano delle “Langhe”

KUENEN, PH. H: and HUMBERT, F. L., 1964. Bibliography of turbidity currents and turbidites.

KUENEN, PH. H. and MIGLIORINI, C. I., 1950. Turbidity currents as a cause of graded bedding.

MANGM, J. PH., 1959-1960. Le nummulitique sud-pyrknkn I’ouest de 1’Aragon. Pirineos, 51-58 :

MANGIN, I. PH., 1962. Traces de pattes d’oiseaux et flute-casts associb dans un “facies flysch” du

F’RENTICE, J. E., 1962. Some sedimentary structures from a Weald clay sandstone at Warnham Brick-

Derbyshire, England. J. Sediment. Petrol., 30 (2) : 193-208.

pretation. Elsevier, Amsterdam, 168 pp.

Manchester Geol. J., 2 (1) : 3743.

sium) - Proc. Geol. SOC. London, 1581 : 71.

Orogenic Belts (a Symposium) - Proc. Geol. SOC. London, 1587 : 76.

(tra Acqui e Bubbio). Riv. Ifal. Paleontol., 66 (4) : 589-603.

In: A. H. BOUMA and A. BROUWER (Editors), Turbidites. Elsevier, Amsterdam, pp.222-246.

J. Geol., 58 : 91-127.

1-631.

Tertiaire pyrbnkn. Sedimentology, 1 (2) : 163-166.

works, Horsham, Sussex. Proe. Geologists’ Assoc. Engl., 73 (2) : 171-186.

Gnaccolini’s observations are in concordance with the present author’s findings 40 km to the east in the same basin, where the very thick Lower Miocene sequence outcropping west of the Scrivia River along the southern rim of the Po Basin consists almost entirely of bathyal graded beds of a turbiditic nature. a In Ireland intracratonic Namurian graded beds, similar to those described by Allen, occur in several places. They are followed upwards by shallow-water deltaic deposits and are underlain by shales containing goniatites (for instance near Castleisland, Kerry).

DIRECTIONAL PROPERTIES OF A MIOCENE TURBIDITE, CALIFORNIA

J . H . SPOTTS and 0. E. WESER

California Research Corporation, La Habra, California; Stanabrd Oil Company of California, Western Operations, Inc., Ventura, California (U.S.A.)

SUMMARY

A turbidite exposure in the Topanga Formation (Miocene) in the Santa Monica Mountains, California exhibits an unusual number and variety of linear sole features. Seven types of tool and scour markings (groove, bounce, prod, brush, skip, flute, and cusp casts) with directional significance have been measured and described. The name cusp cast is introduced here for crescentic, asymmetrical features, not previously described, which occur singly or in rows of several casts that merge or coalesce to form irregular linear features in some instances. The depressions responsible for cusp casts may represent current scour. Statistical data for 2,106 linear sole features indicate very strong preferred orientation, even though there is a 70" range in orientation of individual features. Dimensional grain orientation of fifteen samples consistently diverges approximately 45" from the sole features. Parallelism between sand grain orientation and the major set of fractures (including both open and closed fractures) suggests a genetic relationship between these two directional features. Petrographic and fabric data support the conclusion that grain orientation produced sufficient anisotropy in rock strength to influence the orientation of fractures.

INTRODUCTION

In the past decade, the information available on sedimentary sole structures in turbidity current deposits has been rapidly increasing. Most of these data concern European exposures because of the abundance of good outcrops in European turbidite sequences and alarge group of workers in that area. An unusually well-developed, small sandstone sole in Miocene turbidites of the Topanga Formation is exposed in the Santa Monica Mountains in Southern California. The exposed sandstone sole is small, approximately 7 by 19 ft., but it contains a remarkable number and variety of tool markings. Several varieties of scour markings are also present. The sand bed is well-cemented and the sole surface is overturned and dipping 74". It thus provides excellent conditions for studying the form, variation and orientation of sole features.

The outcrop is located in a road-cut on Mulholland Drive approximately 0.8 miles

200 J. H. SPOTTS A N D 0. E. WESER

west of Las Virgenes Road. It is about 30 miles northwest of downtown Los Angeles (Fig. 1).

Although well exposed here, sole features are not ubiquitous in turbidite outcrops and are rarely found in subsurface cores. Other directional features such as grain orientation and current-rippling or cross-bedding must be used for paleogeographic reconstruction in the absence of sole marks. Geologists working in turbidite sequences have long been interested in particle or grain orientation relative to linear sole features and the abundance of linear markings in the Mulholland Drive outcrop provided an excellent opportunity for statistical comparison of grain orientation and sedimentary

\ \ \ \ SAN JOAWIN \

V A L M Y I \ /

/ ---/’ ‘\

Fig.1. Index map, southern California.

DIR

EC

TIO

NA

L PR

OPE

RT

IES O

F A

MIO

CE

NE

TU

RB

IDIT

E

PLATE I

0 I 2 3 - FEET

Photograph of sandstone sole in turbidite sequence in Topanga Sandstone (Miocene) in the Santa Monica Mountains, California. The exposure is on Mulholland Drive, approximately 0.8 miles west of Las Virgenes Road in Los Angeles County. The sandstone is overturned and dips approximately 74"

0 toward the observer. Direction of current movement is toward the lower left. -

202 J. H. SPO

TT

S AN

D 0. E. W

ESE

R

h) 0 h)

Moon grain orientation (approximately 500' grains) plotted ot location of oriented sample

Mean orientation of sole features plotted at centers of sectors (approximately 2 x 3 ft.) into which outcrop was divided for descriptive and measuring purposes

Open fractures

Closed fractures

Fig.2. Orientation of fractures, grains and sole features, Topanga Sandstone outcrop, Mulholland Drive, Santa Monica Mountains, California.

0 m

DJRECTIONAL PROPERTIES OF A MIOCENE TURBIDITE 203

structures. If a consistent relationship between grains and marks can be established, directional properties of turbidites could be obtained in any sample that could be oriented in space. Grain orientation can be determined on any arenaceous sediment and thus the amount of directional data pertaining to paleogeography could be greatly increased. This would be particularly useful in areas of poor outcrops and in subsurface work.

In addition, the outcrop has a system of open and closed fractures. Orientation of the two systems (open and closed fractures) has been analyzed in relationship to other directional properties (Plate I, Fig.2).

PREVIOUS WORK

Several workers have been active in recent years in the descriptive and interpretive aspects of sole markings. Comprehensive studies that also include some excellent illustrations include works by KUENEN (1957), RADOMSKI (1958), DZULYNSIU and SLACZKA (1959), TEN HAAF (1959), and DZULYNSKI and SANDERS (1962). Photographs and detailed descriptions of sole marks are also given by GLAE~~NER (1958), R~~CKLIN (1938), PEABODY (1947), CUMMINS (1958), and BIRKENMAJER (1958). The terminology and interpretation of genetic significance of sole marks is diverse; and, unfortunately, there has been no concerted effort to standardize the nomenclature. In general, the terminology of DZULYNSKI and SANDERS (1962) is followed in this paper.

Considerably less work has been done on sand grain fabric in turbidites and its relationship to other directional features. KOPSTEIN (1954), RADOMSKI (1958), and TEN HAAF (1959), made limited investigations of sand grain, pebble and other particle orientation. SPOTTS (1962, 1964) found a consistent divergence between dimensional grain orientation and groove and flute casts in a Miocene turbidite of the Los Angeles Basin. Very little investigation has been done on local variations in grain orientation along bedding planes or regional grain fabric relationships primarily because of the tedious work involved in obtaining valid statistical measurements.

METHODS OF STUDY

For purposes of description and statistical measurement, the outcrop was divided into a grid system of 2 x 3 ft. sectors with black tape. Twenty complete and partial sectors were outlined (Fig.3). Each sector was photographed close-up and the orientation of all measurable linear features was determined with a goniometer and T- square on 8 x 10 inch enlargements. Angles were measured with the strike of the strata as a reference line. Because of curved trails at the terminal ends of some features, the direction of each marking was measured at the point of first contact with the bedding surface. Orientation of each type of feature in each sector was tabulated separately. The exposed surface was examined for possible engraving tools which could

204 J. H. SPOTIS AND 0. E. WESER

have made the sole features, and several possible impacting tools are described in a later section.

Samples of shale were collected for determination of depth of water at the site of deposition by paleoecological techniques.

BCILE IN FT. - 0 1 2

Fig.3. Sketch of outcrop showing grid system for reference and statistical measurements. See Plates I1 and 111.

Fifteen oriented sand samples were taken from the thin 1-2 inch sand bed immediately overlying the grooved and fluted surface for measurement of grain fabrics. Sand grain imbrication studies were made on six of the oriented sandstone samples; these were the only samples that were sufficiently well-laminated that the bedding could be accurately defined in thin-sections perpendicular to bedding planes.

The fracture pattern was measured by tracing the fractures onto an overlay for an enlarged photograph (15 x 32 inch) of the entire exposure. The distinction between open and closed fractures was made on the overlay by examination of the outcrop in the field. Orientations of the two types of fractures were recorded separately.

PLATE lI

Photographs of sole features on Topanga Sandstone, Santa Monica Mountains, California. Direction of current movement is toward the lower left in all figures. Photographs represent portions of sectors

of outcrop as noted; see Fig.3 and Plate I for location of sectors on the outcrop. A. Prod casts made by impacting tools of different sizes. Some prod marks (P) show curved longi-

tudinal traces and bent or overturned keels. Other features are flute casts (F), bounce casts (E), and long, broad grooves. Sector 3.

B. Skip casts (S) and prod casts (P). Short prod cast nearest right margin was cut by very blunt tool. Sector 4.

C. Brush cast (ER), bounce casts (E), groove casts (G), and prod casts (P). Sector 2. D. Large, well-developed flute cast (F) with upcurrent tip of flute removed. Note curved and recli-

ning prod casts (P) in upper center of figure. Vertical and horizontal black lines are tape used for dividing outcrop for analytical purposes. Sector 14.

DIRECTIONAL PROPERTIES OF A MIOCENE TURBIDITE

PLATE I1

0 6 12

205

INCHES

206 J. H. SPOTTS AND 0. E. WESER

PLATE 111

6 12

INCHES

DIRECTIONAL PROPERTIES OF A MIOCENE TURBIDITE 207

GEOLOGIC SETTING

The Topanga Sandstone in the Mulholland Drive outcrop is part of a thick sequence of turbidite beds in a rather small orogenic basin of relatively short duration. The basin formed during the strong mid-Miocene tectonic activity that affected most of southern California. Turbidite sediments deposited in the basin were derived from several directions; the orientation of sole features in the Mulholland Drive exposure suggests a southeasterly source for these particular sands.

