deep sea drilling project initial reports volume 79marine sediments (wurster and stets, 1982, figs....

APPENDIX.MICROPALEONTOLOGICAL AND SEDIMENTOLOGICAL ASPECTS OF HIGH ATLAS

CRETACEOUS ONSHORE SEDIMENTS (ATLAS-GULF, MOROCCO)1

Arif Butt, Universitàt Tubingenand

Johannes Stets and Paul Wurster, Geologisches Institut der Universitàt Bonn2

ABSTRACT

Micropaleontological and sedimentological data of the Lower to mid-Cretaceous sequence in the Western High At-las of Morocco support the existence of a deltoid/triangular Atlas-Gulf. Transgressions and regressions in the Gulf areadocumented by the micropaleontological record include significant transgressive events during the Berriasian to Valan-ginian, early Barremian, late Aptian, and Turanian, and regressions in the late Hauterivian and late Barremian to earlyAptian. Frequent sea-level oscillations are recorded in the Cenomanian. Continental, lagoonal, littoral, and inner tomid-shelf conditions are deduced from micropaleontological and sedimentological data. Intertonging of marine andnonmarine paleoenvironmental conditions exhibits transitional characteristics between the Atlantic province and the in-ner part of the Gulf. Assuming a steady subsidence of the Gulf area because of its location in the mobile High Atlasbelt, eustatic changes in sea level may be the most important factor controlling sedimentation, paleoenvironment, andpaleobathymetry in the Atlas-Gulf.

INTRODUCTION

Since 1975, a working group of the Geologisches In-stitut der Universitàt Bonn has conducted geological fieldwork on the Cretaceous of the High Atlas area of Mo-rocco to reconstruct the Cretaceous geography of the re-gion (Behrens et al., 1978, Behrens and Siehl, 1982, Wur-ster and Stets, 1982, Stamm and Thein, 1982). Thiswork is equivalent to the offshore activities of the DeepSea Drilling Project. The onshore activities of the Bonnworking group were initiated by Dr. Hans Closs as ameans of estimating the continental influence on ocean-ic sedimentation.

One of the basic aims of the onshore activities in thecoastal basins of Morocco was to establish a precise lith-ologic and stratigraphic subdivision of the Cretaceousrock series. This was done in cooperation with research-ers from the University of Tubingen (Wiedmann et al.,1978, 1982), who erected standard sections for the Cre-taceous near the Atlantic coast between Agadir and CapRhir, and near Essaouira. The Askouti section describedin this paper represents the eastern landward facies ofthe High Atlas Cretaceous deposits. Located about 20km inland (Fig. 1) the Lower to mid-Cretaceous se-quence of Askouti contrasts with the western marginfacies near Agadir. It displays frequent alternation ofmarine and nonmarine sediments and exhibits charac-teristics transitional between the open-marine Atlanticprovince to the west and the basin margin province to

Hinz, K., Winterer, E. L., et al., Init. Repts. DSDP, 79: Washington (U.S. Govt. Print-ing Office).

2 Addresses: (Butt, present address) Al Rahim 50 II B, Model Town, Lahore, Pakistan;(Wurster, Stets) Geologisches Institut der Universitàt Bonn, Nussallee 8, D-53OO Bonn 1, Fed-eral Republic of Germany.

the east. The eastern province is characterized by a moreabrupt alternation from lagoonal to continental and open-marine sediments (Wurster and Stets, 1982, figs. 2, 6).

Detailed study of the Western High Atlas began in1930 with work by Roch. It was continued by Ambroggi(1963) and Duffaud et al. (1966). Some important geo-logic aspects of the Mesozoic deposits of the WesternHigh Atlas were also discussed by Ager (1974). AlthoughAmbroggi made a detailed study of stratigraphy and pa-leontology, little attention was paid to environmental,ecological, and bathymetric aspects of the Cretaceous.Wurster and Stets (1982, fig. 9) established a sedimenta-tion model for the Lower to mid-Cretaceous sequenceof the Western High Atlas, using lithological data be-cause the sediments are often barren of foraminifers. Inthe Askouti area the microfossils are locally rich, andthis model is now corroborated by the micropaleonto-logical record provided by A. Butt.

GEOLOGICAL SETTING

The Askouti section is situated at the southwesternedge of the Western High Atlas mountain range, in theImouzzer des Ida Ou Tanane area. Toward the south it isbordered by the Plain of Souss, which is filled with Qua-ternary sediments. The Mesozoic rock series cropping outin the southwestern High Atlas extends from the Triassicto the Cretaceous. In general, younger sediments succes-sively appear toward the coastline, as the mountain chainplunges toward the Atlantic Ocean. This geological situ-ation is modified (Fig. 1) by anticlinal and synclinalstructures that are the structural response to a fault pat-tern which affected the Paleozoic basement. In contrastto the structural interpretation of Rod (1962), this chap-ter does not distinguish a distinct fault cutting throughthe Mesozoic—called the "Agadir fault"—in this region.

923

A. BUTT, J. STETS, P. WURSTER

Tertiary, Cenozoic

Upper Cretaceous

mid-Cretaceous

Figure 1. Geology of the southwestern edge of the Moroccan High Atlas and location of the Askouti sec-tion.

The Askouti section is located at the southern flankof one of these anticlinal structures, the anticline of DjebelLgouz. Here, the Cretaceous sequence crops out in thevalley south of the small village of Askouti. Beddingdips steeply toward the north at the inverted limb of theanticline. According to the correlation of the Cretaceousrock series with those farther to the west and in theAmeskhoud area to the east, the profile is affected bytwo minor faults (see Fig. 3, later). Nevertheless, fromthe stratigraphic point of view, the Askouti section con-tains the complete Lower to mid-Cretaceous sequencefrom which the micropaleontological and sedimentolog-ical aspects of onshore basin development are deduced.

