16. mineralogical and geochemical investigations of ... · during leg 79 on the mazagan plateau....

16. MINERALOGICAL AND GEOCHEMICAL INVESTIGATIONS OF SEDIMENTS ON THEMAZAGAN PLATEAU, NORTHWESTERN AFRICAN MARGIN

(LEG 79, DEEP SEA DRILLING PROJECT)1

Hervé Chamley and Pierre Debrabant, Université de Lille I 2

ABSTRACT

Detailed mineralogical and geochemical studies were performed on samples from selected time intervals recoveredduring Leg 79 on the Mazagan Plateau. The uppermost Albian and Cenomanian sediments of Sites 545 and 547 can becorrelated on the basis of mineralogy and geochemistry; these sediments illustrate differential settling processes and theexistence of hot climates with alternating humid and dry seasons in the African coastal zone. The upper Aptian to Albi-an black shales of Site 545 point to an irregular alternation of tectonic activity and relaxation stages, allowing differentbehaviors in the reworking of soils, crystalline rocks, and sediments born in peri-marine basins. The barren lower Meso-zoic reddish sediments and evaporitic series of Sites 546 and 547 are characterized by a strong physical erosion of sialiclandscapes, without clear evidence of post-depositional metamorphic events. At Site 546 strong early diagenetic pro-cesses in a confined evaporitic environment affect both the mineralogy and the geochemistry of pre-Miocene rocks.

INTRODUCTION

Mineralogical and geochemical investigations have beenmade on selected lithofacies representing specific timeintervals, from sedimentary materials of Sites 545, 546,and 547 of the Deep Sea Drilling Project Leg 79, on theslope of the Mazagan Plateau, off Morocco. The Meso-zoic carbonate platform in this area is structurally con-trolled by either diapiric structures or sialic basement(Fig. 1) (site chapters, this volume). The aim of the studywas to obtain information on the stratigraphy, paleoen-vironment, and diagenetic evolution of the sediments.Detailed studies have been made on the upper Albian toCenomanian green nannofossil claystone recovered atSites 545 and 547 and on the lower Mesozoic red clays,halite, and associated facies encountered in cores fromSites 546 and 547. We also have investigated samples ofupper Aptian to Albian sediments from Site 545, andCenozoic clayey to calcareous oozes from Site 547. Ta-ble 1 summarizes the sites studied.

ANALYTICAL PROCEDURES

The X-ray diffraction method was as follows. The samples weredissociated in water, then calcium carbonate was removed in 5N hy-drochloric acid. Excess acid was removed by successive centrifuging;deflocculation was improved using a microhomogenizer. The fractionsmaller than 2 µm was collected by decantation, following settling timesdetermined by using Stokes' law; then oriented pastes were made onglass slides. A Philips Model 1730 diffractometer (copper radiation)was used to make the X-ray diffraction scans at 2°2 θ/min. Three dif-fractograms were made (1) from 2.5° to 28.5°θ on natural samples;(2) from 2.5° to 14.5° θ on glycolated samples; (3) from 2.5° to 14.5°2θ on samples heated for 2 hours at 490°C. The quantitative evalua-tions obtained are based on peak heights and areas (Chamley, 1979).The heights of illite and chlorite 001 peaks (diagram for glycolatedsample) were taken as references. By comparison with these values,values for smectite, palygorskite, sepiolite, vermiculite, and irregular

Sialic basement high Diapiric structure

Figure 1. Location of Leg 79 sites.

Normal fault

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

2 Address: Sédimentologie et Géochemie. ERA 764 CNRS, Université de Lille I, 59655Villeneuve d'Ascq, France.

mixed-layer clays were corrected by addition of peak height (×1.5-2.0 according to the crystallinity of each species), whereas valuesfor well-crystallized kaolinite were corrected by subtraction (× 0.7-0.5, depending on kaolinite crystallinity). The relative proportions ofchlorite and kaolinite were determined from the ratio of the heights ofthe 3.54 and 3.57°Å peaks, respectively. When this ratio is 1, theamount of chlorite is assumed to be twice that of kaolinite. Data aregiven in percentages, the relative error is estimated at ± 5%. Addition-al data concern the bulk mineralogy obtained by X-ray diffraction onrandomly oriented powders.

497

H. CHAMLEY, P. DEBRABANT

Table 1. Site summaries.

Site

544

545

546

547

Location

33°46.00'N09°24.26'W33°39.86'N09°21.88'W33°46.07'N09°33.09'W33°46.08'N09°21.00'W

Water depth(m)

3607

3150

3992

3940.5

Penetration(m)

235

701

129

1030

Nature ofbottom sampled

Gneiss

Dolomite

Halite

Mudstone

Age and numberof samples

early Mesozoic 3

late Aptian toCenomanian 25

early Mesozoic 27

Pliocene, Paleocene 6Albo-Cenomanian 39early Mesozoic 14

Electron-microscopy observations were made with a Siemens trans-mission microscope, on less than 8 µm particles deposited on coppergrids covered by a collodion film after carbonate removal and physicaldeflocculation.