Faunal evidence indicates a water depth of several hundred feet at the site of deposition. This is considerably shallower than most Tertiary turbidites in southern Cali- fornia. The sand bed is thin with an average thickness of about one inch. The sandstone is a poorly sorted, fine-grained, subangular, slightly argillaceous and micaceous arkose with minor amounts of metamorphic rock fragments. The thin turbidite bed shows a very slight degree of normal graded bedding. The overlying bed is another thin (1-2 inch) graded sandstone. This upper sand is medium-grained but otherwise petrographically similar to the thin, fine-grained sand on the face of the outcrop.

SOLE MARKINGS

The sole marks are classified primarily on the mode of formation of the depressions responsible for the casts and they are divided into two major categories, scour markings and tool markings. Scour markings are formed by the cutting action of the current on the sea bottom. Tool marks are made by the impact of current-transported, large particles against the muddy sea bottom. Several types of individual sole markings are illustrated in Plates I1 and 111.

Tool markings

Tool markings are much more abundant than scour features on the outcrop. These markings are believed cut by relatively large, transported particles that strike the sea

PLATE IU

Photographs of sole features on Topanga Sandstone, Santa Monica Mountains, California. Direction of current is toward the lower left in all figures. Photographs represent portions of sectors as noted;

A. Cusp casts, a row of several individual casts which have almost coalesced to form a linear feature. Sector 13.

B. Several small bounce and prod casts that show intersecting features (I), diversity of directions, curved trails (T), and bent keels ( K ) . Sector 7.

C. Detail of intersecting fracture system. Open fractures are diagonal, upper right to lower left and closed fractures extend horizontally through center of photograph. Both sets show some offset here. Sector 5.

D. Group of cusp casts (C), unusual ribbed prod cast (P) in upper left and another very blunt prod cast (P) above cusps. Sector 6.

see Fig.3 and Plate I for location of sectors on the outcrop.

208 J. H. SPOlTS AND 0. E. WESER

bottom as they are carried along by turbulent flow. The tools are usually considerably larger than the average grain size in sandy sediments. The distinction in morphology of the tool markings is based on relative velocity and the angle of incidence of impacting particles, degree of turbulence in the current, and the nature of the substratum.

In defining the shorter tool markings such as prod marks, brush marks and bounce marks, we have departed slightly from recent subjective terminology and have used the definitions given below.

DeJinitions ( I ) Bounce casts - short impact marks whose longitudinal profile is symmetrical.

The deepest penetration of these marks, therefore, is in the center of the cast and their terminations merge at equal rates with the sandstone sole. Bounce casts provide only directional data and no information on sense of current movement.

(2) Prod casts - impact marks whose longitudinal profiles are asymmetrical. The deepest point of the trace is off-center in the longitudinal section. Usually the downcurrent termination merges more abruptly with the sandstone sole than the upcurrent termination. Rarely, however, because of an exceedingly high impact angle, these relations are reversed. Thus these features in most cases are very reliable for determining current direction.

(3) Brush casts - impact marks having a crescentic depression around the downcurrent termination. The depression is the pressure ridge in front of the impacting tool.

Several types of tools were available to make the markings. Seaweed, charcoal, mollusk fragments, fish bones, and relatively large rock fragment grains which have been found on the sandstone sole could have been impacting tools for most of the tool markings observed.

Groove casts These occur singly or in groups, and are some of the most prominent features.

Plate I shows a few groove casts extending completely across the outcrop face. Some strongly etched grooves range from one to two inches wide and up to 1-2 inch deep. Others are delicate lines which are visible only on the larger scale photographs. (Plates I1 and 111.)

Bounce casts These are the most numerous markings and the longer ones grade into groove casts.

In this report all groove casts shorter than 12 inches were termed bounce casts. Most of the bounce casts are fairly straight and exhibit little secondary deformation.

Prod casts These casts exhibit the greatest variety of shapes and sizes and are second in abun-

dance to the bounce casts. Their paths can be straight or curving in an arc up to 50". The angle of incidence varies from very low to 60". Prod marks show a wide range in size and their profile ranges from smooth to distinctly ribbed. These casts generally


have the largest depth to length ratio, which commonly is 1/1 and occasionally may be as high as 3/1.

Many prod marks exhibit extreme deformation and the sharp, deep prow may be bent over so that it is almost parallel to the sandstone sole. This shows that, in spite of the high degree of deformation, the original outline of the mark is well preserved. Cer- tainly this deformation took place before lithification and probably in a plastic state shortly after deposition, but the mud had sufficient cohesion to preserve the thin, delicate shapes.

Brush casts These also show a variety of shapes and sizes. Generally, however, their trail is

relatively straight and short. Both the longitudinal and transverse profiles are usually smoother than those of prod casts. Generally brush casts are also not etched as sharply or deeply as the prod casts.

It is possible that brush casts are formed after the prod casts and perhaps after a thin sand layer has been deposited on the lutite bottom. Any sharp or small projectile striking a mud bottom can make a deep, sharply etched impression. If a mud ridge is formed, it may be carried away by the current, and the marking would be called a prod cast. However, a thin sand coating over the mud bottom would cushion the impact of the tool and the marking would then be muted in outline and depth. Any mud ridges formed during this type of impact would be protected from erosion by the sand cover and the feature would be classified as a brush cast.

Skip casts A few excellent examples of skip casts were noted, see Plate 11. One skip mark

appears to have been made by a fish vertebra and is similar to one shown by DZULYNSKI and SLACZKA (1959).

Scour markings

Scour markings are not as abundant as tool markings in the outcrop studied. DZULYNSKI and SANDERS (1962) recognize several varieties of scours but only two are present here.

Flute casts Several scattered flute casts are illustrated in the right half of the photograph

(Plate I). A well-developed example is also shown at higher magnification in Plate 11. A row of flute casts is located in the center-right portion of the outcrop. The individual casts are fan-shaped and only poorly or incipiently developed.

Channels A well-developed scour channel is located near the left margin of the photograph

(Plate I). The channel has a minimum length of 2 ft. and apparently extends below the


outcrop surface. Near the upcurrent end, it is only a few inches across but it flares out to 12 inches at the downcurrent termination. It is triangular in cross-section with the depth of the channel ranging from 1-3 inches.

Cusp cast

A feature not previously described in the literature and first seen on the Mulholland Drive outcrop is hereby termed a “cusp cast”. This feature may be formed by current vortices, although the possibility of plastic flow of the substratum cannot be elimi- nated.

These casts occur mainly in groups parallel to the current direction although isolated ones are also present. Individual cusp casts are round to oblong in outline but the features are not symmetrical with respect to the current direction. The perimeter of the cast on one side of the flow direction merges gradually with the sandstone sole, whereas the other half of the feature is steeply undercut. A train of these casts is shown on Plate 111. This asymmetry about the line of current flow may impart a directional significance to cusp casts but a bztter understanding of the origin of these markings is needed to evaluate this possibility.

Cusp casts differ from the flute casts in that they lack a deeper upstream end and are not elongated in a downstream direction. Like flute casts, however, cusp casts do form rows or trains of several individuals and apparently merge to form major cusp casts.

ORIENTATION OF MARKINGS

Seven types of sole markings in the outcrop reprzsenting several mechanisms of formation have directional significance. Cross-cutting and deformational relations indicate that not all types were formed simultaneously. If specific types of features are associated with certain phases of the marking current, shifts in current direction with time could result in different mean orientations for different types of sole markings. To test this possibility, orientation data for each type of feature were obtained for each of the 20 sectors and the entire outcrop. Orientation measurements for 2,106 such features were made. These data are listed in Table I.

The relative abundance of the various markings is shown by the totals for the outcrop. Approximately 50 % of the features are bounce marks and prod marks account for 30 % of the total. The other types of tool markings are less abundant, brush marks, 13 %, and groove marks, 6 %. Slightly more than 1 % of the directional features are scour markings, including cusp casts.

Four levels of comparison of statistical directional data for the sole markings were made, (1) the variation in average direction for each type of marking within a sector and between sectors, (2) comparison between sectors of the mean orientation direction of all markings within a sector, (3) the composite directional data for each type of marking for the entire outcrop and (4) the orientation of all markings for the whole exposure.

TABLE I

ORIENTATION DATA OF SOLE FEATURES

(Showing number of features and mean direction for each type of sole marking in sectors of outcrop; see Fig.3) ~ ~~~

Sector valud ~~~ casts casts cmts casts casts Total Mean

no. dir. no. dir. no. dir. no. dir. no. dir. no. dir. no. dir. no. dir.

10 12" 76 12" 40 9' 17 12" 1 11" 144 11" 7 8" 85 12" 70 13" 22 8" 184 11' 6 8" 52 12" 35 9" 8 8" 1 -2" 102 10" Z

5 17" 55 19" 39 16" 10 19" 109 17" 6 7" 64 15" 33 11" 8 13" 1 33" 5 11" 117 13" 8 5" 60 12" 41 10" 13 12" 122 11" 7 13" 54 13" 36 15" 5 12" 1 17" 103 14"

11 12" 21 13" 11 16" 8 16" 1 32" 1 -1" 53 14" 2 15" 29 14" 10 5" 10 4" 51 11" 12 12" 57 14" 31 14" 25 13" 2 21" 127 14" 20 7" 102 15" 50 10" 25 9" 3 16" 200 12" 9 7" 64 14" 34 13" 27 5" 1 3" 2 -3" 137 11" 5 11" 126 16" 54 13" 24 13" 4 4" 213 15" 3 9" 70 15" 59 14" 32 4" 1 21" 165 12" 4 14" 16 9" 20 10" 9 14" 1 6" 50 11" 1 24" 8 . 13" 3 11" 1 37" 1 8" 14 14" $ 1 21" 7 13" 5 12" 3 3" 33 11" 17 9" 5 8" 1 29" 59 11" 2 17" 10 19" 2 23" 14 19" m

- Groove Bounce Prod Brush Skip Flute cusp casts casts

-

3 E fi 8

9 14" 58 13" 46 14" 15 10" 1 lo" 129 13" F

3 3 *

1 13 14" 5

1

4

Sector no.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Total 131 1,047 636 264 8 5 15 2,106

Mean dir. 10" 14" 12" 10" 21 5" 8" 13"

Sector values include total number and mean direction of all features within a sector of the outcrop. Mean directions are measured clockwise from the c! vertical grid lines of the outcrop photograph (approximate dip direction). L

212 J. H. SPOTIS AND 0. E. WESER

For variations within a sector, several sectors have too few features to obtain significant results. Scour and skip marks are not sufficiently abundant in any one sector on this level to be evaluated statistically. For the remaining sole marks, there is a high degree of preferred orientation in all sectors (Fig.2). The maximum variation in direction within any sector is in sector 15 where there is a 9" range. A study of the deviation of each mark type within a sector and between sectors indicates a remarkably consistent orientation pattern. In other words, there is no persistent deviation in average direction of any type sole marking from any of the other sole markings in any one sector or over the entire outcrop.

