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________________________________________________ OC __ E_A_N_O_L_O_G_'C_A __ Stratigraphy, structure, paleoenvironment S)'nthesis Pal cocnvÎronmcnt Subsidence hi slory Mauga n Escarpmcnt and subsidence history Synlhèsc Pa léocnvironnerncnl Subsidence Escarpeme nt de Mazagan Maroc of the Mazagan Escarpment off central Morocco : a CY AMAZ synthesis ABSTRA CT Ulrich vo n Rad , Jean -Marie AU lc ndc , Étienne Ru c ll an and CYAMAZ group CY AM AZ group: J.-M. Auzcndc ". U. von Rad b , B. P .tepck b , M .Cous in d , H. Dostmann b, M. El M. Jaffrczo r, Y. Lancelot f, E. Ru c ll an " T. Stei- ger h • I FREMER , Centre de Brest, BP n0 337 , 29273 Brest Cedex, France. b Bundcsa nstalt für Gcowisscnscha rt cn und Roh slOfrc (BRC) , P ostfach 510153 , D 3000 Hann ayc r 51 , FRG. c IFREMER, 66 A ve nue d'Iéna, 75 116 Paris Cedex, France. d CE RQV . BP nO 48, 06230 Villefranche sur Mer, France. C Mini stère de l'Énergie ct des Min es, Rabat . Morocco. f Université Pi crrc ct Maric Curie, 4 place Ju ssieu ,75230 Pa ri s Cedex 05 , France. 1 Univers it é de Bretagne Occidentale-G IS , Océanologie CI Géodynamique , Avenue le Gorgeu. 29200 Brest. France. h Institut für Pa laontologie und hi storischc Geo logie der U ni versitat , Richard - Wagner-SIr. 10 , D 8000 Münche n 2, FRG. Th e stratigraphy and str ucture of the o ld , starved pa ss ive mar gi n of the Mazagan Plaleau and the adjace nt Esc arpme ll t which extcnds from 1000-3 000 m water dcpth was studicd du ring the co financed French-German CY AMAZ dcep diving campai gn which oblained 130 in-situ samples, supplcmented by direct sea floor observation s du ring 18 dive traverses. The fa ci es cvolution of the Mazagan car bonatc platform bctween Kimmeridgian and Valanginian times WolS ma inl )' influe nced by blockfaulting and sca-Icvcl flu ctuation s. Reg ress ive peri ods occurred during Kimmer id gianffilhonian and Late Berrias ia n tim es, and arc scparatcd by a late Tithonian/ea rl y Berriasian transgression. T he drowning of Ihe main carbonate platrorm and the Early Cretaccous 10 Paleoge ne hi story of the hemipelagic to pelagic post-pla tf orm sediments was strongly influenced by vertical lectonics and sea levcl flu ctuations. ?U pper Berriasian to ? I-Iau te ri vian quartz-bcaring bioclastic wack esto nes docume nt Ihe transition from the carbo nate platform 10 the hemipelagic deposition on the drow ned plalform margin . Wcll·be dded calcarenites in the El Jadida Canyon area arc intc rpreted as turbidit es, forming the mi ssing link bctwcen a postulalcd Wealdcn-type delta and a maj or d ce p-sea fan. A conspieuous iron oo id - and bclemnite rich, conden sed horizon documents a ross il hardground nea r the Ncoco- mi nn shelfbrca k. Mid ·C retaccous, he mi pclagic marlstones ar c overlain by Upper Crelaceous nannomicrites, limcsto ne breccias and phosphorites. The y document several upwe ll in g and phosphati za tio n cve nts, foll owed by rcworking and mass waslin g. During Jura ss ic 10 mid ·C rc ta ceo us block- raul t in g eve nl S, mi grating in a landward direction, the carbonate plmf o rm was strU C lured into a succession of blocks, eo ntrolled by old Hercy nian !aults Irending 160" or 20" (At lantic direction) or 90- 161
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Page 1: Stratigraphy, structure, paleoenvironment - Archimerarchimer.ifremer.fr/doc/00247/35830/34340.pdf · Stratigraphy, structure, paleoenvironment S)'nthesis PalcocnvÎronmcnt Subsidence

________________________________________________ OC __ E_A_N_O_L_O_G_'C_A __ A_CT_A_,_,_~_4_,_N_'_S_P~~~----

Stratigraphy, structure, paleoenvironment

S)'nthesis Palcocnv Îronmcnt

Subsidence hislory Maugan Escarpmcnt

Mo~

and subsidence history Synlhèsc Pa léocnvironnerncnl

Subsidence Escarpement de Mazagan

Maroc of the Mazagan Escarpment off central Morocco : a CY AMAZ synthesis

ABSTRACT

Ulrich vo n Rad , Jean-Marie AUlc ndc , Étienne Rucllan and CYAMAZ group

CY AM AZ group: J.-M. Auzcndc ". U. von Rad b, B. B iju - Du va l ~ , P.tepck b, M .Cousin d ,

H. Dostma nn b, M. El Asri~, M. Jaffrczo r, Y. Lancelot f, E. Rucllan " T. Stei­ger h

• IFREMER, Centre de Brest, BP n0337, 29273 Brest Cedex, France. b Bundcsanstalt für Gcowisscnscha rtcn und RohslOfrc (BRC), Postfach 510153, D 3000 Hannaycr 51 , FRG. c IFREM ER, 66 Avenue d' Iéna , 75 116 Paris Cedex, France. d CERQV. BP nO 48, 06230 Villefranche sur Mer, France. C Ministère de l'Énergie ct des Mines, Rabat . Morocco. f Université Picrrc c t Maric Curie , 4 place Jussieu ,75230 Paris Cedex 05 , France . 1 Université de Bretagne Occidentale-G IS , Océanologie CI Géodynamique , Avenue le Gorgeu. 29200 Brest. France . h Institut für Pa laontologie und historischc Geologie der Universitat , Richard­Wagner-SIr. 10, D 8000 Münche n 2, FRG.

The stratigraphy and structure of the o ld , starved passive margi n of the Mazaga n Plaleau and the adjace nt Escarpme ll t which extc nds from 1000-3 000 m water dcpth was studicd du ring the cofinanced French-Ge rman CY AMAZ dce p diving campaign which oblained 130 in-situ samples , supplc mented by direct sea floor observations du ring 18 dive traverses. The facies cvolutio n o f the Mazaga n carbonatc platfo rm bctween Kimme ridgian and Valanginian times WolS mainl)' influe nced by blockfaul ting and sca- Icvcl fluctuations. Regressive periods occurred during Kimmeridgianffilhonian and Late Berriasian times, and arc scparatcd by a late Ti tho nian/ea rly Be rriasian transgression . T he drowning of Ihe main carbonate platrorm and the Early Cretaccous 10 Paleoge ne history of the hemipelagic to pe lagic post-platfo rm sedi ments was st rongly influenced by ve rtical lectonics and sea levcl fluctuatio ns. ?U pper Berriasian to ?I-Iau terivian quartz-bcaring bioclast ic wackesto nes docume nt Ihe transition from the carbonate platform 10 the hemipelagic deposition on the drowned plalform margin . Wcll ·bedded calcare nites in the El Jadida Canyon area arc intcrpreted as turbidites, formi ng the missing link bctwcen a postulalcd Wea ldcn-type del ta and a major dcep-sea fan. A conspieuou s iron ooid- and bclemnite rich, condensed horizon documents a rossil hardground nea r the Ncoco­mi nn shelfbrca k. Mid·Cretaccous, hemi pclagic marlstones arc ove rla in by Upper Crelaceous nan no micrites, limcsto ne breccias and phosphori tes. They docume nt seve ral upwell ing and phosphatiza tio n cvents, followed by rcwork ing and mass wasling. During Jurassic 10 mid·Crctaceous block- raul ting eve nlS, migrating in a landwa rd direct io n, the ca rbonate plmfo rm was strUClured into a succession o f blocks, eontrolled by o ld Hercynian !aults Irending 160" o r 20" (At lantic direction) or 90-

161

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U VON RAD (Ir al

RÉSUMÉ

120" (Mcd itc rra ncan direction). An important phase of vertical tcetonism is markcd by the Neoeom ian denudation of the esca rpment. Downfaulting of blocks and mass wastÎng events were accentualCd du ring Eocene and Miocene times. but conti nue until today. Subsidence was non-uni fo rm with at least 3 periods of accelerated subsidence during major short-term block-fault ing even ts. A precursor of the present stcep Mazagan Esea rpment is at least 120 Ma o ld ; thc csca rpme Ol was mainly formed and maintained by vertical tectonics and only slightly infJucnced by non­deposilional hardground formation (bypassing), gravitational mass wasting, defacing, and carbonate dissolution.

Oceanol. Acta, 1984. Submersible Cyana studies of the Mazagan Escarpment (Moroccan continental margin) , CY AMAZ cruise 1982, 161-182.

Stratigraphie, structure, paléoenvironnemen l el histoire de la subsi­dence de l'escarpement de Mazagan au la rge du Maroc central : synthèse des résu ltats de la campagne CY AMA4

La stratigraphie ct la st ructure de la marge passive du plateau de Mazagan et de l'escarpement adjacent (e ntre 1000 ct 3000 m de profondeu r) ont été étudiées du rant la campagne de plongées CYAMAZ (cofi naneée par la France ct la RFA). A l'occasion de 18 plongées, on a prélevé 130 écha ntillons ct observé directcment le fond de la mer. L'évolution des faciès de la plate-forme carbonatée de Mazagan entre le Kimmérid­gien ct le Valanginien a été princi palement infl uencée par des basculemen ts de blocs et des fluctuations du fond mari n. Des périodes régressives se situent au Kimmérid­gienffithonique , ainsi qu 'au Berriasie n supérie ur. Elles sont séparées pa r une transgression datant du Tithonique supérieur au Berriasicn inférieur. L' immersion de la plate-forme carbonatée et l' histoire Crétacé inférieur il Paléogène des séd iments post-plate-forme hémipélagiques â pélagiques, ont été fortement marquées par des fluctuations du niveau de la mer CI par la tectonique verticale; cn particulier une régression du Berriasien supérieu r suivie d'une élévation rapide du niveau de la me r au Valanginien supérieur. Les « wackcstones » biocJastiques li quartz du Berriasien supé rieur à Hauterivien indiquent la transition depu is la platc- forme carbonatée jusqu'au dépôt hémipélagiq ue sur la bordure immergée de la plate­forme. Les calcarénitcs bien litées dans la région du canyon de El Jadida sont interprétées comme des turbidites. formant le lien absent entre un delta de type « Wealdien » ct un « deep-sea fan » . Un ho rizon très mince , condensé el bien e n évidence, riche en ooïde de fer et e n bélemnites, a nnonce un « hardground » fossile il proximité de la rupture de pente au Néocomien. Des marnes hémipélagiques datant du Crétacé moyen sont recouvertes de micrites pélagiq ues à nannoplancton du Crétacé supérieur, de brèches calcaires ct d'une succession hétérogène de phosphori­tes et de brèches phosphoritiques. Ces dépôts confirment l'existence de plusieurs « upwellings» ct phosphatisations suivies de remaniements et de glissements cn masse. Le basc ulement des blocs pendant Je Jurassique supérieur et le Crétacé moyen provoque un recul de la plate-forme en direction du con tinent. Ces blocs so nt contrôlés par des directions tardi-he rcyniennes NI60 et N20 (direct ions atlantiques). N90 ct NI20 (directions méditerranée nnes). Une importante phase de tectonique verticale est ma rquée par la dén udation de l'esca rpement au Néocomien. L'effond re­ment des blocs ct des glissements en masse se situent en particulier au cours de l'Éocène et du Miocène. Ils continuent cependant jusqu'à aujourd'hui. Nous en déduisons une histoire de la subsidence complexe et hétérogè ne, avec au moins trois périodes de subsidence accélérée (non co mpensée par les dépôts) accompagnées d'effondrements importants. Un précurseur de l'actuel escarpement de Mazagan date de 120 Ma au moins. L'escarpement a été créé ct entretenu principalement par la tectonique vert icale. Le non-dépôt (hardgrounds), les gl isse ments en masse, l'é rosion ct la dissolution des carbonates n'ont cu dans 5<1 struct uration qu'un effet limité.

Oceal/ol. Acta, 1984. Études par le submersible Cyana de l'escarpement de Mazagan (marge continentale marocaine) , campagne CYAMAZ 1982, 161-182.