PALEOGEOGRAPHICAL SETTING

A well-defined deltoid sedimentary basin, called theAtlas-Gulf (Behrens et al., 1978) is apparent from pro-files currently available from the Western High Atlas Cre-taceous (Wurster and Stets, 1982). This Gulf stretcheslandward to the east and is bordered by two stable plat-

form areas: the Moroccan Meseta to the north, and theAnti-Atlas to the south. Thin sedimentary units occur atthe margins of these structural and paleogeographicalhighs (Fig. 2). The deltoid/triangular Atlas-Gulf openstoward the Atlantic, and the sedimentary sequence in-creases in thickness toward the interior and toward theAtlantic along the axis of the basin. Toward the east, thesedimentary sequence decreases gradually in thickness,and red beds are found increasingly in the Atlas-Gulf.Accompanying facies changes are discussed in more de-tail by Wurster and Stets (1982); the western margin isconsidered by Wiedmann et al. (1978) and Butt (1982).

The structural position of the Gulf area roughly coin-cides with the Mesozoic Atlas Rift, which here intersectswith the Atlantic continental margin (Stets and Wurster,1982). According to data compiled for the Gulf area,subsidence during Early and mid-Cretaceous time tookplace rather continuously, whereas the neighboring sta-ble platform areas remained elevated. In Late Cretace-ous time conditions changed. From the Turonian on-

924

ASPECTS OF HIGH ATLAS CRETACEOUS ONSHORE SEDIMENTS

Land areas

Basin facies

]TO^°>j Marginal sediments

| | Platforms

| | Mobile belts

Askouti section

Figure 2. General configuration of the Early to mid-Cretaceous Atlas-Gulf and adjacent areas of the Moroccan Meseta and the Anti-Atlas.

ward, two separate basins developed along the northernand southern flank of the rising High Atlas mobile belt.

ASKOUTI SECTIONThe Askouti section is divided into two parts termed

Aa and A (Fig. 3); both are located along the valleysouth of Askouti at approximately 3O°3O.O'N, 9°27.8'W.Part Aa comprises the Lower Cretaceous, part A themid-Cretaceous. The sedimentary sequence is subdividedinto several rock units as generalized in the stratigraphiccolumn of Figure 3. The section was surveyed in detailby Wurster and Stets at a scale of 1:50. A. Butt conduct-ed the micropaleontological research.

Berriasian to lower Aptian SequenceThe lowest rock unit (Aa 270-289 m) conformably

overlies an Upper Jurassic sequence of alternating well-bedded carbonates and marls. This first Cretaceous unitconsists of grey to greenish marls, dolomitic limestones,and arenites. It is followed by a limestone sequence (Aa289-320 m) with interbedded thin layers of marls, inwhich the limestones contain oysters with shell diame-ters up to 120 mm, brachiopods, echinoids, and occa-

sional corals. Above the limestones, gray marls gradeupward into red marls (Aa 320-360 m). A fault formsthe upper contact of the red beds. The next series (Aa360-400 m) starts with intraformational breccias andlayered conglomerates with interbedded marls. Grey togreenish marls again follow with interbedded dolomiticlimestones. The limestones contain quartz (up to 20%)and shell debris. At Aa 400 m the next rock unit againbegins with a basal conglomeratic and calcarenitic se-quence that exhibits occasional large-scale cross-bedding.Pebbles reach diameters up to 5 mm and intercalatedoyster shells range to 40 mm. Layers rich in shell debrisoccur. Above this coarse-grained littoral sediment, redand grey marls follow that are rich in brachiopods, espe-cially at Aa 430-435 m and Aa 441-443 m. The se-quence from Aa 443 to Aa 460 m consists of multicol-ored, red to grey marls, interbedded limestones, andnodular dolomites. Oysters with shell diameters up to 50mm occur in the lower portion of the sequence, whereasthe upper part is unfossiliferous.

Aptian-Albian SequenceAt Aa 460 m the next sequence starts with another

basal conglomerate, consisting mostly of quartz pebbles,that represents the main transgressive event of the EarlyCretaceous. This conglomerate is overlain by marls andcalcarenites followed by a well-bedded sequence of greymarls and interbedded micritic limestones that containcomplete shells and shell debris of small oysters, brachi-opods, other mollusks, and ammonites up to 492 m. Theammonite faunas indicate the first occurrence of openmarine environments within the gulf. According to Wied-mann (pers. comm., 1977) this rock unit belongs to thelate Aptian (Gargasian, Clansaysian).

The following rock series, from Aa 492 to A 610 m,consists mainly of green to olive marls with bituminouslayers and frequent interbedded yellowish layers of cal-carenites and calcareous sandstones, a few up to 10 cmthick. In the lower part (Aa 500 m) are oxidized smallammonites and mollusks, in the upper part small oys-ters and other mollusks occur. The lower sequence is notcomplete: a fault truncates the unit. In the uppermostpart (A 550-610 m) are well-bedded and nodular lime-stones and calcarenites that contain mollusk shells andshell debris.

The next unit above (A 610-805 m) consists of grey togreen marls with four intercalated arenitic rock sequenc-es (series 1-4, Fig. 3), each 15 to 20 m thick. These con-sist of reddish to pink calcareous sandstones, grey andwhite limestones, and dolomitic limestones. Within thecalcareous sandstones cross bedding, ripple cross bed-ding and lamination are observed. In the basal parts ofthe dolomitic limestones intraformational breccias areoften found. Trace fossils are rare, whereas oysters withmaximum shell diameters up to 120 mm and coquinabeds are abundant.