A comparison between sectors of the combined average orientation of all sole markings within one sector shows little variation from sector to sector. At this level of comparison, the combined average values of all sectors are statistically significant. The uniformity of these orientations is illustrated in Fig.2. The small variation in orientation pattern of all sole markings is apparently random about the flow direc-

Fig.4. Orientation of fractures, sand grains and sole features, Topanga Sandstone, Mulholland Drive outcrop; * = miscellaneous sole features: flute, skip and cusp casts.

DIRECTIONAL PROPERTIES OF A MIOCENE TURBIDITE 21 3

tion, and is not related to any consistent variation in direction of current across the outcrop face.

A study of the relationship between the orientation of different markings for the entire outcrop shows similar well-oriented patterns. At this level of comparison, skip marks are still insignificant but the scour marks provide relatively more significant data than for the sector-to-sector relationship. These data are listed in Table I and the results are plotted in Fig.4 which shows the frequency distribution of direction for each type of mark relative to a composite diagram of all marks for the entire outcrop. The shapes of the frequency polygons for groove, bounce, prod and brush marks are all similar. The flute and cusp marks indicate a slight directional deviation (6") from the composite for tool marks. It does not appear, therefore, that the current changed direction during the interval of current-marking on the sea floor. The polygon for all markings shows skewness toward the clockwise direction and this pattern is repeated for each principal type of tool mark.

Finally a summary rose diagram plotted with 5" class intervals for all sole features is illustrated in F i g 5 With reference to the dip direction the structures are mainly restricted between 5" counterclockwise to 30" clockwise, i.e., a range of 35". The mean direction is approximately 13" clockwise. The range in orientation for individual features spans 70", even though statistically the over-all pattern is very well-oriented. The strong preferred orientation indicates a fairly constant direction of current flow during the formation of the sole features; the wide angular range in individual features probably results from turbulent motion within the essentially unidirectional current.

GRAIN ORIENTATION

Dimensional grain orientation on fifteen oriented samples from the outcrop was measured to determine the relationship between sole features and depositional current direction. The angular relationship between linear sole features and orientation of long axes of sand grains in turbidity current sandstones has been reported by SPOTTS (1964). This study showed that there was a fairly consistent angular divergence between sole features and grain orientation indicating that the earlier marking phase of the current diverged by approximately 45" from a later depositional phase throughout the deposition of 100 ft. of thinly bedded Miocene sands in the Point Fennin area of the Los Angeles Basin. The abundance of linear sole features in the Mulholland outcrop offered another excellent opportunity to examine these angular relationships further.

The location of the samples examined for grain orientation is indicated in Fig.2 by the position of the center of the doubly-barbed arrows which show mean grain orientation. The samples were collected so that thin sections could be obtained stratigraphi- cally above the grooves and other sole features but still within the sand bed which contains the features. The orientation of sand grains within the casts may be affected by the micro-relief of the bottom at the time of deposition and this material was


ORIENTATION OF Y O 6 SOLE FEATURES

1 1 3 0 FRACTURES

ORIENTATION OF FRACTURES

w € N uo CLOILD

COMPOSITE GRAIN ORIENTATION

I5 SAMPLES ~ ?+I8 GRAINS

I'

91 FRACTURES

ORIENTATION OF CLOSED FRACTURES wai CWYD FRACTURES snow WILL QTYT

Fig.5. Directional features of Topanga Sandstone, Mulholland Drive outcrop, Santa Monica Moun- tains, California.


avoided for directional measurements. Thin sections were cut parallel to bedding and the orientation of the long axes of approximately 500 sand grains per section was measured. The mean grain orientation was determined by the method described by CURRAY (1956) for statistical analysis of two-dimensional directional data. In addition to grain orientation parallel to bedding planes, sand grain imbrication was measured for several samples by examining thin sections perpendicular to bedding. Imbrication sections were cut parallel to mean grain orientation in the bedding plane and normal to the bedding plane. S P O ~ (1964) and MCBRIDE (1962) have shown that maximum imbrication in turbidity current sands is parallel to grain orientation in the bedding plane. Imbrication sections were measured in the same manner as the bedding plane sections.

Grain orientation in the bedding plane is summarized in Fig.6. The orientations are plotted in the bedding plane, i.e., the resultants have not been rotated into the vertical

0 R

..A i.

APPROXIMATELY 500

B R A I N S P E R S A M P L E

Fig.6. Preferred grain orientation of fifteen samples of Topanga Sandstone. See Plate I for sample locations. Orientations plotted in plane of bedding.


plane. Mean orientations range from 8"-51" counterclockwise from the strike direction as viewed from the stratigraphic bottom; n.b., the outcrop is overturned. There is a strong clustering of resultants at approximately 40" but the asymmetrical distribution of the entire group shifts the mean grain Orientation of all the samples to approximately 35" counterclockwise from the strike.

The distribution of resultants as illustrated in Fig.2 shows a weak tendency for samples toward the left end of the outcrop to be oriented closer to the strike direction. The variations within fairly narrow limits show no specific trend across the outcrop.

The composite grain orientation (7,518 grains), i.e., a single orientation diagram constructed from all the grain orientation data for the entire outcrop, shows a mean of 36" counterclockwise from strike (Figs), which compares closely with the 35" mean for the 15 resultants for individual samples. The asymmetrical or skewed distribution of means is also shown by the composite fabric (Fig.5).

GRAIN IMBRICATION

Imbrication of sand grains, i.e., the angle of inclination between long axes of grains and the bedding plane, was determined for 6 samples. Imbrication studies were restricted to samples for which the bedding could be accurately defined (k 2-3"). Sections were cut normal to bedding, parallel to the direction of orientation in the bedding plane and the trace of the bedding plane was used as the reference direction for measurement of imbrication. Approximately 500 grains per sample were measured.

Sand grain imbrication is inclined downward in an upcurrent direction as deter-

STRATIGRAPHIC TOP

CURRENT

'r STRATISRAMIC TOP

PER BAMCLL

SCHEMATIC CROSS SECTION OF OUTCROP NOTE: Slmlo ore owrhmed

Fig.7. Imbrication of sand grains in six sections perpendicular to bedding and parallel to preferred grain orientation in bedding plane.


mined from the asymmetry of numerous sole features that indicate current sense as well as direction. The circular diagram in Fig.7 indicates the imbrication in a vertical plane with reference to stratigraphic top and structural dip. The outcrop sketch shows the present structural orientation and the imbrication attitude. Imbrication data show a mean imbrication of 14" inclined downward in an upcurrent direction with a range from -6-22" in an upcurrent direction. This imbrication attitude is the "negative angle of attack" described by RUSNAK (1957) and others as the position of maximum grain stability with respect to continuing fluid movement.

Similar imbrication results are described by SPOTTS (1964) in a detailed study of Miocene turbidity current sands near Point Fennin, in the Los Angeles Basin. Hydro- dynamic theory and the experimental results of RUSNAK (1957) and SCHWARZACHER (195 1) also indicate downward inclination in the upcurrent direction. Imbrication data from modern and ancient sediments show both types of imbrication and the com- plications appear related to grain size and size distribution and the environment of deposition or depositing medium.

ORIENTATION OF FRACTURES

Another striking feature of the outcrop is a well-developed fracture system. The major fractures are shown in the photograph (Plate I), and the outcrop sketch (Fig.2) illustrates the details of the fracture system. There are two types of fractures present in the outcrop, open and closed (see Plate III). The closed fractures are generally shorter, more numerous and show a more diffuse, branching pattern. Most closed fractures show a small amount of offset, usually less than an inch. The upthrown side of most of the closed fractures or minor faults is toward the lower right as the observer faces the outcrop. The relative movement of the upthrown blocks is considered to be toward the stratigraphic top and thus away from the observer, n.b., the strata are overturned. There are fewer open fractures; they are longer and form a simpler network. Only a few of the open fractures show a detectable offset. The open fractures are probably tensional, relatively recent in age, and are probably related to near surface adjustments during removal of overburden and erosional development of local topography. The closed fractures are apparently older and may be related to the adjustment of a sloping sea bottom to a rapidly deposited sediment load or tectonic activity.

The orientation pattern for all the fractures (Fig.5) indicates a fairly strong but bifurcated maximum and another minor maximum at approximately 90". The bifurcated maximum shows peaks at 15" and 35" counterclockwise from the strike and a Small maximum at 65" clockwise. This pattern represents a total of about 130 fractures.

The pattern for the orientation of closed fractures only is generally similar, however, it does not contain the minor maximum n o m l to the major trend. The closed fractures show the bifurcated major trend in precisely the same position as for the entire fracture system. The sketch in Fig.2 shows that the closed fractures primarily constitute one set with the major trend as outlined above. The open and apparently later


fractures show two well-developed sets, one of which coincides with the closed set and another which is in a perpendicular position that accounts for the minor maximum at 65" clockwise from the strike line. It is obvious that the sole features have had little effect on the fracture orientation because there is no tendency for fractures to follow linear sole structures either on an individual or overall statistical basis.

RELATIONSHIP OF DlRECTIONAL FEATURES

Each of the three types of directional features (sole features, fractures, and grain orientation) that have been studied show a relatively high degree of preferred orientation. A comparison of the angular relationship between the preferred directions provides some clues to the possible genetic association between the various features (Fig.4, 5). The mean grain orientation diverges from the mean sole marking orientation by approximately 45" counterclockwise. Turbidity currents can be divided into an earlier, sole marking phase and a later phase when the bulk of the sand was deposited. If the grain orientation is indeed parallel to the direction of the later phase of the current, then the earlier phase of the current flowed in a distinctly different direction. Similar results were obtained by SPOTTS (1964) for groove and flute casts and grain orientation in Miocene turbidites (Mohnian) in the southwestern part of the Los Angeles Basin. The divergence for these Mohnian schist sands was 40-50" but clockwise rather than counterclockwise (from groove to grain direction) for the strata restored to remove structural dip. It appears likely that earlier and later phases of the same current at some locations diverge possibly as a consequence of local submarine topography, however, we have not been able to work out sufficient topographic details to explain observed angular relationships precisely. Turbidity current flow is probably faster during the earlier or marking phase and the direction is more strongly controlled by inertial forces than the later, slower phase of the same current. The different phases would react differently to submarine topographic features and the slower phases might be much more susceptible to changes in direction due to submarine relief.

