43. PALYGORSKITE, SEPIOLITE, AND OTHER CLAY MINERALS IN LEG 41

43. PALYGORSKITE, SEPIOLITE, AND OTHER CLAY MINERALSIN 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

Leg 41 holes, drilled near the northwest margin ofAfrica, penetrated Mesozoic and Cenozoic sediments.The <l µm fraction of these sediments containsmontmorillonite, kaolinite, hydromica, chlorite, mixed-layer minerals of the mica-montmorillonite andchlorite-montmorillonite types, palygorskite, andsepiolite.

STRATIGRAPHIC AND LITHOLOGICOCCURRENCE OF MAGNESIAN SILICATES

Occurrence of magnesian silicates of the palygorskiteand sepiolite type proved widespread and is shown inFigure 1. These minerals occur in the Albian of Site 368and the Cenomanian of Site 370. Palygorskitefrequently occurs with sepiolites; this is unusual forplatform deposits. Palygorskite also occurs in Eocenesediments: lower Eocene of Hole 366, lower and middleEocene of Hole 370, middle Eocene of Hole 369, andupper Eocene of Hole 368; in Hole 367, palygorskiteoccurs in Upper Cretaceous and lower Eocenesediments.

Magnesian silicates are associated with the followinglithologies (Figure 2):

1) Clay and claystone with gentle wavelike lamina-tions (Hole 368, Upper Cretaceous to lower Eocene).

2) Claystone with interlayers of sandy silty material(Hole 370, lower to middle Eocene; Hole 368, upperEocene).

3) Nannofossil marl alternating with claystone andsiltstone (Hole 370, Cenomanian to upper Paleocene).

4) Nannofossil marl with burrows (Hole 369,Albian).

5) Limestone with interbeds of clay (Hole 369,middle Eocene; Hole 366, lower Eocene).

Tables I through 5 and Figure 2 show that in Holes366 and 369, magnesian silicates are associated withorganogenic clay and carbonate sediments, whereasthose of Holes 368 and 370 are associated withterrigenous and, at Site 368, with partly chemogenicsediments.

MICROSCOPIC FEATURES OF PALYGORSKITICAND PALYGORSKITIC-SEPIOLITIC ROCKS

Clays and claystones of nearly pure palygorskitic-sepiolitic composition occur as dim, dark gray, double-refracted masses. These masses occur with fine grains,plates of brown biotite, remains of plants, spores andpollen, globules of pyrite, and pyritized cherty fossils.

The clay mass is frequently filled with rhombo-hedrons of diagenetic dolomite. The texture of clays is

flocculent, cirrose, cellular, or lumpy. Because ofsimilar optical features, palygorskite and sepiolite areindistinguishable from each other in thin section. Fine-grained terrigenous material is negligible in clays of thistype; we recognized no volcanogenic material. Paly-gorskitic monomineral clays usually contain a greateradmixture of quartz and are better recrystallized.

Claystones with interbeds of silty material consist ofelongated plates of hydromica and scaly, slightlydouble-refracted masses of palygorskite-kaolinite,which cement angular grains of silt-size quartz. Authi-genic rhombohedrons of dolomite permeate the entirerock.

Limestone containing palygorskite is composed of apelitomorphic mass of calcite that includes organicremains: coccoliths, foraminifer tests filled with clayand cherty matter, diatoms, and radiolarians. Paly-gorskite may occur throughout the rock (Sample 34-3,83-85 cm), or less frequently as independent aggregates(Sample 35-3, 104-106 cm).

MINERALOGY OF SEPIOLITESAND PALYGORSKITES

We could not determine the chemical composition ofsepiolites in Leg 41 cores, because they occur withpalygorskite or other minerals. Palygorskite of Leg 41deposits shows intense X-ray peaks which differentiateit readily from sepiolite (Mumpton and Roy, 1958):(110), 10.5Å; (200), 6.44Å; (130), 5.3Å; and (310), 4.3A(Figure 3).

The palygorskite DTA scans are characterized byabsence of an exothermic peak at 860°C (as insepiolite), lower temperature of the mid-endothermaleffect at 490-510°C, and by more intense endothermicpeaks at 255°-270°C.

The oceanic palygorskites are similar in compositionto those of the Russian platform (Table 6). Theycontain up to 10% AI2O3 and over 9% MgO, which isrepresentative of the Russian platform. The Tiθ2content in palygorskites is about the same as in otherclays. In sepiolite, however, Tiθ2 is usually absent; thisis regarded as additional proof of authigeneity. Thecarbonate content in palygorskitic clays does notexceed 1%, and organic carbon is only 0.42%; this isrepresentative of palygorskitic clays of the arid zone.The iron sulfide content is 0.44%.

Possibility of Isomorphic Substitutions

There are differing viewpoints concerning thepossibility of isomorphic transformation of paly-gorskite into sepiolite, and vice-versa. Sepiolite andpalygorskite may be intermediate members of the iso-

1087

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

370 369

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Palygorskitic sediments

Palygorskite-sepioliticsediments

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Figure 2. Lithologic associations of magnesian silicates in Leg 41 sediments.

1088

TABLE 1Clay Minerals in Hole 366

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Sample(Interval in cm)

5-3, 90-92

11-1,50-52

13-2, 77-79

14-3, 85-87

14-3, 93-95

15-1,47-49

16-2,14-16

24-2, 115-118

27-2, 87-89

32-3, 99-100

34-4, 83-85

35-3, 104-106

38-3, 48-50

39-3, 18-20

40-3, 74-76

42-3, 120-122

44-3,81-83

45-3, 39-41

Lithologo-Genetic Type

Radiolarian-diatom foraminiferalnannofossil chalk

Nannofossil chalk with interbeds ofvolcanic ash with mud-eaters' tracksNannofossil chalk with an admixtureof volcanic ashNannofossil chalk with an admixtureof ashNannofossil chalk with an admixtureof ash

