sedimentological control on the clay mineral distribution

8/6/2019 Sedimentological Control on the Clay Mineral Distribution

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SEDIMENTARYGEOLOGY

ELSEVIER Sedimentary Geology 94 (1995) 229-243

Sedimen tological control on the clay mineral distributionin the marine an d non-marine Palaeogene deposits

of M allorca (Western M editerranean)M. Ingks a, E. Ramos-Guerrero b

aDep. Geoquim ica, Petrologia i Prospeccio Geol&ica, Univ ersitat de Barcelona, Zon a Unicersit ciria de Pedralbes,08071 -Barcelona, Spain

b Dep. Geologia Dincim ica, Geofisica i Paleontologia. Universitat de Barcelona, Zona Uniuersitriria de Pedralbes,08071-Barcelona, Spain

Received 14 February 1994; revised version accepted 18 July 1994

Abstrac t

During the Middle Eocene-Oligocene a marine and non-marine succession, about 10 00 m thick, was depositedon Mallorca. Palaeoenvironmental interpretation of these deposits was obtained from sedimentological and palaeon-tological data in earlier studies.

The non-marine environments recorded are: alluvial, fluvial (channel and flood plain deposits) and lacustrine(prevailing terrigenous, organic-rich or carbonate sedimentation). Marine environments are represented by littoraland shelf deposits. In most of these palaeoenvironments, terrigenous sedimentation prevailed except in the marineshelf, where mixed sedimentation was dominant, and in the carbonate and organic-rich lakes. In general, Palaeogenefreshwater lakes were perennial, open and exorheic, w ith carbonate waters.

The Palaeogene deposits were derived from Jurassic and Early Cretaceous pelagic and hemipelagic marls. Theclay mineral assemblage of these source-area rocks was mostly smectite, interstratified illite-smectite and illite. Theweathering of these materials under high temperature and rainfall favoured the hydrolysis of clay minerals and theformation of kaolinite.

X-ray diffraction, TEM and EDX analysis were carried out on 108 samples of palaeogene mudstones. Claymine rals identified w ere illite, interstratified illite-smectite, smectite, chlorite and kaolin ite.

The various Palaeogene environments (marine, transitional and non-marine) can be distinguished on the basis ofdifferent clay mineral assemblages. These assemblages are related to weathering and diagenetic processes as well asto the distance from the source area.

Alluvial sediments contain smectite and kaolinite with subordinate amounts of illite. All these clay minerals are ofdetrital origin. Smectite and kaolinite are present in all environments but the proportion of kaolinite to smectiteincreases with the distance from the source.

The K-rich interstitial waters derived from illite hydrolysis in the source area favoured the formation ofmixed-layer illite-smectite in the alluvial flood plain where the stagnation of waters d uring dry periods allowed theconcentration of dissolved ions.

Fluvial deposits contain interstratified illite-smectite, smectite, kaohnite, illite and chlorite in variable amounts.Variations in the proportion of illite and the occasional occurrence of chlorite was attributed to compositionaldifferences in the source area and variations in the sediment supply input. The terrigenous and carbonate lakes0037-0738/95/$09.50 0 1995 Elsevier Science B.V. All rights reservedSSDI 0037-0738(94)00089-l


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230 M. lng6, E. Ram os-Gu errero /Sedim entary Geology 94 (199.5) 229-243

preserved the detrital clay mineral assemblage carried by the rivers. Organic-rich lakes contain mainly kaolinite andsmectite with less illite.

Littoral deposits contain kaolinite and illite with minor amounts of smectite and interstratified smectite-illite.Shelf deposits are mostly formed by illite and kaolinite.

1. Introduction

Climate has a strong influence on rock alter-ation and clay minerals are often the main prod -uct of this process. Clay minerals deposited indiverse sedimen tary environments may be a detri-tal association which reflects the composition ofthe source area or may be directly related to theclimatic parameters which controlled the weath-ering of rocks. Moreover, post-depositionalchanges are not infrequent and the occurrence ofauthigenic clays provide s information about thesedimentary environments. The relationship be-tween clay minerals and environmental condi-tions has drawn attention to clay minerals aspalaeoenvironmental and palaeoclim atic indica-tors (Keller, 1970). Reviews of the current stateof knowledge can be found in Charnley (1989)and Weaver (1989).