162

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INTRODUCTION

The Mazagan Plateau area represe nt s the oldest Mesozoic, weIl cxposed , sediment-sta rved continenta l margin of the Atlantic Ocean (Fig. 1). He re wc can study the entire margin evol ution from the Triassie to mid-JurassÎC ca rly-rift and Callovian continental break-up to the history of the Jurassic construction , destruct ion and drown ing of the oute r margin of a carbonate platform and to the Cretaceous-Teniary post-platform sedimentation and tectonics. The Maza­gan Plateau bc longs tO the group of Me5Ozoie carbo­nate platforms constructed at the margins of the circum-global Tethys (James, Mountjoy, 1983). The Mazagan paleo-shelf-edge lies weil landward of the supposed ocean-cont inent boundary (Fig. 1). Ven ica l tectonics and sea-lcvcl fl uctuat ions cause dramatic effccts - drowning or exposure - at the shcl f-slopc break of such carbonate platforms (Pitman, Golov­chenko , 1983). During the French-German CY AMAZ cruise wc co ncentrated our cffons on the study of the supcrbly exposed ce nt ral and sou thern parts of the Mazagan Escarpme nt , of El Jadida Canyo n, and of a small fault sca rp on the Mazagan Plateau propc r (Auze nde el al,

, " , ' " Prerif Olis tostrom~

1

n '

/

/

/

~J " ....... 10

~ , -" lél , 6 " W . ,... - - l

L-.....!.11u. , :0

Œ:d 1 , " - "

Figure 1 Geological and SlmClI/ral map v/ lire !>!onxu", cOII/inewal /IIargin Il/rd adjaC/.'w NOTlIr ... esl Africa (modified from I/inl. ct al .. /982. Ilrâr Fig. 9). Legend: / ~ co<ls/(l1 basill$ wi/Ir main/y Cf",nuic fill ; 2 ,.. cO<lslal basi,r:; wi/Ir mainly l'alfuloic Mesozoic jill : 3 .. l'olcanic mass 0/ emrary /slaml archipelago ; 4 = SI/be,op 0/ l'dg/" 0/ bll,ied upper ! urassic cafbollale plalform (offtlrore) ; S = uutero{J 0/ UpIH'r }"rassic carbmwle pialformed/,'C .. 6 = ?7"riassic soli diapir zone (no/ shQw.r lamfword of 4, c.g. in fuJ,wuÎra Basin): 7 .. OUlCTO{JS or SlIbcrops of Precambria" li) Pafeozoic siafic basemenl ; 8 = fimÎl 0/ diapiric Sl fIlClUres (oceammrd limil = magnelÎC Ulromaly S-3 of Roe5ef. 1981, (Js.5Umed to coitrcide morl' Of iess wilh /Iw ocean/colI/i­,u:m boumlory); 9 = 1 sec. 11\17" sedimem isv{Jilclr ; JO = 5ea ... afd ex /e,1I of Miucene nappes or olis/os/romes oflhe Ri/ amI Be/Îc MQlfIllIli,rs: If = loca/ion v/profiles (Fig. / 6./. / 62): / 2 = VSVP si/es: /3 = KC figures 2 011/13 for de/ail. A = Agadir. B '" Basin , K = CrelilUOIIS.

163

CYAMAZ CAMPAIGN SYNTHESIS, MAZAGAN ESCARPMENT

this vol. ; see Fig. 2). These data hcJpcd to supplement the wea lth of new in formation gained by the fOUf DSDP Sites 544-547 during IPOD Lcg 79 ( I-l inz el al., 1982 ; Wintercr , I-linz, 1984) and by previous geophy­sical and dredging surveys (Re nz el al. , 1975 ; Wiss­mann , vo n Rad , 1979; Hinz el al. , 1982).

The main objectives of the CY AMAZ eruise (see also Auzcnde el al., this vol. ) we re the study of: a) the stratigraphy, facies evolution and tcrminat ion of the Late Jurassic carbonate buildup ; b) the stratigraphy, nature and development of thc starved post-platform sedimentation; c) the Mesozoic paleoenvironme nt and paleo-ocea­nography; d) the temporal and spatia l dcve lopment of the struct ural features of the Mazagan Esca rpme nt ; and e) the subsidence history , as modified by ve rtical lectonics, sedi mcnt accum ulation , erosion and sea­levcl fluctuations. The main prerequisites for the solution of these problems arc a) a large set of represe ntative samples across diffe re nt parts of the ca rbonate platform and its Cretaeeous-Tert iary eove r ; b) good in-situ observa­tions of the (micro-)struct urc of the plateau ; and c) a good biost ratigraph ic control.

Unfonunatcly, there were majo r shorlcom ings of these conditions : First, wc were able to colleet " only" 130 roc k sa mples, mostly take n from outerops (il/ situ ) or ve ry close to them. Although the sampling intervals we re not stat istically representative and although we might have missed important lithotypcs and stratigraphie levels, our data base is an order of mag nitude beller alld more exacl Ihall Ihat uf CO!lve ll­t ional dredging and co ring surveys. The second major problem of the CY AMAZ cruisc was the lack of reHable biostratigraphic control , espccially for the platform ca rbonates. Alt hough the limestones arc gencra lly not diage netieally altered , they commonly con tai n only facies-diagnostic fossils, allowi ng only a rough age estimat ion (e.g. .. Late Ju rassic to ca rly Neocomian " ). The biostratigraphie control Is belle r in the post-platform se ries, altho ugh also the re the lack or poor preservation of ca1ca rcous nannoplankton or forami nifera often preve nted deter­minations to the stage leve l (cf Jaffrezo ; Jaffrezo et al. ; èepck , !-Iagn ; Steiger, Cousin ; a Il in th is vo!.). A wealth of dala and interprctations was produeed du ring a nd afte r the SEAZAGAN and CYAMA Z crui scs. Th is info rmation ranges from the fields of morphology and geophysics (bascd on mult ibeam ec hosounder and seismie rcfleetion profiles) to bio­stratigraphy, fac ies analysis, scdimenlology and geo­chemistry. In this papcr wc allempt to sy nthesize the most important result s of the previous ninc chapters, and to compa re the geological deve lopme nt of the Mazaga n Platea u with simila r carbonate platforms around the ce ntral Atlant ic Ocean.

We will al50 add ress fo ur majo r problems of the deve lopment of passive continenta l ma rgi ns enclosing o ld ca rbonate platform sequences : 1) What causes the abrupt termination o r drown ing of carbonate platforms and Ihe stratigraphie turni ng point towa rds he mipclagic conditions?

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U VON RAD Ir Ir

2) ln what ways do globa l sea level fluctuations and venical tectonics influence the evolution of the post­platform seque nce ? 3) What shapes the steep esca rpment of carbonate platforms ? 4) What are the tectonic controls on the subsidence history of this margin?

GEOLOG ICA L AND PHYSIOGRAPHICAL SET­TING

The central Moroccan cont incntal margin is one of the bcst studicd examplcs of a very old, sedime nt-starved passive margi n (Fig. 1). The Northwest African margi­nai or coastal basins with their thick MeSQzoic-Ceno­zoic sedimenta ry fill (Tarfaya , Essaouira/south Atlas and Rharb Basins) arc scparated by the old Paleozoie shields o f the Anti-Atlas Mountains a nd the Moroccan Meseta. The front of the Jurassic carbonate platform occurs ncar the present shelf edge and seaward of this front . we see a zone of scismically detectcd diapiric structures which rcpresent the deposits of an carly- rift e\'apo rite basin. Paleozoic granite was cored , drcdged and drilled (DSDP site 544) on a subsided fault block in front of the Mazagan Plateau (Wissmann , von Rad , 1979 ; Kreuzer el af .• 1984). The outer limit of the diapiric zone probably çoincides roughly with the ocea n/continent boundary ( !-l inz el al. , 1982; Rocser, 1982).

The Mazaga n Escarpment is located about 200 km west of Casablanca and eonstitules an almost 3000 m high submarine cliff, locatcd betwccn thc :scaward edge of thc Ma7..agan l'la tea u and the Seine Abyssal Plain. Reconstructions of the cent ral Atlantic at the end of the Liu ssic show the location of the Mazugan Escarpment betwcen the Arrican continent and a structural high in the northern part of the Nova Scotian margin ; bot h margins were sc parated by a narrow ellrly- rift graben. fi lied by evafXlritic sedime nts (Jansa. Wiedmann. 1982; Wissmann , Rocse r, 1982 ; Ol ivet el al" 1983). Sccause of its steepness, the Mazagan Escarpment provides an except ional oppor­tunity to stud)' the Mesozoic to Te rtiary stratigraphy, pllleoc nvironmcm. and subside nce history o f a nearly sediment-free external carbonate platform. Because the Upper Jurassic to Paleogene cont inental margin sediments of the Atlantic Ocean arc exposed a t this esea rpmcnt. they can bc directly observed and sam­pied fro m a submc rsible . Figure 2 shows the ba thymetry of the Mazagan Plateau (Auzende el al., 1983) lInd the location of the 18 CYANA dives. Figure 3 represe nts a structural map o f the area (see Ruellan el al., this 'lolo). Our Cyana divcs supple mented the info rmation of fo ur DSDP/IPOD sites fro m Leg 79: site 545 on the slope , sitc s 544 a nd 547 on and near Il subsided base ment high , and site 546 on a salt diapi r (Hinz et al. , 1982; and in press). Eightee n dives c nabled uS to take 130 rock sample!l betwcen 3000 m (Iower diving limit o f CYANA) and about 1000 m and more than 6000 COIOf photos during 73 hours o f observation. 8 divcs (No. 84-90, 101) were madc in the sout hern pan o f the steep esea rpmen t (Fig. 5), and 5 dives at its

164

ccntral part (9 1,94-98). Three dives were dcvoted to the upper serics of thc geologica l section : onc on the top of the Mazaga n Plateau (92) and two in the vici nÎty of El Jadida Ca nyon (99, 100) which strong1y erodes the sout hern scarp.

STRATIGRAPHY, FACIES AND PALEOENVI­RONM ENT EVOLUTION

The order tO describe the heterogeneous suite of C Y AMAZ samples, wc applied the methods of micro­facies analysis (Flügcl , 1978). 17 main micro facies (MF) types and seve ral subtypcs we re distinguishcd on thc basis of palcontological and scdimentologica l propcrties (see the Table) and arc describcd and intcrpreled in detail by two prcvious papcrs (Steige r, Cousi n ; von Rad , this voL). Figure 6 summarizes thc stratigraphie fesults of the CYAMAZ expcdition , showing sed iment facies, thickness and approximatc agc of six diffcrent P.1rts of the Mazagan margin which ail had a different development during the past 160 Ma : Morocca n Oasin (sites 370/416). lowcr Maza­ga n slopc (including si te 545) , central and southcrn Mazagan Escarpment, El Jad ida Canyon area, and southeastern Mazagan Plateau horst.

The Upper Jurassic to Oerriasian shallow-water plat­form carbonates havc a thickness of a few hund red to about 800 m (Ruellan et (lI. , this voL). They are partly overlain by Neocomian decpcr-water. hemipclagic , clastic limcstoncs "nd ?t urbidites (usually Q to 10 m, 10 a maximum of 300 m). I-Ie mipclagic mid-Creta­ccous (Iate Aptinn to Cc nomanian) nanno-marlstones (250-300 m) arc restrÎctcd to the lower Mazagan slope. Pe lagie Upper Cretaceous sediments (nannomi­cri te, phosphorites, lime stone breccias) arc discon ti­nuous and o nly a few tc ns of meters thick and separated by uneonfOrtnities from Ihe overlying Paleo­gene pelagie foraminiferal wacke- and packstones and Neogene nanno chalks to oozes.

Renard ( this voL) desc ribes the geoc hemistry (major and tfilce cleme nts) o f the platform "nd post-platform sedi ments, co rrclates this information with the micro­facies types, and attempts a " chemostratigraphy ".

Evolution or the Late Jurilssic to 8erriasian carbonate platrorm

Aceording to Leg 79 results (Jansa el al. ; Stcige r. Jan5.1. 1984). the LatC Jurassic shallow-wate r carbo­natc defXlsit io n started wi th a basa l sa ndy and ooli tic unit (" carbonate ramp stage ") during a mid-Jurassic regressio n. Artcr the brcakup of Pangaea . approxima­te1y 155- 165 Ma ago, a series of Bathonian to Oxford­ian transgrcssions started the evolution of the carbo­nate ramp with fault-contro lled high subsidence rates. The )'c llowish-brown ammon ite-rich quart z-bcaring deepc r-water limestones (" ammonitico rosso ,. fac ies) from the Vema dredge V3Q- RD 38 (Rc nz el al., 1975) arc the only palcontologica lly weil identified (middJc) Oxfordian rocks from the Mazagan Escarpment (3300-3 150 m prcsent water dcpth). Site 545, loeated on the Maz..1gan slope, has the fac ies of a down­fau lted platform cdge with pcriplatform talus in front

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165

CYAMAI. CAMP,fJGN SYNTHEStS. MAZAGAN ESCARPMENl

Figure 2

BUlh)'lIlt'lric m(IJI of 11r~ MIJzIJgIJ'J Pfateau ond Escarpm/!m ",llh loco/lon of CYAMAZ dil'es 0111/ DSD I' Leg 79 SÎ/f'S ( H.J,~fla'J et al.. titis \'01.).

