Characteristics of manganese nodules from the Central Indian Basin: Relationship with the sedimentary environment

Marine Geology, 101 (1991) 249-265 Elsevier Science Publishers B.V., Amsterdam

249

Characteristics of manganese nodules from the Central Indian Basin: Relationship with the sedimentary environment A. Martin-Barajas a'l, E. Lallier-Verges b a n d L. Leclaire c'* aLaboratory for the Geochemistry of Sedimentary Rocks, University of Paris South, Orsay, France bLaboratory for the Geology of Organic Matter, University of Orleans, 45067 Orleans Cedex, France CMNHN Geology Laboratory, 43 rue Buffon, 75005 Paris, France (Received S e p t e m b e r 12, 1990; revision accepted J a n u a r y 29, 1991)

ABSTRACT Martin-Barajas, A., Lallier-Verges, E. and Leclaire, L., 1991. Characteristics of manganese nodules from the Central Indian Basin: Relationship with the sedimentary environment. Mar. Geol., 101: 249-265. The hydrogenetic and diagenetic manganese nodules from the CIB show an unequivocal genetic relationship with Neogene sedimentological patterns. Hydrogenetic nodules were observed at the top of the sedimentary column and interstratified in thin sequences of biosiliceous sediments and underlying Miocene(?) red clays.In cores from topographic highs, Early to Late Pliocene radiolarian fauna were found at the base of the biosiliceous deposits. These condensed biosiliceous sediments are less than 4.0 m thick, and periods of non deposition and/or erosion may have occurred. In the central deep area (11-15 ° S), significant biogenic deposition began during the Early to Late Pliocene as a result of the development of a high biogenic productivity belt to the south, producing the favourable conditions for diagenetic accretionary processes for Mn nodules. This indicates growth of hydrogenetic nodules prior to the Late Pliocene and the subsequent inception of diagenetic accretion. Formation of the most recent diagenetic nodules is associated with higher rates of sedimentation in the deep-sea troughs, where the siliceous sediments are much thicker. This should promote the diagenetic mobilization of Mn and its precipitation under oxic and suboxic conditions. Nevertheless, diagenetic nodules are restricted to the upper 40 cm of sediments younger than 400,000 years, suggesting fast-growing diagenetic nodules and the dissolution of buried nodules below the first 50 cm of siliceous oozes. Hydrogenetic nodules are formed by dense layers of 6MnO 2 Fe(OH)a and amorphous silica, and they show smooth texture and botryoidal shapes. Analysis of bulk and selected portions of layered crust or rind shows very low Mn/Fe ratios ( < 2) and relatively high Co and Ti contents. In most cases, the cores of hydrogenetic nodules are fragments of altered ash layers from the Indonesian Volcanic Arc, which is located more than 2500 km to the east. The ash layers are also interstratified with Miocene(?) red clays. Diagenetic nodules show a granular texture and comprise concentric layers with dendritic or columnar structures, mainly of I0 A manganate. Higher Mn, Ni and Cu contents are observed in this phase. Late diagenetic enrichment of these nodules is continuous within the upper 40 cm of Recent ( < 0.4 m.y.) biosiliceous sediments, which favours (a) the replacement of the silicate phases (biogenic silica, clay minerals and volcanic glass) by F e - M n oxides, (b) a metallic uptake (Cu > Ni) that enhances the stability of early diagenetic 10/~ manganate (buserite), and (c) the formation of todorokite. Some nodules, referred to as mixed in the literature, show hydrogenetic internal layers which grade outward to a diagenetic crust. This transitional character suggests slow changes in the sedimentary environment as growth advances. The nodules of the CIB and the East Equatorial Pacific (EEP) are similar in terms of both metallic composition and accretionary patterns. However, the nodules of the CIB are considerably younger and present a continuous accretionary history. The history of the manganese nodules from the CIB is related to the post-Late Miocene sedimentary and geodynamic evolution of this basin.

a'lPresent address: CICESE, Epinoza 843, Ensenada, B.C., Mexico tDeceased 0025-3227/91/$03.50

© 1991 Elsevier Science Publishers B.V. All rights reserved.

250

Introduction The manganese nodules from the Central Indian Basin (CIB) (Fig. 1) are poorly understood compared with those from the East Equatorial Pacific (EEP). Early works (Bezrukov and Andrushchenko, 1974; Leclaire and Perseil, 1979; Perseil and Jehanno, 1981; Cronan and Moorby, 1981) indicate that the nodules from the CIB have metal contents and mineralogical features which are comparable with the Ni + Cu-rich nodules from the EEP. Recent published data suggest that the growth of CIB nodules follows accretionary processes that are similar to those of the EEP nodules, and these characteristics are related to diverse sedimentary environments which produce either diagenetic or hydrogenetic types of nodules (Rao, 1987; Mukhopadhyay, 1987; Jauhari, 1987; Ahmad and Husain, 1987). The purpose of this paper is to establish a relationship between the evolution of the sedimentary patterns in the CIB, the accretionary processes involved in nodule growth and the late diagenetic enrichment which produced Ni+Curich nodules. Detailed descriptions and analytical data are presented in Martin-Barajas (1988). Methods The nodules and the associated sediments were sampled during the MD14 and MD28 cruises of the R.V. Marion Dufresne between 50 and 17°S and 74 ° and 87°E (Fig. 1). The samples were collected using box cores (SIPAN, 1 m 2 and AET, 0.25 m2), piston cores (12-18 m long and 10 cm diameter) and dredging. The cores and representative dredge samples were preserved at 4°C and 80% humidity. These samples constitute a part of the Museum National d'Histoire Naturelle (MNHN) GEOCORES collection (Caulet et al., 1984). The manganese nodules were studied at different scales in order to classify all macro- and microscopic features. A systematic description (size, shape, texture and internal structure) of 50 nodules from twelve dredge hauls allowed us to identify the main morphological types using the AFERNOD system (Pautot and Hoffert, 1984); the na-

