I. CALCIUM-CARBONATE AND SAND-FRACTION ANALYSIS OF CENOZOIC AND MESOZOIC SEDIMENTS FROM THE MOROCCAN BASIN

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1 I. CALCIUM-CARBONATE AND SAND-FRACTION ANALYSIS OF CENOZOIC AND MESOZOIC SEDIMENTS FROM THE MOROCCAN BASIN Marthe Melguen, Centre Océanologique de Bretagne, BP, 9 Brest Cedex, France INODUCTION As the DSDP Sites 4 and 46 were essentially drilled to reach deep Mesozoic sedimentary sequences, only very few and spaced Cenozoic cores were recovered (Figures and ). Consequently it is almost impossible to try to reconstruct in the light of these few cores the evolution of the Cenozoic sedimentary facies off Morocco. Only some major lines of this evolution could be drawn. Concerning the Mesozoic sediments, while it was easy to measure the calcium carbonate content, it was almost impossible to sieve the sand fraction and, consequently, to study its composition. This is the main reason why the present study is limited to the Cenozoic. Furthermore, samples from Site (Leg 4) were selected in order to complete the Cenozoic sedimentary sequence of Site 46 (Leg 0). The present coarse fraction study is a complementary study to the previous one already done on board the R/V Glomar Challenger during Leg 0. At that time, all the samples selected on board for micropaleontological purposes were also analyzed by the present author in order to appreciate their sand fraction composition and preservation. ANALYTICAL METHODS Samples taken on board the R/V Glomar Challenger were approximately 0 cm. Calcium carbonate content has been determined ashore for each sample using a Bernard calcimeter. For each sample the sand fraction (6-000 µm) was sieved, dried, and weighed. No H O was used, to avoid an artificial fragmentation of the planktonic foraminifers. The composition of the total sand fraction was studied under the microscope, and proportions of the different components were visually estimated using the chart of Terry and Chillingar (9). For this purpose, the sand fraction was a few times divided in sub-fractions and a representative subfraction was put on a plane surface under the microscope. Special attention was given to the preservation of calcareous biogenic components and especially to that of planktonic foraminifers. For each sand fraction the proportion of fragments of tests of planktonic foraminifers was estimated. The degree of fragmentation of planktonic foraminifers observed in the coarse fraction is considered to reflect the degree of carbonate dissolution (Berger, 9a, 9b; Melguen and Thiede, 94). With increasing dissolution the abundance of planktonic foraminifers decreases, while their fragmentation and the abundance of benthic calcareous foraminifers increase (Melguen and Thiede, 94; Adelseck, 9). Furthermore, the dissolution of calcareous fossils leads to a relative enrichment of fish debris in the sediments. RESULTS AND COMMENTS Results are presented in Tables through 4. Site 4 All data are presented on Figure and in Table. Unit Nannofossil marl and nannofossil ooze (Cores 4-, 4-, 4B- and 4B-; 0 to 0 meters; Pleistocene to upper Miocene. CaCO content: 4 to. per cent. These values agree perfectly with the facies determination. content: 6. to. per cent. These values are higher than those deduced from the smear slides observation. Composition: The sand fraction is essentially a "planktonic-foraminifer sand" containing more than per cent planktonic foraminifers, associated with minor amounts of benthic foraminifers (<%), echinoid spines (<%), radiolarians ( %), ostracodes (<%), sponge spicules (<%), and mollusks (0.