The geochemical procedure was the following: The samples weredried at 105°C, crushed, and homogenized. Then 0.2 g was subjectedto alkaline fusion, solubilized by HC1, diluted to 100 ml, and treatedfluoronitrically in a bomb at 150°C and 50 bars for SiO2 and A12O3determination. Also, 1 g was subjected to fluoroperchloric treatment,solubilized by HC1, and diluted to 100 ml. The dilutions were used forcolorimetric analysis of TiO2 and P2O5 and for spectrophotometricdetermination of other major and trace elements by atomic absorp-tion analysis, using a Type 5000 Perkin Elmer automated spectropho-tometer. The reproductibility of the measurements is ±3% for majorelements, ± 10% for trace elements.

LATE CRETACEOUS TO EARLIEST PALEOCENE

The Upper Cretaceous to lowest Paleocene claystonesto marlstones of Hole 547A (Cores 32A-38A) are markedby abundant smectite (80%) accompanied by palygor-skite (10%), illite (5%), and little amounts of sepiolite,chlority, and irregular mixed layers. Such an assemblageis well known during this period, especially in the earli-est Paleogene of The northeastern Atlantic, and is con-sidered as reflecting hot and humidity-contrasted cli-mate on adjacent landmasses (Mélières, 1978; Chamley,1979).

LATE ALBIAN AND CENOMANIAN,SITES 545 AND 547

Upper Albian to Cenomanian deposits of Site 547consist of nannofossil claystone to mudstone with intra-formational clay pebble structures and slump structures(Cores 547B-5 to 547B-2, 547A-73 to 547A-39, 350 mthickness), while those of Site 545 consist of green nan-nofossil claystone with some slump structures (approxi-mately Cores 545-40 to 545-29, 124 m thickness (Fig. 2).In spite of these differences, the clay mineralogy andbulk geochemistry are fairly similar at both sites. Smec-tite is very abundant (50-90% of clay minerals) and isassociated with kaolinite (5-25%), palygorskite (tracesto rarely 45%), illite (traces to 10%), chlorite and irregu-lar mixed-layer clays (traces), quartz (common), andopal-CT (rare) (Plate 1, Figs. 1-4). These mineralogicalsimilarities suggest a comparable origin for the differentspecies in both sites. A predominantly detrital origin forthe clay assemblages is interpreted based on previousstudies on the Moroccan margin and in the whole NorthAtlantic Basin (Mélières, 1978); Chamley, 1979; CEPM,1980; Chamley et al., 1980) and also is supported by theextent of resedimentation structures, high sedimentationrates, and absence of correlation between detailed li-

thology and clay mineralogy. The abundance of Al-Fesmectites and kaolinite indicates the probable impor-tance of pedogenic processes on the landmasses and theexistence of hot climates with alternating wet and dryseasons (Chamley, 1979). The data from Leg 79 agreewell with those from Legs 41, 47, 48, and 50 from theeastern North Atlantic.

The inorganic geochemistry changes moderately withdepth in the sedimentary column, and the variations ob-served depend chiefly on the variations of the CaCO3content (13-65%). Metalliferous accumulations do notoccur (Figs. 3,4): the detrital character of the sedimen-tation (parameter D) dominates everywhere; the absenceof manganese precipitation (parameter Mn*) indicates areduced environment and a high sedimentation rate (De-brabant and Foulon, 1979). The aluminoferrous charac-teristic of geochemical parameters results from the pres-ence in noticeable amounts of smectite (Fe) and kaolin-ite (Al).

In spite of this general homogeneity, minor but sig-nificant mineralogical and geochemical changes occurwith depth in the sedimentary column and permit strati-graphic correlations between Sites 547 and 545 (Fig. 2,Table 2).

The most important break occurs in the latest Albi-an, close to the Albian/Cenomanian boundary (Cores547A-66 to 547A-64; Cores 545-38 to 545-37). It corre-sponds to a significant decrease of illite, palygorskite,potassium, magnesium, and phosphorus and a correla-tive increase of smectite, kaolinite, aluminum, and iron(Fig. 2 and 5; see also Table 3). The good correlation ex-isting in both Sites 547 and 545 for the late Albian andlatest Albian-Cenomanian time intervals is clearly sum-marized in Figure 3, which shows the respective abun-dances of A12O3 and MgO. Additional differences be-tween both time intervals can be observed in Sites 545and 547 (Figs. 3 and 4), namely a decrease of CaO andan increase of 103 Sr/CaO at the late Albian/latest Albi-an boundary, which probably indicate a selective disso-lution of calcite in a reducing diagenetic environment(Maillot and Robert, 1980) and the transfer of stronti-um from carbonates to smectites.