Nevertheless, the use of clay minerals aspalaeoclima tic indicators is limited because fac-tors other than climate, such as lithology or to-pog raphy , strongly influence the rates and prod-ucts of weathering processes. Transport andpost-depositional changes can also modify theoriginal clay assemblage. For these reasons thelimitations of clays as palaeoclima tic indicatorshave been reviewed by many authors (e.g. Singer,1984; Charnley, 1989; Curtis, 1990).

We have selected a study area where, duringthe Palaeoge ne, the depositional environmentswere mainly detrital, with very active transportprocesses although in some areas carbonate andmixed sedimentation occurred.

The purpose of this paper is to describe themineralogy and the clay mineral assemb lages inthe mudrocks and to establish a relationship be-tween the clay mineral assemblages, the weather-ing proce sses and the depositional environments.

2. Geological settingMallorca is the largest island of the Balearic

Archipelago, located in the Western Mediter-ranean over the Balearic Promontory, which con-stitutes the northeastern prolongation of thealpine Betic Range (Fig. 1A).

The island of Mallorca is made up by Meso-zoic and Tertiary rocks folded and thrusted dur-ing the Alpine compressive orogeny, which prob-ably started in the Oligocen e, but reache d itsmaximum intensity during the Early-Mid dleMiocen e (Burdigalian-Langhian). The totalshortening was greater than 50% and transportdirection was toward the northwest (Ramos-Guerrero et al., 1989b). This SE-NW shorteningobviously affected the Palaeogene palaeogeo-graphic evolution, pro ducing abundant lateral fa-ties change.

After the Langhian the tectonism changed,and a distensive phase took place forming horstsand grabens. The horsts are formed by structuredpre- and synorogenic rocks and constitute themajor reliefs of the island (Sierras de Tra-muntana and Llevant) as well as other minorreliefs in the Central Zone. The grabens forme dbasins that were filled by post-Langh ian sedi-ments, and constitute the lower and flat CentralZone of the island (Fig. 1B ).2.1. The Pa laeogene o f M al lorca

On Mallorca, Palaeogene rocks crop out insmall and tectonically disconnected areas (Fig.1B). Two depositional sequences bounded by un-conformities were recognized in the Palaeogeneof Mallorca by Ramos-Guerrero et al. (1989b)(Fig. 2). The lower sequence (D.S.1) is MiddleEocen e in age (Late Lutetian-Bartonian), whe re-as the upper sequence (D.S.11) is Late Eocene-


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M. Ingl&, E. Ramos-Guerrero /Sedimentary Geology 94 (1995) 229-243 231

Oligocene in age. Each depositional sequence iscomposed of a set of stratigraphic units.2.2. The Lower Depositional Sequence (D.S.Zj

This sequence lies unconformably over aMesozoic basem ent, mainly composed of EarlyCretaceous rocks, and results from the sedimen-tation on a stable shelf with two clearly differenti-ated palaeogeographical doma ins: toward thenorthwest the sequence is made up of lacustrine

deposits, wh ereas toward the southeast it isformed by littoral and marine shelf sediments.Both the northwestern lacustrine and the south-eastern marine dom ains remained separated by athreshold where no sedimentation occurred du r-ing the Middle Eocene.

The northwestern lacustrine deposits consti-tute the Peguera Limestone Formation (Fig. 21,and have been interpreted as palustrine to shal-low lacustrine sediments. The lacustrine basinswere extensive, with permanent water (Ramos-

0MALLORCA

:. . . .. . . . . . .. . . . . . .. . . . . .. . . . . . . .. . . . .. . . . .

. . . . .. . . . . .. . . . .

. . . .

. . . . . . . . . . .. . . . . . . .

Structured rocks (Mesozoic toMajor taleogene OUtCroPsPostorogenlc rocks

n Studled sectionsFig. 1. (A) Location of the Balearic islands in the Western Mediterranean Sea. (B) Geological sketchlocation of the outcrops studied.

of Mallorca island and


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23 2 M. In&s, E. Ramos -Guerrero /Sedimentary Geology 94 (1995) 229-243

Guerrero et al., 1989a). Terrigenous sedimenta-tion was limited to the supply systems inputpoints. Locally, the lacustrine sequence includesa lower part with mineable coal and coaly facies.The lacustrine carbonate deposits as well as theassociated detrital sediments of the PegueraLimestone Formation are logged and sampled(logs l-4 and 6 in Fig. 3).

