43. Palygorskite, Sepiolite, and Other Clay Minerals in Leg 41 Oceanic Sediments: Mineralogy, Facies, and Genesis

Home , Kaolinite, Montmorillonite, Palygorskite

43. PALYGORSKITE, SEPIOLITE, AND OTHER CLAY MINERALS IN LEG 41 OCEANIC SEDIMENTS: MINERALOGY, FACIES, AND GENESIS

P.P. Timofeev, V.V. Eremeev, and M.A. Rateev, Geological Institute of the USSR Academy of Sciences, Moscow, USSR

INTRODUCTION flocculent, cirrose, cellular, or lumpy. Because of similar optical features, palygorskite and sepiolite are Leg 41 holes, drilled near the northwest margin of indistinguishable from each other in thin section. Fine- Africa, penetrated Mesozoic and Cenozoic sediments. grained terrigenous material is negligible in clays of this The montmorillonite, kaolinite, hydromica, chlorite, mixed- gorskitic monomineral clays usually contain a greater layer minerals of the mica-montmorillonite and admixture of quartz and are better recrystallized. chlorite-montmorillonite types, palygorskite, and Claystones with interbeds of silty material consist of sepiolite. elongated plates of hydromica and scaly, slightly double-refracted masses of palygorskite-kaolinite, STRATIGRAPHIC AND LITHOLOGIC which cement angular grains of silt-size quartz. Authi- OCCURRENCE OF MAGNESIAN SILICATES genic rhombohedrons of dolomite permeate the entire Occurrence of magnesian silicates of the palygorskite rock. and sepiolite type proved widespread and is shown in Limestone containing palygorskite is composed of a Figure 1. These minerals occur in the Albian of Site 368 pelitomorphic mass of calcite that includes organic and the Cenomanian of Site 370. Palygorskite remains: coccoliths, foraminifer tests filled with clay frequently occurs with sepiolites; this is unusual for and cherty matter, diatoms, and radiolarians. Paly- platform deposits. Palygorskite also occurs in Eocene gorskite may occur throughout the rock (Sample 34-3, sediments: lower Eocene of Hole 366, lower and middle 83-85 cm), or less frequently as independent aggregates Eocene of Hole 370, middle Eocene of Hole 369, and (Sample 35-3, 104-106 cm). upper Eocene of Hole 368; in Hole 367, palygorskite occurs in Upper Cretaceous and lower Eocene MINERALOGY OF SEPIOLITES sediments. AND PALYGORSKITES Magnesian silicates are associated with the following We could not determine the chemical composition of lithologies (Figure 2): sepiolites in Leg 41 cores, because they occur with 1) Clay and claystone with gentle wavelike lamina- palygorskite or other minerals. Palygorskite of Leg 41 tions (Hole 368, Upper Cretaceous to lower Eocene). deposits shows intense X-ray peaks which differentiate 2) Claystone with interlayers of sandy silty material it readily from sepiolite (Mumpton and Roy, 1958): (Hole 370, lower to middle Eocene; Hole 368, upper (110), 10.5Å; (200), 6.44Å; (130), 5.3Å; and (310), 4.3A Eocene). (Figure 3). 3) Nannofossil marl alternating with claystone and The palygorskite DTA scans are characterized by siltstone (Hole 370, Cenomanian to upper Paleocene). absence of an exothermic peak at 860°C (as in 4) Nannofossil marl with burrows (Hole 369, sepiolite), lower temperature of the mid-endothermal Albian). effect at 490-510°C, and by more intense endothermic 5) Limestone with interbeds of clay (Hole 369, peaks at 255°-270°C. middle Eocene; Hole 366, lower Eocene). The oceanic palygorskites are similar in composition Tables I through 5 and Figure 2 show that in Holes to those of the Russian platform (Table 6). They 366 and 369, magnesian silicates are associated with contain up to 10% AI2O3 and over 9% MgO, which is organogenic clay and carbonate sediments, whereas representative of the Russian platform. The Tiθ2 those of Holes 368 and 370 are associated with content in palygorskites is about the same as in other terrigenous and, at Site 368, with partly chemogenic clays. In sepiolite, however, Tiθ2 is usually absent; this sediments. is regarded as additional proof of authigeneity. The carbonate content in palygorskitic clays does not MICROSCOPIC FEATURES OF PALYGORSKITIC exceed 1%, and organic carbon is only 0.42%; this is AND PALYGORSKITIC-SEPIOLITIC ROCKS representative of palygorskitic clays of the arid zone. Clays and claystones of nearly pure palygorskitic- The iron sulfide content is 0.44%. sepiolitic composition occur as dim, dark gray, double- refracted masses. These masses occur with fine grains, Possibility of Isomorphic Substitutions plates of brown biotite, remains of plants, spores and There are differing viewpoints concerning the pollen, globules of pyrite, and pyritized cherty fossils. possibility of isomorphic transformation of paly- The clay mass is frequently filled with rhombo- gorskite into sepiolite, and vice-versa. Sepiolite and hedrons of diagenetic dolomite. The texture of clays is palygorskite may be intermediate members of the iso-