Cenomanian-Turonian SequenceThe sequence from A 805-1125 m consists mainly of

grey marls. Intercalations of limestones and calcarenitesshow cross stratification, shell layers, and coquina beds.

925


1200

1100

1000

* 900

800

700

600

600

.§ 500

I 400

300

Lithology Rock series

Bathymetry

— 0) M-Stratigraphy ~ _ j .

rr

Massivecarbonateseries

Oyster marlsandlimestoneseries

Gray marlswithdolomite,limestones,andcalcareniteseries 1—4

Olive greenmarls,interbeddedyellowsandstones

Limestone marlsConglomerate

Red beds, dolomites

Marls

ConglomerateMarls, limestone

Conglomerate

Red beds

Limestone

Marls, limestone

Turonian

1125

Cenomanian

746Vraconian

-L720T 7 1 0

Albian

Fault

500

lateAptian

earlyAptian—

lateBarremian

Barremian398

360

Fault

Hauterivian289

Berriasian— >-

r7--1137] Layered sandstone

4 ^ • : . . ' | Calcarenite

'"Zf.ßl, Crossbedding

Transgression

Regression

Figure 3. Generalized profile of the Lower and mid-Cretaceous sequence at Askouti, containing standard lithol-ogy, rock units, biostratigraphic data, and paleobathymetry. Sample number in text corresponds to the posi-tion in sections Aa and A; stratigraphic boundaries correspond to data in Table 1.

926


Rich assemblages of oysters with shell diameters up to150 mm suggest nearby oyster reefs. Trace fossils, mol-lusks, and several fragments of echinoids indicate peri-ods of rich benthic life in some places and at certaintimes. Dolomite, red marls, and gypsum are also ob-served. Alternation of these quite different rocks withinthis sequence suggests that the sediments accumulatedunder fluctuating shallow-marine to lagoonal conditions.

The uppermost rock unit (A 1125-1200 m) consistsof a massive carbonate sequence with limestones anddolomites (Fig. 3). The limestones are often rich in nod-ules and layers of chert. This unit is followed in the fieldover large areas and is one of the most important refer-ence horizons of the Cretaceous in the High Atlas. Itrepresents the second main transgressive event in theCretaceous Atlas-Gulf (Stamm and Thein, 1982).

BIOSTRATIGRAPHYSeveral marlstone samples and thin sections of the car-

bonate facies were studied to document the following fo-raminiferal stratigraphy. The stratigraphic scheme (Ta-ble 1) is applied following van Hinte (1976). Diagnosticspecies used in this report are listed in Table 2.

Lower Cretaceous: Berriasian-Aptian (Aa 270-500 m)In the lower part of the section, samples Aa 287.0

and Aa 287.7 are dominated by Buccicrenata italica withsome rare specimens of Triplasia (Plate 1, Fig. 2). Oc-currence of B. italica may indicate a Berriasian through

Table 1. Biostratigraphic summary of the Askouti section.

Interval*1

(m)

270-287

289-360

360-398

398-460

460-500

500-710 ±

± 720-746

746-1125

± 1130-1200

Ages with diagnosticforaminiferal species

Berriasian-ValanginianBuccicrenata italica

HauterivianDorothia kummi

BarremianChoffatella dedpiensDorothia kummi

late Barremian-early AptianBarren

late AptianGlobigerinelloides ferreolensisClavihedbergella bizonaeGlobigerinelloides blowi

AlbianFavusella washitensisTicinella bejaouaensisT. primulaHedbergella amabilisH. planispiraGlobigerinelloides gyroidinaeformis

VraconianHeterohelix moremani

CenomanianPraealveolinaPseudodomiaCribratina texanaGavelinopsis

Turanian"Zone à grandes Globigérines"

See Figure 3.

Table 2. Diagnostic species of foraminifers cit-ed in this chapter.

Gavelinella intermedia (Berthelin)Globigerinelloides blowi (Bolli)Favusella washitensis (Carsey)Clavihedbergella bizonae (Chevalier)Cribratina texana (Conrad)Valvulineria gracillima (Dam)Buccicrenata italica Dieni and MassariHedbergella infracretacea (Glaessner)Heterohelix moremani (Morrow)Globigerinelloides ferreolensis MoulladeHedbergella sigali MoulladeGlobigerinelloides gyroidinaeformis MoulladeEpistomina spinulifera (Reuss)Pseudonodosaria humilis RoemerChoffatella dedpiens (Schlamberger)Lamarckina lamplughi (Sherlock)Tichinella bejaouaensis SigalHedbergella planispira (Tappan)Hedbergella amabilis (Tappan)Dorothia kummi Zedler

Valanginian age for the lowermost rock unit (Aa 270-289 m, Fig. 3). Ascoli (1976) reported B. italica from theCretaceous shelf basin of Nova Scotia, North America;thus an isochronic biostratigraphic level between the HighAtlas and Nova Scotian basins is indicated. Samples Aa296.0 and Aa 299.0 contain rare specimens of Dorothiakummi, Ammodiscus, and Lenticulina, abundant echi-noid spines, and small mollusks that suggest a probableearly Hauterivian-Valanginian age. The red bed faciesof Hauterivian age (Aa 330-360 m, Fig. 3) is barren ofmicrofossils.