The divergence observed between grain orientation and sole features may also be due to a divergence between normal current circulation in the basin and turbidity currents. Under these conditions, the scour and tool marks would be cut by normal oceanic currents that prevailed at the depositional site between relatively short, sporadic periods of turbidity current activity. This might explain the divergence in directional features that persisted throughout 100 ft. of section in Miocene turbidites in the Los Angeles Basin (SPOTTS, 1964). However, it is not likely that the depressions in the fine-grained sediment that generally preceded the casts could be cut by normal currents. These currents were apparently depositing clay and silty clay between the periods of turbidite deposition. These currents apparently could not move particles large enough to have cut the grooves and other marks. The size of the tools observed and the apparent force of impact of the tools on the bottom indicate erosion by vigor- ous currents such as a dense, heavily laden, fast-flowing turbidity current.


The range of influence of Corioli's force on turbidity currents at different stages has been suggested as another possible cause of the angular relationship. The implication is that Corioli's effects would depend on the velocity, relative density, and possibly the dimensions of the turbidity current and thus might change with time. Corioli's forces may have observable effects on current directions but these are difficult to assess precisely because of our lack of knowledge concerning the three main factors listed above. Corioli's forces are not the most significant factor responsible for the divergence because the marking-phase currents at Point Fermin and Mulholland Drive outcrops were flowing in the same general direction and sense and yet subsequent depositional features diverge in opposite directions, clockwise at Point Fermin and counterclockwise at Mulholland Drive.

The fracture patterns for closed fractures and the entire fracture system show an interesting general parallelism with the preferred grain orientation. The mean fracture direction is approximately 30" counterclockwise from the present strike and the mean orientation direction is 36" in the same direction. The close angular relationship suggests a genetic relationship between the two features. Three-dimensional orientation of the sand grains suggets that directional grain orientation is a primary depositional feature of this sandstone and that it has not been greatly affected by tectonism, even though the beds are overturned. This evidence would indicate that the fracture orientation is a consequence of grain orientation. The relatively strong grain orientation in the sand produces an inherent directional "grain" or anisotropic distribution of rock strength so that fractures will tend to develop parallel to the grain orientation. The shear strength in a granular medium with preferred orientation of elongate grains is less in directions parallel to the orientation than transverse to it.

MCBRIDE and YEAKEL (1963) in a study of the relationship between parting lineation and rock fabric show that the lineations are parallel to preferred grain orientation. Parting lineation, as the term implies, are partings or microfractures with strong linear orientation that are observed on bedding surfaces. Statistical analyses of two types of sandstones, a lithic sandstone from the central Appalachians, Bald Eagle (Oswego, Upper Ordovician) and a calcarenite from the Oakville Formation (Miocene) from central Texas show parallelism of long axes of grains and parting lineation in individual beds even though parting lineations differed as much as 60" between beds. The grain fabric imposes an anisotropic strength to the sandstone bed so that the direction of partings or microfractures are strongly influenced.

The possibility that the grain orientation is a secondary or deformationzrl feature must be considered. Strata that have undergone sufficient tectonism to be steeply overturned might show some internal rotation and rearrangement on a grain-to-grain scale. Petrographic and petrofabric evidence for the Topanga Sands at this locality do not support any explanation based on grain rearrangement. If the grain rearrangement occurred in a nonlithified state, the delicate sole features would certainly have been deformed or destroyed. No evidence for significant grain fracturing or chipping, rolling or rotation was observed in thin section. The imbrication data, which agree very well for the sense of current movement, are probably the strongest evidence

220 J. H. SPOTFS A N D 0. E. WESER

against mechanical grain rearrangement. If tectonism has reoriented grains from primary depositional position to an orientation parallel with the major set of fractures, the imbrication directions would probably not be so well preserved and would not show the fairly consistent relationship to primary erosional features which we observe. The upcurrent downward inclination is predictable from hydrodynamics and has been observed in experimental studies by SCHWARZACHER (1951) and RUSNAK (1957) and in Miocene turbidites by S P O ~ (1964).

In view of strong evidence against post-depositional mechanical grain rearrangement, we conclude that preferred dimensional grain orientation imparts sufficient anisotropy in rock strength to influence the orientation of fractures. Evidence in this case is restricted to a single, thin sand bed, however, we suggest that the phenomenon may be more extensive. In areas where grain orientation is consistent throughout a considerable stratigraphic thickness, fractures that extend through several beds may be influenced by the regional or general direction of preferred grain orientation. We might expect general grain orientation to persist throughout any stratigraphic interval representing any period during which basinal configuration was perpetuated. SILVER (1961) suggested that regional persistence of sand grain orientation may account for persistence of joint orientation over larger areas such as the Colorado Plateau, but unfortunately there is insufficient petrofabric data available to support that hypothesis on a regional scale. Data presented here for a small Miocene turbidite indicate that a genetic relationship between fracturing and dimensional grain orientation is a probably valid concept.

ACKNOWLEDGEMENT

We are very grateful to F. F. Sabins and E. A. Zubak for the photographs used in this report.

REFERENCES

BIRKENMAJER, K., 1958. Oriented flowage casts and marks in Carpathian flysch and their relation to

CUMMMS, W. A., 1958. Some sedimentary structures from the Lower Keuper sandstones. Liverpool

CURRAY, J. R., 1956. The analysis of two-dimensional orientation data. J . Geol., 64 : 117-131. DZULYNSKI, S. and SANDERS, J . E., 1962. Current marks on firm mud bottoms. Trans. Conn. Acad.

DZULYNSKI, S . and SLACZKA, A., 1959. Directional structures and sedimentation of the Krosno beds

GLAESSNER, M. E., 1958. Sedimentary flow structures of bedding planes. J. Geol., 66 : 1-7. KOPSTETN, F. P. H. W., 1954. Graded Bedding ofthe Harlech Dome. Thesis, Rijksuniversiteit, Gronin-

KUENEN, PH. H., 1957. Sole markings of graded graywacke beds. J . Geol., 65 : 231-258. MCBRIDE, E. F., 1962. Flysch and associated beds of the Martinsburg Formation (Ordovician), Cen-

flute and groove casts. Acta. Geol. Polon., 8 : 117-148.

Manchester Geol. J. , 2 (1) : 37-43.

Arts Sci., 42 : 57-96.

(Carpathian flysch). Ann. SOC. GPoI. Pologne, 1958,28 (3) : 205-260.

gen, 97 pp.

tral Appalachians. J. Sediment. Petrol., 32 : 39-91.

DIRECTIONAL PROPERTIES OF A MIOCENE TURBIDITE 22 1

MCBRIDE, E. F. and YEAKEL, L. S., 1963. Relationship between parting lineation and rock fabric. J.

PEABODY, F. E., 1947. Current crescents in the Triassic Moenkopi formation. J. Sediment. Petrol.,

RADOMSKI, A., 1958. Sedimentological characteristics of the Podhale flysch. (English summary). Acta

RUCKLIN, H., 1938. Stromungsmarken im unteren Muschelkalk des Saarlandes. Senckenbergiana

RUSNAK, G. A., 1957. The orientation of sand grains under conditions of unidirectional fluid flow.

SCHWARZACHER, W., 1951. Grain orientation in sands and sandstone. J. Sediment. Petrol., 21 :

SILVER, C., 1961. Recent studies of joints. Bull. Am. Assoc. Petrol. Geologists, 45 : 681-683. SPOITS, J. H., 1962. Sand-grain orientation and imbrication in turbidity-current sandstones (Abstract).

SPOITS, J. H., 1964. Grain orientation and imbrication in Miocene turbidity current sandstones,

TEN HAAF, E., 1959. Graded Be& of the Northern Apennines. Thesis. Rijksuniversiteit, Groningen,

Sediment. Petrol., 33 : 779-782.

17 : 73-76.

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California. J. Sediment. Petrol., in press.

102 pp.

BIBLIOGRAPHY OF TURBIDITY CURRENTS AND TURBIDITES

PH. H. K U E N E N ~ ~ ~ F. L. H U M B E R T

Geological Institute, State University of Groningen, Groningen (The Netherlands)

In 1957 A. BALLY published a list of 223 references dealing with turbidity currents and their deposits. A revised list in mimeographed form was issued by the Geological Department of Groningen in 1960. Several persons kindly furnished additions.

The present list containing over 650 items does not include papers on slumping. Papers describing flysch-like rocks are only listed if the concept of turbidity flow is dealt with (whether accepted or rejected).

The authors request that omissions and additions will be brought to their notice, preferably by sending reprints, for inclusion in a later supplement.

Abbreviations of the names of journals and serial publications, are according to the system developed’by Chemical Abstracts, List of Periodicals, 1961.

ALLEMANN, F., 1956. Geologie des Fiirstentums Liechtenstein (siidwestlicher Teil) unter besonderer Beriicksichtigung des Flyschproblems. Thesis, Univ. von Bern, Bern, 244 pp.

ALLEN, J. R. L., 1960. The Mam Tor Sandstones: A “turbidite” facies of the Namurian deltas of Deibyshire, England. J. Sediment. Petrol., 30 : 193-208.

ANDERSON, T. and F L E ~ , J. S., 1903, 1908. Report on the eruptions of the Soufrikre in St. Vincent in 1902 and on a visit to Montagne Pel& in Martinique. I, 11. Phil. Trans. Roy. SOC. London, Ser. A,

A U B O ~ , J., 1955. Les couches de passage au flysch dans l’est du Pinde mbridional (synclinal de Tirna-Perliango, Thessalie, Grke). Compt. Rend. SOC. GPoI. France, 1955 : 137.

AUBOUIN, J., 1959. Granuloclassement vertical (graded bedding) et figures de courants (current marks) dans les calcaires pun: les brkhes de flanc des d o n s gkosynclinaux. Bull. SOC. GPoL France, SPr. 7 , 1 : 578-582.

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APPENDIX

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TURBIDITES

ARNOLD H. BOUMA

Geological Institute. State University, Utrecht (The Netherlands)

SUMMARY

Deposits of turbidity currents are reported from many areas all over the world, with ages varying from Precambrian to Recent. The concept of turbidites is accepted by most geologists. In spite of all the investigations carried out on this subject, a number of problems is still under discussion, for instance, the initial type of movement, the hydraulic properties of a turbidity current and its velocity and erosional power, the formation of sedimentary structures, etc.

Turbidites are not restricted to flysch, nor to a certain petrographical composition, a specific phase of an orogeny, nor to a certain age, nevertheless many turbidite series belong to a flysch unit, are pre-orogenic and built up by alternating layers of graywackes and shales. These deposits play an important role in the paleogeographic reconstruction of many areas. Some turbidite formations are important as oil bearing rocks. Continued research on ancient turbidites and on recent deep-sea sands will be necessary to obtain acceptable answers to many disputed questions.

INTRODUCTION

In this paper the author will attempt a synthesis of some of the results given in the present volume by Kuenen, Stanley and Bouma, Rizzini and Passega, KelBng, McBride, Marschalko, Ten Haaf, Plessmann, Meischner, Van Straaten , Bourcart, De Raaf, and Spotts and Weser. In the following, references will be made to papers appearing in this book as well as to works published elsewhere. Therefore, when the author’s name is not followed by a year of publication, his contribution can be found in this book.