1087 P. P. TIMOFEEV, V. V. EREMEEV, M. A. RATEEV

370 369 368 367 366 70 30 cu Hm Ml 315 o 350 — αi Ml c Hm Ml, K Q> -i O •α o ad. K, K 400 CJ S — Ml, ad. ^ Ch ad. M, 170 Ch Z>LLJ K,Hm,Ch Φ 460 cu Ml 150 tz CU M Hm CU Ml 8 Z α> α> ad. Ch, α

M M, K •? α> *- CJ K ad. PI ~ O Ch Hm 300 Hm owe r _i 600 310 Ml Z,PI,MI

α_ en e 650

middl e L c 350 Hm c PI ro PI, M 355 LU -Q ad. Ml,

sno a > Lowe r < K M 430 3

530 ta c Hm 800 M -a n e Eocen < K Ml, ad. M

PI r Cr e ;en e ad. PI CJ α> o 850 Sp Q- cu ü 620 Q. — manian - r Paleoc e M O cu C Q. Ml K 590 Palygorskitic sediments ö % c 700 • ro c •— Palygorskite-sepiolitic c c Ml • ― ro M co ro Hm sediments ••P lα Hm cEu εo t c K << K ro cu CO O 820 PI = Palygorskite 740 K = Kaolinite Sp = Sepiolite c Z = Zeolites 810 ro Hm Hm = Hydromica (illite) K M = Montmorillonite oO o Ad. M Ml = Mixed layer minerals cu Ch = Chlorite 900 Z ad. = admixture 955 Figure 1. Occurrence of palygorskite and sepiolite in Leg 41 sediments.

HOLE 367

Claystones Limestones Claystones Clays and Limestones with inter- P with interbeds P with inter- claystones with interbeds of sandy of clay matter beds P beds of P silty material of silty clay material material en e K s m 1 leoce r C M Mio c sP a m 1 H § m 1 LU K T3 C taceo u ε & H 2 P m 1 u H Lowe r Eocen e Middl e Eocen

Alternation Nanno-marl Clay and Clays and of nanno- with burrows claystones P claystones marls with with gentle M claystones P 03 wavelike M and silt- c33O 3 lamination P stones K

M Eoce r

D O S m 1 H P K s-lowe r -uppe r P a Albia n s S e r Cret a Q. I CL ò D omania n M P = Palygorskite

Ce n CL K = Kaolinite S = Sepiolite c • Clinoptilolite H Hydromica M = Montmorillonite m I = mixed layer minerals Figure 2. Lithologic associations of magnesian silicates in Leg 41 sediments.

1088 TABLE 1 Clay Minerals in Hole 366

Sample Clay Minerals Facies Associations Age (Interval in cm) Lithologo-Genetic Type Fractions

Radiolarian-diatom foraminiferal Mixed-layer (M-H), kaolinite, Facies of organogenic bioturbidic Montmorillonite-hydromicaceous, rmos t o f ;en e 5-3, 90-92 nannofossil chalk zeolite sediments with kaolinite parts ' Lowe i Oligo <

-< of ash kaolinite of influence of volcanism hydromicaceous), in some interbeds— ftS3 14-3, 93-95 Nannofossil chalk with an admixture Mixed-layer (M-H), kaolinite, montmorillonitic-chloritic with an •s of ash hydromica, an admixture of chlorite, admixture of kaolinite, hydromica, mixed-layer (M-H) chlorite * 1t•H 15-1,47-49 Nannofossil chalk with an admixture Mixed-layer (M-H) ft of ash P 16-2,14-16 Alternation of nannofossil chalk with Mixed-layer (M-H) with transitions interbeds of porcellanite between them 24-2, 115-118 Alternation of nannofossil chalk and Mixed-layer (M-Ch-H) Organogenic sediments with interbeds Mixed-layer (montmorillonite- <ëu o limestone with interbeds of porcellanites of porcellanites (?) and limestones chlorite-hydromicaceous) o W and siliceous nodules (Above—interbeds of porcellanites, 27-2, 87-89 Alternation of nannofossil chalk and Mixed-layer (M-H) below—interbeds of limestones) limestone with interbeds of porcellanites m and siliceous nodules

morphic series talc-pyrophyllite, with progressive substitution of Al for Mg positions in octahedral layers , o of the montmorillonite type. Martin-Vivaldi and Cano- Ruiz (1956) have supported this idea. But in comparing o 2 chemical compositions of sepiolite and palygorskite in •s i Leg 41 sedimentary rocks, we recognized no reliable features of isomorphism. All Russian-platform O O carboniferous sepiolites that we studied, from both the 111 arid zone (middle and upper Carboniferous) and the n o ö to cβ O humid zone (lower Carboniferous), were completely >, 8 g pure. Chemical analyses of sepiolites, after exclusion of carbonates, yielded typical compositions (Table 2). B >> to Rare deviations from the standard composition resulted from admixtures of other minerals. Chambers (1959) found a thick bed of sepiolite in the sedimentary deposits of Vallecas (Spain) to be homogeneous. Thus, we are unable to find any transitional members on the basis of the Al and Mg contents of sedimentary bedded zon e o l matio n H o sepiolites and palygorskites. to ^ c to Studies by Nagi and Bradley (1955) and by Preisinger | fa g (1959) showed significant differences in the structures O to ^- V. of sepiolite and palygorskite. Palygorskites may be regarded as intermediate minerals—with compositional nd i 1 ^ extremes Mg3/OH2Si4θio (magnesian-montmorillonitic) and Ah/OhhSi