%). Degree of carbonate dissolution: foraminifers are very abundant (-%) and relatively well preserved. The fragmentation varies from to per cent and decreases obviously from core (%) to core (-0%), suggesting that carbonate dissolution decreased from late Miocene to Pleistocene times. Furthermore, the presence of common (0%) pteropods at the top of core 4- indicates that this site was situated above the CCO during the Pleistocene. Unit II Alternating marl and nannofossil chalk (Core 4-; 0 to 99 meters; middle Miocene). CaCO content: to 9 per cent. content:. to. per cent. The sand is probably very fine, because it was considered as silt in the smear slide analysis. Composition: As in the previous unit, the sand fraction is essentially constituted of planktonic foraminifers (80-9%), associated with small amounts of benthic foraminifers (-%), radiolarians (<0.-%), sponge spicules (-%), fish debris (<%), and glauconite (0.-%). Volcanic glass is common (-0%) in 4-, CC, and terrigenous minerals are abundant in 4- (68-%). Pyrite is present throughout (-%). 8

2 M. MELGUEN Age 8 α ü w 0 Early PLIO Fraction 0 Aggregates and Diatoms 0 Pteropods Lithologic Units I Nannofossil marl and nannofossil ooze E r oo- Alternating marl and nannofossil chalk Nannofossil chalk ç IV Mudstone (with occasional chert) Per Cent of y\_ Via Pelagic clay Per Cent of Fraction Figure. Variations in carbonate content and sand-fraction content with respect to total sediment at Site 4. Also shown are variations in the most-significant terrigenous and biogenic components in the sand fraction (6-000 µm) and variations in the degree of fragmentation of the planktonic foraminifers. 00- Age 46 0 Fraction Aggregates Clastic Components 0 0 Micas 0 Plant 0 Forami nifers and Diatoms Lithologic Units I Nannofossil marl and nannofossil ooze Turbidites: sandstone, diatom-rich nannofossil marl and chalk Turbidites: mudstone, siltstone, sandstone, gravel, and rare porcellanite PALEO -<!m r < ALBIAN APTIAN IV Nanno. marl V Claystone silty clayst. some siltstone and fine sandstone Per Cent of Per Cent of Fraction Figure. Variations in carbonate content and sand-fraction content with respect to total sediment at Site 46 and Site. Also shown are variations in the most-significant terrigenous and biogenic components in the sand fraction (6-000 µm) and variations in the degree of fragmentation of the planktonic foraminifers. 86

3 TABLE Site 4 Sample (interval in cm) 4--, ,8-84 -, 0- -4, 0- -, ,9-96 -,-6 -, - -,0- -, ,-4 4-,68-4-, 0-4-, - 4-,4-6 4-, , ,0- -, ,0- ^, , , - -6,4^ 4A--, 9-6-,-4 6-, 0-6-, , -9 -,6-8 9-, , 6-8 -,6-8 ll,cc- -, - -, - -,8-0 4-, - 4B--, , 0- -, - CaCO Fraction Aggregates Micas Pyrite Glauconite 0. < < Diatoms 0. Fraction (6 µm) Content Siliceous Spicules < < < < < (%) < < 0 0 < < < < < 0 < < Echi- Plant Volcanic noids Bivalves Glass OO to

4 00 to 0O TABLE Site 46 Sample (interval in cm) CaCC Fraction Micas Pyrite Aggregates Glauconite Diatoms Siliceous Spicules Fraction (6 µm) Echi- Plant Volcanic noids Bivalves Glass 46--,- -,6-8 -, = ~ 9 =6 = < = = 0 46A--, 8-0 -,8-84 -,-99 -, -4 -, ^t -, -9,CC - -, , ,9-9 -, , , 0-0 -, 6- -,8- -4, ,-4-4, 4- -4,- -, -9 -,4^ -, , -,CC -,CC 9-.CC - -,6-8 6-,-6 6-, , , 0- -, 0- -, 6-9 -, 0- -, -6 9-, , , - 9-,-6 9-, ,9-0 0-,6-6 0-, -4 0-, ,69-0-, , 6- -, -44 -, ,4-4 -,0- -, = = 0 =T 0 < < = < = < < < < 0 0 = = 80 sl 0 0 = 0 < - 6 < <0 = = = < - < =0 0 0 l < < 0 = < = = ""9 0 9 =0 = = = = 0 0 < < 0? < = =0 =0 0 = = =0 = 0 =0 0 =0 0 =0 < =0 = 0 0 < < = 0 =0 = =0 < < =T - = s= 4

5 TABLE Site Sample (interval in cm) --,0- -, , 0- -4,0- -,0- -,80-8 -,0- -, , -4 -,0- -, 0- -,0- -, -6 -, 88- -, ,0-4-, ,- 4-, - 4-, 0-4-, , , 8^0 4-4, 0- -, 0- -, 0- -, , 0- -,-6 -, 0-0 -, 0- -4, 0- -, 0- -6, 0-6-,0-6-, , -4 -,- -, 0- -, , 9-8-,- 0-, , , - -, 8-0 -, , -8 -, 9- -,- -, -9 6-, ,9-4 6-,- -,0- -, - 9-, , 9^ 0-, -4 Xotal Sediment CaCθ Fraction Aggregates = == < 0 <] IO < 0 < Micas? Pyrite <0. ~ Glauconite < < 0. < 4 0 < < T Diatoms < 0 Fraction (6 µm) Siliceous Spicules 0 < < = < < 0 < < 0 0 <0 0 0 < = 0 < IO =^ < slo < 0 < < < 0 < < < <0 <0 < 0 < < Echi- Plant Volcanic noids Bivalves Glass =0. ^0. - < - = 0. o c CO O Z PI z σ in Z α