The general inorganic stratigraphy reported here couldbe useful in order to support the biostratigraphical scalein a depositional environment characterized by notice-able dissolution processes and by sedimentary reworking.

Significant lateral changes also occur if comparingthe clay mineralogy of Sites 547 and 545 (Fig. 2).

Site 545 Site 547

IlliteSmectiteKaolinitePalygorskite

tr-10%60-75%15-25%tr-10%

(maximum 45%)

tr-5%65-90%10-20%tr-5%

(maximum 35%)

Smectite is more abundant at Site 547. As deduced fromprevious studies (Millot, 1964; Chamley, 1979), smectiteappears to originate chiefly from the reworking ofcoastal soils and surficial coastal sediments, while other

498

MINERALOGICAL AND GEOCHEMICAL INVESTIGATIONS, MAZAGAN PLATEAU

Site 545 SSEWater depth: 3150 m

NNW Site 547Water depth: 3940.5 m

421.5-

450-36-1,7237-2, 4038-2, 10038-3, 10139-2, 5940-1,6440-5, 6841-3,78

255

i-i-i-: i ε -3 0 0

-350

-400 jb

-450

-500

531

750-

772-

Mixed layers

Smectite j = ^ K a o l i n i t e [Palygorskite

Figure 2. Cretaceous clay stratigraphy and tentative mineralogical correlations, Sites 545 and 547. A and B indicate Holes 547A and 547B. For up-dated biostratigraphic correlations see chapters by Leckie (this volume) and Wiegand (this volume).

minerals are mainly reworked from various rocks (illite,palygorskite) and upstream soils (kaolinite). Smectite iswell known in modern marine environments for its abili-ty to settle later than other minerals, especially illite andkaolinite (Whitehouse et al., 1960; Gibbs, 1977). Thus,it is suggested that during the mid Cretaceous differen-tial settling processes occurred off the northwestern Af-rican margin. These processes determined the preferen-tial sedimentation of illite and associated minerals atSite 545, which is located at the foot of the Mazagan Es-carpment, and the preferential sedimentation of smec-tite at Site 547 located more distally. The parallel miner-alogical variations recorded at both sites indicate a moreproximal situation for Site 545 favoring supply fromrock and soil products, a more distal situation for Site547, favoring supplies from soil products downstream.

LATE APTIAN TO MIDDLE ALBIAN, SITE 545

The lower part of Site 545 Cretaceous green nanno-fossil claystones (Unit III) represents the late Aptian tomiddle Albian (Cores 545-56 to 545-41 approximately).This sequence is characterized by slump structures, mi-crofaults, and low-angle slide surfaces, pointing to resedi-mentation processes (site chapter, this volume). Illite,smectite, and palygorskite are the three major clay min-erals, the relative proportions of each increase or de-crease independently of the lithology or the depth ofburial. Three major palygorskite peaks are apparent,marked by abundant bundles of well-preserved fibers inthe sediments (Plate 2, Figs. 1, 2) and by high MgO/A12O3 ratios. In some intervals the three clay mineralsare present in comparable abundances (Plate 1, Figs. 5,

499


Clay minerals (%)

Chlorite E==l Kaolinit<

Smectitei i Mixed layers

IPalygorskite

60 80

Sample(level in cm)

29-1,24/2,24

30-1,6331-1,7732-1,3333-1,40

36-1, 7237-2, 4038-2, 10038-3, 10139-2, 5940-1, 6440-5, 6841-3, 78

46-1,75

47-4, 48

48-5, 78

49-4, 8

50-4, 57

51-6, 28

Figure 3. Cretaceous clay mineralogy and bulk geochemistry, Site 545.

6). Illite-rich levels correspond to low A12O3/K2O ratios.A strongly reduced character (Index Mn* < 0) occurs inthe deposition environment, as well as a highly alumi-nous-detrital influence (D close to 0.7, Fig. 3). Slightphosphate concentrations appear at Sample 545-56-6,59 cm (also magnesian rich and strontium poor) andSample 545-44-3, 78 cm, suggesting temporary lowersedimentation rates. Occasional tectonic activity alongthe Moroccan continental margin during this time periodmay be responsible for higher sedimentation rates andthe combined reworking of continental soils (smectite),or continental rocks especially from peri-marine basins(palygorskite), and of various marine sediments (i.e.,Chamley, 1979). A major break occurs in Core 545-40:the decrease of illite and potassium, the increase ofaluminoferrous smectites, and the presence of phos-phates suggest lower sedimentation rates, the reworkingof surficial continental formations (especially soils),and a tectonic relaxation during the late Albian and Ce-nomanian.