| g ENVIRONMENT OF SEPIOLITE AND PALYGORSKITE FORMATION Magnesian silicates occur most abundantly in clay rocks of Holes 368 and 370, particularly in sections where material was supplied from Africa. The terrigenous material derives from the Senegal River basin; the coarse fraction suggests deposition by turbidity currents, but does not indicate local volcanic sources. The occurrence of palygorskitic-sepiolitic rocks in Hole 370 is related to an underwater canyon or delta. The Lower Cretaceous to middle Eocene section of Hole 370 has the character of the underwater debris cone from the lower continental slope. Sedimentary 'a textures, contacts of layers, and grain-size distribution to in coarse clastic layers confirm that from the Lower >, -r Cretaceous to the upper Tertiary, coarse clastic -σ material was deposited by turbidity currents. xto a Magnesian silicate clays occur less abundantly in c organogenic carbonate-clay rocks of Holes 366 and 369. In Hole 369, palygorskite is related to pelagic sediments deposited near the continental slope of the undrained coast during the Eocene arid climate.

OB pUB I3AVOI ' UBIUBQ Coarser terrigenous material is absent because this region received no sediment from northwest Africa

1090 MINERALOGY, FACIES, AND GENESIS OF MINERALS IN OCEANIC SEDIMENTS

TABLE 2 Clay Minerals in Hole 367 Sample Clay Mineral Facies Zone Association Age (Interval in cm) Iithologo-Genetic Type Fraction

Pliocene 4-3, 54-56 Foraminifer-radiolarian- Montmorillonite, kaolinite Organogenic-clay sediments Montmorillonite containing nannofossil marl with hydromica (zone of quiet sedimentation) with interbeds of silty material Early Eocene 14-3,18-20 Clay zeolite containing Na-mo ntmor illonite Clay sediments (zone of Montmorillonite- clinoptillolite quiet sedimentation) zeolite with sepiolite Paleocene- 15-3,70-72 Silty clay K-montmorillonite (-30%) Silty-clay sediment (zone of Montmorillonite- Late kaolinite (~30%) a steep slope) kaolinite- Cretaceous hydromica (~30%) with hydromica with palygorskite palygorskite and sepiolite Late 16-3,118-120 Silty clay Na-montmorillonite Silty-clay sediment (zone of Montmorillonite- Cretaceous kaolinite a steep slope) kaolinite- hydromica hydromica with palygorskite Late 17-3,92-94 Claystone with Na, Mg, Ca-montmorillonite Silty-clay sediment (zone of Cretaceous horizontal lamination hydromica with a steep slope) palygorskite and kaolinite Early Albian 23-2, 64-66 Claystone with interbeds Montmorillonite with Silty-clay sediment (zone of late Aptian of fine-grained siltstones hydromica and kaolinite a steep slope) Early Aptian- 24-3,79-81 Claystone with interbeds Na-montmorillonite Silty-clay sediment (zone of Montmorillonite Barremian of fine-grained siltstones hydromica, kaolinite a steep slope) with hydromica

αliu rvαkJliillLt 24, CC Claystone with interbeds Mg, Ca-montmorillonite Silty-clay sediment (zone of of fine-grained siltstones hydromica (20%) a steep slope) Early 28-2, 73-75 Limestones with interbeds Hydromica (illite) Organogenic sediments with Hydromica- Cretaceous of clays kaolinite (20%-30%) interbeds of clay matter kaolinite with (zone of quiet sedimentation) montmorillonite during Cretaceous and Tertiary time (Seibold and Supply of Palygorskite and Sepiolite From Hinz, 1974). Clastic material was trapped and Northwest Africa deposited in the Gulf of Tarfaya, and only clay was Elouard (1959) studied Eocene sediments north of transported to the continental slope. the Senegal River basin, in the region of the mouth of In the region of Hole 366, on the Sierra Leone Rise, the Senegal, and in the territory of Mauritania—i.e., Cenozoic sediments are largely open-marine pelagic near Hole 368. Here, the basement rocks are trans- facies, resulting from open-ocean microfauna in the gressively overlain only by middle Eocene deposits. absence of any terrigenous material except eolian. On These epicontinental deposits reflect chemogenic the Sierra Leone Rise, the middle Miocene sediments sedimentation with formation of limestone, dolomite, were subject to conditions similar to those at present. chert, and palygorskitic clay containing Palygorskite probably could have been supplied to the montmorillonite. Elouard (1959) showed that 65 km pelagic sediments (Holes 366 and 369) only through from the boundary of the basin, the clay fraction is eolian transport. This accords with the diverse composed entirely of palygorskite. Toward the accompanying clay minerals—montmorillonite, mixed- boundary of the basin, palygorskite is replaced by layer minerals, kaolinite, etc. (Table 4)—in clayey montmorillonite. Near the shoreline, both are replaced interbeds of palygorskitic limestones. by detrital kaolinite brought in with sandy material. Palygorskitic-sepiolitic rocks occur in Dahomey, Ivory Coast, Nigeria, Niger, Gabon, the Sudan, and Transfer and Redeposition of Palygorskite and others. This testifies to the regional importance of the Sepiolite Particles epochs of palygorskite formation on the African As to genesis of clays, Millot (1964) suggests that continent. Coincidence of the epochs of palygorskite particles of magnesium silicate cannot survive transformation in oceanic and epicontinental sediments portation. Other sediments indicate, however, that should not be overlooked. The oldest occurrence is at there has been stable redeposition by fluvial processes the top of Cretaceous (Maestrichtian), the maximum is or deep-sea currents. Goldberg and Griffin (1970) in the Eocene, and the third occurrence is in the discuss eolian transfer of clay particles. Thus, clay Miocene. particles can be transported in many ways: by wind, river runoff, redeposition as result of shore- and Genesis of Palygorskite and Sepiolite in Leg 41 bottom-abrasion, and oceanic currents. Transport of Oceanic Sediments palygorskite and sepiolite in turbulent currents is there- Analysis of genetic and facies types of palygorskite- fore probable. bearing deposits shows that genesis of these magnesian