The water of the Eocene lakes was character-ized by high carbonate and low sulphate contents.The lack of evaporites suggests the existence ofan open lacustrine system where, however, persis-tent anoxic conditions may have occurre d locally(Ramos-Guerrero et al., 1989a).

The marine sediments on southeastern Mal-lorca constitute the SEnv estida Calcarenites For-mation (Fig. 2). This unit is forme d by littoral andmixed shelf sediments, in whic h organic bioclasticproduction was substantial. The main lithologiesare bioclastic calcarenites as the littoral fa cie%and silts and marls as open shelf marine facies.The silty facies often contain large monospecificpopulations of non-reworked N u m m u l i t e s , whichhave been interpreted as N u m m u l i t e s banks. Themarine facies of the SEnv estida Calcarenites arepresented in log 11 (Fig. 3).

Remains of turtles and crocodiles which indi-cate warm climatic co nditions have been identi-

NW SE

0

_ _ _ _ - \-- .a._. I/ ,-. -. _m Gaklent Fm. . . .

Fluvio - alluvial.GravelsSandsMarls

Lacustrine - oalustnne:Carbon&eTerngenousCoaly facles

Marine.LittoralShelf

&& Reefal facies

- Unconformity \ Tectonic boundaryFig. 2. Stratigraphic scheme of the Palaeogene of Mallorca (modified from Ramos-Guerrero et al., 1989b) and location of thesections studied.


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M. In&s, E. Ram os-Gu errero /Sedim entary Geology 94 (1995) 229-243 2 33

fied in the lacustrine facies (Hugueney andAdrover, 1982; Jimenez-Fuentes et al., 1989-1990). The fossil association and the lacustrinehydrochemical characteristics allow us to at-tribute warm and humid climatic conditions tothe Eocene period.2.3. The Upper Depos i t ion a l Sequence (D.S .I I )

In the Upper Sequence (D.S.11) two cycles canbe distinguished: a marine and transgressive lowercycle, overlain by an upper continental and re-

NW

gressive cycle characterized by an alluvial systemprograding toward the southeast.

The lower transgressive cycle is made up oflittoral and marine shelf sediments, Priabonian-Early Rupelian in age. These sediments lie un-conformably on and onlap toward the northwestthe Mesozoic or Palaeogene (D.S.1) basement.

Toward the northwest, along the Sierra deTramun tana, the littoral sediments of the Alar6Calcarenites Formation (Fig. 2) are the mostabunda nt. The main lithologies of this unit arebioclastic calcarenites, conglomerates, marls and

7 SE

Cala 4

B

Blanca. ... ..Fm

69

.-.i. L-....1.

10Ir..1

?? YIIY I.. Alar6. \. \\

Fm

Fig. 3. Simplified stratigraphic logs of the studied outcrops and samples position. Location in Figs. 1B and 2


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lutites. Toward the south and southeast the Alar6Formation laterally ch anges to marine shelf sedi-ments with reef-limestones, bioclastic calcaren-ites, lutites an d marls. Thes e open marine sedi-ments form the Son Sastre Lutites Formation, theGaldent Limestone Formation and the CalvariMarls Form ation (Fig. 2). The littoral facies havebeen studied and sampled in logs 2-6 and 8 (Fig.3), whereas the marine shelf facies have beenstudied in log 8 (Fig. 3).

The upper regressive cycle is formed by analluvial system , Oligocene in age and represen tedby the Cala Blanca Detrital Formation (Fig. 2).This unit reflects a rapid lateral facies variation,from the proxim al cong lomeratic alluvial depos itsto the northwest toward the distal deposits, lo-cated to the southeast, which are composed oflutitic flood plain depos its and lacustrine sedi-ments w ith mineable coal beds (Ramos-Guerreroand Marzo, 1989).

The proxim al alluvial facies are gravels andother detrital deposits made up of non-confinedsheets of debris flows (Ramos-Guerrero andMarzo, 1989). These facies are mainly located inthe southern part of the Sierra de Tramuntanaand other localities of the Central Zone, wherelog number 7 was studied and sampled (Fig. 3).