EARLY MESOZOIC, SITES 546 AND 547

Sediments of latest Triassic to earliest Jurassic agehave been collected at Sites 546 and 547 (Figs. 6, 7). AtSite 546 we have studied grayish red gypsiferous sandyclays (Cores 546-17 and 546-18, 149-156.5 m) where Mi-ocene microfossils are mixed with Mesozoic elements, aswell as halite banded with grayish red to grayish green

and gray clayey streaks (Cores 546-18 and 546-20,156.5-192 m). In Hole 547B we have considered thegrayish red sandy mudstones, locally interbedded withdark gray sandy mudstones (Cores 547B-25 to 547B-34,924-1030 m).

Sites 546 and 547 are characterized by the abundanceof chlorite and illite in the clay fraction, with these be-ing the only clay minerals in most sedimentary levels(Plate 2B, Figs. 3, 4). Quartz is ubiquitous. Dolomite,gypsum, and halite are frequent and are associated withrelatively high amounts of MgO and frequently withNa2O or K20. Lithium is the most typical trace elementand probably accompanies the micaceous minerals. Thepresence of a sialic basement very close to the bottom ofHole 547B suggests the possibility of strong erosionalprocesses acting on a poorly weathered continentalcrust. Traces of irregular mixed-layer clays occur locallyonly: Samples 546-20, 141 cm; 547B-34-2, 110 cm; and33-3, 0 cm. The rareness of chemical alteration productscould be due to the importance of physical alteration ef-fects on a high-relief continental area at the time of de-position. Another cause of the peculiar clay mineralogyobserved could be the occurrence of epimetamorphicevents after sediment deposition, as it has been shown inthe Permo-Triassic of northern Morocco (Robillard andPique, 1981). But there is no lithologic or petrographicevidence of any metamorphic influences off the Moroc-can margin, an area located far away from the tectoni-

500


421.5-

4 5 0 -

500-

— 550-

600-

650-

7 0 0 -

7 5 0 -

AgeSample

(level in cm)

Clay minerals (%)

| Chlorite F~jKaolinite

I Smectite T j Mixed layers

Illite [Palygorskite

80.39A-1,12-42'40A-2, 50•41A-1,13

I42A-2, 80

I43A-2, 64

|44A-2, 71

I45A-2, 16

I46A-2, 60

|47A-2, 50

'48A-2, 50

149A-2, 50

150A-2, 80

I51A-2, 50

152A-2, 50

|53A-2. 50

i54A-1,30/

2,30

'55A-2, 60

|57A-2,50

J58A-2, 50

I59A-2, 60

|60A-2, 50

I61A-2, 50

I62A-2, 50

I63A-2, 50

|64A-2, 50

66A-2, 50'66 A-2, 136I67A-1,1OO -

3A-2,115 -B9A-2,50 -

I70A-2,50 -'71A-2,50 -I72A-2, 60

J2B-2, 6073A-2, 50

1B-3, 48I5B-2, 50

CaO (%)

10 20 30

10JSrCaO

2 3 4

Q

0.6 0.7

Mn* = log

EMn samp. /Mn shal./

Fe samp.πFe shal. J

-0.5 0+0.5

AI,02 ^ 3K 2 0

8 10 12i i i i

MgOAI 2 O 3

2 3 4

Feo02^3

MgO

0.1 0.2 0.3

772-I

Figure 4. Cretaceous clay mineralogy and bulk geochemistry, Site 547.

cally active Atlas Mountains. Moreover, some mineral-ogical and geochemical differences do exist between Site546 and Hole 547, and vertically oriented changes occurabove the salt at Site 546 and not in Hole 547B. Thesedata cannot be easily explained in an epimetamophic con-text (see later). Thus, we do prefer the hypothesis of astrong mechanical erosion of sloped continental relieves.

In spite of a comparable background of inorganiccomponents, the lower Mesozoic reddish sediments ofSite 546 and Hole 547B show significant differences,which are summarized in Table 4.