1091 TABLE 3 Clay Minerals in Hole 368

Sample Facies Zone Associations of Age (Interval in cm) Lithologo-Genetic Type Qay Mineral Fractions

1-5, 72-74 Nannofossil oozes and nannomarls Mixed-layer (M-H) with varying ratio of

9- 9 material 15-3, 93-95 Qaystone, horizontally laminated Mixed-layer (Ch-M-H), kaolinite C with interbeds of sandy-silty o material

»H 17-4,54-57 Qaystone, horizontally laminated Palygorskite, kaolinite, mixed-layer

OH with interbeds of sandy-silty (M-H) OH material 18-4, 85-87 Claystone, horizontally laminated Montmorillonite, kaolinite, hydromica with interbeds of sandy-silty material 22-5, 88-90 Clay, brown, horizontally- Kaolinite, montmorillonite, hydromica, laminated, enriched with mixed-layer (M-H) zeolite 25-2, 65-67 Claystone, horizontally laminated Palygorskite, a small admixture of montmorillonite § 26-2, 80-82 Claystone, horizontally laminated Palygorskite, a small admixture of ,>» montmorillonite *-( 29-1, 68-70 Claystone, horizontally laminated Montmorillonite, palygorskite Palygorskite-montmorillonitic OS 30-2, 58-60 Claystone, horizontally laminated Palygorskite, mixed-layer (M-H) DO CD 31-2, 78-80 Claystone, horizontally laminated Palygorskite ü 34-2, 61-62 Claystone, horizontally laminated Palygorskite a 36-2, 38-40 Claystone with gentle wavelike Palygorskite, sepiolite

lb i tracks, cryptohorizontally laminated palygorskite (zone of quiet sedimentation) (sometimes an admixture of < 42-1, 79-81 Nannofossil marl with rare mud-eaters' Palygorskite, mixed-layer (H-Ch) mixed-layer minerals and tracks, cryptohorizontally laminated kaolinite) 49-4, 69-70 Nannofossil marl with rare mud-eaters' Palygorskite, mixed-layer (M-H), tracks, cryptohorizontally laminated a small admixture of kaolinite

Note: Packets in mixed-layer minerals: M = montmorilloriitic, H = hydromicaceous, Ch = chloritic. The first component of the associations is given in the largest amounts. TABLE 5 Clay Minerals in Hole 370

Sample Clay Mineral Facies Association Age (Interval in cm) Lithologo-Genetic Type Fractions 12-1,113-115 Claystone, silty, with interbeds of Mixed-layer (H-M), hydromica, Silty-clayey sediments Mixed-layer-hydromicaceous- ö coarse-silty and fine-arenaceous chlorite, palygorskite (zone of weak sea currents) palygorskitic a material with oblique lamination w z 14-4, 99-100 Claystone, silty, with interbeds of Mixed-layer (M-H), hydromica, w i coarse-silty and fine-aranaceous chlorite material with oblique lamination x> •Ö 15-2, 98-100 Claystone, silty, with interbeds of Mixed-layer (M-H) and (H-Ch) coarse-silty and fine-aranaceous z o GO m σ ü w z o H TABLE 5 - Continued

Sample Gay Mineral Facies Association Age (Interval in cm) Lithologo-Genetic Type Fractions < 0.01 mm (Conditions of Formation) of Clay Minerals

18-2, 136-138 Alternation of interbeds of coarse- Montmorillonite, palygorskite, sepiolite, Montmorillonite-palygorskite- CD grained siltstone with nannofossil chlorite sepiolitic ft containing marls and claystone with 3 oblique intertruncated lamination •S 20-2, 68-71 Alternation of interbeds of silty Montmorillonite, mixed-layer (Ch-H), a marl and claystone with oblique, an admixture of kaolinite ε intertruncated lamination 23-4, 100-102 Alternation of interbeds of silty Montmorillonite, mixed-layer (H-M), Oo marl and claystone with oblique, kaolinite intertruncated lamination 24-3, 86-88 Claystone, nannofossil containing, with Mixed-layer (M-H), kaolinite interbeds of silty-arenaceous material with oblique mtertruncated lamination 24-5, 18-19 Gaystone, nannofossil containing, with Mixed-layer (M-H), kaolinite Silty-clayey sediments Mixed-layer-hydromicaceous- interbeds of silty-arenaceous material (zone of weak sea currents) kaolinitic