The lower Barremian marls and interbedded limestonesamples in the interval Aa 380 to 398 m contain variableamounts of ostracodes and of calcareous benthic andagglutinated foraminifers. The assemblage also includessporadic distribution of small mollusks, echinoid spines,and a few bryozoans. Typical Barremian species includeDorothia kummi and Choffatella dedpiens in addition toTrochammina depressa and species of Lenticulina, Ha-plophragmoides, and Ammobaculites. The upper Barre-mian-lower Aptian facies (Aa 398-460 m, Fig. 3) is al-most barren of microfossils.

The overlying marls and limestones in the Aa 460-500m interval contain relatively abundant foraminifers. Plank-tonic species indicate a late Aptian age (samples Aa443.5; Aa 475.5; Aa 481.0; Aa 490.7; Aa 497.1). TypicalAptian species include Globigerinelloides ferreolensis,G. blowi, Clavihedbergella bizonae, Hedbergella infra-cretacea, H. planispira, H. sigali, and Ticinella bejaouaen-sis. Some benthic taxa are Vaginulina, Lenticulina,Dentalina, Frondicularia, Nodosaria, Epistomina spin-ulifera, Gavelinella intermedia, and Lamarckina lam-plughi. In addition, the assemblage also shows sporadicoccurrence of Dorothia, Textularia, Tritaxia, and Reo-phax. Sample Aa 481.0 typically contains upper Aptianspecies, and planktonic: benthic ratios average 20:80(Plate 1, Fig. 1). In general, the upper Aptian samplescontain relatively abundant nodosariids, whereas rota-loid forms and agglutinated foraminifers are rare.

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Mid-Cretaceous: Albian-Turonian(Aa 500-A 1200 m)

The Aptian-Albian boundary occurs at approximately500 m, whereas the Albian extends upward to more than710 m in the Askouti section (Fig. 3).

The Lower Albian marls contain rare planktonic for-aminifers, but benthic foraminifers are frequent and di-verse. Typical planktonics are Ticinella bejaouaensis,Favusella washitensis, T. primula, Hedbergella amabi-lis, and H. planispira. Typical benthics are Valvulineriagracillima and Epistomina spinulifera. Nodosariids areabundant with a high frequency of lenticulines, but ag-glutinated foraminifers such as Textularia, Dorothia,Reophax, and Haplophragmoides are rare; sample Aa517.5 yields an abundant assemblage of Trochamminadepressa.

The middle and upper Albian series (samples Aa 552.2,Aa 557.0, Aa 560.0, A 627.5, A 647.5, A 680.0, A685.9, A 688.0, A 689.0, A 692.5, A 699.0, and A709.5) in the interval from 552 to 710 m are nearly de-void of pelagics, and the upper Albian samples from A605 to 710 m are barren of planktonic species. However,some middle Albian species include Globigerinelloidesgyroidinaeformis, Hedbergella amabilis, and H. plani-spira. These foraminifers are epipelagics (they inhabitedthe upper few meters of the water column) and indicatenearshore conditions. Benthic foraminifers are rare tofrequent, and ostracodes show variable abundances; echi-noid spines, small mollusks, and fish teeth occur as mi-nor components in the samples. Interestingly, the upperAlbian sample yields relatively abundant fresh-or brack-ish-water algae (charophytes, Plate 2, Fig. 1), and ostra-codes. Typical benthic foraminiferal species are Valvu-lineria gracillima, Pseudonodosaria humilis, extremelysmall specimens of Dentalina, and relatively commonlenticulines.

The uppermost Albian, or so-called Vraconian, in-cludes oyster limestones and interbedded marls (samplesA 735.0; A 760.5; A 784.7; A 802.7; A 844.0). The marlsamples contain abundant epipelagic heterohelicids suchas Heterohelix moremani (samples A 760.5; A 802.7).The assemblage also includes other minor componentssuch as ostracodes, small mollusks, and agglutinated fora-minifers such as Haplophragmoides. The interbeddedcalcareous limestones and calcarenites yield specimensof Dicyclina, miliolids (Quinqueloculina, Cuneolina), andshell debris, including echinoid spines and algal frag-ments (A 735.5; A 847.7).

The first occurrence of Praealveolina in sample A846.3 marks the Vraconian/Cenomanian boundary; theCenomanian is represented in the interval from A 846 to1125 m in the Askouti section. The Cenomanian sequencedisplays an upward continuation of the underlying Vra-conian facies. Thin sections of samples A 846.3, A866.5, A 874.3, and A 1046.0 include imperforate fora-minifers such as Praealveolina, Pseudodomia, Quinquelo-culina, and Dicyclina, algal fragments, and shell debris.These microfossils are embedded in sparry oolitic andintraclastic micritic matrix (Plate 3, Figs. 1-3).

The marl samples A 877.2, A 879.0, A 921.3, and A972.5 represent an early Cenomanian age. They contain

rare to common benthic microfossils, whereas plankton-ic species are absent. The lower Cenomanian assemblageincludes Quinqueloculina, Cribratina texana, Cuneolina,Daxia, and Gavelinopsis. In addition to this benthic fau-na, the assemblage yields abundant ostracodes in somesamples; small mollusks, bryozoans, and echinoid spinesare present as minor components. Sample A 993.5 inthe upper part of the early Cenomanian is barren of mi-crofossils; the washed residue contains only gypsumfragments. Sample A 1001.5 consists mainly of aggluti-nated foraminifers including Haplophragmoides, Am-mobaculites, and Reophax (Plate 2, Fig. 2). The upperCenomanian samples (A 1014.2, A 1037.1, A 1046.5, A1071.5, A 1073.5, A 1100.0, and A 1125.0) display vari-able amounts of ostracodes and calcareous benthic fora-minifers (Plate 2, Fig. 3). The benthic forms includeAmmobaculites, Cribratina texana, Haplophragmoides,and Cuneolina. The rotaliid forms such as Gavelinopsisare frequently distributed in the upper Cenomaniansamples. Other miscellaneous microfossils such as echi-noid spines, bryozoans, and small mollusks were found.