6 M. MELGUEN Core/Section/Level Sampled (cm) TABLE 4 Hole46A 46A--4, - -4, -8 -,6-6 -, -4 -, 4-4-, , 09-4-, - 4-, 6-4-, - 4-, ,-9 4,CC 8 6-,0-6-, 4-6-, , 4-6-,-8 6-,9-9 8-, -8 8-, , 0-8-, -4 8-, - 8-, ,^ 9-, , -9 9-, , , 0-0-, , , ,0-0-, 0-0-, - -,-4 -,4- -,6-8 -,4-6 -, - -,8-84 -, 0-0 -, , - -, -8 4, 09-9-, -4 9-, - 0-, - 0-, 0-0-, , ,69-0-, - 6-, , -4 -, -4 -, -8 CaCθ Fraction # TABLE 4 - Continued Core/Section/Level Sampled (cm) -,- -,86-8 -, , 6-8-,-4 8-, , , - 4-, 49-4,CC 44-, , , , , ,9-9 0-, 0-0-, ,-9 -,4-4 -, 9-4 -, 09-0 CaCθ Fraction Degree of carbonate dissolution: foraminifers are generally very abundant (80%) throughout this unit. Their fragmentation is higher (-0%) than in unit I, which probably reflects greater carbonate dissolution, which could be related to higher oceanic productivity. Unit III Alternating nannofossil chalk and siliceous-debrisbearing marl (Cores 4-4 and 4-; 99 to meters; middle and lower Miocene). CaCO content: to. per cent. content:.4 to 4. per cent. Composition: Throughout this unit the sand fraction is alternately rich in biogenic particles (planktonic foraminifers or radiolarians) or terrigenous particles (quartz). The chalky layers contain per cent planktonic foraminifers, while the marly layers contain only to 0 per cent planktonic foraminifers, but as much as 0 per cent quartz, per cent radiolarians and from to per cent diatoms. The relatively high abundance of biogenic siliceous particles might be related to an increase in oceanic fertility. The association of quartz and radiolarians in the same layers may reflect transport from the continental slope by turbidity currents. As in the previous unit, pyrite is common (-%). Degree of carbonate dissolution: The preservation of planktonic foraminifers in unit III is very similar to that in unit I. Their fragmentation varies from to per cent and is highest in the darker marly layers rich in pyrite. Post-depositional dissolution might have occured. 80

7 CALCIUM-CARBONATE AND SAND-FRACTION ANALYSIS Unit IV Mudstone; probably with intercalated sandstone and conglomerate, and perhaps chert. (Cores 4A- through 4A-6, Section, - cm; to 46. meters; lower Eocene to upper Paleocene). CaCO content: About. per cent. content: About. per cent. The sand content is very low, compared to higher units. On the other hand, there are intercalations of pebbles (4A-). composition: The sand fraction along Core 4A- is very different from that in other cores. It is essentially a foraminifer (% benthic, 0% planktonic) sand, rich in quartz (0-%) and bearing fish debris (-%) and chert fragments (0-%). No siliceous microfossils are present. The fragmentation of the planktonic foraminifers is close to 0 per cent. The sand fraction of core 4A- is rich in siliceous debris (<%), planktonic foraminifers (<0%), and pyrite (-0%). Degree of carbonate dissolution: foraminifers are much better preserved (fragmentation <%) than in the previous units. Unit V Marlstone with intercalation of nannofossil chalk and limestone (core 4A-6, except for 0 to cm of Section ; 46. to 49 meters; upper and lower Paleocene). Carbonate content: 44 to 84 per cent. content: to. per cent. As for unit IV, the sand content is very low. composition: Aggregates are abundant (- 9%), but they result from induration of the sediment. If we except these aggregates, which in reality belong to the clay fraction, the sand fraction is composed of planktonic foraminifers (<0%) associated with benthic foraminifers (<0%), radiolarians ( 0%), quartz (< 0%), and minor amounts of diatoms ( %), fish debris (<%), glauconite ( %), and echinoids ( %). Pyrite is abundant (-0%) in a few levels (e.g., 4A-6-, -9 cm). The presence of glauconite associated with benthic foraminifers, echinoids, and fish debris suggests that at least part of the sediment was transported by turbidity currents or slumping from the continental slope. Degree of carbonate dissolution: The degree of fragmentation is very low (<%). foraminifers are well preserved. Their apparent abundance decrease is due to dilution and not to dissolution. Unit VI Claystone and dolomitic shale with interbeds of