44-2, 40-42 Nannofossil containing marl alternating Hydromica, mixed-layer (Ch-H), (zone of currents in the kaolinitic with interbeds of silty material with kaolinite deltaic area) «*-< ^ H-l oblique intertruncated lamination

Note: Packets in mixed-layer minerals: M = montmorillonitic, H = hydromicaceous, Ch = chloritic. The first components in the associations have the largest amounts. MINERALOGY, FACIES, AND GENESIS OF MINERALS IN OCEANIC SEDIMENTS silicate minerals can differ even within the lithologic subsidence to a great depth. Or they could have been section of one hole. In continental facies of Africa, carried into these basins from the arid zone of Africa by palygorskites are related chiefly to carbonate sedi- wind. ments. Likewise, in Leg 41 sediments the most sig- The palygorskites in the clay fraction of pelagic nificant amounts of palygorskite occur with slightly sediments from Holes 366 and 369 are terrigenous, as carbonaceous clays and claystones. confirmed by the presence of such minerals as Comparatively pure monomineralic palygorskitic or montmorillonite, mixed-layer minerals, kaolinite, and sepiolitic clays, nearly devoid of terrigenous material quartz. Also, Pow-foong Fan and Rex (1972) say that and associated with some dolomite, are likely to form in lower Pliocene to lower Miocene limey nannofossil through a chemogenic or chemogenic-diagenetic oozes of Hole 136, palygorskite occurs with mica, process. Formation of these rocks in Holes 368 and 370 montmorillonite, kaolinite, quartz, hematite, and occurred at depths below the critical level of carbonate chlorite in the <2 µm fraction. They give a similar accumulation, very near the African continent. association of minerals accompanying palygorskite, Chemogenic formation of palygorskite and sepiolite with small variations, for Mesozoic and Cenozoic was possible here not under arid conditions, as usually sediments of Hole 135 and Holes 137 to 144. Von Rad occurs, but in an environment of normal marine and Rösch (1972) also point out that in many samples sedimentation, owing to an intense inflow of dissolved of pelagic and hemipelagic clays from Leg 14, Mg cations, possibly as Mg(OH)2, and of silica from palygorskite is associated with montmorillonite, the area of tropical weathering and laterite formation.1 kaolinite, and quartz. Even in the Recent epoch, less Such weathering and laterization is known to have favorable for palygorskite formation than the Cenozoic occurred on the African continent (Millot, 1964). and Late Cretaceous, continent-to-ocean transfer of Heating of the oceanic waters may also have been palygorskite particles occurs, as does the formation of important near the continent. palygorskite-bearing oceanic sediments. Palygorskitic clays with admixtures of terrigenous particles and accompanying clay minerals could not TABLE 6 have resulted from mineral selection during eolian or Chemical Composition of Magnesian Silicates of Oceanic Sediments fluvial transport. Authigenic, chemogenic-diagenetic of Carboniferous Deposits of the Mid-Carbóniferous Russian Platform formation of palygorskitic clays therefore seems most Palygorskite probable. The second type of palygorskitic clays and clay- Oceanic Hole 368 Sepiolite stones, with interbeds of sandy-silty material (Holes Sample 29-1, 61-63 368 and 370), was formed by transfer of palygorskitic, Components early Eocene Platform Platform lacustrine, and marine epicontinental sediments, 53.44 58.22 61.73 52.61 53.52 probably as turbidity currents from the Senegal River SiO2 0.48 0.45 0.43 - - delta (Hole 368) or from a submarine canyon (Hole TiO2 A12°3 9.60 10.71 11.01 1.58 1.64 370) into the deep oceanic environment. The clay Fe2°3 3.97 3.02 3.08 0.71 0.34 fraction usually contains palygorskite, mont- FeO 0.44 0.33 0.33 0.36 0.44 morillonite, kaolinite, hydromica, mixed-layer MgO 9.55 8.79 7.08 19.95 19.46 CaO 2.36 1.03 0.50 4.82 8.47 minerals, occasional chlorite, etc. This is true in Lower K Cretaceous sediments of Hole 370 and in upper Eocene 2° 1.26 1.53 2.40 0.27 0.43 to lower Miocene sediments of Holes 368 and 370. Na2O 0.57 0.40 0.03 1.02 2.50 H2O- 8.36 8.56 7.30 6.72 4.31 Millot (1964) recognized accompanying minerals in H2O+ 9.97 6.96 6.11 11.96 8.89 sediments of similar age in the continental facies of Total 100.00 100.00 100.00 100.00 100.00 adjacent Africa. These palygorskitic-sepiolitic rocks of the arid belt are widely developed in northwest Africa; TABLE 7 their thickness sometimes reaches 500 meters (Millot, Molecular Mg:Al Ratio in Oceanic 1964), and they would have been susceptible to wind and Russian Platform Palygorskites erosion and transport to the ocean. Molecular The third and fourth facies types of palygorskite- Ratio bearing rocks are represented by organogenic lime- Locality Geological Age Mg:Al stones with interbeds of clay matter and nannofossil marls. These are typical pelagic sediments of an open Hole 368 Early Eocene 1:1 sea or of an oceanic basin which bordered the Sample 29-1, 61-67 cm undrained coast of Africa during the arid climate of Russian Platform Middle Carboniferous 1:1 k Early Cretaceous and Eocene times. To explain their Kashirsky horizon C2 presence, the magnesian silicates of the regions of Holes Steshevsky horizon C^ 1:1 366 and 369 would seem to require epicontinental seas in the Late Cretaceous and the Eocene, with extremely C 1:1 shallow, strongly heated water, and chemogenic sedi- 2 mentation of palygòrskite-sepiolite, followed by c| 2:1 ck C 2:1 'Other evidence from Leg 41 suggests that Mg could also be 2 supplied by brines emanating from evaporitic sediments deeper in the ck 2:1 section.