The lithologic change at A 1125 m (Fig. 3) coincideswith the biostratigraphic boundary, marking an impor-tant stratigraphic horizon at 1125-1200 m in the Askoutisection that can be correlated in the entire High Atlasregion. Sample 1139.0 exhibits a foraminiferal biomi-crite microfacies (Plate 3, Fig. 4) containing small-sizedand abundant hedbergellids. The hedbergellids in the fine,muddy matrix correspond stratigraphically to the Hed-bergella lehmanni Zone—"Zone à grandes Globigérines"of the lower Turonian proposed by van Hinte (1976).This zone is also identified in the western facies of theAtlas-Gulf (Wiedmann et al., 1978; Butt, 1982).

PALEOECOLOGY, PALEOENVIRONMENT, ANDPALEOBATHYMETRY

After the deposition of the Upper Jurassic shallow-water carbonate platform facies (Adams, 1979), the At-las-Gulf evolved into a near-shore shelf environment dur-ing the Berriasian through Valanginian. The interbed-ded oyster shell beds and marly limestones containingabundant lituolids such as Buccicrenata italica (Plate 1,Fig. 2) and rare Triplasia suggest an intertidal watermass within the littoral zone, with water depths of a fewmeters. Rare specimens of textulariids such as Dorothia,nodosariids such as Lenticulina, and Ammodiscus, in-cluding rare bryozoans near the Valanginian-Hauter-ivian boundary, imply a progressive deepening of the basinduring the Cretaceous transgression (Fig. 3). The Hau-terivian red bed facies, however, suggest a regression andlowering of the sea level.

The Lower Barremian facies apparently represent la-goonal to inner-shelf environments with oscillating brack-ish conditions following the Hauterivian shallowing event.This interpretation is based on the presence of relativelyabundant ostracodes, nodosariids such as Lenticulina,and variable amounts of foraminifers such as Haplophrag-moides, Ammobaculites, and Trochammina depressa,as well as other miscellaneous microfossils, such as echi-noid spines, small mollusks, and rare bryozoans.

The upper Barremian to lower Aptian deposits (Fig.3) reveal nonmarine fluviatile to deltaic activity. These

928


sediments document a retreat of the sea level, revealinganother basinwide regression of marine conditions.

The upper Aptian marls contain abundant nodosari-ids such as Lenticulina, Nodosaria, Frondicularia, andDentalina, rotaliid forms such as Gavelinella and Epis-tomina, and rare to common small planktonic foramini-fers. Sample Aa 481.0 consists of a relatively diverse fo-raminiferal assemblage with a planktonic: benthic ratioof 20:80 that suggests an inner-shelf environment withopen sea conditions. The upper Aptian flooding, how-ever, marks a basinwide transgression revealing both asubmergence and elimination of the early Aptian deltaicenvironment in the inner Atlas-Gulf basin.

The late Aptian deep-water shelf environment con-tinued during the early Albian period. Although the lowerAlbian facies reveal a marked decrease of the planktonicspecies, the benthic foraminifers are more diverse; theyinclude upper Aptian long ranging and diverse nodosa-riids and rotaliid forms such as Valvulineria gracillima.The lower Albian bituminous marls also contain someagglutinated foraminifers such as Reophax, Saccamina,Trochammina, Haplophragmoides, Dorothia, and Tex-tularia. Such facies may signal calcite depletion relatedto reducing conditions in a relatively deep shelf-basinenvironment.

The deep-water shelf environment continued, throughthe middle Albian, but during the late Albian the abun-dance of the microfossils was greatly reduced; the plank-tonic foraminifers are absent, and benthic forms arevery rare. In contrast, some upper Albian samples con-sist mainly of abundant ostracodes and charophytes,whereas others include miscellaneous microfossils suchas echinoid spines and smal mollusks. The upper Albi-an microfossils suggest a sh, Uowing shelf basin, and thecharophyte assemblage indicates brackish to freshwaterconditions (Plate 2, Fig. 1).

The uppermost Albian or Vraconian carbonate facieswith interbedded marls contains abundant heterohelicidsand rare ostracodes, small mollusks, and a few aggluti-nated foraminifers. These microfossils suggest deepen-ing of the basin following the upper Albian shallowing.The interbedded calcarenites that contain algal fragmentsand the associated miliolids indicate near-shore deposi-tion.

The Vraconian carbonate depositional environmentcontinued during the Cenomanian period. Imperforateforaminifers such as Praealveolina, Pseudodomia, Quin-queloculina, and Cuneolina, in association with algalfragments, echinoid, and shell debris (Plate 3, Figs. 1-3)embedded in micritic and oolitic matrix, indicate oscil-lating low- and high-energy environments. The praeal-veonid microfacies shown in Plate 3 (Figs. 1-3), com-prising Praealveolina, Pseudodomia, and Cuneolina, wasalso documented from the mid-Cretaceous shallow-wa-ter deposits in the Tethyan region (Hamaoui, 1979). Thealgae and larger foraminifers such as Praealveolina andCuneolina favored warm, sunlit conditions of the litto-ral zone. Accordingly, interbedded gypsum and red-bedfacies suggest intense, warm, hypersaline to oxidizing con-ditions. Sample A 1001.5, comprising agglutinated fora-minifers such as Rheophax, Haplophragmoides, andAmmobaculites, indicates fluctuating hyposaline or salt

marsh conditions. Similar depositional environments forthe Upper Cretaceous marginal sediments of the Horse-shoe region of southern Alberta were proposed on thebasis of agglutinated associations by Wall (1976).