Laterally, the proxima l alluvial-fan depos itschange to fluviatile depo sits who se main litholo-gies are well sorted conglomerates, sandstonesand lutites; am ong the fluviatile depo sits channelfilling and lacustrine sequenc es have been identi-fied interbedded between flood plain lutitic sedi-ments and palaeosoil horizons. The fluviatile fa-ties of the Cala Blanca Fo rmation are studied inlogs 3 to 7 (Fig. 3).

Clast petrolog y and palaeocu rrent analysisprove the existence of a source area, constitutedby Middle Jurassic-Early Cretaceous carbonaterocks (Colom, 1975) and located toward thenorthw est of the island, in the present-day Cata-lano-Balear Basin (Fig. 1A).

Toward the east and southeast, in a distalposition, fluvial plain and lacustrine facies aredominant. Ramos-Guerrero et al. (1989a) charac-terized tw o main lacustrine facies assemb lages inthis area: detrital lacustrine and organic-rich la-custrine facies.

The main Oligocene lacustrine basins wer ealso perennial, with fresh and carbonate-rich wa-ter, but their a rea1 extension was smaller than inthe Eocene (D.S.1). Both lacustrine facies, detri-tal and organic-rich, have been studied and sam-pled in logs 9 and 10 (Fig. 3), in the C entral Zoneof Mallorca.

Palynological an d palaeobotan ical assemb lages(Alvarez-Ramis and Ramos-Guerrero, 1986; Al-varez-Ramis et al., 1987; Ramos-Guerrero andAlvarez-Ramis, 1989-1990 ) and crocodilia andturtle (Hugueney and Adrover, 1982, 1989-1990)remains from the lacustrine deposits of the CalaBlanca Formation sugg est tropical to sub-tropical(warm and humid) climatic conditions during theOligocene.Disp ersed organic matter is present in all con-tinental Palaeog ene sedimen ts, but is associa tedwith the lacustrine facies (Eocene and Oligocene)whe re it is most abundant, and locally thick accu-mulations of lignites and coaly facies are present.Organic geochemistry allows us to attribute thekerogen to types II and III, pointing to a substan-tial macrop hytic contribution. Nev ertheless minoralgal contributions can also be expected (Ramos-Guerrero et al., 1989a). These data support thehypothesis of the existence of a stable w atercolumn in the lacustrine basins.

3. Analytical procedureA total of 108 samples were collected repre-

senting alluvial, fluvial, lacustrine (carbonate, ter-rigenous and organic-rich), littoral and marineshelf environments. Sampling took into accountthe diversity of sedimentary environments in thePalaeogene of Mallorca; the location of samplesis show.n in Fig. 3. For comparative purposeseleven samp les, of similar lithology to that in-ferred for the source area during the Palaeogene,were obtained from Jurassic and Early Creta-ceous units.

A portion of each sample was dispersed indistilled wate r and was hed until deflocculationoccurred. The < 2 pm fraction was separated bycentrifugation of the suspension. Oriented mountsof the < 2 pm fraction were prepared for X-ray


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M. Ingl&, E. Ram os-Gu errero /Sedim entary Geology 94 (1995) 229-243 235

diffraction by gravity settling on glass slides. Claymineralogy w as determined from diffraction pat-terns obtained using samples that were air dried,ethylene glycol solvated and heated to 550C dur-ing 2 hours. X -ray diffraction analyses were car-ried out on a Siemens D500 X -ray diffractometerusing a CuK a radiation.

Ten representative samples of the diverse en-vironments and the source area were furtherstudied by transmission electron microscopeequipped with a microanalyzer system in order todetermine the qualitative composition of smec-tites and interstratified minerals and also to iden-tify the non-clay minerals in the < 2 pm fraction.Observation and analysis were performed in aHitachi H-800 MT with H-8010 STEM and SEMsystem and X-ray microanalyzer.

4. Results4.1. M inera log ica l comp os i t ion o f the < 2 pmfrac t ion

The main constituents of this fraction are thefollowing:

Zl l i t e is recorded in 89% of the samples stud-ied. TEM observations revealed that illite occursas irregularly shaped grains with micaceous as-pect (Fig. 4a). Illite and kaolinite are usually thecoarsest grains in the < 2 pm fraction.