1097 P. P. TIMOFEEV, V. V. EREMEEV, M. A. RATEEV

368 368 10.6 31-2 (78-80) 34-2 (61-62) 368 368 36-2 (38-40) 36-3 (37-39)

368 12.17 54-3 (71-73) 368 46-4 (60-61)

368 37-4 (80-82)

368 39-5 (69-70)

3-34 mn 3.25 4.67 3.12 | 4.08 5.07 4.26

Figure 3. X-ray diffraction scans of Leg 41 magnesian silicates.

1098 MINERALOGY, FACIES, AND GENESIS OF MINERALS IN OCEANIC SEDIMENTS

369A δ'3C representative of normally sedimentary rocks and 49-4 (69-70) biogenic carbonates. This means that the carbonate carbon includes considerable carbon from organic matter. Pyritization and carbonation (dolomitization) of the sediments are related to diagenetic, and evidently to early diagenetic, transformations. We found no indica- tions of hydrothermal activity in the isotopic compositions of sulfur and carbon. Such observations on genesis of palygorskite and sepiolite do not deny, however, local processes of transformation of magnesian silicates closely related to volcanism and activity of hydrothermal solutions. For example, the transformation of volcanogenic montmorillonite into palygorskite may occur in interstitial waters with a high content of magnesium cations. Another type of palygorskite formation is related to the occurrence of palygorskitic veins in sediments and as coating on manganese nodules. And finally, Bonatti and Ioensuu (1968) have described a third type: formation of palygorskite under the influence of hydrothermal solutions during serpentinization of iron-rich minerals in Atlantic abyssal sediments. With all this in mind, however, we cannot deny the role of chemogenic sedimentation and chemogenic- Figure 3. (Continued). diagenetic formation of magnesian silicates and fluvial or eolian transport of these minerals from arid zones into oceanic sediments. Evidence Against Volcanic Origin of Palygorskite and Sepiolites in Leg 41 Sediments OTHER CLAY MINERALS The following evidence argues against the assumed Montmorillonite occurs in rock facies reflective of effect of hydrothermal flow of magnesian solutions: the quiet sedimentation by weak currents (Millot, 1964) occurrence of palygorskites and sepiolites in different (Hole 368, Upper Cretaceous; Hole 366, lower Eocene). facies; their occurrence in carbonate rocks peculiar to It results from weathering of soils in tropical areas with deep-sea red clays; monomineral palygorskite clays long dry seasons. In the tropical dry climate, soils with with no traces of hydrothermal metasomatic replace- montmorillonite are produced in poorly drained ment, decoloration, or disturbance of textural features depressions by interaction of silica, alumina, and (lamination), and frequently without pyroclastics. magnesium liberated by hydrolysis during hot humid The isotopic compositions of sulfur and carbon in periods. Millot (1964) points but, however, that such palygorskite-bearing rocks of Holes 366, 368, and 370 formation of montmorillonite was, in principle, provide an important additional argument. Table 8 possible not only on the continent but directly in those shows that the isotopic composition of sulfide sulfur is sedimentary depressions where molassic sediments mostly negative, about -2O°/oo. Such values are peculiar were formed. to sedimentary-diagenetic sulfides that result from Kaolinite in the Leg 41 sediments resulted from sulfate reduction. They may mean that sulfides tropical weathering processes and subsequent fluvial appeared in the uppermost layer of sediments under and/or eolian transport. The hydromica is mostly conditions of free exchange of the oozy and bottom water; i.e., sediments may have inherited sulfide sulfur dioctahedral illite without expanded packets and is from the moment of their accumulation, at the earliest probably detrital. The chlorite may have resulted from stages of diagenesis. washout of magmatic rocks or outflow from arid zones; Despite low concentrations of carbonates in it is not well preserved during laterization. The mixed- palygorskite-bearing clays, we attempted to determine layer minerals are of two types: illite-montmorillonite the isotopic composition of the carbonate (Table 9). and chlorite-montmorillonite. The illite-montmoril- Some carbonate has carbon with an isotopic composi- lonite gives asymmetric X-ray diffraction peaks: at tion that is lighter than normal sea carbonate. The 13.6Å (untreated); at 17.3Å (treated with glycol); and at latter is characterized by the value <513C = 0, whereas 9.9Å (heated to 550°C). The chlorite-montmorillonite <513C of the organic matter is approximately -25°/oo shows peaks at 14.5Å (untreated); at 16.99 A (treated (Table 9). Table 9 shows the data on Hole 368 and, for with glycol); and at 13.8Å (heated). Both types of comparison, those on core material from Hole 366, mixed-layer minerals resulted from degradation of which contains considerable amounts of carbonate. minerals on the African continent. When treated with hydrochloric acid, the samples from Hole 368 liberate CO2 only after the reaction vessels are CONCLUSIONS heated, which suggests a dolomitic carbonate composi- After studying mineralogy and facies types of tion. The isotopic composition of carbonate carbon in palygorskitic and palygorskitic-sepiolitic oceanic Hole 368 is intermediate between extreme values of sediments of Leg 41, we conclude the following:

1099 P. P. TIMOFEEV, V. V. EREMEEV, M. A. RATEEV

TABLE 8 Isotopic Composition of Sulfide Sulfur in the Core of Deep-Sea Holes, Hole 368

Sample Facies Concentration 6 34 (Interval in cm) Type of Sediments Associations of Clay Minerals Age (mg/g) (7oo)

29-1,68-70 Red deep-sea clays Montmorillonite, palygorskite 6.5 (quiet sedimentation) 30-2,51-53 Red deep-sea clays Admixture of sepiolite 7.3 -23.3 (quiet sedimentation) 30-2,58-60 Red deep-sea clays Palygorskite, admixture of 2.3 (quiet sedimentation) mixed-layer mineral 31-2, 78-80 Red deep-sea clays Palygorskite, admixture of 2.3 (quiet sedimentation) mixed-layer mineral 31-2,71-73 Red deep-sea clays Palygorskite 0.9 +15.6 (quiet sedimentation) 34-2,51-53 Red deep-sea clays Palygorskite 5.5 - (quiet sedimentation) 34-2,61-62 Red deep-sea clays Palygorskite 7.4 (quiet sedimentation) 36-3, 37-39 Red deep-sea clays Palygorskite-sepiolite 42.9 -20.2 (quiet sedimentation) uI o 36-3, 68-70 Red deep-sea clays Palyg or skite-sep iolite W 15.4 (quiet sedimentation) >, 37-4, 80-82 Red deep-sea clays Sepiolite, palygorskite 15.6 (quiet sedimentation) 3 39-5, 69-70 Red deep-sea clays Sepiolite, palygorskite 1.3 -23.4

(quiet sedimentation) Cβ 40-3, 68-70 Red deep-sea clays Sepiolite-palygorskite 3.6 (quiet sedimentation) ö 41-2,61-63 Red deep-sea clays Sepiolite-palygorskite 13.6 -22.2 (quiet sedimentation) 3 41-2, 70-70 Red deep-sea clays Sepiolite-palygorskite 4.6 -22.2 (quiet sedimentation) 42-2,62-63 Red deep-sea clays Sepiolite, palygorskite 14.5 -24.9 (quiet sedimentation) 44-4, 68-70 Red deep-sea clays Sepiolite, palygorskite 3.6 (quiet sedimentation) 45-4, 84-96 Red deep-sea clays Sepiolite, palygorskite 12.5 -28.4 (quiet sedimentation) 45-4, 91-92 Red deep-sea clays Sepiolite, palygorskite 14.4 -27.9 (quiet sedimentation) 46-4, 60-61 Red deep-sea clays Sepiolite, palygorskite, 0.5 -19.5 (quiet sedimentation) montmorillonite, quartz 47-5,69-70 Red deep-sea clays Sepiolite, palygorskite, 13.6 (quiet sedimentation) montmorillonite

Note: Analyses by V. I. Vinogradov.

TABLE 9 a. The first type is pelagic palygorskitic-sepiolitic Isotopic Composition of Carbonates in clay with dolomite, but without terrigenous or Deep-Sea Holes of Leg 41 volcanogenic material. Formation occurs by chemogenic-diagenetic processes in the pelagic zone 13 Sample Concentration δ C of the ocean adjacent to a continent with tropical or (Interval in cm) of CO2 (mg/g) (7oo) arid climate. The zone is characterized by an abnormally intense inflow of magnesium [apparently 368-27-3, 41-43 3.4 -13.8 in the form of Mg(OH)2] and silica from the areas of 368-30-2,51-53 1.5 -18.9 368-34-2,51-53 15.3 -12.4 laterite formation, and by irregularly high heating of 368-36-2, 79-81 3.4 -14.9 oceanic waters. ; 368-37-4,71-73 1.0 -18.0 b) The second type is palygorskite-bearing clay 368-45-4, 84-86 4.4 — and claystone with interbeds of silty material, 366-2-3, 82-84 70.4 +4.2 frequently contains mica, montmorillonite, chlorite, 366-3-3, 70-72 169.2 +3.5 366-7-3, 72-74 190.7 +3.3 or kaolinite. This type formed under the influence of 366-11-1,50-52 166.5 +3.2 suspension currents transporting deltaic sediments 366-19-1, 105-107 132.0 +4.2 from the Senegal River and an underwater delta or 366-21-2,61-63 198.0 +2.8 canyon in the vicinity of Hole 370. 366-24-2, 106-108 52.8 +2.7 c) The third type is pelagic limestone and 366-40-3, 74-76 165.0 +3.1 nannofossil marl with interbeds of palygorskite- bearing clay material. The clay fraction