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U VON RAO el "

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· ~5 e

StrUl'/urlJ/ rrwp of r~ MIJ:IJ8IJn Plo~all and Escarpmm/. IsochronrJ .. drp/h of orous/ic basunenl m su:. '/"W'/'. / .. folliu ont)' obun'rd ln lM plarlorm. 2 .. foulu onl)' obun'rd in lM plQ/form l'ovrr. J .. rrwpr follllS (pla/form + l'OVtr). 4 .. al'olls/ic baMmt nl hlghs. 5 .. prtsllmtd [o"fls. 6 " prtsumt d sail diaplrs. 7 " sialic bIJstfMnI ( pIJ/ta:oic grallodioritr. tiC. ).

of the devcloping palea-cscarpment (Steiger, Jansa. in press). In the deepcr forcslopc area (site 547) , wc find proximal resediments intcrbcdded with nodular limestones and pe lagie waekestoncs (for a more dctailed comparison of CY AMAZ results wilh thase from Leg 79 see Steiger. Cousin , this voL). FOJ1unately. the carbonates wcrc not secondarily do lomitized , as in sa many o uterops of the Moroeea n coastal basins. The study of the microfaeies of the platform carbonates of the CY AMAZ cxpcdit ion a llowcd a more detailed reconstruction of the evolu­tion of the carbonate platrorm bctwcen Kimmcridgian and Valanginian fÎmes (Fig. 7 and 8).

166

Ste ige r and Cousin (lhis vol.) diffcrentiated thrcc facies eauscd by the formation of the Mazagan Escarpment facies during Kimmcridgian times:

a) a ncritie platfo rm margin facies of massive , stroma­tolitic, pcloida l limestQnes with rapid, baetcrial lithifi· cation , high accumu lation rates , spongc growth (abou t 50 m water depth) and shallow eora liferous env iron· menlS (facies A) ;

b) a scaward hemipe lagic , subtidal to upper-bathyal pe riplatform facies of mieri tic en lpioncllid limcstones and bioclastic. oolitic limcslOncs with ealpioncllid· bca ring lithoclasts (facies B) ; and

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' f---";'=--"" --";;-~:::::C';"~ n. ' '' l EAP~(T[O O'AG~ '"

·r

Figure 4

Seozogt/ll .wisnrle profile A aaoss 1>10:080'1 Pla/eal< and Escorpmt n/. A: original profile. 8 : li/le drawillg.

..... ".. .'.

CYAMAZ CAMPAIGN SYNTHESIS, MAZAGAN ESCARPMENT

-.

..

_. .. - -- Il .. 00 ~

l '" Ntogtlle·Ql/oremuT)'. Z - r QligoccI'c (-CllrI)' !'t1ùx.mcj. 3 - Upper Crnoccou4 10 Eau",! • ., - Uppu CNl'UCflOII,. oS _ Lo_r Crt"<lUOIIS dtt~r·"'Ofer deposits. 6 - Upper 1urassle 10 IJerriasioll (OrbOliOle pliJl{rJrm. 7 - Triossle· Lia~ic el·oporiles. rtdbeds, ele .. 8 = P"{;ombriuli 10 Paleo: oic lia/le bll.wmtlI/.

.' .<"":.'"

""" ,. P"f'" ~ " "".. .. aI"

'" 1 . . ..... ..........

• 0<>

----. --0

,,0<>

167

.~,

• " • .. .. •

Figure 5 SclœnWlic diogrom of morplla/agie Olld SlmClurt 01 t~ soU/lwm Mozogo/l éKOf ' P"II:nt (txample oltli\'e 87. Y. Lu/lcelQf). NII/Ilbers desigmllc samples. lu - Uppa Jurassic. Ku - Upper Cf('fa(eQUS . l ' - Paleogene, N . Neogene.

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U VON RAD &f .1

rable Dtftl/illOlJ lIf nlJ('rofo('~s (MF) 1J'J)tS /-/8 of CYAMAZ wmplu (/illrofocKJ descripliOlr. pult'(I('III'jrOi/melll ami age). Modifted after l'lm Rad (,Iris "01., Tab. J),

M F

". 18

18.1

17

17, 1

16

J5 15,1 15.2

14

13

12

" 10

"

9

8.2

8.3

8.4

7 7.1 7.2

6 6.1 6.2 '.3 6.4

'.1 5,2 '.3

" '.1 ·U 4,) 4 . .\ .\,5

'3

"

'1

Lilhofociu deJCriplioll Paleoem'Iff)llnU'flI

soft to ~miconsolid, pelagie foram nanna oozc/chalk pelagie·bathyal

grecn pla~lie calcar. clay

pelagie foramin ifc ral (globigerinid) paek-/waekesl. pelagie·bathyal slope dcposit eonJ,()lid:ued (mieritc) -dito·, glauconile·rieh "aricly OUler shclfluppcr slopc

:t silicified radiolarian chalk wilh porceJlanilc/quartz ehert nodulcs

nannomicritefnanllO chalk lo·marlstone :!: reef)'siaililed chalk :!: phospha l i~ed calcareous clay-/mulstone

limestone breecias (mainly mierilic inl raclasls)

plKh.phorile brcedalconglomenue will! componcnts of MF8. Il. 12

laminatcd (mlerograded), :!: dulomitizcd phosphoritc (- phosphalized micritcJealcarenile)

phosphorites - :!: phosphatilcd, massive echinoderm-mollusk micrites

quartl-bcaring nanno marl-/claystone

upper slope - ?upwelling pelagie.bathyal .

pelagie slopc dcposit

reworking in dceper willer?

sJopc wi lh slump breccias and/or dcbris flow deposits ($Ofl sedimenl deformalion) and slump balls (100-3)

upper slopc - hcmipclagle? (microlaminalion - ? Or minimum la)'er?)

claslie slope sediments (as MF 9)'phosphatiled in La te Crclac. limes ( '!upwelling evcnt)

hemipelagi<:-balhyal (1upper slopc)

belcmnite- (and quartz-) bearing, Fe oolile eehioodcrm micrile (parti)' oolitÎC ironslone)

rieh nardground on slope/ouler shelf 1 (condensalion hori­U1n) ,,', reworkinglb)·passing/diS!.Olu tion - fe rrogini-1.lllion. Fe oolilc formation

Quan z·bearing (eehinoderm.mollusk) micrites mieri­lic qlz-ocaring int ruciaSlic packstone wil h CI)'fleiml fimlSsku

micrilÎc qt;t·bcaring eehinoderm-mol1usk <k:bris pack ­)LoJlc/ .. -açkeslone

mienlÎc qlz·bcaring glauconite/phosphorilc-rleh eehi· noderm·mollu~k debns paek$lone/watkeSlone

micritic ech i n. - mollu~k dcbris paekstoncJwackc~1.

Interclastic wackeSlone intrachmic pack - to wackcstone dolomkrilc, slighll) laminated, qlz'bearing

NcnlÎC fenestrai limeSioncs nerilic fenestrai algal bindslone ncri lic fenestrai peloidal pacblone neritic fenestrai bioclastic p;lckstone laminated fene~tral pcloidal packstone

Neritic ool il ic gr~in~I.lbindsl."" .. aekeSI. nerilÎc ooli lic algal biTKlslonc nerille oolilÎc grainSiOnc nerilie ooli lic bioclastic waeke~lone

Neriuc bioclu~lic pcloidal grainSlOne ncrilie bioclaSIÎC grainslOne ncritÎC bioclaSlie wad-:csl0ne/grainSlOtle neritie biocla~lie pcloidal pachtonc netitic algal bindstone " , coral debris f1Critic intradu)ttc packslone

Columnar stromatolilk peloidal paCkSlO f1C (- maSloi.c croslul pcl~parLIc) , including nerilÎc ulgal bindSionc ". coral debris and palehcs of mieroblOClastÎc grain­stone (,!; sil. spong.)

!-orc·slope bioclll)lic oolilÎc grainslone .... ith Calploncl­lid lithoclll~ll>

balhyal (outer shelf 10 slope) terrig. influx. rcst ricted ('!in lrll tidal) cnvironmcnt wi lh Ic rrigenous innu~ (regressh'c phase)

bioclasliC'lerrigenous slopc sedimenls: ?lUrbidi­Icsl~lumps (can)'onfuppcr fan fllcles ',1)

QUler shclfluppcr stopc, " Iransgrcssive" breccia (shclf edgc)

more hemipclagie (calcareous), slope dcposil

intra,to supratidal lagoon (ncar~hore, ?sabkha) rcSlricled circulation. e,aporilic

shallow sublidal to inlertidal (algal maIS - Iofenlcs)

oolile shoal or rcworked into ncarby

lagoon (differcnt seuings)

lagoonal dcbris. "cry shallo .. · waler high-energy lagoon ?Iow·energy 11Igoon high-encrgy lagoon, '!pcrirecfal ?near-reer debris. ?algal paleh recfs 13&oon. ?intertÎdal

high,e ncrg) lagoon "Lch eyanobaclcrian st romalolillf; pelmÎcritÎc erosts (fasc ouildup of platrorm margin 1)

fore· slope breecia (hcmipelllgic)

Hemipclll~ic bioclastic paclstone .. ith c~lpioncliids dcepcr fore·rccf slopc ('!20-JOOm). ~mall 'l''tmge (and ~ihccou~ sponge remam~) biohcrm~

168

M. Mioc. ·Plioccnc

(·Qual.)

Paleoccnc·Eoc.

(-E, Oligoccne) Eocene, Neogene

(1Palcogenc)

Late Cretac. (?Late Crclae. ) O ligo· Mioccne

(Tur.-) jI.-laaSIr.)

mid-IO laIe CrcI3C. ( LI , ApL·Sanl.)

laIe Crclaccous (LI . Turon,-Camp.)

LaIC Cretaccous (Ca mpan.- Mallstr.)

LI. Apt.·E, Alb.

'!Valan~nian. Ilaulenvian (·E. Aptian)

LI. Malm 10 [Jarre ' mian

(BeH,') Valung.­lIaul. (·E, Apt .)

(?f ,) eretac,

Od .-Maam. (?mid­CreL)

('!t:.arly) Cretaceous

'!Ti thonian

Ikrnasian

?Tilhonian

" ?Bcrriasian

LI. Malm· IJcrriasia Il

U. Malm

LI. ·Iithon.· Berrias.

U . l'ilhan.· ·(L) Ikrria~.

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Figure 6

CYAMAZ. CAMPAIGN SYNTHESIS. MAZAGAN ESCARPMENT

,M'" "",,,' 1

_.-, ...... , ... "' ... , ,--OIU"'l .........

Time-s{ra{igropllic Sllmnwry of cr AM Al reslIl15. correlll/ed wüh seo le ~'eI j/l/clI/l/limls 01111 nwp' lee/ol/ir 0' sedimelllologicoi el'eIllS. Seo-le,'eI Clm'e IJfte' Voit CI al. (1977) olld Voit CI al. 0 11 p,es5), T,ollsgre.uio,1 (Tjf'egressioll (Il) mrve of MorOCCOII CQQSIOI blJsil lS ' l'fers /0 ,elo/i" e seo lel'el chDII/,'I!s, DIsQ jllj/uellced by re"ical/ec/Oll ies, $IIbsidlmce. D((llm lllDtiOll alld trosioll 'OIes Dlld i.s compi/ed from \Viedmallll ct al. (1978), Behrells CI al. (1978), Behrens alld Siehl (1981) und olher sou TreS. IItJ1ched a' eDS du,illg l,a" S8,essirJ/ls: polemitl l "mde'/SI'd sec/ions. SlrlJligraphie colum llS sho ... sedifMlII foc~s, Ihiek/ress (m), alld mierofoc~s mmlb/'r (sec Tab. J. Dlld l'On Nad, lhis 1"0/ .. Fig. J Jo, symbols). Abbn~ÎQlions: P .. plwspho,ire, ® • plwspho, ire conglomerale, ph • plwSplutlizDlioll e~elll, up"' '' up ... elling e~elll, gy .. gray. gn - g'een.

e) a la ndward shallow platform facies o f intc nida l to shallow-subtida l calca rcous l1l icri tic and dolo mitic deposit s (fe nestrai limcstollcs. dolomi tes; facies C).

Accordi llg to cvide nce discussed by Steige r and Cou· sin (this vo L) , facies A is restrictcd 10 the Ki mme rid· gian 10 (midd le) T itho ll ian , facies B 10 Ihe late Tithonian 10 (ca rly) Berriasian, whcreas the age o f facies C might range from Titho nian to Bcrriasia n.