marlstone, dolomite, and limestone (Cores 4A- through 4A-; 49 to 04. meters; Cenomanian to upper Albian). Sub-Unit Via (Core 4A-; 49- m) This core can be separated from the rest with respect to its carbonate content, sand-fraction composition, and preservation. Carbonate content: per cent. content: 0. per cent. composition: This sand fraction is a typical dissolution residue, with only trace of planktonic foraminifers (00% fragmented), but abundant radiolarians (80%) and fish debris (0%). The terrigenous content is low: per cent quartz and per cent micas. Degree of carbonate dissolution: The planktonic foraminifers are almost nonexistent and completely fragmented; consequently the sediment of Core 4A- might have been deposited at or very close to the CCD. Nevertheless, the abundance of biogenic siliceous particles and of fish debris might reflect relatively high oceanic fertility, which may be partly linked to post-depositional dissolution. Sub-Unit VIb (Cores 4-8 through 4A-4; -04. m) Carbonate content: to 6.8 per cent. content: 0. to 9. per cent. The fluctuations are still partly related to the presence of abundant (0- %) clay aggregates. composition: foraminifers and radiolarians are alternately dominant in the sand fraction. foraminifers vary from to 0 per cent, and radiolarians from to 4 per cent. They are associated with fish debris (-0%), benthic foraminifers (0.-%) and pyrite (-%). Furthermore, bivalves are present in Cores and 4, where they reach respectively and 0 per cent. They may have been transported from the continental slope and reflect the allochthonous nature of part of the sediment. The sand fraction is devoid of terrigenous particles, except in Core 4, which contains per cent quartz and per cent micas. Degree of carbonate dissolution: foraminifers are well preserved (fragmentation %). Sub-Unit Vic (Cores 4A-; m) The only sample taken in this sub-unit contains 8.4 per cent carbonate. It was almost impossible to sieve the sand fraction. Site 46 All data are presented on Figure and in Tables, and 4. Unit I Nannofossil marl and nannofossil ooze (Cores 46-, 46A--, -; 0 to about 00 meters; Quaternary to middle Miocene). CaCO content: 0. to per cent. The first value characterized the marly, light-olive-gray nannofossil marl, the second one the light-gray nannofossil ooze. content: 0. to.6 per cent. Composition: The sand fraction is essentially constituted of planktonic foraminifers (0-%), associated with quartz (< 0%) and with small amounts of micas (<%), benthic foraminifers (-%), fish debris (0.- %), echinoids (0.-%), pyrite (< %), and glauconite (< 0%). Aggregates are present in most of the samples and vary from to 0 per cent. 8

8 M. MELGUEN Degree of carbonate dissolution: The fragmentation of the planktonic foraminifers varies from to per cent, but is close to per cent in most of the samples. That means that these sediments were deposited well above the lysocline. Unit II Graded sequences of sandstone, diatom-rich nannofossil marls, nannofossil marl and chalk (Cores 46A--, cm through 46A-, - through -; 00 to 4 meters; early Miocene to late middle Eocene). CaCO content:.4 to 9 per cent. The lowest value characterizes the very dark-gray layers, the highest one corresponding to the olive-gray to white nannofossil chalks. content: 0. to 6. per cent. The highest values correspond to samples with large amounts (0-%) of clayey-quartzose aggregates, where quartz is of silt size and consequently not relevant to this fraction. Composition: The presence of turbidites throughout this unit explains the large fluctuations of the sand-fraction composition. Dominant components are planktonic foraminifers (-%) and radiolarians (-80%). They are associated with diatoms (-%), benthic foraminifers (-0%), echinoids (-%), fish debris (- 0%), quartz (-0%), pyrite (-%), and glauconite (-0%). One of the major points characterizing unit II is the presence and relative abundance of radiolarians and diatoms, which were absent in unit I. They