1100 MINERALOGY, FACIES, AND GENESIS OF MINERALS IN OCEANIC SEDIMENTS

quartz. Formation of this type of palygorskite- rocks of northwest Africa. Montmorillonite and mixed- bearing deposit took place in carbonate pelagic layer minerals could have been brought from the sediments near drainless parts of the arid continent; lateritic areas of arid zones, or could have resulted from particles of palygorskite were supplied by eolian diagenetic alteration of volcanogenic material. transport. d) On the basis of Leg 14 cores, a fourth genetic type of palygorskitic-zeolitic clays, not observed by us in Leg 41 sediments, may result from diagenetic REFERENCES transformation of volcanic ash (von Rad and Rösch, Bonatti, E. and Ioensuu, O., 1968. Palygorskite from Atlantic 1972). deep-sea sediments: Am. Mineralogist., v. 53, p. 975. 2) On the basis of new data, fluvial and eolian Chambers, G.P., 1959. Some industrial applications of the transport of palygorskite-sepiolite particles seems clay minerals sepiolite: Silicates Industr., v. 24, no. 4. possible, as does redeposition of the particles. Our Elouard, P., 1959. Etude géologique et hydrogéologique des conclusions are in good agreement with Wirth's (1968) formations sédimentaires du Guebla Mauritanien et de la data on eolian transport of palygorskite from the arid Valée du Senegal: These Sci. Goldberg, E.D. and Griffin, J.J., 1970. The sediments of the Senegal River area. The source for palygorskite in the northern Indian Ocean: Deep-Sea Res., v. 17, p. 513-537. Red Sea was also shown by Müller (1961) to be Hartmann, M., Lange, H., Seibold, E., and Walger, E., 1971. continental, as was that for palygorskite in the Persian Oberflachensedimente im persischen Golf und Golf von Gulf (Hartmann et al., 1971). The occurrence of Oman Geologisch-hydrologischer Rahmen und erste, sedi- palygorskite and sepiolite in Upper Cretaceous and mentologische Ergebnisse: "Meteor" Forchungs- Paleogene sediments only, and their paragenesis with ergebnisse, v. 4, p. 1. authigenic clinoptilolite and with slowly deposited clays Hathaway, J.C. and Sachs, P.L., 1965. Sepiolite and about 20-25 m.y. old confirms the diagenetic origin of clinoptilolite from the Mid-Atlantic Ridge: Am. Min- these magnesian silicates (von Rad and Rösch, 1972). eralogist., v. 50, p. 852. Palygorskite and sepiolite probably are not forming at Martin-Vivaldi, J. and Cano-Ruiz, J., 1956. Contribution to present. The occurrence of palygorskite in the surface the study of sepiolite. pt. Ill: Nat. Res. Council Publ., 456. Millot, G., 1964. Géologie des argiles: Paris (Masson et Cie). layer of Atlantic Ocean sediments would seem to Müller, G., 1961. Palygorskit und sepiolith in tertiaren und suggest their formation in oceanic sediments near the quartaren sedimenten von Hadramaut (S-Arabien): Neues continents, but it is more likely a result of fluvial or Jahrb. Mineralogic Abhandl., v. 97, p. 275. eolian transport. Mumpton, T.A. and Roy, R., 1958. New data sepiolite and 3) Palygorskite is detrital, and its quantitative attapulgite: Fifth Natl. Conf. Clays and Clay Minerals, increase toward the continent cannot always be Proc, Washington. observed, depending on the submarine topography and Nagy, B. and Bradley, W., 1955. The structural scheme of the nature of suspension currents. sepiolite: Am. Mineralogist., v. 40, p. 885-892. 4) We agree with von Rad and Rösch (1972) that a Pow-foong Fan and Rex, R.W., 1972. X-ray mineralogy studies. In Hayes, D,E., Pimm, A.C., et al., Initial Reports surplus of cations in interstitial waters is necessary for of the Deep Sea Drilling Project, Volume 14: Washington optimal chemogenic or chemogenic-diagenetic forma- (U.S. Government Printing Office), p. 677-726. tion of sepiolite and palygorskite. Origins can vary Preisinger, A., 1959. X-ray study of the structure of sepiolite. extensively (Hathaway and Sachs, 1965). We recognize Sixth Natl. Conf. Clays and Clay Minerals, Proc, the inflow of silica by rivers draining the regions of London. laterization as a contributing factor for formation of Seibold, E. and Hinz, K., 1974. Continental slope construc- magnesian minerals in sediments of Leg 41. tion and destruction West Africa: In Burk, C.A. and 5) Most other minerals of the clay fraction of Leg 41 Drake, C.L. (Eds.), The geology of continental margins: oceanic sediments are detrital. Kaolinite is known to New York (Springer-Verlag), p. 179-196. abound in the crusts of laterization. Dioctahedral mica von Rad, W. and Rösch, H., 1972. Mineralogy and origin of and trioctahedral chlorite are unstable in the profile of clay minerals, silica and authigenic silicates in Leg 14 sediments. In Hayes, D.E., Pimm, A.C., et al., Initial laterization, but they can remain preserved to a certain Reports of the Deep Sea Drilling Project, Volume 14: extent; this might explain their limited quantitative Washington (U.S. Government Printing Office), p. 727- distribution in sediments of Leg 41. They can become 752. more abundant during increasing aridity. In addition, Wirth, L., 1968. Attapulgites du Senegal Occidental: chlorite can be related to washout of old magmatic Laboratoire Géol. Univ. Dakar, Rapport no. 26.

1101