In the past, difficulties have been encountered in the interpretation of sediments showing a rhythmic building pattern, and having coarse-grained beds alternating with fine-grained deposits. The coarse material was supposed to be deposited in shallow water and the fine sediments in deep water. It is hardly possible to accept the idea of basins repeatedly changing from shallow to deep in geologically very short times. By several steps the idea of re-deposition of sediments by a type of density current became introduced into the geological literature. BAILEY (1930,1936) described the phenomena

I

248 ARNOLD H. BOUMA

of graded bedding. DALY (1936), in his contribution about the origin of submarine canyons, mentioned the influence of density currents moving along the bottom and causing erosion; this was the reason for KUENEN (1937) to set up a series of experiments, and to connect density currents with the phenomena of graded bedding. The results of Kuenen were combined with the publications of MIGLIORINI (1943, 1944, 1949, 1950a, b) in two well-known contributions (KUENEN, 1950; KUENEN and MIGLIORINI, 1950), thus completing the introductory stage of this subject, on which only a small number of scientists were working at that time. Many investigators over- came their initial opposition and since then the number of contributions has increased rapidly (see KUENEN and HIJMBERT).

Many problems concerning turbidity currents, submarine canyons and turbidites are not yet solved. Discussions are still going on about the properties and hydraulic conditions of turbidity currents, their origin, velocities, volume, erosional power, the distances they can travel, the surfaces they can cover and the way of depositing their load. Probably such properties may vary widely due to the amount of variable factors. More-over, these are discussions whether certain deposits are turbidites or not (e.g., KINGMA, 1958; KUENEN, 1960) and which are the sedimentary properties that are indicative of turbidites (see DE RAAF; R~ZZINI and PASSEGA). Will it be possible to make a model in which all characteristics are presented and which fits all turbidites, as tried by BOUMA (1 962, pp.48-54) ?

The present author’s opinion is that all the contributions in this volume will help to direct further research. The references given by KUENEN and HUMBERT certainly over- come the difficulties of gathering enough information about papers published.

METHODS

Much work has been done already on ancient turbidites, for example on current directions, sedimentary structures, fossil content, grain size distributions, sand/clay ratios and petrographical analyses. Excellent contributions exist (see KUENEN and HUMBERT) on these points, as well as on the forming of sedimentary structures and on the paleogeography of many parts of the world. Research will continue, more data will be obtained and other interpretations will be given.

But more detailed observations require many data, and the comparison of groups of properties becomes time-consuming. Data can be represented in a descriptive way, or reduced to formulas (BIRKENMAJER, 1959), or graphs (DOEGLAS, 1959; BOUMA and NOTA, 1961; BOUMA, 1962; VAN DER LINDEN, 1963), or by a combination of these methods. The graphical representation is a very useful method but may take too much time for long sections. Especially in large areas or in regions where several types of sediment belong to a single group (for example in flysch series), the investigator may obtain too many data for easy handling. Depending on the type of work several methods can be used. One is the facies model as introduced by POTTER (1959) and developed for turbidites by BOUMA (1962). This idea is also used by STANLEY (1963)

TURBIDITES 249

for the Grts d’Annot and by MEISCHNER (p. 160) for his allodapic limestones. Another method is the computer programme. Field and laboratory data have to be transferred into machine codes; once this is done the computer takes over the time-consuming parts such as selections, sequencing, grouping, etc. Data collected by STANLEY (1961) were later translated into an IBM computer programme to verify the method. Stanley found that a considerable amount of time can be saved by using such a programme.

Differences and variations within the depositional history of flysch series in one area can sometimes be made apparent by granulometric analyses, especially by pre- senting these data in a CM diagram (RIZZINI and PASSEGA). However, most of the methods known have still to be verified on different localities, containing turbidites, fluxoturbidites and non-turbidites, before their real value can be fully understood.

STRATIGRAPHY, PETROLOGY AND SEDIMENTARY STRUCTURES

Turbidites are not restricted to one stratigraphical age. They are known from Precam- brian to Recent (see KUENEN, pp. 17-18). KELLING reports Precambrian and Paleozoic turbidites from Britain, MCBRIDE from various stratigraphical units between Pre- cambrian and Pliocene for the United States, while VAN STRAATEN describes a Recent one from the Adriatic.

KUENEN erglains that component minerals, grain size distribution and fabric are no positive criteria, but that the term “turbidite formation” is purely genetic and invokes a specific transport and deposition mechanism. Some turbidite formations consist of alternating arenaceous to pelitic material and pelagic sediments. Sometimes both contain fossils (e.g., NATLAND and KUENEN, 1951), while others are nearly sterile. Also, series are known without positively identifiable pelagic deposits (BOUMA, 1962). The gravel, sand, silt and clay content may vary within an area, or from area to area, without changing the turbiditic character. Some calcareous turbidites are known (KuE” and TEN HAAF, 1956; TEN HAAF, 1959; MEISCHNER, 1962, t h i s volume). MEISCHNER uses a number of criteria to designate his allodapic limestones as turbidites, and they are more or less the same as were used by other authors to determine non-calcareous formations as turbidites. Meischner uses the type of sequence, characteristics of the ideal bed, graded bedding, the absence of shallow-water features, the pelagic intercalations in between non-pelagic detrital limestones, and the presence of some sole markings like flute and groove casts. PLESSMANN reports turbidites with different petrographical aspects, from one geosynclinal basin.

The many sedimentary structures, known from turbidites, are not absolutely decisive (see e.g., KUENEN; KELLING; DE RAAF; SPOTTS and WESER), because many of them are also reported from non-turbidites. To which extent such structures are really the same or may have minor, but characteristic, differences is not yet known. More detailed work will be necessary and other methods, like radiography (HAMBLIN, 1962; CALVERT and VEEVERS, 1963; BOUMA, 1963), might be useful to gather the required information.

250 ARNOLD H. BOUMA

Relative succession of a number of sedimentary properties, as presented in the turbidite facies model, the absence of shallow water structures (KUENEN, pp. 19-20), the rhythmic appearance of detrital material with normally a more or less pronounced graded bedding, together with the occurrence of some typical sole markings and some other layer structures such as clay pebbles and convolute lamination, may become the best indicators to determine if a deposit consists of turbidites.

DEEP-SEA SANDS AND TURBIDITES, SUBMARINE CANYONS

The similarity between deep-sea sands and turbidites was noted long ago (see KUENEN and references given on pp.5-7; BOURCART), but not well proven. VAN STRAATEN reports convolute lamination observed in a core collected in the Adriitic.

The present author collected oriented rectangular samples in some submarine canyons off southern California and off the southern tip of Baja California, Mexico (BOUMA and SHEPARD, 1964). The samples obtained from the axes of the canyons commonly present a rhythmic succession of coarse sand or gravelly sand and pelites. The most common sedimentary structures are parallel lamination, current ripple lamination, minor scour and fill structures, animal burrows, locally graded bedding in thin layers (up to 5 cm), internal load casts and slump structures. Most of these structures have been described by MOORE and SCRUTON (1957) and by GORSLINE and EMERY (1959). In spite of the presence of some sedimentary structures known from turbidites, the characteristic succession of the intervals of the turbidite facies model has not been reported. The single occurrence of one interval of the facies model is not common in ancient turbidites. From this the conclusio? can be drawn that the presence of some of the above-mentioned sedimentary structures does not represent a true interval of the model.

Laterally from the canyon axes, the sediments are mostly clayey and locally contain thin sandy or silty beds. Sedimentary structures are normally not visible by eye, but radiographs show mainly burrows and slump structures.

The present writer collected only one sample from a small channel in the outer fan of the La Jolla canyon off southern California, at a depth of 562 fathoms (1,029 m). This sample is sandy at the bottom and grades upward into pelite; graded bedding is just visible. A radiograph shows the lower three intervals of the complete turbidite facies model. The upper two intervals of the model were present in the sample, but were lost (Fig.1).

Information obtained from samples collected by means of gravity and piston cores in submarine canyons and adjacent troughs (e.g., ERICSON et al., 1952; EWING et al., 1958; GORSLINE and EMERY, 1959; EMERY, 1960; SHEPARD, 1961; SHEPARD and EINSELE, 1962), together with the two above-mentioned samples, may prove the existence of recent turbidites.

The relation with submarine canyons is not yet completely understood. Observa- tions in canyon heads (e.g., DILL, 1964) indicate that turbidity currents do not start at

TU

RB

IDIT

ES

251 E Fig.1. Radiograph of a Recent turbidite, collected from a channel in the outer fan of La Jolla Canyon off southern California, at a depth of 562 fathoms (1,029 m). Only the lower three intervals of the turbidite facies model as given by BOUMA (1962, fig.8) are present. The upper two intervals were lost during removal of the sample from the sampler. The re-worked pelite on top is due to re-deposition because of wrong handling

during storage of the sample. The three white spots on the photograph represeiit clay pebbles.

,-

252 ARNOLD H. BOUMA

shallow depths (< 85 m). Dill measured sediment movements, even fast ones, and Wing and emptying of parts of the canyon heads. Strong earthquakes do not have influence on these processes (Dill, personal communication, 1963).

From all this the conclusion may be drawn that Recent turbidity currents will initiate in the “shallower” parts of the submarine canyons where sufficiently steep slopes provide enough energy to start a turbidity current. The data available at the present time make it probable that their deposits can only be found where the bottom slope is nearly absent, as on the outer parts of submarine canyon fans and in the adjacent troughs.

Material not transported by a real turbidity current and presumably deposited on the higher parts of the submarine fan may form the so-called fluxoturbidites (Dzu- LYNSKJ et al., 1959) or undaturbidites (RIZZINI et PASSEGA, p.71-72).

FLYSCH VERSUS TURBIDITES

In a foregoing paragraph it is already indicated that turbidites are not restricted to a certain stratigraphic interval and that certain petrological compositions or sedimentary characteristics are not necessary.

The majority of ancient turbidites are encountered in flysch or flysch-like formations, and are part of geosynclinal sediments, which do not make the terms flysch and turbidites synonymous. KUENEN (p. 17) states that the term “turbidite formation”, which is purely sedimentological and invokes a specific mechanism, cannot be equated with any definition of “flysch”.’

Some of the contributing authors to this volume (STANLEY and BOUMA; RIZZINI and PASSEGA; MARSCHALKO; TEN HAAF) use the term flysch in the title of their paper. They describe not only the turbidites of a certain area, but more the whole complex of sediments in a flysch formation, of which the turbidites form a part. Some of the mentioned investigators also describe other flysch units as wild flysch, exotic flysch, etc.

PALEOGEOGRAPHY

Many geologists are using turbidites in flysch series, for obtaining data on paleogeography, post-depositional processes such as sliding, or basin conditions.