Nannofossil chalk with an admixtureof ashAlternation of nannofossil chalk withinterbeds of porcellaniteAlternation of nannofossil chalk andlimestone with interbeds of porcellanitesand siliceous nodulesAlternation of nannofossil chalk andlimestone with interbeds of porcellanitesand siliceous nodulesLimestone, homogeneous with thethinest interbeds of clay matter andoblique wavelike laminationLimestone, homogeneous wjth thethinest interbeds of clay matter andoblique wavelike laminationLimestone, homogeneous with thethinest interbeds of clay matterand oblique wavelike laminationLimestone, homogeneous with interbedsof clay matterLimestone, homogeneous with interbedsof clay matterLimestone, homogeneous with interbedsof clay matterLimestone, homogeneous, with thethinest interbeds of clay matter andoblique wavelike laminationLimestone, homogeneous, with thethinest interbeds of clay matter andoblique wavelike laminationLimestone, homogeneous, with thethinest interbeds of clay matter andoblique wavelike lamination

Clay MineralsFractions <O.Ol mm

Mixed-layer (M-H), kaolinite,zeolite

Mixed-layer minerals (M-H)

Mixed-layer (M-H), an admixture ofkaolinite, hydromica, zeolite?Montmorillonite, an admixture ofkaoliniteMixed-layer (M-H), kaolinite,hydromica, an admixture of chlorite,mixed-layer (M-H)Mixed-layer (M-H)

Mixed-layer (M-H) with transitionsbetween themMixed-layer (M-Ch-H)

Mixed-layer (M-H)

Mixed-layer (M-H), palygorskite

Mixed-layer (M-H) or (M-H-Ch),palygorskite, montmorillonite(?)

Mixed-layer (M-H-Ch), palygorskite

Mixed-layer (M-Ch) or mixed-layer(M-H-Ch)?Montmorillonite, quartz

Montmorillonite, quartz

Montmorillonite, quartz

Mixed-layer (M-H)

Mixed-layer (M-H)

Facies(Conditions of Formation)

Facies of organogenic bioturbidicsediments

Organogenic sediments of the zoneof influence of volcanism

Organogenic sediments with interbedsof porcellanites (?) and limestones(Above—interbeds of porcellanites,below—interbeds of limestones)

Organogenic sediments (zone ofweak currents)

Associationsof Clay Minerals

Montmorillonite-hydromicaceous,with kaolinite

Mixed-layer (montmorillonitic-hydromicaceous), in some interbeds—montmorillonitic-chloritic with anadmixture of kaolinite, hydromica,chlorite

Mixed-layer (montmorillonite-chlorite-hydromicaceous)

Mixed-layer (montmorillonite-hydromicaceous) with palygorskite

Montmorillonitic

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morphic series talc-pyrophyllite, with progressivesubstitution of Al for Mg positions in octahedral layersof the montmorillonite type. Martin-Vivaldi and Cano-Ruiz (1956) have supported this idea. But in comparingchemical compositions of sepiolite and palygorskite inLeg 41 sedimentary rocks, we recognized no reliablefeatures of isomorphism. All Russian-platformcarboniferous sepiolites that we studied, from both thearid zone (middle and upper Carboniferous) and thehumid zone (lower Carboniferous), were completelypure. Chemical analyses of sepiolites, after exclusion ofcarbonates, yielded typical compositions (Table 2).Rare deviations from the standard compositionresulted from admixtures of other minerals. Chambers(1959) found a thick bed of sepiolite in the sedimentarydeposits of Vallecas (Spain) to be homogeneous. Thus,we are unable to find any transitional members on thebasis of the Al and Mg contents of sedimentary beddedsepiolites and palygorskites.

Studies by Nagi and Bradley (1955) and by Preisinger(1959) showed significant differences in the structuresof sepiolite and palygorskite. Palygorskites may beregarded as intermediate minerals—with compositionalextremes Mg3/OH2Si4θio (magnesian-montmoril-lonitic) and Ah/OhhSi<jOio (aluminum-montmoril-lonitic)—between talc and pyrophyllite. Substitution ofAl for Mg can be of three types (after S.G. Dromeshko,personal communication), within the followingmolecular ratios:

Mg:Al = 2:1Mg:Al =1:1Mg:Al = 1:2

In palygorskite from the Russian platform we were ableto establish only two types: Mg:Al = 1:1 and 2:1 (Table7), without any gradual transitions. Leg 41 palygorskiteis of the second type (Table 7).

ENVIRONMENT OF SEPIOLITE ANDPALYGORSKITE FORMATION

Magnesian silicates occur most abundantly in clayrocks of Holes 368 and 370, particularly in sectionswhere material was supplied from Africa. Theterrigenous material derives from the Senegal Riverbasin; the coarse fraction suggests deposition byturbidity currents, but does not indicate local volcanicsources.

The occurrence of palygorskitic-sepiolitic rocks inHole 370 is related to an underwater canyon or delta.The Lower Cretaceous to middle Eocene section ofHole 370 has the character of the underwater debriscone from the lower continental slope. Sedimentarytextures, contacts of layers, and grain-size distributionin coarse clastic layers confirm that from the LowerCretaceous to the upper Tertiary, coarse clasticmaterial was deposited by turbidity currents.

Magnesian silicate clays occur less abundantly inorganogenic carbonate-clay rocks of Holes 366 and369. In Hole 369, palygorskite is related to pelagicsediments deposited near the continental slope of theundrained coast during the Eocene arid climate.Coarser terrigenous material is absent because thisregion received no sediment from northwest Africa

1090

MINERALOGY, FACIES, AND GENESIS OF MINERALS IN OCEANIC SEDIMENTS

Age

Pliocene

Early Eocene

Paleocene-LateCretaceous

LateCretaceous

LateCretaceous

Early Albianlate Aptian

Early Aptian-Barremian

EarlyCretaceous


4-3, 54-56

14-3,18-20

15-3,70-72

16-3,118-120

17-3,92-94

23-2, 64-66

24-3,79-81

24, CC

28-2, 73-75

Clay

Iithologo-Genetic Type

Foraminifer-radiolarian-containing nannofossil marlwith interbeds of siltymaterial

Clay zeolite containing

Silty clay

Silty clay

Claystone withhorizontal lamination

Claystone with interbedsof fine-grained siltstones



Limestones with interbedsof clays

TABLE 2Minerals in Hole 367

Clay MineralFraction <O.Ol mm

Montmorillonite, kaolinitewith hydromica

Na-mo ntmor illoniteclinoptillolite

K-montmorillonite (-30%)kaolinite (~30%)hydromica (~30%) withpalygorskite

Na-montmorillonitekaolinitehydromica

Na, Mg, Ca-montmorillonitehydromica withpalygorskite andkaolinite

Montmorillonite withhydromica and kaolinite

Na-montmorillonitehydromica, kaolinite

Mg, Ca-montmorillonitehydromica (20%)