The facies modc1 for Ihc Kimmeridgian to (middJc) Tithonian (Steiger and Cousin , this volume) shows a vcry broad shallow-wate r ca rbonate ban k with a rather steep, probably fau lt-cont rolled plal fo rm slope (Fig. 8, 1). The sea levcl was more or Jess slalionary. and bccausc the high growth raIe of carbonale accu­mulatio n equa lled the leelon ic subsidence raie, the wa te r depth re maincd ve ry shallow,

The pclo idal packsto llcs (MF 3) wc rc bio logica lly lithified by fasi-growing stromalolitic crusts (possibly

169

cyanobacterians) inlO rigid Sl1lall-scale stromalolitic domes and eolum ns, and later ce mented by sparhe. This helpcd to sta bilizc the platform margin (Sle ige r and Cousin. this voL). Sil iceous spo ngcs which hclpcd 10 dale this facies liS pre-l'it ho nian grew o n the substratc of early-diagc nctica lly lithified . stromatolit ic pc lo idal packslone fo rl1ling il knobby sca floo r, Lang and Ste igc r (this vol.) diseuss also the diagenctic evolu tion of the sponges. suc h as Ihe dissolut io n o f opaline silica, calci fi cation o f Ihe spongcs. and Ihe ir buria l by pe loida l sediment . The prese nce of a pcriplat fo rm ta lus facies in front of a faulted ban k margin and of a pcJsparitic low-e nergy back rccf facies, Iypical for the inlerior Bahama Bank , is hypothetical (see Fig, 8. 1 and Ja nsa el al. , 1984). According 10 Ste iger and Cousin (this voL) and Ilüssne r ( 1985). a mo re or less co nlinuous, hummocky .. pe lsparite ramp " with ca rbonate sand ba rs but no ind ication of genuine ree f buildings deve lopcd during

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U VON RAO 81 a l

" • c L.ASS.t

'., .... r: :.::.:.: :'7.~:-::' : .~:.: ."7:.':': :-::~

8(RRIAS_VALA NG , q . ~~"'7=-'~ # ... '":'::' .............................. . - - _.... . ...... - - .

•• _ . 1'" J'." 1

, II.PT IAN_Al . . . . . . ...

"'" ~

.. -~_ .. . ......... '-... <._ .. .. , ... _._ .. 'if

~"""""'~~"""" '.' '...... .... . , '.' . . '. j

~PTIU / "' .!U !_U-'l --

.. IlfIlR--····· ~ ._" ...... -.. --.. -. .. - . . . , .... '. 11, •

,--LAn tR[T IPALEOGE NE lUE ( ~[1 _!\l1.{OG{ NE

~~ ~"""""".""""" . . . . . . . . . . . . . .... ' ... . .. - - - . . .....-' . ', ,' •••• • , ... " '1 ,

n .... __ •• !.!L_._ ... "-~"'" .. _ ...... ... . __ .. ~ .._, ... _.

.'" "~.,:,,=...

..

__ ï 6 j' ,., .--NEOGENE · OIJU

Figure 7

1-. """ "'-:/1"·

~(OGU(

- " .. " .. .. ~ , .. _." ,-- .... /". ,

.. : .. mul /'1211mspa1Ik pfOfi/~s 12CTQS$ Ih~ ,\{1I:12g1211 P/(lI<12U 12r~12 slrol\'ing lhe Liossk 10 Quol~mor)' SirI/Cil/ roi ~I'olm/On (Fig. 7. J) and the Vo/(lnginion IQ N~o~~ focks ~\'Oimion (fig_ 7.2). NumM1s d~sigrIQl~ nrkro[ocks (MF) "umht'TS (T(lb. J).

Kimmeridgian times betwCCIi the coastlinc and the Mazagan Plalcau arca.

The late Tithonian 10 (carly) I3crriasian transgression caused a first changc towards a deepcr-water facies (Steiger, Cousin , this vol. ; Fig. 8.2). This transgres­sion was mainly duc to rapid tectonic subsidence not compcnsated by carbonate accumulation, and to a lesser degree to a global SC3 levcl risc. Thcrcfore. fault block::. with slromatolitic packstones were cove­red by hemipclagie , calpionellid-bearing bioclastic wackestoncs (MF 1) with redepositcd talus from cxpo­scd older Jurassie platform outcrops. Sil iceous sponges were redeposited as pcriptatform talus into eomparmi­vcly deep (?50· 100 m) w:Her, where ealpionellids were deposited in a subtidal to upper bathyal environ· ment (see Lang. Steiger , this voL). According 10 Steiger and Cousin (this voL), a landward lagoonal grainslone facies developed for the first lime during the pcriod.

During a global (I<ue) Berriasian to (carly) Valangi· nian sca level lowstand (Fig. 8.3) calpionellid wade­slone deposits were locally eroded and redeposited into the pcriplalform lalus (MF 2). A low-energy facies is indieated by pcloidal waekestones. The most landwnrd facies is documemcd by intra- ta supratidal . more-or-Iess dolomitic paekslones. rich in imraclasts

'70

or bioc lam (MF 6n). Steiger and Cousin (this vol.) report sedimcmological evidc ncc (vadose d iagenesis) for a partial cmc rgcnee of the carbonate pl:lIform du ring this laie Berriasian to (carly) Valanginian regression_ Terrigenous quartz grains, cspccially in a quartz-bcaring. dolomitized. intraclastie paekstone with reworkcd ClypeillQ jflrassica (MF 8.1) might document a regrcssion and the vieinity of a continent. Another expia nation of the sudden quartz inpui and cal pionellid Iimestone intraclasts would be a subma­rine erosional event duc to loca l teclon ics (Schlager. pers. com mun .. 1984). This facies indieates a tran si­tion from the platform 10 the post-platform phase. ln most localities (e.g. , site 545). however , there is a major unconrormity bctwcen the platform carbonates and the o\'erlying Cretaecous dcepe r·water mierites (F;g.6).

Figure 9 shows a paleogeographie map of the laie J urassie. This sketch map does nOI differcntiale bctween the threc differen! stages. shown in Figure 8.1·8.3. The Mazagan Plateau is today characterized by a series of tault blocks wi lh systems of (aults st rik illg about 20" and 150· 1800. Wc bclieve that the main L1te J urassic platform margin dcve lopcd along a major fault zonc which formed on an old , rejuvenated margin·paraUcl Hcreynian lineament. Espceially

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~

(Y AI1AI

,,,' -.......... , ........... ....... -.. _ .. ,,,. ,- ,,,_'. "' ... , ...... , ,-- 9- 1. A c-

: _ - ~----

(Y A I1AI

LAU TIlHOlllA/I_ I[AII\. YI 8EIIRlASIA/I

'~~~' ·9- · ··~· - · · -'i---~-~-~­:-~- --

"

• • , • , '9' 1

n. AtU 8EIII!I.f.S _ VALA/lfMlAII

• " 0 " " "

0

" 6 " 6 6

t-ïgurc 8

{ Y A Il A

-o.

El'olIIIiOIl of Iht! MUZUN"" corbOIlUl1! plillfo r", bf M efll Kimml!rill­gilill Ulld Va/lJ/lgllI ;(/II l inU's. Numbfrs Ju iglltJ/t! MF (microforlts) Illimbers (sec TClb. 1).

du ring the late Titho nian to Oe rriasiun transgressio n pcri-platfo rm ta lus was shed downslopc [ro m an ex posed escarpme nt to the area o f Site 545. Site 544 is located at Ihe lowermost fault block which was also ca ppcd by platform carbonates, whercas at Site 547 pe lagie noo ula r limesto nc was deposited , mixed wilh proximal foreslopc talus which was probably de rived [ro m the" Si te 544 horst <1 (Stc ige r, Jansa , 1984). Presence of a very wide , sha l10w backrecf fac ies of banks and lagoo ns is indicated in Figure 9 by the dashed pattern (see also Fig. 10).

Tcrmination (drowning) or the Mazagan carbonate platform (fig. 11-12)

O ne of the majo r prob lems of the cvolution of passive conti nenta l margins Is the cause of the terminatio n o f cu rbonate platfo rm growth . Figure 13.2 shows a schemat ic facies sc(lucnce o f ne ri tic platform ca rbona­tes, ove ria in by eonde nsed hardgro und seque nces rich in ammonites, bc lemnites, iron ooids, fcrromangancse

171

CYAMAZ CAMPAIGN SYNTHESIS. MAZAGAN ESCARPMENT

Figure 8. 1

Kimmt riJgüm 10 n l/umÎllII (ftgTt!nion). Till! faults. fh f ptriplolform /a /liS p cits B (IIIJ Iht! buckTffl forits C Cl ' t t mirdy h)ptJlhtlkCl/. Acco,Ji'lg 10 Sit igtr Clnd COlIsi,1 (Ihis " 01. ) " fOllli lil/O/4S. Iwmnllxky .. pe/s1"',i lt! TIImp .. (M F 3 will, millOT ;l1IerrCl/(l{iolls 01 Mf' 4) miS'rl IUH'f e.l islt d (/lIr;lIg /hll/ lime.

Figure 8.2 LaIt Til/lfm;,," /0 (tilT/Y) 8trfklS;tl l/ ({ftl lrJg,t!ssiulI).

Figure 8.3 (u./t) O .. " ",s;",, tQ Vil lQIIgillûm (n:gn:u ioll ).

A - II/: rilic ~ /IIl/l0 "'- ""Cllt'f facits (M f 3, 4.1. 4.4. 5. J). B .. ht mipûugk faeks e.g . ... i lh e"/piOlldlids (M F 1.2). C o. lIt'fi lie mjcritir Cl l/d $Und)' faeks (Mf" 5.3, 6.2. 6.4. 7. J. 7.l , 8. J).

o r phosphoritic crusts, o r by he mipclagic , quartz- and glauconite-rich, fo raminifera l nanno chalk s. Above anothe r unco nfo rmity follows a sequence o f pelagie nanno chalk s. Such seq uences arc very typielll for many Early J urassic outcrops in the Alps or une J urassic exposures in G reeee (Be rnoulli , Je nkyns, 1974 ; Ogg el al.. 1983). From the I-Ielve tie Alps, Bergne r el al. (1 982) dcscribcd a Barre mian to lower Aptian carbonate plat form phase (Sehran enkalk ) overlain by clasties during the carly Aptian transgres­sion (Brisis..'lndste in) , a mid- Aptian to Albian (Ce no­manian) glauco nitie- phospho rit ic condensatio n ho ri­zon (Lochwa ldschieht , etc.) , and pe lagie T uron ian nanno limesto ncs (Sccwe rk:tlk). They report II sim ilar cocval sequence fro m the weste rn I-l igh Atlas.

What is the cau se o f this conspieuo us stratigraphie turning point which abruptly terminates the bui ldup o f neritic cnrbOllilles ? Sc hlage r (1 981) spcaks of " the pa radox o f drowned ca rbo nate plat fo rms ". bccause no rmlilly the growth rate o f cora l recfs is al leaSI le n times as fast as the ave rage rates o f sea level rise or

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U VON RAO et al

LA TE JURASSIC PLATFORM

8' [llJ. . ~

~J , .

~.

D· D' D' -. ---~'-- -

- - ""..:II --~ - ~ -------, '----.". __ .. __ J

--d----,' c.;; - • -r---

o " . "

".

Figure 9

Palrogrograplllc Sktr<'h fMp oliM .. pptr JuraSSIe 10 BtrrulSl/l'I r/lrbonalt plalform (partIr modifitd ofltr Slt'Rtr. J/lI/.SQ. 1984 ,' Wimtrtr. Hilrz. 1(84). I.t'gtnd : 1 - burkrul (/ogoonol fitrits. lII irrv/aries MI'6·7),' Z - shalloK' plalform margin (slrolll{l(oWic pe/oidal par/!.S/Ollt. MI-" 3) .. 3 - to'trul/aIIlS (ltemipelagir bioc/aSlir pllrks/Olll' wilh cillpion(/Iids ond si/irtlJlls .plJ/lgt ff.'/lUli/ls. MF 1) " 4 - c/l, bQ/lalt bun/!. /lI NW Iowa Mazagalt bloc!.: (sitt 544. grail/S' IOlltlq/lllobllrleriun CT/ISIS),' 5 ". lIodlilar det~,-,,'altr limeslolle. brtCCUlS alld III,bul,les of Klmmerldgiul/ n8' . "..Iagk' ... dirnenlS of 'lïlhO/tiat/ /0 NtoclJmÎtlfl age (si/t 547),' 6 - dup-Waltr pt'Iagic mlldSlOntllimes/one .... irh dis/al ""bidlles (sile 416) .. 7 "= Paleo:oic grani/t lglleÎ.ss (slib/ll.'fiullJr :mbnUlrint OIl/CropS); 8 '" omer limil 01 C/l,bQ/,alt (nmp ill OxfordulII li",.. .. 9 -r:'tOtS('nrpmem (major fouit ;:Ollt),' 10 - rrwjtJr paieofoll/l " 1 - IIIIlSS " 'IlSllIIg from palelX'scarpml'm,' 12. OSOP Sile.

subsidence. According to Schlager (1981) , the follo ­wing causes or combinat ion of causes ca n bc responsi· bic for the tcrmination of ca rbonate plat forms (in the order of importance for the Mazaga n area ; see Fig. 13. 1) : a) drowning by rapid (i.e. > 1 mm/yr. ), short · term sea Icvel risc ; espccia lly a shon regression might have exposcd the carbonate bank, killed the rccfs. and reduccd thc growlh potcnt ial of the recf builders during the following rapid sea Icvel risc ; b) drown ing by pulses of rapid tectonic subsidence which surpassed thc carbonate accumulation rate. for example by bloc k-fauhin g during extcnsional tectonÎCs (rifting) ; c) envi ronme ntal Stress and the smnll growth polcntial of the stromatolitic buildups. as compared to recent cora l rccfs. Other possible factors arc regional massive terrestrial and freshwater input from deltas (drastic drop in salinit y. murky waters) du ring regressive cpisodcs, and plate-tectonic drift to higher latitudes. The latter might have been the main ca u~ for the drowning o f Ihe northward drifting, diachronous carbonate plalforms off easte rn North America which lie now off New Jersey, New England , a nd Nova Scotia (Jans."l. 1981). Off N\V Africa. howe\'er . the

VALANG.-BARREM. I-E.APTIANI 1 PLATFORM ORO WNING.WEALOEN_TYPE ClASTICS 1

D· t/-' cP'

c Z

c z ,

~,.. ... '''' ... , .. ,..w, .. , L:?"