seem to be at least partly transported from the continental slope by turbiditic currents, together with fine quartz, glauconite, echinoids, traces of bivalves, and even with benthic foraminifers. Within the turbiditic sequences, the coarse fraction is mainly hemipelagic and rich in radiolarians, but most poorer in planktonic foraminifers. The decrease of the planktonic-foraminifer population is thus more related to dilution by turbiditic material than to carbonate dissolution. Another point is the local enrichment of the coarse fraction in pyrite (up to %), indicating the degree of reduction. Degree of reduction probably is related to the abundance of organic matter in an area of high oceanic productivity, as reflected by the relative abundance of biogenic siliceous particles. Degree of carbonate dissolution: The degree of fragmentation of the planktonic foraminifers is highly variable (-0%). Fluctuations are probably related partly to the cyclicity of the turbidites and partly to the oceanic fertility. Turbiditic currents transported to the deep basin well preserved planktonic foraminifers. They also rapidly embedded the foraminifers already deposited in the basin, thus protecting them from intensive dissolution. On the other hand, they could also bring from the continental slope organic-matter-rich sediment which might contribute to post-depositional carbonate dissolution. Unit HI Turbidities: mudstone, siltstone, sandstone, and gravel, with some porcellanite and dolomitic marlstone (Cores 46A-4, 46A--, and 9-8 to the upper part of -8; 4 to 64 meters; middle to early Eocene). As unit III was barely sampled at Site 46A (0 cm in 46A-4 and cm in 46A--), we had to consider the corresponding section at Site. CaCO content: 4.9 to. per cent. Most of the samples could be classified either as calcareous mud (0% < CaCO < %). Both types alternate within the turbiditic sequences, but marls are more frequent at the base of the unit (-64 m). content: 0. to 6.6 per cent. As well as the carbonate content, the coarse fraction content fluctuates highly inside the turbiditic sequences. Furthermore, the presence of abundant clayey-quartzose aggregates (too hard to be sieved) is partly responsible for the apparent fluctuations. This is particularly obvious at Site in Core (Section, - cm), where the sand fraction reaches. per cent but contains 8 per cent clay aggregates. Composition: On the basis of the sand fraction composition, unit III is extremely different from unit II. In unit III the sand fraction is essentially of terrigenous origin. If we exclude the aggregates, the quartz content is on the average close to per cent and even reches per cent. It is associated with planktonic foraminifers (-%, % average) benthic foraminifers (-0%), radiolarians (-0%), fish debris (-6%), pyrite (-%), glauconite (-%), and micas (<%). There are not diatoms in this unit. Degree of carbonate dissolution: Compared to the planktonic foraminifers of unit II the foraminifers of unit III are better preserved (fragmentation <0% on the average). One exception however is Core 6, Section, to cm, where fragmentation reaches per cent. No obvious reason for this exception appears. Unit IV Nannofossil claystone and marlstone (lower part of Core -8,CC through Core -9; 64 to 66 meters; Paleocene). Unit IV was not receovered at Site 46 and for this reason was defined at Site. The present study of unit IV is based on only one sample (9-, 6-8 cm). CaCO } content: per cent. content: per cent. Composition: The major difference from the previous unit is the drastic increase in radiolarians (%). They are associated with benthic foraminifers (%), planktonic foraminifers (0%), quartz (0%), glauconite (%), and fish debris. Unit V Claystone, nannofossil claystone, and silty claystone, with minor siltstone, mudstone, and pebbly mudstone (Cores 46A-,CC and 46A-6, -0 to -; 66 to about 880 meters; Albian to Barremian). Because of the increase in compaction and induration of the sediment with depth, it was more and more difficult to sieve the sand fraction. From unit V through unit VI it was impossible to continuously analyze the sand fraction. In fact, most of the residue of the sieve consist- 8