Hydromica (illite)kaolinite (20%-30%)

Facies Zone(Condition of Formation)

Organogenic-clay sediments(zone of quiet sedimentation)

Clay sediments (zone ofquiet sedimentation)

Silty-clay sediment (zone ofa steep slope)






Organogenic sediments withinterbeds of clay matter(zone of quiet sedimentation)

Associationof Clay Minerals

Montmorillonite

Montmorillonite-zeolite withsepiolite

Montmorillonite-kaolinite-hydromica withpalygorskite andsepiolite

Montmorillonite-kaolinite-hydromica withpalygorskite

Montmorillonitewith hydromica

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Hydromica-kaolinite withmontmorillonite

during Cretaceous and Tertiary time (Seibold andHinz, 1974). Clastic material was trapped anddeposited in the Gulf of Tarfaya, and only clay wastransported to the continental slope.

In the region of Hole 366, on the Sierra Leone Rise,Cenozoic sediments are largely open-marine pelagicfacies, resulting from open-ocean microfauna in theabsence of any terrigenous material except eolian. Onthe Sierra Leone Rise, the middle Miocene sedimentswere subject to conditions similar to those at present.Palygorskite probably could have been supplied to thepelagic sediments (Holes 366 and 369) only througheolian transport. This accords with the diverseaccompanying clay minerals—montmorillonite, mixed-layer minerals, kaolinite, etc. (Table 4)—in clayeyinterbeds of palygorskitic limestones.

Transfer and Redeposition of Palygorskite andSepiolite Particles

As to genesis of clays, Millot (1964) suggests thatparticles of magnesium silicate cannot survive trans-portation. Other sediments indicate, however, thatthere has been stable redeposition by fluvial processesor deep-sea currents. Goldberg and Griffin (1970)discuss eolian transfer of clay particles. Thus, clayparticles can be transported in many ways: by wind,river runoff, redeposition as result of shore- andbottom-abrasion, and oceanic currents. Transport ofpalygorskite and sepiolite in turbulent currents is there-fore probable.

Supply of Palygorskite and Sepiolite FromNorthwest Africa

Elouard (1959) studied Eocene sediments north ofthe Senegal River basin, in the region of the mouth ofthe Senegal, and in the territory of Mauritania—i.e.,near Hole 368. Here, the basement rocks are trans-gressively overlain only by middle Eocene deposits.These epicontinental deposits reflect chemogenicsedimentation with formation of limestone, dolomite,c h e r t , a n d p a l y g o r s k i t i c c lay c o n t a i n i n gmontmorillonite. Elouard (1959) showed that 65 kmfrom the boundary of the basin, the clay fraction iscomposed entirely of palygorskite. Toward theboundary of the basin, palygorskite is replaced bymontmorillonite. Near the shoreline, both are replacedby detrital kaolinite brought in with sandy material.

Palygorskitic-sepiolitic rocks occur in Dahomey,Ivory Coast, Nigeria, Niger, Gabon, the Sudan, andothers. This testifies to the regional importance of theepochs of palygorskite formation on the Africancontinent. Coincidence of the epochs of palygorskiteformation in oceanic and epicontinental sedimentsshould not be overlooked. The oldest occurrence is atthe top of Cretaceous (Maestrichtian), the maximum isin the Eocene, and the third occurrence is in theMiocene.

Genesis of Palygorskite and Sepiolite in Leg 41Oceanic Sediments

Analysis of genetic and facies types of palygorskite-bearing deposits shows that genesis of these magnesian

1091


Age

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1-5, 72-74

4-3, 92-94

5-4, 73-756-5, 75-777-5, 90-92

8-4, 72-74

9-4, 83-84

11-2,68-70

13-3,75-77

14-2, 75-77

15-3, 93-95

17-4,54-57

18-4, 85-87

22-5, 88-90

25-2, 65-67

26-2, 80-82

29-1, 68-7030-2, 58-6031-2, 78-8034-2, 61-6236-2, 38-40

36-3, 37-39


Nannofossil oozes and nannomarls


Nannofossil oozes and nannomarlsNannofossil oozes and nannomarlsNannofossil oozes and nannomarls



Qaystone, horizontally laminatedwith interbeds of sandy-siltymaterialQaystone, horizontally laminatedwith interbeds of sandy-siltymaterial

Qaystone, horizontally laminatedwith interbeds of sandy-siltymaterialQaystone, horizontally laminatedwith interbeds of sandy-siltymaterialQaystone, horizontally laminatedwith interbeds of sandy-siltymaterialClaystone, horizontally laminatedwith interbeds of sandy-siltymaterialClay, brown, horizontally-laminated, enriched withzeolite

Claystone, horizontally laminated

Claystone, horizontally laminated

Claystone, horizontally laminatedClaystone, horizontally laminatedClaystone, horizontally laminatedClaystone, horizontally laminatedClaystone with gentle wavelikesmall discontinuous laminationQaystone with gentle wavelikesmall discontinuous lamination

Qay Mineral Fractions <O.Ol mm

Mixed-layer (M-H) with varying ratio ofpackets; kaolinite; quartzMixed-layer (M-H) with varying ratio ofpackets; kaolinite

Mixed-layer (M-H), kaoliniteMixed-layer (M-H), kaoliniteMixed-layer (M-H-Ch), kaolinite, a smalladmixture of chloriteMixed-layer (M-H), kaolinite, anadmixture of hydromica and mont-morilloniteMixed-layer (M-H-CH)

Kaolinite, hydromica, montmorillonite,admixture of mixed-layer (M-H)

Kaolinite, mixed-layer (M-H), admixtureof ülite

Mixed-layer (M-H), kaolinite,admixture of hydromica

Mixed-layer (Ch-M-H), kaolinite

Palygorskite, kaolinite, mixed-layer(M-H)

Montmorillonite, kaolinite, hydromica

Kaolinite, montmorillonite, hydromica,mixed-layer (M-H)

Palygorskite, a small admixture ofmontmorillonitePalygorskite, a small admixture ofmontmorilloniteMontmorillonite, palygorskitePalygorskite, mixed-layer (M-H)PalygorskitePalygorskitePalygorskite, sepiolite

Palygorskite, sepiolite

Facies Zone(Conditions of Formation)