·:~ .In .. Figure JO

'"

• \

"aleoS"ogruph~ skt/ch fMp of/hl' Vn/t",ginion 10 Hnf1'(.'mlall (tarir tlp/illn) p!n/jo,m dro ... nillg Ilnd .. Wta!dtll-I)'pt .. c/nstic dl'poSlliO/r. I.t'gtlld ,' 1 - Ihilr Irllrdgrollnd dtposits (bt!ltmllite- n'Id qlln,tt.bto. ,illg. ium ooid-, icl, tclrillodl'f1/r mier;le, MF9); 2 ,. qllartz·bt,·aring «hi'lode",r mic,ill' (?lIIrbiJites 0' c/nSlic slof/" d.'posils; Mf'8),' J .. prox;mlll IIIrbidity r""l'lIts. Slllll/I's. DebriS jlows ,' 4 - dislIIl IIIrbidily CII"tlllS " 5 - pa/I'u-sltl'If tdS".

172

latitudinal shift of the Mazaga n Plateau bctween Late Jurassic and mid-Cretaceous times was insignificant.

The fact that in the Mazagan area the platform was sucecssivcly drowned , as blockfaulting probably pro­gressed from the ocea n towa rds the contine nt (Bosc l­lini , 1973; Ruellan et al. this \'01. ; Steiger. J 'lns.."l, 1984 ; \Vinlcre r, Hinz, 1984), suggests that a tecton ie subsidence pulse , coinciding with the late Berria­sian/Valangin ian o nsct of transgression , is the main cause for the drowning of the Mazagan platform. To us climatic changes or short-te rm rapid tectonic subsi· dence episodes (possibly a!tsociated with drifting e\'ents?) are more attractive ex pia nations for the platform drown ing than global sea- Ievcl fluctuatio ns and plate-tectonie moverncnts which are too slow to bccome effective.

Unfortu nately. the time o f the .. d rown ing event ,. can o nly be indirectl y estim;lIcd as (mid)-Va langi nian from thc unintcrruptcd fossi! rcco rd in the deep Moroccan Basin Site 416 (Schlager, 1980). The thick seq uence o f distal turbidites deposited there o n a deep-sca fan shows a characteristic dirrc rentiation o f

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Figure 11

APTIAN-(ENOMANIAN

~ r' 1 ~, "l

'\ ....... ,- -•

czaut:t

=

, -

---

, - ' .,r' ","" ~7.://

,

.

, , ,

Paleogeographic skelcl. map (Aplion la C4!/lomlmiall), lLgelld.­J ""? $(Indy fIQ /IIW marl- 10 cwyslOtI4! « j()(} m "'OIU dep'h). 2 = quoTl!.b<orillg IUl/IIIO mil" (> 1 ()(){) m WUler depth . M I-" JO} ; J '" slumpJ tmd debr i.s j/OWJ .. 4 ,., IrUflSport of cloy und sill (in po" afle r Will/I'ftr. Hin:. /984.

Figure Il

@ DROWN\NG SY RolP.(l SIfORT - TUIM S l RISE>

1"1 4SSIV( HRRUTR lNPtlT

>GROWTH POl Of (ARBPl l>l"'./Y/r! ':::.' ':::'''':' . .. , ..... __ .. _.\ ._' .... , 1 , ••

" -" ,. .. ,>1 Pl ol TE _THT .. JIoIO . ... ... ",,, ~--, .,/ DRifT ID HIGHER ::~= .. :. ...... .,-/ LATITUDES '_ , .... '. /

d ~_' ... .,,, .. -­~.-t • . ,-c..OJ

/

TERMINA HON 0'

(ARBONA lE PLATFORMS ......... ENVIRSIRESS

Il ... <1 • .• IoiooO ....... ".,

ORO .... NING BY PULSES OF ..... ,. •• , . ... ~" ... ,.J RolPIt) fECT _SUSSIO f.>1 .. a/rrl> ( ARB AliU/'L

1 • .• __ ' ''''''' .....-...... ~ • • 1

CYAMAZ CAMPAIQN SYNTHESIS. MAZAGAN ESCARf'MENT

lATE (RETA(E OUS-PAlEOGENE

.. , • • • El-,

.. ïgure 12

= "

,

••

f'a!eogeographic sktlch map of lire Lme CrtlaceolOsll'a!eo/;j"IIc. lLgrlld.- ! - IIndiffrff!fuimed Uppa Crl'/uceOIIS 10 Paleogelle sedi­,tI4!/IIS .. 2 - Pa!eogelle f'4!wgie {tIromiliiferal mie, ile (M F 17) .. 3 =? ElKelle rndiowriun mlld.Stonelchuf (M F 16): 4 '" CIr .. ,, ; j - Upf'4!r Cre/Mj"()/IS pelagic Ilallnomic, ir.. (Mf' Jj) ; 6 " Upper Cre/Qum' $ IimeS/DlI" brcccio (M F 14) .. 7'" Upper CrelactOllS plrospltorilt'$ (MF H ill) .. 8 - Uppl'" CrelactOIiS phosplrori/e breccia (Mf /3).-9 - /.Il/c Crf laceoll.ç/l'ulcog"'I!f slll/ups arld tlebri.s j10ws (JI~mly modified {mm /O/lsa, l'MI ).

n,,,,,,

l'o/e/J/ illf Cil liseS {tir IIII! la mino/ioll (" drowlling ") of !ossU ClUbo'llllt pl(l/forms (aflcr Sclrlagrr, /98/). Tite mOSI likef)' cm,ses {tir Ille lermÎlJOlioll of l ire Mu!OgulI ca rbonolc pl/l lform are l'IIIIJI/usiud by lIol/eli flllllerl! (13./). I:igurc }J,2 : ske /clr slwwillg I)'picol l'ff/ieul fudes seqllel/ce o l'erl)'illg drowned carbollille p/OI{tIrm.s (pli - phQsphor i/c, glc - gloucurlile),

two facies (see <t lso Fig, 6): a) T ithonia n 10 mid­Valanginian gray ca lci-Iurbiditcs wi tll micritc, ooids and nc rilic skelewl grains. derived (ro m Ihe growing Mazagan ca rbona te plalfo rm ; b) lalc Va langi nian 10 Hautc ri vian green 10 brown turbid ilcs lacking micrit ic

173

limesto lle and ne ritic fossils, but wit h a n upwa rd increasing conte nt of reworkcd phospho ri te and ooids wilh quan z nucJe i. Sc hlager (1 980) suggcsis that this docume nts the d rowning o f the carbonale platfo rm , maybc by a s1igh1 intra-Vala nginian sca 1cvel d rop ,

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U VON RAD el al

followcd by a rapid sea Icvc l rise (Vail and Milchum, 1977). This dale fils well 10 the rough age est imales for Ihe drowning event, inferred from Leg 79 informa­tion (" post-Berriasian to pre- Aptinn " : Jansa et al. ; Steiger, Jan5<l, 1984) and from our C YAMAZ data (" post-Bcrriasian. probably pre-Haule rivian " : Stei­ge r, Cousi n ; von Rad , th is voL).

Earl)' Cretaccous hemipe lagic c1astic sed imentat ion

Figures 7 and JO show the morphology and paleogeo­graphy during Valanginian to Barre mian times, Arter the drowning of Ihe platform, nondeposit ion, bypas­sing. or erosion predominated along most part s of the Mazagan Escarpment. The fo rmer platform margins beeame submarine horsts. Only along the ce nt ral esca rpment a thin sequence of hemipe lagie , quart z­rich echinoderm micrites, and eo nde nsed iron ooid­ammonite-bc le mnite-rieh beds (MF9) we re deposited, ln the present El Jadida Ca nyon area, however, wc discove red a > 200 m thiek sequence of wc ll-bcdded bioclaslic turbiditcs whieh were probably dcrived from the Morocca n Meseta o r the " Atlas Gu lf " via a paleo-eanyon system. Furthe r downslopc, at sile 416, a 750 m th ick seq uence of dislal tu rbidites interbcdded with pe lagites was deposited in an outer fa n or abyssal pla in c nvi ronment (see also Fig. 6). Thus wc thi nk we have found the missing link in a huge " \Vea lden­type" delta system bctween the alluvial to ncarshore claSlics of the coastal basins (Behre ns el al. , 1978) and the deep-sea fan of Ihe Moroccan Basin (La ncelot , \Vinle re r, 1980; Priee, 1980; Schlager , 1980 ; von Rad , Sarti , in press). The main resuh s of a paleoc nvironme ntal sludy of the heterogc nco us Early Crclaeeous lit hofacies types (vo n Rad, this vol. ; see also Fig. 6 ; Tab. 1) arc: 1) The lower Neocomian (probably Be rriasian 10 Valanginian) quartz-bcaring inlraelastie. dolomite­rich paekstoncs (MF 8. 1) occur on ly locally and indieate a transition from the ca rbonate platform 10 a restrÎcled inter-to supratidal shallow lagoon or sabkha se tt ing, inOuenced by terrigenous quartz input. 2) The quartz-bearing ec hinoderm (erinoid)-mollusk pack-to wackestones of Berriasian tO carly Aptian age (MF 8.2) arc (bio-)c lastic, deeper-water shclf 10 slope sands. The 150-200 m th ick, weil bcdded seque nce, obscrved in the El Jadida Canyon area , was probably dcposited by turbidity currents or ma ss nows in a canyonlintercanyon e nviron me nt. Wc cannol. howe­ve r, cxclude the possibil ily that these sands arc non­turbiditie, open-marine calearenites, deposited on the drowncd carbonate plat form, sim ilar to the th in glauco nite-rich, eonglomeratie ..,ariety MF 8.3, deposi­ted near the paleo-shelf edgc. 3) A conspicuous, very thin. quartz-bcaring iron-ooid rich ec hinode rm micrite wjth conce ntrations of belem­nites and ammonites (MF 9) is a condcnsed Berriasian 10 ?basal Haute rivian condensation horizon. formed near the old shelf-break. The iron ooids and the partly ferruginous malrix o riginated from d irect, multi-stage precipitatio n of goeth ite around preexisling nuclei and in the matrix in a decper-marine hardground (a round 100 m ?) environment , imerrupled by exten­ded pcriods of nondeposit ion, dissolution, and e ro­sio n.

174

Mid-Cretaecous hemipelllgic nannofossil ma ri de posi· tion

The late Aptian onset o f several global mid-Creta­ceous transgressions marked a major stratigraphie turning point towards hemipelagie conditions. Figures 7 and 11 show a palinspastic profile and a paleogeogra­phie sketch map of the Mazagan area during the Late Aptian to Ce nomanian , The upper Aplian-Albian (-Cc noman ian) hc mi pe lagic, quartz-bearing nanno marlstones (MF 10), sampled during the CY AMAZ expedit ion and in DSDP Sites 545/547, were deposited only at a nd beyond the foot of the pa leo-escarpment. From seismie evidenee wc infe r a (?more sandy) nanno marl-/limestone seq uence landwa rd of the main paleo-escarpment. The paleocscarpmem itself was an area of nondeposition o r erosion and the source of major slumps and debris Oows towards the Mazagan slope (see Fig. 10 ; Steige r, Jansa, 1984).

Lute Cretaccous pelagie sedimentation

A major transgression wi th a peak du ring Turonian times marked the Late Cretaceous period , which is eharacterized by rather thin, intermittent seque nces of pe lagie sedimen ts separated by unconformit ies. Sedimentation was rest rieted to the arcas to the cast (Iandward) and southwest (seaward) of the more or less nondepositional paleo-escarprnent (Fig. 12). Figure 7 , however, shows that ove rlapping Uppe r Crctaceous sedi ments eove r extensive parIs of the Mazagan a rea and level sorne of the old, blockfaulled horsts.