The intermittent evaporitic and brackish environmentof the late Cenomanian implies a retreat of the sea level.Interbedded marls containing rotaliid forms such as Ga-velinopsis and agglutinated forms such as Cribratina tex-ana and Cuneolina, with variable ratios of ostracodes tobenthic foraminifers and a total lack of pelagic foramin-ifers, suggest oscillating inner-shelf to lagoonal deposi-tional environments during the Cenomanian (Fig. 3).

During the Turonian, a major facies change occurred.Lithologic data document the cessation of the shallow-marine Cenomanian environments. Abundant hedbergel-lids (Plate 3, Fig. 4) were apparently deposited in mid-shelf environments with open sea conditions. The innerAtlas-Gulf basin reveals a greater water depth that coin-cides with a large-scale submergence and a transgressionof the entire Atlas region during the early Turonian.This increase in water depth also corresponds to thedeepening of the western margin of the Atlas coastal ba-sin, suggesting a synchronous transgressive event.

PALEOCEANOGRAPHIC REVIEWIn summary, microfossils from the Lower to mid-Cre-

taceous sediments of the Askouti section document thedevelopment of lagoonal to mid-shelf environments.Combined with lithological data, microfossil data fromthe section record frequent changes of depositional en-vironments. According to all the data now available, theproposed sedimentation model is based on the assump-tions of continuous subsidence in the Gulf, lack of ma-jor climatic changes in this region, and a somewhat ele-vated position of the bordering highs. The model is sub-stantiated by the character of the marginal facies and ofthe sediments in the interior of the Gulf. Terrigeneousinflux from the continent may have continued duringthe Early to mid-Cretaceous under these conditions.

Figure 4 shows the sedimentation model which wasproposed by Wurster and Stets (1982) for the inner partof the Atlas-Gulf using sedimentological data only. Epi-sodic rises of the sea level, shown on the left, correspondwith the position of the littoral zone, on the right. Sedi-mentological and paleoenvironmental data show thatsubsidence in the Atlas-Gulf was nearly offset by sedi-mentation during the Cretaceous. According to our model,minor variations or oscillations of the sea level causedmajor transgressions or regressions that had a strong in-fluence on benthic and planktonic life and controlledthe terrigeneous influx from the adjacent continent.High-standing sea levels restricted the elastics from thecontinent to the inner part of the basin, whereas thelowering of sea level allowed the clastic material to reachthe Atlantic coastal margin.

In the sedimentation model the Askouti section is sit-uated to the west, far away from the strong influence ofcontinental conditions (Fig. 4). The micropaleontologi-cal data support this model. The low frequency of plank-tonic foraminifers prohibited us from using planktonic:benthic ratios as a reliable paleobathymetric parameter.

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Turanian

Aptian

Barremian

Atlantic Ocean

Deep sea sediments

Africa

6 Marine sediments

Coastline

Continental sediments

Sea level

Littoral trend

Figure 4. Sedimentation model of the Atlas-Gulf: interpretative sketch elucidating the migration of the littoral zone and the facies distribution,caused by several stages of a rising sea level; based on Wurster and Stets (1982).

Nevertheless, small-sized planktonics reveal epipelagiczone activity from a near-shore water mass. The benthicforaminifers also lived under stressed biotope conditionsand were influenced by sediment influx derived from alowering of sea level. The syndepositional subsidencewas nearly continuous, but markedly lower in compar-ison to the western margin of the Atlas-Gulf (Wied-mann et al., 1978). In response to sea level changes, thebasin experienced episodic marine and continental con-ditions during the Early to mid-Cretaceous period in theAskouti area.

The upper Barremian-lower Aptian deltaic and con-tinental facies and the bituminous olive green marls ofearly Albian age are equivalents of the deep-sea blackshale in the Atlantic Ocean (Fig. 4). The environmentsof the organic-matter-rich Early Cretaceous facies arediscussed by Schlanger and Jenkins (1976) for the othercoastal basins around the Atlantic. These authors ar-gued that such facies may indicate oceanwide anoxicevents during the Early to mid-Cretaceous because ofthe restricted circulation and a maximum expansion ofthe oxygen-minimum zone (Arthur, 1979; Einsele andWiedmann, 1982; Butt, 1982; Ryan and Cita, 1977).

Following the frequent Cenomanian oscillations in sealevel, the inner Atlas-Gulf was submerged under a deeperwater mass during the early Turonian. According to Ar-thur (1979) and Roth and Bowdler (1981), deep-waterconnections within the Atlantic improved at the end ofthe mid-Cretaceous, resulting in better ventilation andin the replacement of black shales by a multicoloredclay and chalk facies (Fig. 4). Structural opening of theNorth and South Atlantic may have produced this majorpaleoceanographic change (Butt, 1982), which in turncontrolled the contemporaneous flooding of the coastalbasin by the rise in sea level (Sliter, 1977; Wiedmann etal., 1978, 1982; Lancelot and Winterer, 1980; Wursterand Stets, 1982).

Among the variables thought to be responsible forchanges of lithofacies, paleoenvironments, paleoecolo-gy, and paleobathymetry in the Askouti section and else-where in the Gulf area, changes in sea level may havebeen the most important factor.