Organogenic sediments (zone of quietsedimentation) (alternation of nanno-fossil oozes with nannofossil marls)

Organogenic-clay sediments of thequiet sedimentation zone (in the upperpart mostly organogenic-clayey, andin the lower-more clayey sedimentswith an admixture of silty material)

Associations ofQay Minerals

Mixed-layer (montmorillonite-hydromicaceous with a varying ratioof packets) with kaolinite, lessfrequently chlorite

Kaolinite-mixed-layer (montmorillonite-hydromicaceous), sometimes withpalygorskite

Palygorskite-montmorillonitic

ow>,

37-4, 80-82

39-5, 69-70

40-3, 69-70

41-2, 70-72

42-2, 62-63

44-4, 68-70

45-4, 91-93

46-4, 60-61

47-5, 69-70

Claystone with gentle wavelikesmall discontinuous laminationClaystone with gentle wavelikesmall discontinuous laminationClaystone with gentle wavelikesmall discontinuous laminationClaystone with gentle wavelikesmall discontinuous laminationClaystone with gentle wavelikesmall discontinuous laminationClaystone with gentle wavelikesmall discontinuous laminationClaystone with gentle wavelikesmall discontinuous laminationClaystone with gentle wavelikesmall discontinuous laminationClaystone with gentle wavelikesmall discontinuous lamination

Sepiolite, palygorskite





Palygorskite, montmorillonite ormixed-layer (M-H)Sepiolite, palygorskite, montmorilloniteor montmorillonite-hydromicaSepiolite, palygorskite, montmorillonite,quartzSepiolite, palygorskite, montmorillonite

Deep-water clay sediments with dolomite(zone of quiet sedimentation); in thelower part (layers 39-47) zones of weakcurrents with a small admixture of siltymaterial and areas of discontinuouswavelike lamination

Palygorskite-sepiolitic

Palygorskite-sepiolite-montmorillonite-mixed-layer

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50-3, 52-54

51-2, 60-62

52-5, 85-87

53-3,71-73

54-3,71-73

55-3, 90-92

57-4, 68-70

58-5, 68-70

59-3, 88-90

Alternation of thinly elutriatedclaystone with a sandy-sütyvariety, gentle wavelike smalldiscontinuous laminationAlternation of thinly elutriatedclaystone with a sandy-siltyvariety, gentle wavelike smalldiscontinuous laminationAlternation of thinly elutriatedclaystone with a sandy-siltyvariety, gentle wavelike smalldiscontinuous laminationAlternation of thinly elutriatedclaystone with a sandy-siltyvariety, gentle wavelike smalldiscontinuous laminationAlternation of thinly elutriatedclaystone with a sandy-siltyvariety, gentle wavelike smalldiscontinuous laminationAlternation of thinly elutriatedclaystone with a sandy-siltyvariety, gentle wavelike smalldiscontinuous laminationSilty clay, cryptohorizontallylaminatedClaystone, horizontally laminatedwith interbeds of coaly claystoneAlternation of claystone interbedsand sandy-silty varieties

Hydromica, mixed-layer (M-H),kaolinite

Kaolinite, hydromica, montmorillonite,quartz

Hydromica, mixed-layer (H-M),kaolinite

Montmorillonite, palygorskite


Montmorillonite, glauconite

Montmorillonite, hydromica, mixed-layer (M-H), kaolinite (traces)Hydromica, mixed-layer (M-H), chloritekaoliniteHydromica, mixed-layer (M-H),chlorite, quartz, feldspars

Hydromicaceous-kaolinitic, sometimeswith an admixture of mixed-layer(montmorillonite-hydromica ceous)minerals

Siltstone-clay sediments (zone of weakcurrents)

Palygorskite-montmorillonitic

Coaly-silty-clay sediments (zone ofquiet sedimentation)

Hydromica-chloritic with anadmixture of kaolinite and mixed-layer minerals

Note: Packets in mixed-layer minerals; M = montmorillonitic, H = hydromicaceous, Ch = chloritic.

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Age

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1-3, 84-86

2-3, 82-84

2-4,80-81

3-2,73-75

3-3,80-82

4-2, 92-94

4-4, 80-82

4-5, 84-86

6-2, 73-75

7-5, 84-86

22-3, 70-72

26-4, 70-72

27-5, 91-93

31-4,80-81

34-2, 78-81

35-2, 78-81

40-4, 83-85

41-4, 80-82

42-1, 79-81

49-4, 69-70


Nannofossil oozes, homogeneous,cryptohorizontally laminatedNannofossil oozes, homogeneous,cryptohorizontally laminatedNannofossil oozes, homogeneouscryptohorizontally laminatedNannofossil oozes, homogeneous,cryptohorizontally laminatedNannofossil oozes, homogeneous,cryptohorizontally laminatedNannofossil oozes, homogeneous,cryptohorizontally laminatedNannofossil oozes, homogeneous,cryptohorizontally laminatedNannofossil marl with interbeds of clayenriched with ashNannofossil marl with interbeds of clayenriched with ash

Nannofossil marl with interbeds of clayenriched with ash

Nannofossil marl with abundance ofmud-eaters' tracksNannofossil marl with abundance ofmud-eaters' tracksNannofossil marl with abundance ofmud-eaters' tracksNannofossil marl with abundance ofmud-eaters' tracks

Limestone, homogeneous withinterbeds of clay matterLimestone, homogeneous withinterbeds of clay matter

Nannofossil marl with rare mud-eaters'tracks, cryptohorizontally laminated

Nannofossil marl with rare mud-eaters'tracks, cryptohorizontally laminatedNannofossil marl with rare mud-eaters'tracks, cryptohorizontally laminatedNannofossil marl with rare mud-eaters'tracks, cryptohorizontally laminated

Clay MineralFractions <O.Ol mm

Hydromica, mixed-layer (H-M),admixture of chlorite and kaoliniteMixed-layer (H-M), kaolinite

Mixed-layer (H-M), hydromica,kaoliniteMixed-layer (H-M), hydromica,kaoliniteMontmorillonite, kaolinite,chlorite, mixed-layer (Ch-H)Mixed-layer (M-H and Ch-H),kaolinite, quartzHydromica, mixed-layer (M-H),kaolinite, quartzMixed-layer (M-H and Ch-H),hydromica ,kaoliniteMixed-layer (M-H and Ch-H),hydromica, kaolinite, a smalladmixture of chloriteMixed-layer (M-H and Ch-H), hydro-mica, kaolinite, an admixture ofchlorite