Tcrtiary e\'olut ion (Fig. 12)

ln most places, there is a major hiatus bctween the Cretaccous and Tert iary rocks. Only at the SE Mazagan ho rst (dive 92), ca rly Pa leoce ne ( Danian) pelagie fo ramin ife ra l pac kstones were recove red. The Paleogene (mostly Pa leocene to Eocene) pelagic foraminife ral pack-to wackestones were deposited in a pelagie slope e nviron ment similar to the present one. Radiolarian cha lks with chert nodules (? Eoce ne) indieate increascd silico-plankton fertility. The Te r­tiary record is imerrupted by seve ral uneonformities. The Neoge ne is represented by mid-Mioce ne to Ouaternary soft to semieonsolidated , pelagie foramini­fera i nannofossil OOles whieh cove r Ihe whole Maza­gan area, exce pt for the steepest s10pes, with a thin "'e nee r of aUlochthonous or slumped sediments.

STRUCruRAL EVO LUTION

Muny seismic surveys have becn eonductcd in this area. especia lly by BG R, Lamont-Doheny Geologieal Obsc r\'atory , and lately by CNEXO (see Rucllan et al., Ihis voL). A sin gle-channel profile across the Mazagan Esca rpment (Fig. 4) shows Upper J urassic to lower Neocornian carbonates on tilted fault blacks, ove rlain by a thin Cretaceous and Tenia ry cove r. Owing to the steepncss of Ihe slope and the massive ca rbonates. thcre is very littlc seismie resolution nlong

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c (AR80NATE BUllOUP ( ...... <-"""~

p F~~

PROGRAOAT 1 ON . BYPASSING

E L{:~ T =t/,/>' EROSION/MASS WASTrN(j TECTONI(S (._9,'."" ..... (

COMBINA TION

Figure 14 Cm/Slr/lCliQII(J/. dUlrtlClimw/. /wd dt'formatiollu/ prousws shapi" lJ Iht' SIUp S/Of't'S Qf possÎ"e rrwrgin·'y~ (D rbonale p/mforms.

the cscarpmcnt. Exccpt for th is scismic information and a sma ll number o f widcly spaccd and poorly posit io ned d redgc samples and cores , no info rmation was ava ilablc prior to the CYAMAZ cruise on the stratigraphy and structure of the Mazagan Escarpment bctween 3000 and 1 000 m. Figure 5 shows an unexaggeraled block diagram of the southe rn Mazaga n Escarpme lll . sununa rizing the st ra­tigraphie and tectonic results o f o ne d ive (CZ 87). The slope of the escarprne nt range s from 20" to subvertica l near the edge of the plateau. 51nligh t sedime nt ridges strike perpendicu lar to the depth contours at the fool of the slope . Small, straight canyons dissect the escllrpment which is Slructured by ve rtica l fault s parallcl to the esca rpment and ope n fraclures perpen· d icular to il. O nly the uppe r scarp shows the infl uence of black leelonics. erosion and mass wasting. Neogene na nno oozes arc on lapping or lie in protected pockets. They leslify slu mping o r bypassi ng along the slope. In Ih is area , a major unconformity se pannes the massive uppe r J urassic to Be rriasian shallow·wate r carbonates from the ove rlying bedded Laie Cretaceous to Pa leo­ge ne cover of pe lagie micritic li mesto nes. The Mazaga n carbonate platfo rm wh ieh constitutes the seaward eXlension o f the stable Moroccan Meseta is broke n ilIIo a succession of dow nfau lted and slighlly lilted blocks from Ihe plateau to Ihe foo t of the csca rpmen l (Fig. 3 and 4 ; see Ruellan et al .. th is voL). This faul ting is controlled essent ially by very o ld ('! Hercyn ia n) vertical (to listric '1) fa ulls, tre nd ing ma inly 2<1' (and 1611') (" At lant ic direction " ), as we il as 9()'> (a nd 120") (" Medile rranean d irectio n "). Rue llan et (II. ( Ihis vol.) subdivided the evolut io n o f Ihe Mazagan conlinenta l ma rgin into five mai n stages (Fig. 7.1):

175

CYAMAZ CAMPAJGN SYNTHESrS. MAZAGAN ESCARPMENT

1) Late Triassie (0 Liassie intracontinental rifting with the de posit ion of evaporites ove rlying a redbed envi· m nme nl ( \V inteTer , Hi nz, 1984). The su bsidi ng epi· continental basin , fi l1ed by evaporites, lies essentially seaward o f the Upper Ju rassic carbonate pl<ltform. There were cmbayments into the Moroccan Meseta (e.g. , the" Allas Gu lf "/Essaouira Basin ; see Fig. 1). A Raet ian to Hettangian phase o f carly ri ft ·faulting and subsidence was inferred from Leg 79 evidcnce (\V intere r, Hinz , 1984). 2) From LlIIe Jmassie 10 carly Neocomiall - afte r a postu lated mid·J urassie teclOnic reactivatio n (possibly block-faulting alo ng listric faul ls) and onset of drift ing - mooerate subside nce and bu ildup of a 500-800 (?) m thick carbonate ramp and platform , espec ially on fau lted base me nt highs. Much thi nner, he mipelagic to pelagic sedi me nt s were depositcd in the deepe r areas to the west. Lundward the platfo rm ca rbonates became th inner and the de posit iona l environ me nt locally somewha t decper.

3) During the Early CretaceollS (?Neocomian to Aptian) wc note a very important block-faulting phase which resulted in the outcropping of platform carbonates alollg the oute r edge of tBled bloc ks and the creat ion of sma ll sedirnent-fi lled basins in the adjacent half-grabens. Accord ing to Huessner (1984) Ihis block-faulting eve nl was a re sponse 10 differe nt rates of subsidence , sincc the former western High Atlas rift bccame an "aborted rift· , (afier a mid­Jurassic compression) with slowed·down subsidence , whe reas the At lamic margin conti nued to subside slro ngly. Th is caused a landwa rd retreat of the ca rbonate pla tform. 4) The Upper Cretaeeolls deposits a rc widcly ove rlap­ping Ihe existing rel ief and spread ove r much of the Mazagan Plateau and the adjacent Moroccan Meseta. The maximum transgression was during the tecto ni­ca lly quiet Turon ian times. 5) Numerous unconformit ies (?lower Senonian. ?u p· per Eoce ne, ?mid-Mioce ne) sepa rate the inte rmitte nt Upper Crelaceous to Terliary seque nce. Seismic evi­dencc and the observat ions of « fresh » venical fault s al the prese nt Mazagan Escarpment suggesl tha l the faul t ing is still continuing.

The Triassic 10 Early Cretaceous evolution of the Morocca n margin is dominllted by the rifting and carly drih ing stages of the opc ning of the Atlan tic Ocean , whereas the L'u e Creiaccous to Te rtiary evo lution is innuenced by African eve nt s, such as vertical epc iroge nic moveme nt s of the High At las .. inversion " and the Rif omgeny. The rcfore Ihe devclopme nt of the continge nt Nort h Ame rican and Nort hwesl African conti nenta l margins is very similar d uring the first phase and differe nl during the second phase ( Ruclla n el al. , this vol. ; cf. also Stcts, \Vu rsler, 1982). Figure 15 shows tha l the subsidence of the major tilted faul t blocks migrated progressive ly la ndwilrds : mai nly from scdimentologica l evidcnce. wc postulate that the western most low sialic block (site 544, not show n in Fig. J5) had probably already bee n dow n­raulled lO bathyal Willer deplh during Ti tho nia n li mes (Steiger , Jansa , 1985), lhe main Mazaga n Escarpme llt block du ring Be rriasian 10 Valanginia n (- Haute rivian) times. and the soul heastern Mazagan Plateau horst

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U VON RAD 8f al

LIASSIC .",,, MAU'! [AilL Y (Rn l AT[ ( AtT PAUOC. fOC ,,,,,,, - o. ~ ,. h . , ~ •• ~ o. 1. to .. " ... ~ " , ... , "'.<lft. ,.~ ";., • • : iF'

....... Q 1 D .... ,.1 .......... ,,---- --'''''''1 . .- , ,- !

0

fOOT Of ( (NTRAl l'IAZAGA/f '\ \.-. (S{ AAf'Io'I(/fT , . Sli t § ~5 1 _

~ ", l=::, ::;_ 00 t

! , ..t - ---}~ ! -~ i !l. ~ ~ --. -- I® ....... - . - , , 1

- - - -- - - - • __ 1 ___ , - -, , --@ TOP Of ((/fIltAl ® ,

'" ""'-MAZAGA/f ESCARf't1(HI 1 "

Figure 15 Nml-l fIl Î/Orm slibsidtnet hiJlory and paltobalhymttric tl'olUlion of Iht Mazagan EJcarp~1II (" gtohiJlory diagrams·' wÎlh geological agt plolll'd again.n dtpl/r INlow or abol't Ma Itl'tI), Four dif?rtnl aftos of/hl' prtUnt Ma:agan Siopt EKarp~nI and PIOltali (prtKnt "'altr dl'p/hs : A - J ()(I() m. B - 1 900 ni. C - 1 200 m, D - 1 ()(J() m) Iwl't bl'tll bock/rac~d {rom 0-200 Ma 10 show l/wir Slnlc/li ral. {ocks and paltodtp'h tl'o/mion. Boxtd numINrs undtr" baS<'mtn/" - loml Slibsidtnct ra~s (miMa), unco"tt~d fo r compa(tion etc. Encire/td numbtrs - mkrofa­dts (MF) /ypts (see Tab.I ). J '" (Upptr) Jurrusic pltll/orm (arbolltlltS, KI - I-Owtr CrtlaetC}//s. Km - mid·CftlaetoIiS. KIIIP - UpfJtr Crt/actOllslPa/tQgclll', N" Nrogelle. Figll ft /5 A modifitd afier Will/ul"r alld Hin; ( /984).

(CZ dive 92) probabl)' not bc fore l3arremian to Aptian times.

11 is also noteworthy Ihat the Mazagan Escarpme nt is at least 120 Ma o ld and was since that time only slightly de fo rmed by erosio n , bioge nic or chem ical di ssolution , a nd gravitat ive processes (Fig. 7). Pockcts o r burrows in thc Upper Ju rassic platform limcstoncs arc filled or ove rla in by Lower Cretaccous, Upper Crelaceous . Paleogene or Neoge ne sediments, often de monstra ted by a hand specimen o r Ihin­scction (von Rad , this voL).

SU MM A RY AND COMPA RI SO \VITI-! SI MI -LAR CARBONAT E PLATFO RMS

Strat igraphie a nd struct ural evolution of the Mazagan margin

Figure 6 summarizes the srratigrUI)hic um/ tecronic reSlllrs of thc CY AMAZ eampaign and atte mpts to answer in which way global setl leI/el flllctuations and vertical feCfoniC$ influeneed the evolUlion of thc post­platform seq uence. In add ition 10 VA IL's global sca Icvcl curvc (Todd, Mitchum , 1977; Vail ef al .. in prcss), wc show a transgression- regression curvc which is bascd o n the published evidence from the Mo roccan coastal basi ns and wh ich fits bctter 10 ou r sedimentar)' data. This figure de monslrates the ma jo r

176

teclonic events and unconformities , like the breakup­unconfo rmit )' and thc major blockfaulting episodes. as wcll as Ihe facies cvolution at the Mazaga n Plateau bc twee n mid-J urassic and Paleoge ne times. The evo lu­tion starts with the (Kimme ridgian-) Tithonian nerilic ca rbonale platfo rm phase. possibly preceded by an mid-Jurassic to Oxfordian (- Kimmeridgia n) .. ca rbo­nate ramp phase " . Il is followed by the bioc lastÎC .. fl ysch .. facies, which was found o nly in the palcoca­nyon-fa n system to the south of the pla tea u. AI aboul Ihe same time wc find at the paleo-esca rpme nt (near the shelfbrea k) condensed ha rdgrou nd series (MF 9, MF 8.3-8.4 and part o f MF 8.2). Fro m laIe Aptian 10 Cenomanian times hemipclllgic nanno marIs (MF 10) whe re deposited at the foot of the escarpment. The upper L'lIe Cretaceous is characte rized by pe lagie nanno chalks (MF 15), phospho ritcs (MF II . 12), phospho rite breccias (MF 13), and limestone breccias (MF 14). The phospho rite s indieate increased planklon fe rlilit y, causcd by upwell ing cvents, and slow starved-scdimentllt ion co ndi tions in an upper slo pe/oute r shclf sc tting. After anolher hiat us at the Cretaceousfrertiary boundary, pelagic foraminiferal ehalks, breccias, and radio larian che rts of Paleocene to Eocene age se l in . The Neogene is charactcrized by pelagie foraminiferal nanno ooze depositio n, inter­rupted by seve ral unconform ities, in an e nvironrnent which WOl S very simi lar to the prese nt one. The .. st ratigraphie turning points'· (Sch lager. 1981) arc clca rly influenccd by vertical teetonics. sea level fl uctuations . and possibly also by climatc. a very

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poorly known variable. A late Serriasian regression might have exposed Ihe platform which might have been subsequently karstified (Ste iger , Cousi n , this vol. ; Va il , pe rs. comm.). The rapid Valanginian transgression drowned the plat fo rm below the eupho­tic zone and beyond recovery. The eondensed Iron ooid- and belcmnite-rich horizon mighl corre late with the Valangin ian-ca rly J-Iauterivian transgression. The Wca lde n-type deltas and the ir submarine exte nsion 10 a prodelta-canyon·deep-sea fan system were built forward muinly du ring the I-Iauterivian regression (von Rad , Sarti, in press) . The thick he mipclagic Late Aptian-Albian (·Cenomanian) nanno marIs al Ihe lower slope coi ncide wilh the Late Aptian to Albian transgression. On Ihe olhe r hand , the ca rly Neoco· mian, Aptian , Senonian and Pa leoge ne breccias arc in ou r Interpretat ion eaused by majo r bloekfaulting episodes which increased Ihe relief o f the old esearp­me nlS and triggered local slumps and mass flows.