Site 546 sediments appear to be strongly influencedby the evaporitic environment. Chlorite is 25 to 30%more abundant than in the Hole 547B deposits, and itsmorphology seen by transmission electromicroscopy isexceptionally well shaped and often occurs as auto-morphous polygons (Plate 3, Figs. 4-6). Chlorite abun-dance roughly decreases above the halite deposits of Site546. Regular mixed-layer clays occur as allevardite (il-lite-smectite) and later on as corrensite (chlorite-smec-tite), two minerals that are often associated with saline,

restricted environments (Lucas, 1962). These mineralsare characterized by automorphous forms, partly aslaths for allevardite (?) (Plate 3, Figs. 1-3), and as well-shaped polygons for corrensite (Plate 2, Figs. 5, 6). Thegeochemistry at Site 546 points to the existence of a so-dic character with a hypersaline environment passing in-to a common hemipelagic one: hypersodic (Core 546-20to sample 546-18-2, 144 cm), sulphatic immediatelyabove the salt (544-18-1, 110 cm to 546-17-4, 45 cm),magnesian (546-17-2, 130 cm to 546-17-2, 36 cm) andcalcitic (546-17-1-50, 546-17-1, 18 cm). Such changes donot occur at Site 547, which is marked by a potassiccharacter linked to the illite abundance, and which doesnot show the presence of saline evaporites above thecontinental crust. Microprobe investigations on < 1 µmparticles of chlorite show a magnesian character at thebase of both sites, with an increase of Fe content up-ward. However, the chlorite is more strongly enriched inMg at Site 546 (Core 546-18) than at Site 547. To con-clude, the reddish sediments of Hole 547B are probablythe result of the fast erosion of emerged sialic rocks with

501


Table 2. Mineralogical and geochemical correlations between Site 547and Site 545 black shales.

Site 547a Site 545Cores

51A-52A54A-55A57A-64A66A-73A+ (5B-2B)

Data

00.3700.06

(0.16)

Data

0.2000.18

Cores

29-3133

34-3738-40

P2O5(%)

51A-64A66A-73A2B-5B

11.32 10.01 29-37

6.55 6.59 38-40

AI2O3 S *g

K2Q ° 851A-64A66A-73A2B-5B

3.20 2.97 29-37

1.23 1.47 38-40 MgO

60A-64A66A-73A2B-5B

37

37-40

39A60A-64A66A-73A2B-5B

29-3137

37-40Smectite §

40A-59A60A-64A66A-73A2B-5B 37-40

39A40A-59A60A-64A66A-73A2B-5B

29-3132-36

37

37-40

IsKaolinite "S 13

11

Palygorskite

Note: ^-^ relative augmentation of clay mineral—»> relative diminution abundance over time.

a A & B indicate Holes 547A and 547B, respectively.

little subaerial weathering. On the other hand, Site 546reddish sediments point to the existence of additionaldiagenetic processes marked by mineral growths in a re-stricted evaporite environment.

CONCLUSIONSMineralogical and geochemical analyses were per-

formed on 115 samples from selected time slices of Leg79 drill sites.

The Upper Cretaceous to lowest Tertiary claystonesto marlstones recovered in Hole 547A are rich in smec-tite and also contain fibrous clays. These sedimentsmineralogically resemble the lower Paleocene depositsof the northeast Atlantic.

The upper Albian and Cenomanian redepositedgreen nannofossil claystones of Site 545 and Hole 547Acontain similar clay and geochemical assemblages: highsmectite contents, very low metalliferous accumulation,reduced environments, strong terrigenous influence, andhigh sedimentation rates. These assemblages suggest theexistence of a hot climate with humidity-contrasted sea-sons along northwest Africa. Moderate but significantvariations occur in the relative abundance of illite, smec-tite, kaolinite, palygorskite, P2O5, A12O3, K2O, Fe2O3,and MgO. The variations recorded are parallel in bothDSDP sites. The trends observed in the inorganic stra-

tigraphy support the biostratigraphical zonation in theseseries, which is marked by dissolution and resedimenta-tion processes. Systematic lower content of smectite andhigher contents of illite and kaolinite at Site 545 com-pared to Site 547 suggest the occurrence of differentialsettling processes, the former site being more proximaland the latter one more distal.

The upper Aptian to middle Albian green nannofos-sil claystones recovered at Site 545 are characterized bystrong variations in the clay mineralogy and the inorgan-ic geochemistry, especially as far as illite, smectite, paly-gorskite, MgO, K2O, and P2O5 are concerned. These var-iations, recorded in an environment marked by reducedconditions, high sedimentation rates, and strong terrige-nous influences, suggest an alternation of tectonicallyactive and relaxed periods on the African margin, possi-bly in relation with the irregular spreading activity ofthe Mid-Atlantic Ridge.

The lower Mesozoic reddish claystones to mudstonesof Site 546 and Hole 547B contain chiefly chlorite andsmectite, associated with Li, and indicate strong physi-cal erosion of high-relief sialic rocks. There is evidenceof marked pedologic or post-depositional metamorphicprocesses. Unpublished studies show that the same resultsconcern the barren grayish red sandy mudstones of Site544. Site 546 halite and associated sediments, as well asthe overlying pre-Miocene deposits, show higher chlo-rite contents, the local presence of regular mixed-layerclays (corrensite, allevardite), higher Na2O/K2O ratios,and upward geochemical sequences marked by succes-sive dominances of Na, SO4, Mg, and Ca parallel to achlorite decrease. All these peculiarities point to the ex-istence, at Site 546 only, of various early diagenetic pro-cesses in an alkaline, confined environment, from hy-per saline conditions to hemipelagic ones.