Smect i t e and mixed- layer i l l i t e -smect i t e : 67% ofthe samples studied contain one or other m ineral.In fact there is a wide range of composition, frompure smectite to diverse degrees of mixed layer-ing illite-smectite. TEM observations reveal thatsmectites and mixed-layer illite-sm ectite have asmaller grain size than illites and kaolinites. Theenergy dispersive X-ray spectra show that thesmectites are of the aluminium type and alwayscontain iron (Figs. 4c and 4d).Interstratified clay mine rals are recorded inapproximately 25% of the samples. In most ofthem a low and broad diffraction peak, at 4.5-7

perm it the identification of the mixed-layer min-erals as illite-sm ectite type with propo rtions ofillite layers rang ing from 40 to 60% calculatedaccording to the method proposed by Moore andReynolds (1989). Whe n only one diffraction peakappears the shape, broadness and expansion arevariable. T his has been interpreted as diversedegrees of interstratification. EDX an alysis re-veal the presence of grains with ratios of alu-minium to silicon lower than the illite but withsome potassium content (Figs. 4e and 4f).

The 7-A minera l s chlorite and kaolinite weredistinguished using a slow-scan record between24 and 25.5028 in order to distinguish the chlo-rite (3.54 A) from the kaolinite (3.57 A) peaks(Biscaye, 1965). Nevertheless in a few sampleswith small amounts of 7-A clay minerals thediscrimination of the two peaks has not beenpossible, in this case we use the term 7-A miner-als only when it is impossible to know for su rewhether we have kaolinite or chorite, or bothminerals together. TEM observations show thatkaolinite frequently occurs as hexagonal-shapedcrystals of variable grain size (Fig. 4g). Chloriteoccurs only in a few Oligocene samp les.

No n - c l a y m i n e r a l s : in the < 2 pm fraction,apar t from clays, a wide variety of other detritalminerals are present. Amo ng them, quartz, cal-cite, goethite and K-feldspar are abunda nt andcan be positively identified on the X-ray diffrac-tion patterns. Small amou nts of apatite and tita-nium oxides were identified during TEM a ndEDX analyses (Figs. 4a, 4c and 4e).4.2. Clay m inera l d i s t r ibu t ion

The clay minerals identified in the Jurassicsam ples of the source area are illite, interstrati-fied illite-smectite and 7-A minerals. Cretaceoussamples contain predominantly smectite withvariable amou nts of illite and occasional minoramoun ts of mixed-layer illite-smectite and 7-Aminerals. The smectites are of the aluminium-richtype. Representative X-ray diffraction pa tterns of


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b

h


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M. Ingl&, E. Ramos-Guerrero /Sedimentary Geology 94 (1995) 229-243 237

Fig. 5. X-ray diffraction patterns of the < 2 Frn fraction, ethylene glycol solvated samples. Representative sample from the Jurassicsource area (A) and representative sample from the Cretaceous source area (B). S = smectite; I-S = interstratified illite-smectite;I = illite; K = kaolinite. Unlabelled peaks correspond to quartz and calcite.

Illite is present in almost all the samp les. Nev-ertheless the abundance of illite varies dependingon the sedimentary environment.

All the environments contain expandab le claymine rals, either sm ectite or mixed-layer illite-smectite. Interstratified mine rals are recorded influviatile, detrital and carbon ate lacustrine , andlittoral facies. Sm ectite is presen t in all the sedi-

mentary environments and it is abund ant in thealluvial, organic-rich lacustrine and shelf facies,where m ixed-layer clay minerals are absent.

Kaolinite is recorded in most of the samplesand is very abunda nt in alluvial, carbonate andorganic-rich lacustrine, littoral and marine shelfsediments.Chlorite is only present in a few samples of

Fig. 4. Transmission electron micrographs of different representative clay samples (left column). Energy dispersive X-ray spectra ofminerals marked with an arrow are depicted in the right column. Vertical scale bar in EDX spectra is equivalent to 1000 counts.Unlabelled peaks correspond to carbon and copper of the support grid and coatings. (a) Illite and goethite (electrodense aggregate)from a shelf sample. (b) EDX spectrum of the illite. (c) Smectite from an alluvial sample. The prismatic, electrodense grain is atitanium oxide. (d) EDX spectrum of the smectite. (e) Interstratified illite-smectite from a fluvial sample. The electrodense mineralis a quartz grain. (f) EDX analysis of the interstratified illite-smectite. (g) Kaolinite from an organic-rich lacustrine sediment. (h)EDX spectrum of the kaolinite.