The sha ping of steep escarpments at carbonate plat­forms

One o f our major objectives was to find out what processcs formed the steep esearpmcnt of this old passive-margin type carbonate platform. Figure 14 shows seve ral possible construetional and dest ructio­nal processes of carbonate platform deve lo pment , independant of thcir applicabi lity to the case of the Mazagan Plateau (cf. Jansa , 1981): a) slope construction by recf growth or carbonale bu ildup ; b) slope accretion by progradation (upbu ilding and oUlbui lding) with slurnps und dcbris nows at the slope and turbidites at the apron ; c) bypassing o f sediment s o r nondeposition wi lh hardgroumls along the steep sedimenl-starverd slope ; d) progradation and bypassing with turbid ites onlap­ping in an upslope direction , a co mmon combinal ion of (b) and (c) ; e) erasion (defadng) and/or mass wasting might hllvc truncated the outer part of progradcd sediments and aClually :111 or most of Ihe outer high-e nergy recr section of a carbonate platfo rm , eausi ng a landward re lreat of the platform slope (Freeman·Lynde et al., 198 1. Schlage r et al., 1984) ; and f) vertica l tectonics (e.g., rotational block-fauh ing) mighl ha ve Iransfo rmed the rifted margin into a sta ircasc o f progressive!y down· faulted fault blocks. Schlage r und G insburg (1981) have predictcd a succes­sio n of ste ps a-b-+c-e: plat rorm slopes steepen as they grow higher ; then they shift fro m accretion to bypassing, and finally 10 erosion. ln the case of the Mazagan Esea rpment wc sec ev idence o f ail thesc processes: Carbonate buildup (cyanobacterian crusts etc.) ca n bc o nly responsible for part o f the re lief during the Late J urassic-early Ncocom ian co nstruct io n of the platform ; prograda­tio n is o nly sec n locally in the <lpron of the slope ; vertica l tcetonics is appare nt ly the most important factor ; and post-carly Neocomian e rosion, nondeposi­tio n and bypassing is ev ident by the hardgrounds and poeket fillings ovcrlying the platform ca rbomlles. Dcfudng and buckcuning o f the cliff, howevc r. were

177

CYAMAZ CAMPAlGN SYNTHESIS. MAZAGAN ESCARPMENT

of minor importance, since the full y ccrne nted, mas­sive pelspa rites have been very resistant to e rosion (Stciger, Cousin, this voL). I-Iowever, local e rosion and bioge nic or chemica l dissolution is indicated by the rounded and pitled surfaces of Ihe Jutassie limestone oulcrops alo ng the esearpment , and e pisodic defadng of the paleo-esearpme nt is ind icaled by the lirnestone breccias in the Miocene- Pliocene debris flows of site 545 (Steige r, Jan5.:1 , 1984).

Palcobathymetry and subsidence history

Another problem of gencral interest is the tectonic control of the subsidence histo ry of starved, passive contine ntal rnargi ns. Figure 15 shows sehcmatic sket­ches of the paleobathymelrie and subsidence evol utio n of four blocks across the Mazaga n slope , Esea rpment und Plateau wh ich all had an ind ividua l subside nce lInd fades history. The subsidence curves arc very differcnt frorn curves for " fat " passive continental margins (l'.g. , Watts. Steckler, 1979 ; von Rad , Ein­sc ie, 1980) or for the expone ntially dccrcasi ng subsi­dence of the cooling ocea nic crust (Pa rsons, Sclatcr, 1978). For the Mazaga n Plateau with its sta rved­sediment condit ions wc invoke a complex history with at least 3 times of structu ration and accclerated subsi· de nce. 1) Rifting during late Trillssic- Liassic limes occured along rej uvcnated Varisea n fault s and produced rOla­t ional fault blocks trending more or less para lle! to the present esca rpment. 2) After the mid·Jurassic onse t of drift , wc have moderatc subsidence (about 30-50 miMa) during the 15-20 Ma o f carbonate buildup under shallow-w:lte r conditions. 3) About 120-130 Ma ago termination of carbonate buildup (a) by a rapid regression followed by a major Va lan ginian transgression, and (b) by a new structura­tion by block-faulting. The subsidence raies increased to up to 85 miMa fo r the lower blocks (Fig. 15A) and up to 100 miMa fo r the El Jadida Canyon area (Fig. 15C), where Lowe r Crelaeeous deeper water sediment s wcre deposited . They were not compcn5.:1· ted by sedimentation. On higher blocks (Fig. 15B), wc obselVed eondenscd hardground formations, fo lio­wed by nondeposit ion <lnd erosion. Thus a precursor of the present Mazagan Escarpment is at least 120 Ma old. Only Ih in, pelagic, dee p-wate r sediments were inte rmille ntly deposited on the slowly subsiding pla­teau an(\ slope. 4) During Ihe Campanilln/Mallst riehtian , Eocene , and possibly also the Mioce ne, we had other structural rejuvenations of the slope after periods of lo ng tectonie quiesce nce and very reduced subsidcnee rates (3-20 miMa).

Compurison of the MU1'..uglln Plateau with other purts of the Jur-J.ssic-Early Cretaceous carbonate platform olT Nort hwest Afrlea

The seawa rd cdgc o f the Upper Jurassic ca rbomllC platform forrns a co nspieuous structura l feature off Ihe Northwest Afriean conti nenta l margin (Fig. 1) which is almost continuous fo r about 800 km from the

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U VON RAD et al

OFFSHORE TARFAYA BASIN

Figure 16.1

.xMnumc cross'Retion of tM Mazagan (lrtiJ (modi­fkd oftu R~I/(Jn el al., this vol., lM" Fig. 6). Nmntwrs dtsigna~ OSDP si'tl ; CZ .. arta txplortd b)' CYAMAZ dkts. Sec Figurt 1 for locoMn. + • g,alli,ic bQRml'n! (Palro:oic), L - ·r"as· sitlLiassic el·aporiIU. rrdbtdJ. CIC.

H ....... _~ ... lor. Jw,.t ..... _ S figurc 16.2

_ . _ -_-=--:"'-- (l~---=--~-- .xMmtJl/C cross-scellon of lM offthort parI of lM nor/Mm Tarfa)"a BaJill NE of Capt Juby (for approxima~ localion $Cc I-7g. 1). Modifitd afiu Mu­rhum and VaU (/977) and Todd and Mitchum (/977). M(I;or Imcol/formilitl alld Ihe buried ra,bollalt plal' form (lrt Olllli"td by Ileavy lil/tl. NOlt sea ... ard l/ricktnil/g ... edgt of (l 10 more ,hall 3 km IMck) Lo ... tr Crtklcrous ekwie suits buryillg IIlt block· pmlled, J/.(tp palro~scarpmtnl ofllTt Upptr }/4faJjie earbom.zlt pla/form. /J.1 - UpfJtr JuraSJIC Puer/a Ca'!Sada Forl1lillion. Kl . l + 1.1 - Lo ... ·trCre/(lerous Tan·Tan FormtJlion (procklfiJ ctc.), KI .3 + 1.4 -mid-CrtfiJuoUS Aguidir FormtJlion. Sec alsa fl inz ct al. (1981, Fig. 1).

" , '

w

." .. --

GUINEA PLATEAU

_.u.

" -- --. ,. "

E

Figure 16.3

" ~-Q?=::~'L] _ _ ___ _ ~'. ~.... .. IVl

Li'le dra ... ing ofttr ai'gu" st/smü: profilt (RRS Sirac· k(eto'l) auosl l/re Guil/ea P/a/eall alld EsCal/"lltn! off GI/intt (WtSI Afrira). Modified afttr JOIltS a/Id Mgbalogu (1981, Fig. $). K,I. ,M.N - rtflee/ors .. Km - ",iJ·C,..wcrous (black sha/t) rejleeWr. AB - acousfie ba5tmtllf. Straligraphie co"elalion I·tr)' ttn!ali .. t.

Figure 16

Comparison of Iht s/rurlllrt of 1//1' North .... tsl Africal/ Uppt'r J"rassie (/0 /o .... er CrelateOIlS) C/l,bol/(l/e p(afform (1/ 33"3(1 N (Ma:al;all Plaltall). 19'N (offshort Tarfaya Basill) and !(»N (G/lil/ta Pla/eall). Ltgelld: Tr " Tri(lssie:} - Jurossie " JI = 10 .... l:r }MOSSie (Llassir) .. 12 - middlt }/Uassie (Dogger): 13 - IIpper J/llassie (Ma lm) ; 13.1" Oxjordia,, : 13.1 = Kinm~,idglall la TithonUJ.n .. K - Crtlateous.' KI .. lo .... er Cre/oceo"s : KI .I - Valallginlan .. KI .2 - lIa/</.(f/I'lal/ la Borremu",. KI.3 = lo ... tr la middlt AplUlI1 : KIA - uppt'r Apliall la 10k'e, Ctntmwnian " K1 - /'pper CrtklCtOuS.. TI' &- E .. Paleoct neIEocent'. T ()/. = Oilgocent' .. T Jj .. MiOUllt .. T I>f 'd.J - lo .... tr middlt. upper Mioctne : T,/ .. Pliocene .. G", Gro .... lh fuullS " J .. mid-Miocent' unconformif)'" 2 - mid-la I..alt Oligoctnt' (' SI}'rÎiJn ") urrconformil" " J .. Pa/rogent (? E. E«ent') unconformily (" PyrtmJean ") .. 4 - tarly Ntoa>mÎiJn ("Ult Cimml'rÎiJ/1 ") lu/Con/i:mnuy wilh ?k.awifitd surface.

Mazagan Plateau in the nOrlh to the nOrlhern Tarfaya Basin in the south ( Ilinz el al., 1982). FUrlher south, off the Western Sahara ( Ranke el al., 1982), Mau reta­nia and nOrlhern Senegal the carbonate platform is dccply buried and lcss evidcnt. It becomes again a prominent morphologie unit off sou thern Senegal and Guinea (Wissmann, 1982; Joncs, Mgbatogu. 1982). Thc present water dcpth of the top of the outcr cdge of the carbonate platform increases southward. from about 2 km at the Mazagan Plateau to 2·3 km off the nOrlhern Tarfaya Basin , to 4-7 km off Western Sahara , Mauretania and nOrlhern Senega!. Only in two regions along thc West Arriean margin is the escarpment of the Mesozoie carbonate platform expo· sed at the pre!>Cnt sea floor : at the Mazagan Plateau off the Moroccan Meseta in the nOrlh (Fig. 16.1) and at the Guinea Plateau off the Cas..1manee in the south (Fig. 16.3). Apparently. these two very stable Paleo-

178

zoic-MeSOloic platforms formed south of the Atores Fracture Zone and nOrlh of the Guinea Fracture zone at the nOrlheastern and southeastern boundary of the Jurass1c Atlantic Ocean (Wissmann, pers. comm.). BOIh plateaus were characterized by highly rcduced subside nce rates and starved sedimen tation or e rosion du ring the pltSI 125 Ma , and hcnce remained exposed or nearly exposed high-standing bascrnent bJocks at the West African margin. Thesc structural highs arc also associated with promontorics of the West African PaleOloic fold bch and corre latc with the contingen t Avalon Uplift (1) nOrlh of the Scotian margin , and the Peninsu lar Arch/South Floridan margin , respcc1ively (W issmann, Rocscr, 1982).