Kaolinite, mixed-layer (M-H),hydromicaMixed-layer (M-H), montmorillonite,kaolinite, hydromicaMixed-layer (M-H), kaolinite,hydromicaMixed-layer (M-H and H-M),kaolinite

Mixed-layer (M-H), zeolite

Palygorskite, zeolite

Montmorillonite, palygorskite, aa small admixture of kaolinite,quartzMontmorillonite, an admixture ofpalygorskitePalygorskite, mixed-layer (H-Ch)

Palygorskite, mixed-layer (M-H),a small admixture of kaolinite


Organogenic-clay sediments(zone of influence of volcanism)

Organogenic-clay sediments(reworking zoneby bottom organisms)

Organogenic sediments(zone of quiet sedimentation)

Organogenic-clay sediments(zone of quiet sedimentation)

Associations ofClay Minerals

Mixed-layer-hydromicaceouskaolinitic (sometimes with anadmixture of hydromica,chlorite, or montmorillonite)

Mixed-layer-kaoliniti c-hydromicaceous

Zeolite-palygorskitic-mixed-layer

Palygorskite-montmorillonitic(sometimes an admixture ofmixed-layer minerals andkaolinite)

yy

o

w

<:<wW

w

5

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


Age

o

§Isi

io.25<

s

ix>• Ö

<u

13


4-2, 68-70

4-3,110-120

5-2,35-36

5-3, 35-36

5-4, 97-99

8-2, 64-66

10-2,88-90

12-1,113-115

14-4, 99-100

15-2, 98-100

16-2, 17-18

17-2, 141-143


Claystone, silty with interbeds ofcoarse silty and fine aranaceousmaterialClaystone, silty with interbeds ofcoarse silty and fine aranaceousmaterialClaystone, silty with interbeds ofcoarse silty and fine aranaceousmaterialClaystone, silty with interbeds ofcoarse silty and fine aranaceousmaterialClaystone, silty with interbeds ofcoarse silty and fine aranaceousmaterialClaystone, silty, with small obliquenot unidirectional and gentlewavelike laminationClaystone, silty, with small obliquenot unidirectional and gentlewavelike laminationClaystone, silty, with interbeds ofcoarse-silty and fine-arenaceousmaterial with oblique laminationClaystone, silty, with interbeds ofcoarse-silty and fine-aranaceousmaterial with oblique laminationClaystone, silty, with interbeds ofcoarse-silty and fine-aranaceousmaterial with oblique laminationClaystone, silty, with interbeds ofcoarse-silty and fine-aranaceousmaterial with oblique laminationAlternation of interbeds of coarse-grained silt stone with nannofossilcontaining marls and claystone withoblique intertruncated lamination

Clay MineralFractions <O.Ol mm

Hydromica, mixed-layer (H-M), anadmixture of chlorite

Hydromica, mixed-layer (Ch-H)and (H-M), an admixture of kaolinite

Hydromica, mixed-layer (H-Ch), anadmixture of chlorite and kaolinite

Mixed-layer (M-H) and (Ch-H),hydromica, an admixture of chlorite,kaolinite?Mixed-layer (M-H and Ch-H), hydro-mica, chlorite

Montmorillonite, mixed-layer (Ch-H),an admixture of chlorite

Mixed-layer (M-H and Ch-H), hydro-mica, chlorite, palygorskite

Mixed-layer (H-M), hydromica,chlorite, palygorskite

Mixed-layer (M-H), hydromica,chlorite

Mixed-layer (M-H) and (H-Ch)

Mixed-layer (M-H and H-M) a smalladmixture of chlorite

Mixed-layer (M-H), and admixture ofpalygorskite


Silty-clayey sediments(zone of quiet sedimentation)

Silty-clayey sediments(zone of weak currents)

Silty-clayey sediments(zone of weak sea currents)


Hydromica ceous-mixed-layer,with an admixture of kaolinite,

Mixed-layer-hydromicaceous,with an admixture of chlorite,montmorillonite, kaolinite?

Mixed-layer-hydromicaceous-palygorskitic

o

W

>•zö

awzw

>zoGOmσüwzH

TABLE 5 - Continued

Age

CD

<OOO<U

P-iIH

α>ftft3

•SaεoO

<fi

C.2ft

<J

c c crt Λ rt•-j a "5

ε.s go C +->

«*-< ^ H-l


18-2, 136-138

19-1,91-93

20-2, 68-71

23-4, 100-102

24-3, 86-88

24-5, 18-19

26-3, 90-92

32-4, 68-70

34-4, 68-71

44-2, 40-42


Alternation of interbeds of coarse-grained siltstone with nannofossilcontaining marls and claystone withoblique intertruncated laminationAlternation of interbeds of coarse-grained siltstone with nannofossilcontaining marls and claystone withoblique intertruncated laminationAlternation of interbeds of siltymarl and claystone with oblique,intertruncated laminationAlternation of interbeds of siltymarl and claystone with oblique,intertruncated lamination

Claystone, nannofossil containing, withinterbeds of silty-arenaceous materialwith oblique mtertruncated laminationGaystone, nannofossil containing, withinterbeds of silty-arenaceous materialwith oblique intertruncated laminationGaystone, nannofossil containing, withinterbeds of silty-arenaceous materialwith oblique intertruncated laminationQaystone, silty, with interbeds ofcoarse-silty and fine-arenaceousmaterial with oblique intertruncatedlamination

Alternation of nannofossil containingclaystone and siltstone with obliqueintertruncated laminationNannofossil containing marl alternatingwith interbeds of silty material withoblique intertruncated lamination

Gay MineralFractions < 0.01 mm

Montmorillonite, palygorskite, sepiolite,chlorite

Montmorillonite, mixed-layer (Ch-H),palygorskite, and admixture of chlorite

Montmorillonite, mixed-layer (Ch-H),an admixture of kaolinite

Montmorillonite, mixed-layer (H-M),kaolinite

Mixed-layer (M-H), kaolinite

Mixed-layer (M-H), kaolinite

Mixed-layer (M-H), hydromica,kaolinite

Mixed-layer (M-H), hydromica,kaolinite

Hydromica, montmorillonite, kaolinite,chlorite

Hydromica, mixed-layer (Ch-H),kaolinite


Silty-clayey sediments(zone of quiet sedimentation)

Silty-clayey sediments(zone of weak sea currents)

Silty-clayey sediments(zone of currents in thedeltaic area)


Montmorillonite-palygorskite-sepiolitic

Montmorillonite-mixed-layerwith kaolinite

Mixed-layer-hydromicaceous-kaolinitic

Hydromica-montmorillonite-kaolinitic

Note: Packets in mixed-layer minerals: M = montmorillonitic, H = hydromicaceous, Ch = chloritic. The first components in the associations have the largest amounts.


silicate minerals can differ even within the lithologicsection of one hole. In continental facies of Africa,palygorskites are related chiefly to carbonate sedi-ments. Likewise, in Leg 41 sediments the most sig-nificant amounts of palygorskite occur with slightlycarbonaceous clays and claystones.