One of the problems is the directional relationship between source area and the deposits of turbidity currents. Did this transport occur in a longitudinal direction or in a transverse direction, compared with the shape of the basin (KUENEN, 1957b; ULLING; MCBRIDE; MARSCHALKO; TEN HAAF) ? Sole markings only indicate the local direction of transport of the turbidity currents. Fluxoturbidites often do not show sedimentary properties from which current directions can be obtained. Even if a longitudinal direction has been measured on several structures, a transverse supply cannot be

TURBIDITES 253

excluded, because sediments transported by a turbidity current and coming from the side will move into the direction of the main axis of the basin. Petrological investigations may give a solution to such a problem. Practically all turbidites known are deposited in the marine environment, but in fresh water environments like Lake Mead (GOULD, 1951) and Lake Geneva identical transport possibilities are known to occur.

For the Alpes Maritimes in France (KUENEN et al., 1957b; STANLEY, 1961; BOUMA, 1962; STANLEY and BOUMA, fig.14) a transverse filling of the basin seems more likely than a longitudinal one. However, the present author found, for the area south of the Argentera-Mercantour massif, that this east-west trending part of the basin can be divided intc depressions elongated north-south. In each depression the turbidity currents moved in a longitudinal direction, form a source area in the south.

Two contributions of this volume (STANLEY and BOIJMA; BOURCART) give a nice example of relief reversal during time. In late Eocene time turbidity currents obtained their load from the Maures-Esterel-Tyrrhenide chain and deposited it in a northern direction into the area south of the Argentera-Mercantour massif. This source area is partly submerged now into the Mediterranean. At the present time (BOURCART), these turbidites and other sediments from the east part of the French Alpes Maritimes, together with crystalline rocks of the Argentera-Mercantour massif, form the source area for turbidity currents running in a southerly direction and depositing their load in the Mediterranean.

Paleogeographical investigations like the ones given in this volume can be of economical value, especially when turbidite series are oil bearing (MCBRIDE, p. 103).

CONCLUSIONS ’

Of all sediments known the turbidites form an important group. Turbidites are found throughout the whole stratigraphic record fossil as well as recent (VAN STRAATEN; BOURCART). They are not synonymous to flysch, in spite of often being part of flysch and flysch-like deposits in geosynclines; they can vary in mineralogical composition although the majority are graywackes and some are limestones (MPISCHNER), but they are characterized by a certain transport and deposition mechanism. Sediments comparable to turbidites may also be deposited in a “shallow” basin. On the other hand sediments are known which present a number of “turbidite” properties without being turbidites (KUENEN, pp.18-20; DE RAAF). Part of this last-mentioned group may be called fluxoturbidites and undaturbidites (RIZZINI et PASSEGA). The lack of shallow- water characteristics (KUENEN; KELLING) and the conformity to a turbidite facies model (BOUMA, 1962; STANLEY, 1963; MEISCHNER), together with other properties recognized from turbidites, may give enough information to determine a sediment as a deposit from turbidity currents. If turbidites form part of geosynclinal sediments, the geosyncline is not only filled by shallow water deposits (MCBRIDE, p. 103).

As mentioned, turbidites are often part of geosynclinal sediments. For paleogeographic and tectodc reconstructions they may be of great help. TEN HAAF was able to

254 ARNOLD H. BOUMA

distinguish two differential processes in the flysch series of the northern Apennines, both due to gravity influences - longitudinal re-sedimentation and transversal sliding. PLESSMANN mentions four types of turbidites, based on differences in petrography, that played a part in the development of the geosyncline east of the river Rhine. MCBRIDE describes two depositional basin types for the United States in which turbidity currents have deposited their load -the linear Appalachian and Ouachita geosynclines and the small steep-walled basins of California. MARSCHALKO points out the importance of sedimentological studies in the Central-Carpathian flysch because it has not been affected by strong folding. This enables him to make detailed studies of the source area and its relationship ro the adjacent flysch deposits. For this area he describes the longitudinal filling from one side by turbidity currents and the submarine slides (wild flysch) along the steepest slopes, transverse to the main axis of the basin.

A unique outcrop in the Topanga Formation in California is described by SPOTTS and WESER, in which they observed seven types of tool and scour markings. Based on many measurements, they found that grain orientation is not parallel to the orientation obtained from linear sole features. A parallelism between sand grain orientation and the major fracture set suggests a genetic relationship.

In this volume some new terms are introduced (RIZZINI and PASSEGA; SPOTTS and WESER). More uniformity in the nomenclature would seem desirable, and can be pro- moted by reviews of certain aspects of turbidites and associated formations all over the world, such as DZULYNSKI and WALTON (in preparation) on the sedimentary structures associated with flysch and graywackes.

Methodology and paleogeography in flysch units are important as a combination as more and more sediments in the geological record are found to exhibit typical flysch characteristics (STANLEY and BOUMA). This is shown also by RIZZINI and PASSEGA who distinguish three orogenetic .phases, to which the sedimentation of the Marnoso- Arenacea basin is related, by using the granulometric characteristics presented in CM diagrams to find different basin conditions.

Though some problems are still under discussion, the study of turbidites has already led to useful applications in various kinds of geological investigation. The variety of the contributions in the present volume will help to show some of the directions in which this new field of research is so rapidly expanding.

ACKNOWLEDGEMENTS

The author wants to express his gratitude to Dr. E. ten Haaf for critically reading this manuscript.

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TURBlDlTES 255

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256 ARNOLD H. BOUMA

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NOTE ADDED IN PROOF

In connection with the data about the facies model (section Methods), recently E. Mutti (Milan, Italy) kindly provided me with a paper by SIGNORINI (1936). In this publication, the Italian author had already described the five sedimentary intervals of the turbidite facies model, types of bedding contacts, and the break in grain size.

I N D E X

Aberystwyth, 15,86,88 - Grits, 80 Abyssal, 192 -depths, 18 - floor, 6 -plain, 5, 6, 7, 8, 10, 11, 12, 13, 17,22, 23, 24,

Adriatic, 1 I , 14, 142, 143, 249,250 Afon Camddwr, Rhayader, Wales, 82,84,86 Alberese, 129, 131, 132 Algae, 7 Allochton, 127,129,130,131 Allodapic limestones, 156, 157, 158, 159, 161,

162, 165, 168, 170, 171, 173, 174, 175, 177, 178,182,184,186,187,188,190,249

25, 142, 148, 152, 154

Alpine flysch, 29 - geosyncline, 16 Alternances de Castel del Rio, 66, 69, 71 Annot sandstone, 35,47,49, 51,52,53, 54, 55,

Apennines, 13,15,28,65,127,130,134,254 Aphanitic limestones, 20 Appalachian Mountains, 94, 95, 100, 102, 254 Apron, 86, 87 Aragon River, 193 Archean granite of Natal, 16 Archipelagic aprons, 5 Arenaria superiori, 129,132,133,134 Arenigian greywackes, 79 Argentera-Merantour massif, 52, 53, 54, 55,

Argiles de Tossignano, 68,71,72,73 Argillescagliose, 129,131, 132, 134 Arkansas, 98, 100, 102 Arpe, 163 Autochton, 127, 129,130,131,133.157 Axial facies, 79 -transport, 88

58, 59, 62

149, 152,253

Baie des Anges, 149, 150, 154, 155 3aja California, Mexico, 250 Bala graywackes, 76 Bala-Valentian, 86,87,89 Banffshire Coast, northeastern Scotland, 77 Banyuls, 151 Barrot Dome, 53,54 Basal transgressive lithofacies, 110, 11 1, 114,

Basin conditions, 252 - floor, 101 Basins, 5 - of California, 91,96, 103

123

Basins ( c h i m e d ) -off Southern California, 5, 12,14,29 Basses Alpes, 26 Bathyal, 4,15,22,26,192, 197,198 - depths, 18,20 Bathymetry, 52,85,90, 181 Beach, 11, 13,23,27 - deposits, 22 -structures, 16 Beisinghausen, 163 Belemnites, 171 Benthonic fauna, 13,143 - Foraminifera, 13,14,15 Benthos, 156, 169, 171, 178,184 Berleburg, 138, 139 Benvyns-Bala arch, 86 Bio-facies, 156, 169 Biohems, 22 Bio-sounder, 26 Biostromes, 16, 22 Biozones, 14 Bird tracks, 18.26, 195,197 Biscay plain, 6 Black shales, 85,86,90 Blown sand, 21 Bluemud, 12 Borderland, 89 Bordighiera, 149 Bottom fauna, 7 Bounce casts, 16,199,204,207,208,211 -marks, 208,210,213 Brachiopods, 139,161,169,180 Brackish, 21 Branisko massif, 107, 108 '

Bray Series south of Dublin, 15 Break in grain size, 81 Brecciola, 130, 135 Brilon, 177, 180 British Columbia, 6 Brush casts, 199,208,209,211 -marks, 208,210,213 Bryozoa, 161 Bundnerschiefer, 16 Burrowing organisms, 7 Burrows, 15,16,21,27,138,143,162,195,250

CaCO,, 7,146,162 Caledonian geosyncline, 79 - orogen, 76, 88 Caledonoid trend, 76 California, 100,101, 199,207,250,251,254 Camargue, 152

258 INDEX

Cambrian, 15, 76,77,78,80 Canada, 96 Canyon axis, 250 -heads, 23, 250, 252 Cap Corse, 149 - d’Antibes, 150 - Ferrat, 150 Capitan-Reef, 187 Caradocian, 79, 87, 88 - succession, 79 Carboniferous, 15, 77, 79, 100, 137, 139, 140,

Cardigan coast, western Wales, 77 Central-Carpathian, 106, 108,254 Central Murrisk, Mayo, western Ireland, 77 - Stable Region, 102 Cephalopods, 180 Chalcedon, 162 Channel fills, 22 Channels, 114, 118,119,154,165,209,250,251 Channel scour, 21 Charcoal, 208 Chminianske Jakuboviany, 119 Cierna Hora Mountains, 107, 108, 110, 111,

Clastic limestones, 156 Clay pebbles, 160,188,250,251 Claystone lithofacies, 110, 11 1, 112 Climat changement, 170 Climatic fluctuations, 7 -rhythm, 3,26,27 Closed fractures, 199, 202, 203, 207, 214, 217,

CM-diagrams, 65,69, 71,73,249, 254 COP, 169, 180 Coastal environments, 3 Code, 39,41,249 Colonsay and Islay, Inner Hebrides, Scotland,

Computer, 36,39,51,63,249 Conglomerate beds, 103 Conglomeratic flysch, 108, 110, 112, 113, 114,

Congo River, 18 Conodonts, 171 Continental Borderland, 103 -rise, 148 -shelf, 23, 101, 148, 150, 151

-terrace, 6, 123, 124 contorted slump, 21 convolute bedding, 156, 159 - lamination, 11,14, 16, 21, 27,47, 66, 71, 76.