The structure of the offshore Tarfa)'lI Bl/sill (Fig. 16.2) is an excelle nt example for an imprcssive Late Jurassie ca rbonate shclf margin with a wcH

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developcd Kimmcridgia n 10 Tilho nian " rec(" and a stccp (10-2O"!) Tilhonian/Berriasilin paleo-escarp­me O! . The Mesozoic carbonate platform is buried by a th ick wedge of Lowe r Cretaceous, c1astic deepcr­water sediment s (Todd , Mitchum, 1977; Mitchum. Vai1 , 1977; I-linz et al. , 1982). The profile (Fig. 16.2) is based o n an industrial mullichannel se ismic line , iO!erpretcd by Mitchum and Vail (1977) , using data from surface geo logy and co mme rcial on- and offshore well s. VlIlanginian dee p-marine clastics (K 1. 1) arc restricted 10 li small slopc basin in froni of the esca rpmeO! with both dee p-marine downlap and onlap aga inst the paleoslope. The Haute rivian regressive sa ndsto nes ove rly d irectly an eroded surface of the o ld ca rbonate platform which was probably subae rially cxposed and karstificd during a major late Bcrriasian 10 mid-Valanginian sea- Ievcl 10wSland (Vail , pers. comm.). The overlying Haute rivian to Barremian ( K 1.2) sediments Cran-Tan Formation) arc a seaward thickening (1 to more than 3 km) seq uence of delta ic sandslones and prodeltaie silty mudstones, charactcr­ized by syndepositiona l growth fau lts. A major regres­sion is ind icated by the shclf facies overriding the slopc facies , after the basin was fi lied to sea levc l. The ovc rlyi ng Aptian to lower Ce noman ian Aguidir For­ma lion (K 1.3 + 1.4) is a seve rallOO m thick seq uencc of marine shales and marIs, deposited during the mid­Cretaccous transgressions. Late Cretaceous sedime nts a rc thin or e roded by a majo r Laie Cre laceous/Pa leo­ge ne (" L1ramide " ) unconfo rmily . The Teniary sedi­mentation 15 inte rrupted by severa l major unconfo rmi­tics, espccial1y during mid-Oligocene and upper mid­Miocene times.

If we compa re the evol ution of the nonhe rn Tarfaya Basin with that of the Mazaga n Plateau , we note the following similarities and differences: a) the evolu­tion, struct uratio n and drowning o f thc Upper Jurassic carbonate platform is very similar. as is the Late Jurassic subsidence hislo ry (al tho ugh the platfo rm

w

CYAMP\l CAMPAIGN SYNTHESIS. MAZAGAN ESCARPMENT

carbonates arc much Ihinne r at the Mazagan Pla­teau) ; b) similar as at the Mazagan Plateau, Ihe relicf betwee n the L'lte J urassic shallow-water platform and the adjacent deep-sea plain o r continental risc was about 2.5·3 km ( l-l in1. el al., 1982) ; c) al tho ugh the Wealde n-type dcltaic clastics o f the Lower Cretaceous ( K 1.2 + 1.3) are si milar to Ihe bioc lastic turbidites of the El Jadida Ca nyon area (MF 8.2), the sedime ma­tio n rates are about 10 times as high in the Tarraya Basin as o n the sedimem-starved Mazagan Plntcllu ; d) also the mid -Cretaccous transgrcssive maris and shales (K 1.4) arc much thicker than Ihe comparable hcmipclagic latc Aptian to Ce no manian nanno marIs tro m the Mazagan slope. A very si milar, thick Cretaceous Wea lden-typc deltaic seque nce with an upward and seaward facies transitio n from contine ntal c1astics to Ingoona l/intertida l depo­silS - de lt a front sedime nt s _ lami natcd prodelta muds was described from the West Sa haran (Cape Bojador) marginal basin (von Rad, Ei nse le, 1980; von Rad , Arthur , 1979; Ranke el al. , 1982). Dista l lurbidites reached the deep-sca fan. now upliftcd and exposed al the isla nd of Fuerteve ntura (Robenson, Be rnoulli , 1982). The G uinea marginal platform (Lc hner , de Ruiter, 1977 ; Joncs, Mgbatogu, 1982) is very sim ilar 10 the Mazagan area , although much less weil studied (Fig. 16.3). A large part o f the platform has hardly bee n buried by post-platform sediments since the early stages of se paration from Ihe contingent Blake PlateaulFlorida margin. The Upper J urassic 10 Cc no­mania n carbonate plal fo rm is up to 3 km thick and has a rclief of about 3000 m with an inner and an outer escarpment. The plateau has a stcep soulhward­faci ng searp, formcd by the left- Ialera llransform fault of the Guinea Fracture Zonc. T hus the Guinea Plateau and ilS plate-tectonic neighbour, Ihe Blake PlaleaulS Flo rida margin (Fig. 17), had a vcry simil .. r evolut ion as the Mazagan Plateau .

[ . ---- - ----------------- - - --------;.

f''igurc 17

BLAKE PLATEAU BLAKE NOSE

1 .. -

BLAKE ESCARPMENT

BLAKE - BAHAMA BASIN

--

1 MJ,l"-- ~-:-~~__ ---:-= ;: r .. "F-_____ .~ _ _ ,_ , -- - -

P-23".J'i.. --~-- "'" ~~o I-j:j: .,

IkU f'ItC 8ue ... n! 1 8111<. SP'I" Ilidge 1

l· ·V Ui

.~~---------------------------X~------------------~ ... - ''of'!

S«.tiOlr across Hlakt Plu/tau. Blake Esca'plll~.'nt a/ld adjaunllJ/akt- lJuhama Basin (approxima/tir UJI'N). Lint d,uwing of CONRAD ~ismit profite MC 2 /h,Quglr OSOP sitt 39() w;/Il siltS 392 a/ld j34 proj«ft d. Modifkd a[ru Sirt rida/l a/ld EnQs (1979. n g. 1 ; sec afso Shtridan. Grtubttin ct al" 1983). NQlt curbOlIU/t IUl11k IIlUrgin jiK:ies (rufal or OIMr nlUSSÎ\'t or diagtlltlk/lflr aflt rt curbO/ratts 1), idtnliMd ilS Ily{ltroofk rtf/tClQr$ QI·t rf}'illg 1111 opuqut. rtf/tCf;QI//tSS tOllt.

179

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Compa rison of H1ake and Bahama Plateau wit h Mazu­gan Platcau

Figure 17 shows a sche mat ic section aeross the Blake Plateau, Blake Escarpmenl and adjacent Blake­Oahama Basi n. an area which has also been sludied in great delail by seismic surveys (Shipley el al .. 1978; Foiger el al. , 1979), drcdging, roring, seicmifie oce.tn dri lling (Benson , Sheridan el al., 1978 ; Sheridan, Enos , 1979; Sheridan el al., 1983), and subme rsible surveys (USGS dives with Alvi n . 198 1, unpublished). After the breakup of Pangaea at 155- 165 Ma , active sea noor spreadi ng began. followed by a major Callovian transgression , rapid subsidence , and carbo­nate buildup st3rting in Oxfordian/early Kimmerid­gian times (Ogg tI al. , 1982). At Blake Nose an induraled , NeDcom ian , upward-shoaling seq ue nce of open-shelf muds, oolites a nd peritidal sediments overlies a several kilomet res thick Jurassic carbonate platform seq uence. Reef growth und carbonate bui!­dup a t Blake Nose ended with emergence and fresh­water diagenesis (karst development) duri ng a middle 10 late Barremian sea-Ievel lowsland , foUowed by subsidence 10 grente r wale r depths during the follo­wing sea level rise. A condenscd sequence of red goethit ic erusts wi th pisolitcs (very sim ilar to the Iron ooid-rich facies MF 9 o f C Y AMAZ) and nanno fossi l oozcs overl ies erosional surfnces of inte rtidal limesto­nes. During the Aptian the water depth at site 392 had nl ready increased 10 seve ra! 100 m (Sheridan , Enos , 1979). Aecording to Leg 101 result s, a large Juras­sic/Lower Cretaceous .. megabnnk " in the area betwecn the northern straits of Florida and the sout hern Blake Plateau was drowned by a risi ng sea level about 100 Ma ago (Schlage r , Austi n, press rclease: for ODP Leg 101 , April 1985).

As at Mazagan Plateau. a major hia tus spans the late Albian through carly Campan ian. suggesti ng subma­rine erosion and bypassing by strong ?Santonian boltom-fo llowing contour eurrents. Fro m the Santo­niall/Campan ian on , water depth incrcased and the shclf margin shifted landward towards the locus of Tcrtiary to Recent ca rbonate bank accretion (Sheri­dan. Enos, 1979).

Site 534 in the Blake- Bahama Basin documentcd a co mplete reco rd o f Callovian to Ccnoma nian deep-

R EFEREN('l ~'i

Auuodt J .- ~I .. Monll S .. Ruel""n t: .. tY8.l. Cancs balh)mëtriquc~ du Plateau CI <k 1'c.carpcmc nt de El Jadida (t-.·lataglm). Campagne SEAZAGAN (1; ]00000. 1: 50000). l'ubl. CN EXO. Rueil Malmaison.

AUlCnd~ J.·M .. ,'on Rad U .. Ruel""n E .. CYAMAZ Group. ]984. Outline and resul ls of lhe CYAMAZ cruise (Maugan Escarpmc nt . Wesi Morocoo). in: Submusib/~ Cyurw $lIIdWJ of lM MQzQson EscQrp~nf (MarO((Qn conllru'nUl/ ma(8111). CYAMAZ CffllU 1982. edited by J. -M. Au«ndc and M. \'on Rad. OceanoL Acta. ~ $p. S· SB.

180

sea sediments (Sheridan el al., 1983). The Berriasian to Barremian Blake- Bahama Formation contains redeposited clast Îes from the Blake Plateau , especially Hau terivian to Barrcmian turbidites and dcbris nows (Robertson , Blidniek, 1983). This e nvironmcm is comparable . although of much minor importance. 10 the deep-sca fan environ ment reco rded in DSDP site 416 of the Moroccan Basin (Lancelot , Winte rer, 1980). A much thicke r , Wea lden-type Early Creta­ecous decp-sea fan facies was discovered in si le 603 , 800 km NNE o f site 534 o n Ihe " Hattcras Dcep-Se3 Fan" (von Rad elal. , 1984 ; Sani , von Rad, in press).

A similar , 2 kil). Ihick Early Cretaccous to Eocene section o f the Bahama Escarpmem was studied and samplcd by the US submersible Alvin (Freeman­Lynde et al .• 1981). Simila r to the Blake Platcau , it consists of a lower and middle C re taccous sequence of peritida l, lagoonal , patch-recf and bac k-recf limesto­nes , uneonformably overlain by an inte rmittent cover of Maastrichtian and Eoce ne pelagie limeslone . Thesc autho rs and Sehlagc r el al. ( 1984) assume that a 1-5 km wide zone of recf and fore-recf dcposits was removed by erosio nal backcutting of the cl iff, hclped by spalla lion of joint bJocks. For the Mazaga n area , wc assume that bloc k-faulting WllS Ihe ma in factor shaping the stee p pa leo-cscarpme nt and Ihat therc was no major backcuuing of the well-ecmentcd mas­sive Upper Jurass1c peloidal pack- and grainstones.

Acknowlcdgements

Wc thank Ca pl ains Y. Kc ranflech and H. Guidai and the crcw of the R. V. Suroit , as wcll as MT. 1. Roux and the Cya na erew for the most cfficÎenl coolX'ration on board. The CY AMAZ exped it ion was funded by the Ccmre Nationa l pour J'Exploitation des Océans (CNEXO). now IFREMER , the Deutsche For­schungsgeme in schaft (Bonn - Oad Godesbe rg), the Federal Minislry of Rcsea rch and Technology (Bonn) and HG R ( Han novcr). We arc very grateful 10 ail shipboard scicntists and shore-bascd contributors who hclped in the collection and interpretation of the data and exprcss our grali tude to Lu bomir Jansa , Wo lfga ng Schlager , Karl Hinz, E. L. \Vinterer and G. Wissmann fOf revicwing Ihis manu se ripl.

[kohrens M .. Sithl ,\ .. 1982. ScdllTl<:ntatÎOn in Ihe At las Gutf 1 ; LQwcr CrClaccous claslks. in; Gr%g)' of Ihr Norll"."rSI Afrlcalt CO,lIIl1rnt<l1 marSIn. edÎlCd by U. \'on Rad ri <II .. Springcr. Berlin. Heidctberg. New York. 427-438. Ik'hrcns M .. Krunl!;lek K .. Melcr D. F. .. Sçhii rer A .. Slehl A .. Siets J. , The;n J .• Wurstt'r P. 1978. Scdimenta tionsabtau!e im Al la~-Golf (Krcidek(btenbed:cn. Marokko). Ctot. RUlld.«h., 67. 424-453. I~nson W. F. •• S~rldan R. E. rI <II. (~hlpboard scicntific par1) LeS 4.\). 1978. lm/. Rrp. fhtp-~(I 0,ll1m8 ProJ«l. US Go\'. l' .. ml. Off .. Washington D.C. 1005 p.

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U .... ON RAO et /II

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Ab/. ( CH' l ""_