Comparatively pure monomineralic palygorskitic orsepiolitic clays, nearly devoid of terrigenous materialand associated with some dolomite, are likely to formthrough a chemogenic or chemogenic-diageneticprocess. Formation of these rocks in Holes 368 and 370occurred at depths below the critical level of carbonateaccumulation, very near the African continent.Chemogenic formation of palygorskite and sepiolitewas possible here not under arid conditions, as usuallyoccurs, but in an environment of normal marinesedimentation, owing to an intense inflow of dissolvedMg cations, possibly as Mg(OH)2, and of silica fromthe area of tropical weathering and laterite formation.1

Such weathering and laterization is known to haveoccurred on the African continent (Millot, 1964).Heating of the oceanic waters may also have beenimportant near the continent.

Palygorskitic clays with admixtures of terrigenousparticles and accompanying clay minerals could nothave resulted from mineral selection during eolian orfluvial transport. Authigenic, chemogenic-diageneticformation of palygorskitic clays therefore seems mostprobable.

The second type of palygorskitic clays and clay-stones, with interbeds of sandy-silty material (Holes368 and 370), was formed by transfer of palygorskitic,lacustrine, and marine epicontinental sediments,probably as turbidity currents from the Senegal Riverdelta (Hole 368) or from a submarine canyon (Hole370) into the deep oceanic environment. The clayfraction usually contains palygorskite, mont-morillonite, kaolinite, hydromica, mixed-layerminerals, occasional chlorite, etc. This is true in LowerCretaceous sediments of Hole 370 and in upper Eoceneto lower Miocene sediments of Holes 368 and 370.Millot (1964) recognized accompanying minerals insediments of similar age in the continental facies ofadjacent Africa. These palygorskitic-sepiolitic rocks ofthe arid belt are widely developed in northwest Africa;their thickness sometimes reaches 500 meters (Millot,1964), and they would have been susceptible to winderosion and transport to the ocean.

The third and fourth facies types of palygorskite-bearing rocks are represented by organogenic lime-stones with interbeds of clay matter and nannofossilmarls. These are typical pelagic sediments of an opensea or of an oceanic basin which bordered theundrained coast of Africa during the arid climate ofEarly Cretaceous and Eocene times. To explain theirpresence, the magnesian silicates of the regions of Holes366 and 369 would seem to require epicontinental seasin the Late Cretaceous and the Eocene, with extremelyshallow, strongly heated water, and chemogenic sedi-mentation of palygòrskite-sepiolite, followed by

subsidence to a great depth. Or they could have beencarried into these basins from the arid zone of Africa bywind.

The palygorskites in the clay fraction of pelagicsediments from Holes 366 and 369 are terrigenous, asconfirmed by the presence of such minerals asmontmorillonite, mixed-layer minerals, kaolinite, andquartz. Also, Pow-foong Fan and Rex (1972) say thatin lower Pliocene to lower Miocene limey nannofossiloozes of Hole 136, palygorskite occurs with mica,montmorillonite, kaolinite, quartz, hematite, andchlorite in the <2 µm fraction. They give a similarassociation of minerals accompanying palygorskite,with small variations, for Mesozoic and Cenozoicsediments of Hole 135 and Holes 137 to 144. Von Radand Rösch (1972) also point out that in many samplesof pelagic and hemipelagic clays from Leg 14,palygorskite is associated with montmorillonite,kaolinite, and quartz. Even in the Recent epoch, lessfavorable for palygorskite formation than the Cenozoicand Late Cretaceous, continent-to-ocean transfer ofpalygorskite particles occurs, as does the formation ofpalygorskite-bearing oceanic sediments.

TABLE 6Chemical Composition of Magnesian Silicates of Oceanic Sediments

of Carboniferous Deposits of the Mid-Carbóniferous Russian Platform

Components

SiO2

TiO2A12°3F e2°3FeOMgOCaOK2°Na2OH2O-H2O+Total

Palygorskite

Oceanic

Hole 368Sample 29-1, 61-63

early Eocene

53.440.489.603.970.449.552.361.260.578.369.97

100.00

Platform

58.220.45

10.713.020.338.791.031.530.408.566.96

100.00

61.730.43

11.013.080.337.080.502.400.037.306.11

100.00

Sepiolite

Platform

52.61-1.580.710.36

19.954.820.271.026.72

11.96100.00

53.52-1.640.340.44

19.468.470.432.504.318.89

100.00

TABLE 7Molecular Mg:Al Ratio in Oceanicand Russian Platform Palygorskites

Locality Geological Age

MolecularRatioMg:Al

'Other evidence from Leg 41 suggests that Mg could also besupplied by brines emanating from evaporitic sediments deeper in thesection.

Hole 368Sample 29-1, 61-67 cm

Russian Platform

Early Eocene

Middle CarboniferouskKashirsky horizon C2

Steshevsky horizon C^

C 2c|c kC 2c k

1:1

1:1

1:1

1:1

2:1

2:1

2:1

1097


368 10.6

31-2 (78-80)

\J

368

37-4 (80-82)

\J

368

34-2 (61-62)

36839-5 (69-70)

3-34 m n3.25 4.67

3.12 | 4.08 5.074.26

36836-2 (38-40)

36846-4 (60-61)

36836-3 (37-39)

368 12.17

54-3 (71-73)

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

1098


369A49-4 (69-70)

Figure 3. (Continued).