ACKNOWLEDGMENTS

We are grateful to the U.S. National Science Foundation and to theLeg 79 Shipboard Party for giving us the opportunity to study sedi-mentary materials of Mazagan Plateau. The financial support of thestudy was given by CNRS (France) through Grant ATP GGO 1982.Technical and scientific assistance from M. Bocquet, J. Carpentier, F.Dujardin, E. Hanton, M. Leckie, A. Pique, and P. Récourt are grate-fully acknowledged.

REFERENCES

CEPM Laboratory, 1980. Results of X-ray mineralogy analyses of sam-ples from Deep Sea Drilling Project Sites 415 and 416, MoroccanBasin. In Lancelot, Y., Winterer, E. L., et al., Init. Repts. DSDP,50: Washington (U.S. Govt. Printing Office), 707-713.

Chamley, H., 1979. North Atlantic clay sedimentation and paleoenvi-ronment since the late Jurassic. In Talwani, M., Hay, W., Ryan, W.B. F. (Eds.), Deep Drilling Research Altantic Ocean: ContinentalMargins and Paleoenvironment. Am. Geophys. Union, MauriceEwingSeπ, 3:342-361.

Chamley, H., Giroud D'Argoud, G., and Robert, C , 1980. Clay min-eralogy of Cretaceous and Cenozoic sediments off the Moroccanmargin, Deep Sea Drilling Project Sites 415 and 416. In Lancelot,Y., Winterer E. L., et al., Init. Repts. DSDP, 50: Washington(U.S. Govt. Printing Office), 715-724.

Debrabant, P., and Foulon, J., 1979. Expression géochimique des var-iations du paleoenvironment depuis le Jurassique supérieur sur lesmarges nord-atlantiques. Oceanol. Ada, 2:469-476.

Gibbs, R. J., 1977. Clay mineral segregation in the marine environ-ment. J. Sed. Petrol., 47:237-243.

502


Lucas, J., 1962. La Transformation desMinéraux Argileux dans la Sedi-mentation. Etudes Sur Les Argues du Trias. Mem. Serv. Geol.Als.-Lorr., 23.

Maillot, H., and Robert, C , 1980. Minéralogie et géochimie des sedi-ments crétacés et cénozoiques dans 1'Océan Atlantique sud (margeafricaine, dorsale médio-atlantique). Bull. Soc. Geol. France, 22:(7):777-788.

Mélières, R, 1978. X-ray mineralogy studies, DSDP Leg 41. In Lance-lot, Y., Seibold, E., et al., Init. Repts. DSDP, 41: Washington (U.S.Govt. Printing Office), 1065-1086.

Millot, G., 1964. Géologie des Argues: Paris (Masson).Robillard, D., and Pique, A., 1981. Epitétamorphisme du Permo-Trias

dans le Moyen-Atlas septentrional (Maroc): mise en evidence et zo-nation régionale. Rev. Geol. Dyn. Geogr. Phys., 23:301-308.

Whitehouse, V. G., Jeffrey, L. M., and Debrecht, J. D., 1960. Differ-ential settling tendances of clay minerals in saline waters. ClaysClayMin. (7th Nat. Conf.), 1958:1-80.

Date of Initial Receipt: March 1, 1983Date of Acceptance: September 6, 1983

© Hole 545, Cores 41-38 late Albian

• Hole 545, Cores 37-29 latest Albian-Cenomanian

+ Hole 547A, Cores 73-66 andHole 547B, Cores 5 -2 late Albian

Hole 547 A, Cores 64—39 Albian—Cenomanian

Mgo Fe 00,

Figure 5. Geochemical identification of late Albian and latest Albian-Cenomanian time intervals, Sites 545 and547.

503


Table 3. Geochemical analysis.

S&mplc(interval in cm)

Site 545

29-2, 24-2631-1, 77-7933-1, 40-4334-2, 70-7137-2, 40-4238-2, 100-10138-3, 101-10239-2, 59-6140-1, 64-6640-5, 58-6041-3, 78-8044-2, 14-1846-1, 75-7748-5, 75-7749-4, 8-1050-4, 57-5951-6, 28-3055.CC, 17-1956-6, 59-61

Hole 547A

39-1, 4241-1, 1343-2, 6445-2, 1848-2, 5051-2, 5052-2, 5054-1, 3055-2, 6057-2, 5059-2, 5062-2, 5064-2, 5066-2, 13667-1, 10068-2, 11570-2, 5071-2, 5073-2, 50