Coral limestone, 177 Corals, 139, 161, 186 Cordillera, 89, 90

157,163, 171, 182, 187

115,116,119,121.122

219

77

115,118,119,121, 122, 123, 124

- s I o ~ ~ , 8, 148, 149, 150, 151

79,81,117,146,160,162,172,184,250

Cores, 152, 154 Corioli’s force, 219 Cornwall, 87 Corse, 152 County Clare, central Ireland, 77 - Dublin, Ireland, 77 Creep, 3, 5,9, 18,23,24 Cretaceous, 102, 131, 132, 133 Crevasse deposits, 196 Cross bedding, 22,47, 1 1 1,200 Culm, 2,81 Current bedding, 21, 118 -direction, 53, 76, 78, 80, 118, 121, 122, 151,

210 -ripple laminations, I I , 16, 21, 156, 159, 160,

172,250 -_ structure, 23 - -rose diagram, 121 -velocity, 166, 168 Cusp casts, 199,207,210,21 I - marks, 21 3 Cycle, 28 Cyclothems, 20 Czechoslovakia. 187

Dakota Muddy Formations, 102 Dalradian, 77,78,87 Data cards, 39,41,42,43,45,48 Deep-benthonic organisms, 7 Deep-sea floor, 5, 8, 22, 24 -sands, 2,3,4,6,7,8,9, 10, 11, 14, 15, 19,23,

-trenches, 5 - troughs, 6 Deep-water fauna, 15 - shale, 14 deformational structures, 79 Delaware Basin, 94,96 - Mountain, 62 Delta, 21,24,29 Deltaic environments, 3, 198 Denbigshire-Montgomeryshire, northern

Wales, 77,88 Density, 25,26 Denundation, 133 Depositional slope, 124 Derbyshke, northern England, 77 Desiccation cracks, 21 Detrital limestones, 156,159,160, 173,249 Deviation, 101,212 Devilsbit Mountain, central Ireland, 77 Devon, 79, 81, 87 -and Cornwall, southwestern England, 77 Devonian, 15, 102, 138, 139, 140, 157, 163, 171,

177,183,186,187 Diagenesis, 161, 162

24,25,29,30, 146, 148, 149,247,250

INDEX 259

Diapirism, 131 Dielectric anisotropy, 101 Directional features, 214, 218 - properties, 43 -structures, 100 Diving saucer, 148,149,152,155 Dodona, 163 Drag marks, 21,118,165 Dune deposits, 22 - structures, 16 Durance, 152

Earthquake, 8,18,24,27,252 Eastern Liguria, 127,131, 132 Ebro basin, 198 Echinoids, 161 Elongate pebbles, 47,48 Emilia, 127 Emilian, 131, 134 Emsian, 138 Environment, 157,193,196,197,253 Eocene, 49, 52, 55, 56, 58, 61, 101, 107, 108,

112,122,130,132,133,134,193,196,253 Epiros, 186 Erosion, 166,168 Esterel Massif, 53,54 Esterel-Thyrrenide chain, 55 Eugeosynclines, 2 Euxinic phase, 87 - sediments, 87 Euxinic-volcanic suite, 87 Evaporitic conditions, 192, 196 Exotic blocks, 68,72

Experiments, 4,25, 165 - flyKh, 131,132,252

Fabric, 48,49 Facies, 50,169 - model (ideal bed), 248,250,251,253 Fan (submarine fan), 251,252 Fauna, 152 Figtree Series, 16 Fish bones, 208 Flank supply, 90 Flinz-facies, 177, 178 Flood plain, 21 Flow casts, 84 Flute casts, 15, 16,21,47,66,68,71,72,76,79,

80, 82, 83, 114, 118, 156, 164, 165, 172, 192, 194,195,199,204,209,211,218,249

- erosion. 82 - marks, 21 3 Fluvio-marine turbidites, 18 Fluxo-turbidites, 13,21,61,71,72,85,124,249,

252, 253

Flvsch il helminthoides. 129.132 F&ch-like,l, 2, 4, 17; 18, 19, 21, 26, 27, 29,

62,252.253 Flykhoid, 13 1 Foraminifera, 11, 14, 15, 26, 29, 103, 108, 116,

Foreset beds, 16,22 - lamination, 47 Fractures, 199, 207, 212, 214, 217, 218. 219,

130, 146,148,151,161,171

220,254

Galestrini, 132,133 Gedinnian, 138 Genoa, 127,132 Geochemical study, 101 Geometry, 156 Georgia, 95 Geosynclinal axis, 79 - basin, 19,76,88 - sediments, 34,76,89 -trench, 3 Geosyncline, 75,88,90,100 Germany, 15 GiNan district. 79,88 -, southwestern Scotland, 77,85 Givetian, 138,139,140 Glacial varves, 27,28 Glauconite, 29,30 Globigerina ooze, 12,24 Golfe de Genes, 152,154 - du Lion, 152,154 Goniatites, 171,182,184,186,198 Graded bedding, 9,10,13,16,21,27,29,30,34,

47, 50, 51,61,66,68,71,79,81,82, 111, 112, 113, 114, 115, 117, 121, 123, 139, 146, 156, 160, 164, 167, 172, 178, 184, 188, 192, 193, 195,196,197,198,207,248,249,250

Grain lineations, 118 -orientation, 101,199, 200, 202,203,213,214,

-size, 3, 101 Grand Banks, 26 -- earthquake, 8, 12 - R h h e , 151 Gran Sasso, 130 Granulometry, 48,49 graphic presentation, 37, 39,248 Graptolite stipes, 81 Graptolitic black shale, 86,87 Gravitational sliding, 127, 134 Gravity, 6,85 - core, 250 Graywackes, 4,79,86,89,90 Greece, 157,186,187 Grh il ripple-marks, 192, 193, 194, 197 - d’Annot, 15,249

215,216,218,219,220,254

260 INDEX

Groove casts, 15, 16,47,48, 66, 80, 156, 164,

-marks, 210,213 Gulf of Mexico, 6, 12 Gullies, 151 Gypsum, 73,193,197 Gyttja, 180

172,195, 199,204,208,211,218,249

Hagen, 163,182 Hapalotectonic phase, 127 Harlech Dome, northern Wales, 15,77,78,80 Heavy minerals, 54,68,72 Hellenicflysch, 157, 186, 187 Hemi-pelagic, 14, 16 Herdringen, 163,182, 184 Horizontal grading, 156, 164 Hudson sub-sea fan, 10 Hydraulic conditions, 248

Iberia plain, 6 IBM computer programme, 249 Ideal bed (facies model), 159, 162, 164, 181,

182,249 Imbrication, 101, 156, 159, 160, 165, 204, 215,

216,217,219,220 Impact casts, 165 Impacting tools, 204 Impact marks, 118,208 Individual layer, 160 Inorganic matter, 11 Intermediate flysch, 110, 117, 118,119 Internal load casts, 250 Intracratonic units, 198 Ireland, 80,87 Irish Sea, 89 Irregular bedding, 113, 117, 121, 123, 124 Isle of Man, 76 Jsolated hills, 6

Jurassic, 132, 163,184

Kentucky, 99 Killary Harbour, western Ireland, 77 Kilmory Bay, 78 Kirkcolm Group, 79,80 Kirkcudbrightshire, southwestern Scotland, 77,

78,79 Klenov, 124 Klenov-KvaEany-Such& D o h a , 1 13 Koblenz, 177 Konklisi, 186 Krifna, 11 5 Krosno Beds, 15

KvaEany, 119

Laasphe, 139 Lagoon, 21 Laingsburg, South Africa, 28 La Jolla canyon, 250,251 Lake Bonneville, Utah, 94 Lake District, northwestern England, 77,88 - Geneva, 6,253 --Mead, 94,253 Larnellibranchiata, 169,180 Lamination, 9,11,24,27,29,172 Lanarkshire, mid Scotland, 77 Large rock fragments grains, 208 La Roya, 149,150 - Spezia, 127, 133,149 Lateral, 86 - derivation, 89 -filling, 119,121 - slopes, 8 1 - supply, 79,88, 130 Lenticular body, 156 Letmathe, 163, 182,184 Levee, 8 Leveed channels, 5 Liedena, 193,194,195,196,197 -Beds, 196,198 Limestone-turbidites, 137, 139, 140 Linear sole features, 199,200,213,254 Lineation patterns, 47 Liquefaction, 3,9. 18,24 Littoral features, 3 Llandoverian, 77 Llano uplift, 94,102 Lleyn peninsula, northern Wales, 77 Loadcasts, 14,66,71, 118, 121, 188 Loch Awe, western Scottish Highlands, 77, 78 Long axes of pebbles, 119 Longitudinal filling, 84,119,121,122 - resedimentation, 134 - ripples, 154

-transport, 76, 79, 87, 89, 90, 102, 130, 252,

Los Angeles Basin, 14,15,62,203,213,218 Lower Ecca Sandstones, 28 Ludlovian, 77,88,89 Lutite, 86

- supply, 79,88,130

253,254

- balls, 159

Machine processing, 36 Macigno, 15, 129, 130, 132,133,134,192 Magdalena River, 18 Malrn, 157,164,171,184 Manganese, 148,154

INDEX 261

Marathon Basin, 94,102,103 Marginal, 86 - facies, 79 - lithofacies, 106,107,108, 110,119,122 - slope, 84,85 Marine currents, 3,25,26,29 Maritime Alps, 34,35,52,132,253 Marl, 161,172,193 Marnoso-Arenacea, 15,28,71,72,73, 130, 131,

_- formation, 65,66,129 Maures-Esterel-Tyrrhenide chain, 253 Maryland, 95 Massachusetts, 98 Matrix, 169 M. Cimone, 13 1 Medebach, 163 Mediterranean, 6,58,148,149,154,253 Megaripples, 16,21 Mesomicum, 16,110,133 Methodology, 34,62,248,254 Microconglomeratic flysch, 110,112,113,119 Microfauna, 192 Micro fossils, 48,49,50 Microlayers, 82 Microseisms, 23,24 Mineralogical composition, 48,49 Mineralogy, 101 Minorque, 154 Miocene,28,65,107,119,127,130,131,134,152, 198, 199, 201, 207, 213, 217, 218, 219, 220

Mississippian, 102 Mixed bedding, 1 13 MoEidlany, 118 Mohnian, 218 Molluscs, 161 Mollusk fragments, 208 Monghidoro Sandstone, 132 mud pebbles, 14 Mulholland Drive, 199,200,201,202,207,210, 212,214,219