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238 M. I&&, E. Ram os-Gu errero /Sedim entary Geology 94 (I 995) 229-243

\I-S, K

0S,I-S, I,K

6

0As, I, K

5 1 0 1 5 a l 2 5 2 0

Fig. 6. Representative X-ray diffraction patterns of the < 2 Frn fraction, ethylene glycol solvated Palaeogene samples of: (A)organic-rich lacustrine mudstone; (B) alluvial mudstone; (C) fluvial mudstone; and (D) shelf mudstone. S = smectite; I-S =interstratified illite-smectite; I = illite; K = kaolinite. Unlabelled peaks correspond to quartz and calcite.


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M. Inglk , E. Ram os-Gu errero /Sedim entary Geology 94 (1995) 229-243 239

Table 1Percentage of samples in which the various clay minerals are present in the Palaeogene sedimentary environments studied

ISI-SKCh7A

Alluvial

57100

100

_

Fluviatile

874245452938

Detritallacustrine833922611628

Carbonatedlacustrine10028

43100

_

Organiclacustrine100100

100

_

Littoral

831320561643

Shelf

10017_

100100

fluvial, detrital lacustrine and littoral origin of the chlorite) are ubiqu itous, some sedimentary envi-D.S.11 (Late Eocene-Oligocene). ronments are characterized by a definite assem-

Although the clay minerals recorded (except blage distinguishable by the constant presence

Ca rb o n a te lacustnne fme sOrg a n tc r ic h la c u s trme fa C le SM a r m e f a c e s ( httoralo shelf)

Fig. 7. Idealized palaeoenvironmental scheme of the Palaeogene of Mallorca with clay mineral distribution. The order of the clayminerals indicates decreasing relative amounts. In brackets are clay minerals which are of secondary importance.


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240 M. In&s> E. Ramos-Guerrero /Sedimentary Geology 94 (1995) 229-243

and relative proportio ns of some clay minerals. both the source area and the Palaeogene rocks.The distribution of these clay mineral assem- These heavy minerals, wid esprea d over all theblages in the depositional environments (Fig. 7) Palaeoge ne environments, clearly indicate the im-can be summarized as follows. portance of detrital processes.

Al luc ia l . Smec tite and kaolinite are consis-tently present in all the samples. Illite is record edin 57 % of samp les and is relatively scarce.

Flucia l and de t r i ta l lacus t r ine . All the clay min-erals record ed are present in these environmentsalthough the relative proportions are very differ-ent (Fig. 60. The presenc e of chlorite is notice-able in some Oligocene samples.

Carbona te lacus t r ine . All the sample s containillite and kaolinite in varying proportions . Never-theless in the lacustrine deposits of the PegueraLimesto ne (Midd le Eocene) illite prevails overkaolinite and in the carbonate lacustrine depos itsof the Cala Blanca Form ation (Oligocen e) kaolin-ite is more abundant than illite. M ost of thesamp les contain subordinate amounts of smectiteor interstratified illite-smectite.

Kaolinite is the mos t abundant clay mineral inthe Palaeogene samples. Smectite and mixed-layerillite-smectite com e next in terms of abundance.Illite is very wide spread , but is always presen t ina lesser p roportion and with a lowe r crystallinitythan the source area samples. The absence ofdolom ite and magnesium in the clay minerals arenoticeable. The lack of magnesium may be re-lated to the lithological composition of the sourcearea, consisting exclusively of limestones andmarls.

Organic-r ich lacustr ine. These deposits show anhomogeneous mineralogical composition. Illite,smectite and kaolinite are record ed in all sam-ples. Smectite and kaolinite are much more abun-dant than illite.

Li t t o r a l . These environments are characterizedby the presence of illite and kaolinite. Occasion-ally smectite, mixed-layer illite-smectite, chloriteand 7-A minerals occur in variable amounts.When smectite or mixed-layer illite-smectite dooccur, they can be very abundant.