CONCLUSIONSDetailed studies of a Lower to mid-Cretaceous sequence

near Askouti at the southwestern flank of the High At-

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las mountain range corroborate data from Atlantic Oceansediments and from sediments in the interior of the At-las coastal basin of Morocco.

1. The Askouti section is subdivided into several rockunits which reflect frequent changes in sedimentary de-positional environments, ranging from continental redbeds to open marine carbonates. Different transgressiveevents are documented by conglomerates in the Barremi-an and late Aptian and by marine carbonates in the Ber-riasian-Valanginian and in the Turonian; regressions areexpressed by deltaic to fluviatile red beds in the Hauter-ivian and in the late Barremian to early Aptian, and bylagoonal deposits containing gypsum in the Cenoma-nian.

2. The micropaleontological record supported byplanktonic and benthic foraminifers allows an approxi-mate biostratigraphic classification of the rock units.Stratigraphic boundaries are less precise in unfossilifer-ous parts of the section or those barren of conclusiveforaminifers such as those of the Vraconian and Ceno-manian sequences.

3. Foraminifers, ostracodes, charophytes, and othermiscellaneous microfossils and relics display shallow-ma-rine to logoonal and brackish depositional environments,with relatively frequent oscillation of water depths dur-ing the Early to mid-Cretaceous. Marine sediments rangefrom the littoral zone to mid-shelf conditions. The trans-gressions and regressions suggested by the lithologicaldata in the Askouti section are thus sustained by the mi-cropaleontological record. Increasingly frequent changesof living and depositional conditions during the latestAlbian and the Cenomanian are documented.

4. A sedimentation model based on the data now avail-able suggests that eustatic sea level changes versus subsi-dence are considered the main factors that controlled de-positional conditions, paleoecology, and paleoenviron-ment. Within this model, it is suggested that major risesof the sea level occurred in the late Aptian and early Tu-ronian, minor ones in the Berriasian to Valanginian, earlyBarremian, and Cenomanian.

ACKNOWLEDGMENTS

The authors are indebted to Drs. Hilali, Bensaid, and Dahmani(Ministère de 1'Energie et des Mines, Division de la Géologie), Rabat, Mo-rocco, who facilitated the field work in the High Atlas in every respect.For critically reviewing the draft of the manuscript, we thank Drs. H. P.Lutherbacher, Tubingen, K. Hinz, Bundesanstalt fur Geowissenschaftenund Rohstoffe, Hannover, and Don Eicher, Colorado. Thanks are alsodue to Dr. D. Herm, Munich, for providing useful references. WilliamV. Sliter, U.S. Geological Survey, Menlo Park, California, kindly com-mented upon the manuscript, and improved the English style. Fieldwork done in 1975 to 1982 was largely supported by the German Sci-ence Foundation, Bonn (DFG, grants Wu 32/15-20).

REFERENCES

Adams, A. E., 1979. Sedimentary environment and palaeogeographyof the Western High Atlas, Morocco, during the Middle and LateJurassic. Palaeogeogr., Palaeoclimatol, Palaeoecol., 28:185-196.

Ager, D. V., 1974. The Western High Atlas of Morocco and their sig-nificance in the history of the North Atlantic. Proc. Geol. Ass.,85:23-41.

Ambroggi, R., 1963. Etude Géologique du Versant Meridional du HautAtlas Occidental et de la Plaine du Souss. Notes Mem. Serv. Geol.Maroc, 157.

Arthur, M. A., 1979. North Atlantic Cretaceous shales: The record atSite 398, and a brief comparison with other occurrences. In Si-

buet, J . -C, Ryan, W. B. F., et al., lnit. Repts. DSDP, 47, Pt. 2:Washington (U.S. Govt. Printing Office), 719-752.

Ascoli, P., 1976. Foraminiferal and ostracod biostratigraphy of theMesozoic-Cenozoic, Scotian Shelf, Atlantic Canada. Marit. Sedi-ments, Spec. Publ. 1 (B, Paleoecol. Biostratigr.): 653-741.

Behrens, M., Krumsiek, K., Meyer, D. E., Schàfer, A., Siehl, A., Stets, J.,Thein, J., Wurster, P., 1978. Sedimentationsablàufe im Atlas-Golf(Kreide-Küstenbecken Marokko). Geol. Rundsch., 67:424-453.

Behrens, M., and Siehl, A., 1982. Sedimentation in the Atlas Gulf I:Lower Cretaceus elastics. In von Rad, U , Hinz, K., Sarnthein, M.,and Seibold, E. (Eds.), Geology of the Northwest African ContinentalMargin: Berlin (Springer-Verlag), pp. 427-438.

Butt, A., 1982. Micropaleontological bathymetry of the Cretaceous ofwestern Morocco. Palaeogeogr., Palaeoclimatol., Palaeoecol., 37:235-275.

Duffaud, M. F., Brun, L., and Plauchut, B., 1966. Le bassin du Sud-ouest Marocain. In Reyre, D. (Ed.), Bassins sédimentaires du literalAfricain. Assoc. Serv. Geol. Afr., 1:5-12.

Einsele, G., and Wiedmann, J., 1982. Türonian black shales in the Moroc-can coastal basin: First upwelling in the Atlantic Ocean ? In von Rad,U , Hinz, K., Sarnthein, M., Seibold, E. (Eds), Geology of the North-west African Continental Margin: Berlin (Springer-Verlag), pp.396-414.

Hamaoui, M., 1979. Contribution à 1'étude du Cénomano-Turoniend'Israél; comparaisons micropaléontologiques avec quelques regionsMésogéennes [These de Doctorat]. Université Pierre et Marie Cu-rie, Paris.