Murrisk, County Mayo, 79 Miischede, 182

134,254

Namurian, 77,87,140,198 Narbonne, 152 Navarra, 192,194 Near-shore sediments, 89 Necton, 156,159,169,171 Neritic, 3,7,22 -limestone, 193 Nevada, 99,110 New Castle-Muddy Formations, 102 -Jersey, 96 - Mexico, 96,100, 187 - York, 95,96,102

Nice, 149,150,152,154 Non-flysch, 54,55,56,58 Non-marine deposits, 94 Nokturbidite, 249 Normal currents, 9 North American continent, 5 Nova Scotia, Canada, 99 Nummulites, 186, 197 Nusplingen, 184,186 Nuttlar, 163

0 2 , 169, 170 Ocean floor, 8 Ocean-floor topography, 5 Oceanic currents, 218 Ohio, 99 Oklahoma, 97,98,100,102 Oligocene, 13, 52, 55, 56, 107, 108, 122, 127,

Ondragovce, 119 Ooids, 156, 161 Open fractures, 199,202,203,207,214,217 Ophiolites, 129, 131 Ordovician, 15, 76, 77, 80, 81, 85, 86, 87, 88,

Organic hieroglyphs, 15 -matter, 169 - remains, 3 Orientation, 210,211,212,213,214,217 Orogenetic phase, 65,73,247 Orthogeosynclines, 197,198 Ouachita foldbelt, 94,97, 102 - Mountains, 94,100,254 OvEie, 121 Oversteepening of depositional slopes, 18

130,133,192,193,194,195,196,197

102

Palaeoapennine, 127,130,131, 132,134 Paleobasin, 50 Paleocurrent, 41,43,51,100,102 - maps, 36 Paleoecologic studies, 73, 103 Paleogeography, 4,43,50,53,55,58,62,63,75, 102,157,175,200,203,248,252,253,254

Paleoslope, 35,44,52,61 Paleozoic, 15,19,76,78,88,100,249 Paillon, 150, 151, 154 Pamplona, 193 Paralic features, 3 Parallel lamination, 146,160,250 Parting lineation, 100 Peeblesshire, southeastern Scotland, 77, 80 Peka Cava flysch, I92 Pelagic, 62, 85, 103, 111, 116, 142, 143, 156,

- clay, 12 157, 174, 249

262 INDEX

Pelagic (continued) - deposit, 7, 87 - fauna, 13 - sediment, 6,8,11,20,22,24,50 Pelite, 156, 159, 161, 165, 166, 170, 178, 187,

Peloponnes, 186, 187 Pennsylvania, 95 Pennsylvanian, 102 Permian, 28, 150,152, 187 -Reef Complex, 100 Perthshire, Scottish Highlands, 77 Picene flysch, 15,130,134,135 Pietraforte, 131, 132 Piston core, 149,250 Plancton, 156, 159, 169, 171 Plant remains, 7,8, 11, 14,21, 159, 167 - remnants lineations, 118 Pleistocene, 94 Pliocene, 14,15,29, 100,150, 151, 152,249 Po Basin, 198 Point Fermin area, 213, 217,219 Polish flysch, 26 Port Vendres, 152 Posidonian limestone, 182, 183, 188 Postorogenic phase, 65,72,73 -units, 197 Po Valley, 127, 130 Precambrian, 15,19,88,100,247,249 Precipitation, 3, 20 Preorogenic phase, 65,71,73 Pre-paroxismal, 19,34 Pretoria Series, 16 Prod casts, 15,16,199,204,207,208,209,211 -marks, 208,209,210,213 Pseudomorphs after salt crystals, 192, 195, 196,

Pteropod, 11, 148 Puerto Rico Trough, 12 Pull-apart structures, 14, 114, 116, 117, 122,

Punch cards, 36 Pyrenees, 18, 152

188,193,195,196,250,251

197

1 24

Quartz, 30, 146, 161, 162 Quicksand, 24

Radiocarbon dating, 13 Radiography, 249,250,251 Radiolarian cherts, 87 Radnorshire, Wales, 77 Rain pits, 16 Random sampling, 48 Ratios, 51, 53, 108 Recent, 247,249,25 1,252

Rechtsrheinische Geosynkline, 137, 138, 177 Recristallisation, 162 Red clay, 7, 12 Reef-dwellers, 156 Reefs, 16,139,156,169,171,173,174,175, 177,

Repeated grading, 10 Resedimentation, 127, 130, 131, 133, 134, 135,

Reworked fossils, 7 Reworking, 7,62,81,130,184 Rheinisches Schiefergebirge, 138,178,182,184,

Rhena, 163 Rhenish geosyncline, 157 Rhinns of Galloway, southwestern Scotland,

77, 79, 80, 86 R h h e delta, 6, 18 Ridge, 6 Ripple lamination, 9, 16, 146 -marks, 76,80,81,83, 197 River deposits, 16

Rock fragments, 11 5 Romagna, 127 Roots, 21 -in situ, 16 Roiikoviany, 119 Roundness, 161 Rudites, 86, 87

178,180,182,183,186

184,254

188

- flood, 24

Sables de Fontanelice, 66,68,71,72 Saline lagoonal deposits, 193 Salopian, 77, 88 - rocks, 80 Salt pseudomorphs, 16,197 Sand/clay ratio, 68,72,248 Sand dikes, 14 San Diego Trough, 62 Sand grain, 203 Santa Monica Mountains, California, 199,201,

Santerno river, 65,66,67,71,72,73 Sapropel, 180 Sardaigne, 152 Sarigske Hory Mountains, 107 Scaglia, 130, 131, 133 -cinerea, 129, 130 Scisti galestrini, 129, 131, 132 - policromi, 133 Scotland, 76, 81, 87, 89 Scottish Highlands, 87 -trough, 86 Scour and fill, 66,71,250 -marks, 86, 199,207,209,210,212,213.218,

202,204,207,214

254

INDEX 263

Seaweed, 208 Sedimentation balance, 23 Seiches, 9 Seismic prospecting, 22 Self-sustaining, 25 Sequence, 162,192 Shale pebble, 21 Shallow-neritic depths, 20 Shallow water, 26,29,156, 193,247 Shallow-water benthonic Foraminifera, 7,8,12 - features, 3, 12,249,253 - graywackes, 26 - neritic fauna, 16 - turbidites, 16 Sheet floods, 3,18,26,196 Shelf, 29,140, 177,182, 186 - deposits, 22,50 - -edge sediments, 89 Shells, 7 Siegenian, 138 Sigsbee abyssal plain, 12 Silicified parts, 159 Silt, 14,15,173,180, 182 Silurian, 15,76,77,78,79,80,87,88,89 Skip casts, 199,204,209,211 -marks, 209,212,213 Slide, 44, 50, 61, 118, 124, 157, 180, 184, 252,

-bodies, 116, 119, 123 - -conglomerates, 79,86,88 Sliding, 4,21,24, 124, 131 Slump balls, 11 3,114 Slumped beds, 49 Slumping, 3, 5, 8, 9, 20, 21, 23, 53, 61, 86, 103,

108, 114, 116, 117, 122, 123, 124, 151, 157, 164,165,168,171,174,175,182,184, 195

Slump overfolds, 113, 114,116, 118, 122, 124 - rolls, 114,123,124

- structures, 14,84,250 -Sole features,211,212,213,214,217,218,219 -markings, 16,21,27,47,51,76,80, 100,101, 118, 195, 200, 203, 207, 210, 211, 212, 218, 249,250,252

Sorting, 3, 10,27, 110, 112, 113, 156, 161, 166, 167

Sourceareas, 35, 115, 118, 119, 123, 124, 130, 140,253,254

Southern California, 5 -Pyrenees, 192,193,196 - Uplands of Scotland, 15 Southwestern Murrisk, Mayo, western Ireland,

Spilitic effusives, 87 Spines of echinoids, 146 Spigsko-GemerskC Ore Mountains, 107, 115,

254

-sheet, 9

77

116,122

gtefanskA Huta, 1 1 1 Storm surges, 18 Striations, 47 Stromatoporoids, 139 Structural geology, 4 Subflysch, 110,111,112, 118 Submarine cables, 8,24 - canyons,4,5,13,18,19,23 24 89 101,103,

-fan, 101,103,124 - sliding, 108,123 - topography, 218 - valley, 123, 124 Submergenic, 89 Sub-sea fans, 5, 6,7,9, 13,23,24 Subsidence, 4 SuchA D o h a , 119,124 Sun cracks, 16 - -spot cycle, 27,28,29 Surge-waves, 85 Suspension currents, 165,167,174 - flow, 44 Swabian Alb, 157,184 Swamp lignites, 22 Swamps, 16 Symbols, 37,39 Symmetrical sharp-crested wave ripple mark,

- ripples, 195

148,149,151,152,154,248,250,252

16

Tectonic displacement, 134 -uplift, 18 Tennessee, 99 Tertiary, 103, 163 - Coast Ranges, 100 Texas,96,98,99,100,101,102,187,219 Tidal flat, 21 Tides, 7 Tool marks, 76,86, 199,207,208,209,210,213.

Topanga Formation, 199,254 -Sandstone, 201,202,204,207,212,214,215.

Torrential bedding, 114, 115, 118, 119 Torridonian, 77 Toscana, 127, 133 Toulon, 151 Tracks, 66 -of land animals, 16 Transport, 166,168 - direction, 88 Transversal sliding, 134 Transverse flow, 85 -structures, 85 -transport, 102,103,252,253,254 Triassic, 187

218,254

219

INDEX

Troika, 148,149,151,154 Trough, 250 - axis, 85 _- facies, 132 Tsunami, 18 Tuff-turbidites, 140 Tuscan autochton, 132 Twigs, 11 Type of sequence, 156

Ultrahelvetic flysch, 192 Umbria, 127, 130 Undaturbidites, 71,72,73,252,253 Ungraded beds, 193 United States, 93, 100,249,254 Utah, 98

Valentian, 76, 77, 80, 82, 84, 88 Var, 150, 151, 152 Variscan fold-belt, 76 Varves, 27,28 Venturabasin, 13,14,15,96,97 Vertical oscillations, 18 Vicchio series, 130 Villefranche, 15 1, I52

Villafranchian, 130 Vintimille, 149, 150, 153 Virginia, 95 Visean, 77,89,183 Volcanic islands, 5

Wales, 76, 78,80,82,86,87 Wave action, 195 - ripple-marks, 21,22 Weathered surfaces, 21 Welsh Borderland, 89 - trough, 84,86,87,88 Wenlock greywackes, 76 Wenlockian, 77,89 West-Carpathian, 115 Westphalian, 77 Wild flysch, 20, 108, 110, 112, 116, 117, 118,

Window of Bedonia, 133 - of Bobbio, 133 Winnowed sands, 16 Wyoming, 99,102

119,121,122,123,124,252,254

Zipov, 121 Zone of wave action, 72

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