Shel$ These samples are characterized by highkaolinite and low illite contents. Smectite is foundin some samples and is in some places quiteabundant.

The alluvial facies contain kaolinite and smec-tite with minor amounts of illite. Smectite andillite are of detrital origin. C hemical weatherin gof pre-existing clay minerals, probably illite, andto a lesser extent smectite, led to the formation ofkaolinite. Goeth ite and potassium ions are otherproducts of the weathering processes. The pres-ence of both kaolinite and goethite (and occa-sionally hema tite) indicates substantial chemicalweathering. EDX analyses (Fig. 4) show that illiteand smectite are iron rich; this favoured theformation of goethit e. The weatherin g of illite ledto a potassium enrichment of the interstitial wa-ters. The drainage of the area carried the K-richsolutions to the lower zones (Fig. 7) where theformation of interstratified illite-smectite wasfavoured by the entrance of potassium in thesmectite interlayers (Singer and Stoffer s, 1980).

5. DiscussionIn the source area, the clay minerals present

are illite, smectite, interstratified illite-smectiteand 7-A clay minerals; the first two minerals arethe most abundant.

In the Palaeoge ne sediments detrital clay min-erals are dominant. This fact is clearly reflectedby the high content of smectite in the proximalarea. Titanium oxides and apatite are present in

In the fluviatile and lacustrine environments(excep t the organic-rich lacustrine) the detritalclay minerals were preserv ed. Thes e environ-ments are characterized by a complex clay min-eral assemblage composed of detrital kaolinite,smectite, illite and in some places chlorite, as wellas interstratified illite-smectite formed in theflood plain. The detrital clay mineral preservationis consistent with the characteristics of Palaeo-gene lacustrine systems: freshwater, exorheic,perennial and calcium bicarbonate dominated;these conditions do not favour clay mineral trans-formations (Jones and Bowser, 1978; Jones, 1986).

The interstratified illite-smectite formationmechanism has been described by Eberl et al.


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(1986). These authors suggested that wetting anddrying cycles favour the fixation of potassium insmectites and thus the formation of illitic layers.The mudstone deposits of the fluvial flood plainhave decolourations, carbonate nodules androot-marks that indicate palaeosoil developmentunder hydro morp hic conditions. In these condi-tions interstitial wate r stagnation and ion concen-tration during the dry season are favoured. Ac-cording to Moh r and Van Baren (19541, in thesame climatic conditions, rapid interstitial wate rcirculation favoured the formation of kaolinite,whereas slow circulation with temporary stagna-tion made possible the reactions between clayminerals and the dissolved cations.

In the organic-rich lacustrine environment theclay mineral association is com posed of kaoliniteand smectite, both very abundant; illite is alsopresent, but in a lesser propo rtion. In contrastwith other lacustrine environments (carbonateand detrital) neither interstratified illite-smectitenor chlorite are reported. The smectite has goodcrystallinity, similar to that of the smectite fromthe Cretaceous rocks of the source area andalways better than that o f the other Palaeogenesediments. So we suspect that in the organic-richlacustrine environments som e smectite-regenera-tion mechanism was active in spite of the gener-ally held view (e.g. Berner, 1971 ; Styman andBustin, 198 4) that these environments favoursmectite alteration and kaolinite formation. How -ever, an abundance of both kaolinite and smec-tite in the organic-rich lacustrine facies was alsocited by Ingles and Anadon (199 1) in the Palaeo-gene sediments of the Ebro basin.

In the distal environments (littoral and shelf)the proportion s of smectite and mixed-layer il-lite-smectite decrea se, wh ereas kaolinite and mi-nor amounts of illite are the most rep resentativeclay mineral assem blage. The kaolinite increasecan be attributed to the weathering of the smec-tite in the proxim al area.

For all the Palaeogen e sedimentary environ-ments of Mallorca it should be emphasized thatchlorite is only present in the Oligocene sample s.Illite is present in both Eo cene and Oligocen esamp les, but the alluvial and lacustrine Eocen esamp les rec ord the greates t abundance of illite.

The fluctuations in the detrital clay mineral pro-portions must be attributed to the source areacompo sition variations as well as to the change inpalaeocurrents. Howev er, we cannot rule out thepossibility of the existence, during the Oligocen e,of slightly colder periods, during w hich weather-ing was less important, and which allowed thepreservation of chlorite and illite.