Evidence Against Volcanic Origin of Palygorskite andSepiolites in Leg 41 Sediments

The following evidence argues against the assumedeffect of hydrothermal flow of magnesian solutions: theoccurrence of palygorskites and sepiolites in differentfacies; their occurrence in carbonate rocks peculiar todeep-sea red clays; monomineral palygorskite clayswith no traces of hydrothermal metasomatic replace-ment, decoloration, or disturbance of textural features(lamination), and frequently without pyroclastics.

The isotopic compositions of sulfur and carbon inpalygorskite-bearing rocks of Holes 366, 368, and 370provide an important additional argument. Table 8shows that the isotopic composition of sulfide sulfur ismostly negative, about -2O°/oo. Such values are peculiarto sedimentary-diagenetic sulfides that result fromsulfate reduction. They may mean that sulfidesappeared in the uppermost layer of sediments underconditions of free exchange of the oozy and bottomwater; i.e., sediments may have inherited sulfide sulfurfrom the moment of their accumulation, at the earlieststages of diagenesis.

Despite low concentrations of carbonates inpalygorskite-bearing clays, we attempted to determinethe isotopic composition of the carbonate (Table 9).Some carbonate has carbon with an isotopic composi-tion that is lighter than normal sea carbonate. Thelatter is characterized by the value <513C = 0, whereas<513C of the organic matter is approximately -25°/oo(Table 9). Table 9 shows the data on Hole 368 and, forcomparison, those on core material from Hole 366,which contains considerable amounts of carbonate.When treated with hydrochloric acid, the samples fromHole 368 liberate CO2 only after the reaction vessels areheated, which suggests a dolomitic carbonate composi-tion. The isotopic composition of carbonate carbon inHole 368 is intermediate between extreme values of

δ'3C representative of normally sedimentary rocks andbiogenic carbonates. This means that the carbonatecarbon includes considerable carbon from organicmatter.

Pyritization and carbonation (dolomitization) of thesediments are related to diagenetic, and evidently toearly diagenetic, transformations. We found no indica-tions of hydrothermal activity in the isotopic composi-tions of sulfur and carbon.

Such observations on genesis of palygorskite andsepiolite do not deny, however, local processes oftransformation of magnesian silicates closely related tovolcanism and activity of hydrothermal solutions. Forexample, the transformation of volcanogenic mont-morillonite into palygorskite may occur in interstitialwaters with a high content of magnesium cations.

Another type of palygorskite formation is related tothe occurrence of palygorskitic veins in sediments andas coating on manganese nodules. And finally, Bonattiand Ioensuu (1968) have described a third type:formation of palygorskite under the influence of hydro-thermal solutions during serpentinization of iron-richminerals in Atlantic abyssal sediments.

With all this in mind, however, we cannot deny therole of chemogenic sedimentation and chemogenic-diagenetic formation of magnesian silicates and fluvialor eolian transport of these minerals from arid zonesinto oceanic sediments.

OTHER CLAY MINERALS

Montmorillonite occurs in rock facies reflective ofquiet sedimentation by weak currents (Millot, 1964)(Hole 368, Upper Cretaceous; Hole 366, lower Eocene).It results from weathering of soils in tropical areas withlong dry seasons. In the tropical dry climate, soils withmontmorillonite are produced in poorly draineddepressions by interaction of silica, alumina, andmagnesium liberated by hydrolysis during hot humidperiods. Millot (1964) points but, however, that suchformation of montmorillonite was, in principle,possible not only on the continent but directly in thosesedimentary depressions where molassic sedimentswere formed.

Kaolinite in the Leg 41 sediments resulted fromtropical weathering processes and subsequent fluvialand/or eolian transport. The hydromica is mostlydioctahedral illite without expanded packets and isprobably detrital. The chlorite may have resulted fromwashout of magmatic rocks or outflow from arid zones;it is not well preserved during laterization. The mixed-layer minerals are of two types: illite-montmorilloniteand chlorite-montmorillonite. The illite-montmoril-lonite gives asymmetric X-ray diffraction peaks: at13.6Å (untreated); at 17.3Å (treated with glycol); and at9.9Å (heated to 550°C). The chlorite-montmorilloniteshows peaks at 14.5Å (untreated); at 16.99 A (treatedwith glycol); and at 13.8Å (heated). Both types ofmixed-layer minerals resulted from degradation ofminerals on the African continent.

CONCLUSIONS

After studying mineralogy and facies types ofpalygorskitic and palygorskitic-sepiolitic oceanicsediments of Leg 41, we conclude the following:

1099


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


29-1,68-70

30-2,51-53

30-2,58-60

31-2, 78-80

31-2,71-73

34-2,51-53

34-2,61-62

36-3, 37-39

36-3, 68-70

37-4, 80-82

39-5, 69-70

40-3, 68-70

41-2,61-63

41-2, 70-70

42-2,62-63

44-4, 68-70

45-4, 84-96

45-4, 91-92

46-4, 60-61

47-5,69-70

FaciesType of Sediments

Red deep-sea clays(quiet sedimentation)Red deep-sea clays(quiet sedimentation)Red deep-sea clays(quiet sedimentation)Red deep-sea clays(quiet sedimentation)Red deep-sea clays(quiet sedimentation)Red deep-sea clays(quiet sedimentation)Red deep-sea clays(quiet sedimentation)Red deep-sea clays(quiet sedimentation)Red deep-sea clays(quiet sedimentation)Red deep-sea clays(quiet sedimentation)Red deep-sea clays(quiet sedimentation)Red deep-sea clays(quiet sedimentation)Red deep-sea clays(quiet sedimentation)Red deep-sea clays(quiet sedimentation)Red deep-sea clays(quiet sedimentation)Red deep-sea clays(quiet sedimentation)Red deep-sea clays(quiet sedimentation)Red deep-sea clays(quiet sedimentation)Red deep-sea clays(quiet sedimentation)Red deep-sea clays(quiet sedimentation)

Associations of Clay Minerals


Admixture of sepiolite

Palygorskite, admixture ofmixed-layer mineralPalygorskite, admixture ofmixed-layer mineralPalygorskite

Palygorskite

Palygorskite

Palygorskite-sepiolite

Palyg or skite-sep iolite



Sepiolite-palygorskite







Sepiolite, palygorskite,montmorillonite, quartzSepiolite, palygorskite,montmorillonite

Age

IuoW>,

3

Cβ

ö

3

Concentration(mg/g)

6.5

7.3

2.3

2.3

0.9

5.5

7.4

42.9

15.4

15.6

1.3

3.6

13.6

4.6

14.5

3.6

12.5

14.4

0.5

13.6

6 34(7oo)

-23.3

+15.6

-

-20.2

-23.4

-22.2

-22.2

-24.9

-28.4

-27.9

-19.5

Note: Analyses by V. I. Vinogradov.