Site 546

17-1, 1817-1, 5017-2, 3617-2, 5017-2, 13017-3, 417-3, 8917-4, 4518-1, 7518-1, 110

Hole 548B

2-2, 504-3, 485-2, 5025-3, 9825-4, 9126-2, 10026-4, 6027-1, 227-3, 11028-4, 8029-1, 11030-3, 8031-3, 9033.CC, 2134-2, 100

SiO2

34.9031.9035.2040.0039.3012.2022.1039.3019.2029.3036.4032.9028.1036.5025.9021.3022.7030.3028.40

13.0044.0035.7038.8039.5037.8033.3039.1031.2036.0041.0037.1033.5015.8018.1027.2029.0032.4038.50

8.6013.7020.4049.2044.6020.9044.4011.7028.9019.20

34.8039.0042.0046.5047.6048.8044.4048.7047.6047.5041.6041.3044.0048.5050.50

A1 2O 3

13.4312.2913.5916.4514.763.868.3814.575.699.398.978.698.029.705.414.725.397.418.04

6.2218.3213.9515.3615.6515.9014.8517.1612.8213.6515.3914.5212.385.996.759.6610.4110.2213.68

3.534.816.4411.1914.648.1714.294.629.977.63

12.1113.5514.3614.8717.3116.8814.5818.7714.3915.4915.5315.2714.7716.0117.65

Major element oxides (%)

Fe2O3

5.275.395.186.286.681.633.124.662.073.052.672.902.673.171.751.942.112.683.10

2.977.266.456.076.786.255.906.714.985.346.186.125.192.732.653.704.213.825.20

1.792.40

21.576.817.134.214.711.753.932.66

4.725.205.566.854.926.664.317.154.286.345.424.555.666.657.39

CaO

18.0019.7817.4811.5012.6236.8628.6813.3431.0622.8419.3222.6125.9319.9229.6032.5430.9722.5115.38

36.577.4015.2412.6711.3512.8115.7010.3221.1117.7112.7714.1118.3431.5431.1822.7821.4319.4512.51

40.7036.458.904.923.86

25.882.6027.9514.0521.66

17.8915.3711.196.246.025.206.873.848.035.9710.9811.079.356.595.37

MgO

1.582.281.921.692.432.361.992.832.193.011.791.971.852.401.611.511.503.2711.10

1.031.692.121.811.701.961.751.871.602.061.842.252.452.422.033.103.423.563.31

1.101.487.187.457.121.388.282.486.204.59

2.612.743.617.104.895.917.555.145.596.125.015.444.714.163.30

Na2O

1.060.870.941.181.180.520.690.950.610.820.790.770.650.820.560.550.590.560.68

0.461.331.071.311.361.351.171.291.081.131.471.341.080.580.720.820.850.921.13

1.502.031.542.683.243.044.880.962.462.20

1.071.031.280.560.600.560.600.540.560.470.640.480.540.510.58

K2O

1.051.431.531.701.460.701.141.960.981.371.961.901.722.051.301.171.331.651.99

0.661.211.241.211.101.611.341.661.011.391.341.501.300.910.921.571.741.622.17

0.941.341.612.113.012.133.650.852.161.66

1.771.852.354.624.584.223.694.403.503.733.483.473.744.384.70

TiO2

0.400.320.330.390.400.100.200.270.130.170.240.180.180.210.130.130.160.190.20

0.270.500.190.270.450.380.210.310.320.320.280.400.360.160.190.200.210.220.24

0.160.210.290.510.610.350.560.190.370.28

0.230.250.280.360.400.390.330.440.270.380.380.340.330.370.36

P2O5

n.d.n.d.0.20n.d.n.d.0.41n.d.n.d.0.270.240.35n.d.n.d.n.d.n.d.n.d.n.d.n.d.0.20

n.d.n.d.n.d.n.d.n.d.n.d.n.d.0.460.27n.d.n.d.n.d.n.d.n.d.n.d.n.d.n.d.n.d.n.d.

n.d.n.d.n.d.n.d.n.d.n.d.n.d.n.d.n.d.n.d.

0.180.160.22n.d.n.d.n.d.n.d.n.d.n.d.n.d.0.150.16n.d.n.d.n.d.