Lancelot, Y., and Winterer, E. L., 1980. Evolution of the Moroccanoceanic basin and adjacent continental margin—a synthesis. InLancelot, Y., Winterer, E. L., et al., lnit. Repts. DSDP, 50: Wash-ington (U.S. Govt. Printing Office), 801-821.

Roch, E., 1930. Etudes Géologiques dans la Region Meridional duMaroc occidental. Notes Mem. Serv. Geol. Maroc, 9.

Rod, E., 1962. Fault pattern, northwest corner of the Sahara Shield.Am. Assoc. Pet. Geol. Bull., 46:529-552.

Roth, P. H., and Bowdler, J. L., 1981. Middle Cretaceous calcareousnannoplankton biogeography and oceanography of the AtlanticOcean. In Warme, J. E., Douglas, R. G., and Winterer, E. L.(Eds.), The Deep Sea Drilling Project: A Decade of Progress. Soc.Econ. Paleontol. Mineral, Spec. Publ., 32:517-546.

Ryan, W. B. F , and Cita, M. B., 1977. Ignorance concerning episodesof oceanwide stagnation. Mar. Geol., 21:197-215.

Schlanger, S. O., and Jenkyns, H. C , 1976. Cretaceous oceanic anox-ic events: Causes and consequences. Geol. Mijnbouw, 55:179-184.

Sliter, W. V., 1977. Cretaceous foraminifers from the SouthwesternAtlantic Ocean, Leg 36, Deep Sea Drilling Project. In Barker, P.F., Dalziel, I. W. D., et al., lnit. Repts. DSDP, 36:519-537.

Stamm, R., and Thein, J., 1982. Sedimentation in the Atlas Gulf III:Turonian carbonates. In von Rad, U., Hinz, K., Sarnthein, M.,and Seibold, E. (Eds.), Geology of the Northwest African Conti-nental Margin: Berlin (Springer-Verlag), pp. 459-474.

Stets, J., and Wurster, P., 1982. Atlas and Atlantic-structural rela-tions. In von Rad, U , Hinz, K., Sarnthein, M., and Seibold, E.(Eds.), Geology of the Northwest African Continental Margin: Berlin(Springer-Verlag), pp. 69-85.

van Hinte, J. E., 1976. A Cretaceous time scale. Am. Assoc. Pet.Geol. Bull., 60:269-287.

Wall, J. H., 1976. Marginal marine foraminifera from the Late Creta-ceous Bearpaw-Horseshoe Canyon Transition, Southern Alberta,Canada. J. Foram. Res., 6:193-201.

Wiedmann, J., Butt, A., and Einsele, G., 1978. Vergleich von marokkan-ischen Kreideküstenaufschlüssen und Tiefseebohrungen (DSDP):Stratigraphie, Palàoenvironment und Subsidenz an einem passivenKontinentalrand. Geol. Rundsch., 67:454-508.

, 1982. Cretaceous stratigraphy, environment, and subsi-dence history at the Moroccan continental margin. In von Rad, U.,Hinz, K., Sarnthein, M., and Seibold, E., Eds., Geology of theNorthwest African Continental Margin: Berlin (Springer-Verlag),pp. 366-395.

Wurster, P., and Stets, J., 1982. Sedimentation in the Atlas Gulf II:Mid-Cretaceous events. In von Rad, U., Hinz, K., Sarnthein, M.,and Seibold, E. (Eds.), Geology of the Northwest African Conti-nental Margin: Berlin (Springer-Verlag), pp. 439-458.

Date of Initial Receipt: May 24, 1983Date of Acceptance: October 25, 1983

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1 mm

Plate 1. Lower Cretaceous microfossils in the High Atlas coastal basin. 1. Upper Aptian nodosariids; note abundant lenticulines and rare echi-noid spines. Paleobathymetric zone, inner shelf; Askouti section, sample Aa 481.0. 2. Berriasian-Valanginian assemblage of Buccicrenata itali-ca Dieni and Massari (A). Paleobathymetric zone, littoral; Askouti section, sample Aa 287.0.

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1 mm 1 mm

1 mm

Plate 2. Mid-Cretaceous microfossils in the High Atlas coastal basin. 1. Upper Albian charophyte assemblage. Paleobathymetric zone, lagoonalwith brackish or freshwater conditions; Askouti section, Sample Aa 709.5. 2. Upper Cenomanian agglutinated foraminiferal assemblage,showing specimens of Reophax, Ammobaculites, and Haplophragmoides. Paleobathymetric zone, lagoonal with brackish or salt marsh condi-tions; Askouti section, Sample A 1001.5. 3. Upper Cenomanian micro fossil assemblage; note abundant ostracodes and rare foraminifers suchas Cuneolina (A) and Quinqueloculina (B). Paleobathymetric zone, lagoonal-inner shelf; Askouti section, Sample Aa 972.5.

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0.5 mm 1 mm

Plate 3. Photomicrographs of mid-Cretaceous microfacies in the High Atlas coastal basin. 1. Cenomanian praealveolinid biomicrite (A). Paleo-bathymetric zone, near shore-inner shelf; Askouti section. 2. Enlargement of 1. Specimen of Pseudedomia (A)? 3. Cenomanian cuneolinidintraclastic biomicrite. Paleobathymetric zone, near shore-inner shelf; {Cuneoliona (A). Askouti section. 4. Early Turanian globigerinid biomi-crite. Paleobathymetric zone, mid-shelf (Hedbergella lehmanni, "Zone à grandes Globigérines"); Askouti section.

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