The Eocene lacustrine system (Peguera Lime-stone) developed in a stable plate, where thelacustrine basins occup ied wide areas. On theother hand, the Oligocene lacustrine system (CalaBlanca Formation) developed in an area of defor-mation processes related to the Betic orogen.This context had a strong control over the genesisand later developm ent of the sedimentary basinsand sediment supply, mainly terrigenous.

The formation of kaolinite and goethite sug-gests that weathering processes were developedunder high tempe rature and rainfall conditions.On the other hand the formation of interstrati-fied illite-smectite can be related to a seasonalrainfall contrast. T his interpretation agrees withpalaeoecological data previously mentioned,which reflect the existence in this area of similarpalaeoclimatic conditions. In addition, Charnleyet al. (1979) d educe the existence of similarpalaeoclimatic conditions during the Midd leEocene-O ligocene in the Atlantic edge of theIberian plate (DS DP site 398 1, in a latitudinalposition similar to that of Mallo rca, and Charnley(1989) proposed for the same area the existenceof a seasonal rainfall contrast.

6. ConclusionsThe clay minerals in the Palaeog ene mud-

stones of Mallorc a are mainly detrital and resultfrom weathering in the source area as well aspost-depos itional weathe ring in the proxima l en-vironments. How ever, the final clay mineral as-semblages are found to be due as much to theweathering processes as to the sedimentary anddiagenetic conditions prevailing in the sedimen-tary environment.

The distribution of the clay minerals in thediverse sedimentary environments is show n inFig. 7.


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242 M. Ingl& E. Ramos-Guerrero /Sedimentary Geology 94 (1995) 229-243

The alluvial facies are composed of smectite with distance-the organic-rich lacustrine de-and kaolinite with minor illite. Smectite and illite posits are an exceptio n-wh ereas kaolinite distri-are detrital, whereas kaolinite has been formed bution show s the oppo site tendency, increasing inby the chemical weatherin g of preexisting clay proportion with distance. In our opinion this clayminerals, mainly illite. Hydro lysis of these facies mineral distribution results mainly from weath er-as well as the source area, with abundant smec- ing proce sses more than transport and sorting (intite, mixed-layer illite-smectite and illite, under distal areas smectite is locally abundant). On thehigh tempe rature and rainfall, led to the forma- other hand, the transportation processes havetion of kaolinite and goethite while water was been very active as is shown by the sedimentolog-enriched in soluble cations as residual produ cts. ical facies association.

In the fluviatile and detrital lacustrine faciesall the record ed clay minerals are present: kaolin-ite, mixed-layer illite-smectite, illite, smectiteand, in the Oligocen e samp les, chlorite. All clayminerals are detrital in origin exce pt the mixed-layer illite-smectite, whic h was forme d in thefluvial flood-plain, wh ere the imprint of hydro-morphic processes has been recognized and thestagnation of interstitial wate r led to periodicincrease of ion concentration. In these conditionsan increase o f potassium concentration occurredand favoured the formation of illitic layers insmectites by the fixation of potassium , leading inturn to the formation of illite-smectite mixed-layers. Potassium was released during the hydrol-ysis of illite.

AcknowledgementsFinancial support was provided by CICYT pro-

jects GE0 89-0426 and PB 91-0805. X-raydiffraction analysis were carried out in the Insti-tut de Ciencies de la Terra Jaum e Almera(CSIC). TEM observations and analysis were car-ried out in the Serveis Cientifico-Tecnics, Univer-sitat de Barcelona. The manuscript has been im-proved by critical comments and suggestions fromP. At-radon, L. Cabrera and reviewers H. Friis andB.F. Jones.

ReferencesThe carbonate lacustrine facies are characte r-ized by illite and kaolinite, with subordinateamounts of smectite and mixed-layer illite-smec-tite. All these minerals are of detrital origin.

The organic-rich lacustrine facies are mark edby the presence of smectite and kaolinite, withminor amounts of illite. Kaolinite and illite aredetrital. The lack of interstratified minerals andthe high crystallinity of smectites sugg est thatsome sort of regeneration process of these miner-als may be related to the hydrological characteris-tics of these environments.

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sedimentological control on the clay mineral distribution

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