TABLE 9Isotopic Composition of Carbonates in

Deep-Sea Holes of Leg 41


368-27-3, 41-43368-30-2,51-53368-34-2,51-53368-36-2, 79-81368-37-4,71-73368-45-4, 84-86366-2-3, 82-84366-3-3, 70-72366-7-3, 72-74366-11-1,50-52366-19-1, 105-107366-21-2,61-63366-24-2, 106-108366-40-3, 74-76

Concentrationof CO2 (mg/g)

3.41.5

15.33.41.04.4

70.4169.2190.7166.5132.0198.0

52.8165.0

δ 1 3 C

(7oo)

-13.8-18.9-12.4-14.9-18.0

—+4.2+3.5+3.3+3.2+4.2+2.8+2.7+3.1

1) Three genetic types of magnesian silicate rockshave been distinguished.

a. The first type is pelagic palygorskitic-sepioliticclay with dolomite, but without terrigenous orvolcanogenic material. Formation occurs bychemogenic-diagenetic processes in the pelagic zoneof the ocean adjacent to a continent with tropical orarid climate. The zone is characterized by anabnormally intense inflow of magnesium [apparentlyin the form of Mg(OH)2] and silica from the areas oflaterite formation, and by irregularly high heating ofoceanic waters. ;

b) The second type is palygorskite-bearing clayand claystone with interbeds of silty material,frequently contains mica, montmorillonite, chlorite,or kaolinite. This type formed under the influence ofsuspension currents transporting deltaic sedimentsfrom the Senegal River and an underwater delta orcanyon in the vicinity of Hole 370.

c) The third type is pelagic limestone andnannofossil marl with interbeds of palygorskite-bearing clay material. The clay fraction <l µm ispolymineral, and includes palygorskite, mont-morillonite, mixed-layer minerals, kaolinite, and

1100


quartz. Formation of this type of palygorskite-bearing deposit took place in carbonate pelagicsediments near drainless parts of the arid continent;particles of palygorskite were supplied by eoliantransport.

d) On the basis of Leg 14 cores, a fourth genetictype of palygorskitic-zeolitic clays, not observed byus in Leg 41 sediments, may result from diagenetictransformation of volcanic ash (von Rad and Rösch,1972).2) On the basis of new data, fluvial and eolian

transport of palygorskite-sepiolite particles seemspossible, as does redeposition of the particles. Ourconclusions are in good agreement with Wirth's (1968)data on eolian transport of palygorskite from the aridSenegal River area. The source for palygorskite in theRed Sea was also shown by Müller (1961) to becontinental, as was that for palygorskite in the PersianGulf (Hartmann et al., 1971). The occurrence ofpalygorskite and sepiolite in Upper Cretaceous andPaleogene sediments only, and their paragenesis withauthigenic clinoptilolite and with slowly deposited claysabout 20-25 m.y. old confirms the diagenetic origin ofthese magnesian silicates (von Rad and Rösch, 1972).Palygorskite and sepiolite probably are not forming atpresent. The occurrence of palygorskite in the surfacelayer of Atlantic Ocean sediments would seem tosuggest their formation in oceanic sediments near thecontinents, but it is more likely a result of fluvial oreolian transport.

3) Palygorskite is detrital, and its quantitativeincrease toward the continent cannot always beobserved, depending on the submarine topography andthe nature of suspension currents.

4) We agree with von Rad and Rösch (1972) that asurplus of cations in interstitial waters is necessary foroptimal chemogenic or chemogenic-diagenetic forma-tion of sepiolite and palygorskite. Origins can varyextensively (Hathaway and Sachs, 1965). We recognizethe inflow of silica by rivers draining the regions oflaterization as a contributing factor for formation ofmagnesian minerals in sediments of Leg 41.

5) Most other minerals of the clay fraction of Leg 41oceanic sediments are detrital. Kaolinite is known toabound in the crusts of laterization. Dioctahedral micaand trioctahedral chlorite are unstable in the profile oflaterization, but they can remain preserved to a certainextent; this might explain their limited quantitativedistribution in sediments of Leg 41. They can becomemore abundant during increasing aridity. In addition,chlorite can be related to washout of old magmatic

rocks of northwest Africa. Montmorillonite and mixed-layer minerals could have been brought from thelateritic areas of arid zones, or could have resulted fromdiagenetic alteration of volcanogenic material.

REFERENCES

Bonatti, E. and Ioensuu, O., 1968. Palygorskite from Atlanticdeep-sea sediments: Am. Mineralogist., v. 53, p. 975.

Chambers, G.P., 1959. Some industrial applications of theclay minerals sepiolite: Silicates Industr., v. 24, no. 4.

Elouard, P., 1959. Etude géologique et hydrogéologique desformations sédimentaires du Guebla Mauritanien et de laValée du Senegal: These Sci.

Goldberg, E.D. and Griffin, J.J., 1970. The sediments of thenorthern Indian Ocean: Deep-Sea Res., v. 17, p. 513-537.

Hartmann, M., Lange, H., Seibold, E., and Walger, E., 1971.Oberflachensedimente im persischen Golf und Golf vonOman Geologisch-hydrologischer Rahmen und erste, sedi-mentologische Ergebnisse: "Meteor" Forchungs-ergebnisse, v. 4, p. 1.

Hathaway, J.C. and Sachs, P.L., 1965. Sepiolite andclinoptilolite from the Mid-Atlantic Ridge: Am. Min-eralogist., v. 50, p. 852.

Martin-Vivaldi, J. and Cano-Ruiz, J., 1956. Contribution tothe study of sepiolite. pt. Ill: Nat. Res. Council Publ., 456.

Millot, G., 1964. Géologie des argiles: Paris (Masson et Cie).Müller, G., 1961. Palygorskit und sepiolith in tertiaren und

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43. PALYGORSKITE, SEPIOLITE, AND OTHER CLAY MINERALS IN LEG 41

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