9 CALCIUM-CARBONATE AND SAND-FRACTION ANALYSIS ed of indurated clayey aggregates embedding quartzose or biogenic particles. No good estimation of the frequency of the sand size particles was possible. Consequently, the values of the sand content given in Table 4 have to be considered with caution. Unit V was sparsely cored at Site 46. Consequently, it has to be again defined at Site. Carbonate content:.4 per cent. content: 0. to.4 per cent. Composition: The sand fraction is characterized by the absence of biogenic particles, except fish debris (< %), and by the high abundance of pyrite (0.-%). is also locally abundant (-%). Degree of carbonate dissolution: No foraminifers are present either in the sand fraction or in the finer fraction of the sediment. The absence of calcareous particles in the sediment, excepting a few dolomite rhombs, is probably due to dilution of noncalcareous terrigenous material, rather than to dissolution. Nannofossils were recovered in claystone in this lithologic unit at Site. Unit VI Distal turbidites: quartzone sandstone, mudstone, claystone, marlstone (Cores 46A- to 46A-6-, - to -; 880 to 48 meters; Hauterivian to late Valanginian). CaCO content:.4 to 6. per cent. content: 0.0 to 0.6 per cent. Composition: If we except the presence of artificial clayey-quartzose aggregates, the sand fraction throughout this unit is, as in the previous unit, characterized by relatively abundant pyrite (0.-00%) and plant debris (<%). The pyrite constitutes 00 per cent of the sand fraction in Cores (Section, 0-0 cm), 9 (Section, -4 cm), and 0 (Section, - cm). The maxima of plant debris are encountered in Cores 4 (0% in Section, % in core catcher) and 6 (% in Section ). debris is rare, except in Core 9 (Section, 0-04 cm), where it reaches 0 per cent. Degree of carbonate dissolution: Only traces of planktonic foraminifers are present, except in Core where, in Section (8-0 cm) foraminifers constitute 0 per cent of the sand fraction. As in the previous unit, the scarcity of planktonic foraminifers is probably due to dilution, rather than to dissolution. Unit VII Turbidites: alternating quartzose siltstone and mudstone cycles with hard micrite and calcarenite (Cores 46A-6- through 46A-; 48 to 64 meters; early Valanginian to Tithonian). This unit was not cored at Site. CaCO content:. to 8 per cent. content: 0.0 to 6. per cent. Composition: Throughout this unit, it was almost impossible to sieve the sand fraction from the sediment. All the residues obtained on the 6-/rni sieve consist of artificial clayey aggregates, locally containing quartz, micas, and pyrite. No biogenic particles are visible. Degree of carbonate dissolution: The selected samples yield no information about carbonate dissolution. The presence of carbonate cycles with micritic limestone throughout this unit seems however to reflect a low degree of dissolution, even if the carbonate-rich sediment could have been rapidly buried (and thus protected from eventual dissolution) under terrigenous turbiditic sequences. REFERENCES Adelseck, C. G., Jr., 9. Recent and late Pleistocene sediments from the eastern equatorial Pacific Ocean: sedimentation and dissolution, Ph.D. Thesis, University of California, San Diego. Berger, W. H., 9a. foraminifers selective solution with the lysocline. Mar. Geol., v. 8, p. -8., 9b. Biogenous deep-sea sediments: fractionation by deep-sea circulation. Geol. Soc. Am. Bull., v. 8, p. 8-. Melguen, M., and Thiede, J., 94. Facies distribution and dissolution depths of surface sediment components from the Vema channel and the Rio Grande Rise (southwest Atlantic ocean). Mar. Geol., v., p. 4-. Terry, R. D., and Chillingar, G. V., 9. Charts for estimating percentage composition of rocks and sediments. /. Sediment. Petrol., v., p