Sr

61548953145842189965742188952639443744237338943140023789

358352515494547452621515815672579515673631694642573531579

205189431126179331100205159210

6464794008995110126110747126163174168137137

Mn

34247325821622613717423111616312113795121110147116126142

826252332206227242205242279226210258268226153189200195216

136210367222584384410337142247205

221168231610410416931358500521494579726663794

Zn

116110142168242163163184300379542431268252552368242663416

8912612614712116310511612110512611621616389116174116110

74795310595226132105137195

11613713774137100799568958989110100216

Trace eler

Li

36364054441025491624231916211110101519

19624748504749573839414036171928322740

121439127149281575112186

374648117124122131130122121110140121122115

Ni

38535950555644394941803138353229283524

54565259557058514445456047555057494048

30314334444742122723

585669656050886883675072505558

fients (ppm)

Cr

9510410012410262779568631118263785659586059

58211001231181391151249710797118111818211711490117

343252749765111335247

11312514387105901039712810186102828476

Co

151815171612129511559746119

n.d.

151513118121115109131712131115131112

18173716192014n.d.35

101012152013471814181316121716

Cu

10101316161918152999413523353448472527

14122017141629172319201727183222312520

18217491025162113

213022

n.d.n.d.n.d.?

n.d.21

n.d.10474

n.d.n.d.n.d.

Pb

17282430253626242726183027223029312824

36152822282052193130292335503033302743

40405837204479694654

2324245135743102690374819153523

V

1401001201501307090130801701207070805040407060

50140701201401201001401101101301401307080100120100130

3040508011080100408060

110120130901101001001209010010090100100100

Note: n.d. = no data.

Table 4. Main mineralogical and geochemical differences betweenHoles 546 and 547B reddish sediments.

Hole 546,Cores 17-21

Hole 547B,Cores 25-34

Chlorite/illiteRegular mixed-

layer claysHaliteAnhydriteNa2O/K2O

(see also Fig. 7)Vertical evolution

upward

2.3 > C/I > 0.5Corrensite (17 = 3, 89 cm)Allevardite(18 = 3, 18 cm)AbundantPresent1.43 > Na/K > 1.08

Strong: Na-, SO4-, Mg- andCa-rich successive dominancesIrregular and strong de-crease of chlorite abovethe halite-rich deposits,parallel to the main geo-chemical changes

0.5 > C/I > 0.3Absent

AbsentAbsent0.14 ±0.02

Weak: slight increase ofchlorite

504


Site 546 Hole 547B

E 1 5 0 -

Lithology Sample(level in cm)

Clay minerals (%)

20 40 60 80

E 160

,2 170

180

inperVΛVΛ ΛVWAVWfti

20-3,13120-4, 3020-5,0Diapiric structure

(Mixture ofMiocene andpre-Miocenerocks 940- - _ u _ - _ -

950- ; - _ - „ - _

960-

". ] Claystone

- 1 - | Nannofossil ooze

"―~•i] Silty claystone

~—~-j Mudstone

^ Y J Massive halite

D | Dolomite

G Gypsum

Chlorite

111 Smectite

~vjKaolinite

|Palygorskite

^ R e g u l a r

• IrregularMixed-layer clays

a 9 7 0 - : - - - - -

9 8 0 - - - - - -

990- 7 _ — _ - _

1000-

1 0 1 0 - ~ _ - — ~ —

Figure 6. Early Mesozoic clay mineralogy, Sites 546 and 547.

MgO• Hole 547B, Cores 25-34

© Hole 546

K 0 0

Figure 7. Geochemical data, Sites 546 and 547.

Na-O

505


Plate 1. Electromicrographs. (Scale bar = 1 µm.) 1, 2. Cenomanian, Sample 547A-39-1, 12 cm. Abundant smectite, common palygorskite bro-ken fibers, some kaolinite hexagons. 3,4. Cenomanian, Sample 547A-49-2, 50 cm. Very abundant smectite with blurred contours, rare kaolin-ite, and palygorskite. 5,6. Aptian, Sample 545-48-5, 78 cm. Comparable amounts of illite, smectite and palygorskite. Many palygorskite fibersare still in compact bundles.

506


Plate 2. Electromicrographs. (Scale bar = 1 µm.) 1,2. Aptian, Sample 545-55, CC 17 cm. Abundant palygorskite fibers, noticeable amounts ofillite, smectite rare. 3,4. Lower Mesozoic sediments deposited above a sialic basement, Sample 547B-27-2,110 cm. Abundant illite, fairly abun-dant chlorite. 5,6. Lower Mesozoic sediments above a halite body, Sample 546-17-3, 89 cm. Illite, chlorite, and corrensite, as well-shaped andpolygonal sheets.

507


Plate 3. Electromicrographs. 1-3. Early Mesozoic, reddish clayey level in a halite gypsum body, Sample 546-18-3, 8 cm. Very abundant chlorite poly-gonal phyllites, allewardite as broad and long laths (?), illite. 4-6. Early Mesozoic, greenish clay in a halite body, Sample 546-20-4, 30 cm.Abundant chlorite and illite, well-shaped and polygonal phyllites.

508

16. mineralogical and geochemical investigations of ... · during leg 79 on the mazagan plateau....

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