A. MARTIN BARAJAS ET AL.

ture of nodule nuclei from samples from the central deep area was also investigated (Martin-Barajas, 1988). Selected samples were studied in order to identify the relationship between chemical and mineralogical composition at different scales. Samples of the main internal structures (after Marchig and Halbach, 1982) were collected using a microdrill. Thirty thin sections of nodules and host sediment were studied and described using reflected light microscopy and scanning electron microscopy (SEM). Bulk samples were analyzed for Mn, Fe, Cu, Ni, Zn and Co by atomic absorption (AA) using the soluble (4N HCI) fraction. Selected samples of nodule crusts and nuclei were analyzed using an energy-dispersive spectrometry (EDS) probe coupled to the SEM (Link 10000 system). Microprobe analyses (Camebax) were performed on thin sections and polished nodules. To avoid the effects of dilution by the silicateinsoluble phases, the chemical data are often used in the form of inter-element ratios for interpretation. The relative metal content is expressed as Ni/ Mn, Cu/Mn, Mn/Fe and Co/Fe and the C o - N i Cu ternary diagram (Fig. 2), with Co on the hydrogenetic apex and Ni and Cu on the diagenetic base (Halbach et al., 1983; Aplin and Cronan, 1985). Mineral determinations of Fe-Mn-rich crust and cores were made using a Siemens X-ray diffractometer CuKa monocromator with a Ni filter. Mn-oxide phases were studied using transmission electronic microscopy (TEM, Philips 300). The associated sediments were described on smear slides and analyzed by X-ray diffraction. The age of the sediments was determined using the radiolarian assemblage and was calibrated with a paleomagnetic scale (Johnson et al., 1989). The age determinations have an accuracy of the order of 100,000 years and were made by J.P. Caulet at the Geology Laboratory of the MNHN in Paris. Modern sedimentary environment of the CIB Modern sedimentation in the study area is controlled by three main parameters: (a) the equatorial productivity belt, (b) the terrigenous input and (c) the water depth of deposition. In the study area the sediment consist of siliceous oozes. These are widespread in the central deep area at depths

251

MANGANESE NODULES AND SEDIMENTARY ENVIRONMENT IN THE CENTRAL INDIAN BASIN

¢1) 0

o

0

0

0

to

I

ooo~~ ~. 0

,.,

o

m

"

0

0

0

Z

901~1 .I.S ~

~'~

~'~

_

~

0o6

~

I

I .=_ r-,

e~

i:

(-.,

o r~ 0

L~ ,.,q

.=_

b

~ ~

~

E ,.-t

\

/ .=. e.,

0

//"

>.< ow

.r-~

i.:'::: JJJi.:.:',.

=_ f

~b

.. ,..:,

o 0

o

0

o

t,

%

252

A. MARTINBARAJASET AL.

Co

Co

//

/

ST :5

\\

II AETI9C) !# CPITC)

\ \

(~AET 181I A

I

I

CP

17([]/Iw

~, i ST5

/! / !

Ni

i

/

/

"-;~o o_t;'Ik ° o L O = = - t t i ~IL , \ so ,~

A

HYDROGENETIC NODULES FROM THE EASTERN AND SOUTHWESTERN FLANKS OF THE ClB

B

D,.GENE~CNODUL~ FROMTHE OEEPE. ZONE OF THE C,B

C

HYDROGENETIC AND MIXED NODULES FROM BATHYMETRICHIGHS IN THE C IB

, Cu

PAD ~'~/ / ~ST5 j

~

~

Co

-

30)'

~

A ,ST cP 27 2:5

:50

/CP 3 0 ( )

z4 cP 2~ . . /

CP 29

CP28

I~11~... 70

CP :51 ST7

25a~ CP26

ST8

,-w

'11", "% ~ 50

}0 40 Cu

Fig. 2. Three-component diagram showing the relationship between Ni, Cu and Co in nodules from the CIB. Dredges CP23, CP30 and BL2 contain hydrogenetic and mixed type of nodules. Dredges CP24, CP25, CP26, CP27, CP28, CP29 CP31, ST7 and ST8 contain diagenetic nodules (data from Table 2).

ranging from 4800 to 5500 m. Carbonate nannooozes cover most topographic highs (above the 4500 m depth) located along the flanks of the Chagos-Lacadive Ridge and the Ninety-East Ridge (Fig. 1). In the CIB the CCD is situated between 4500 and 4800 m (Kolla et al., 1976). Pulses of sediments from the Bengal Fan have been found as far south as 7°S (Emmel and Curray, 1984). However, two dredge hauls located at 10°

and 8°S (CP20 and CP18) contain fragments of turbidite coated with an Fe-Mn crust, which may represent ancient pulsations of the Bengal Fan. Furthermore, geochemical evidence of terrigenous input as far as 8°S is suggested by Nath et al. (1989). To the south, the transition between siliceous oozes and red clays occurs at approximately 14°S and denotes the limit of the high biogenic productivity belt. Some works, however, suggest

MANGANESE NODULES AND SEDIMENTARY ENVIRONMENT IN THE CENTRAL INDIAN BASIN

that modern biosificeous sedimentation is restricted to the area north of 12° S (Johnson et al., 1989).

Neogene sedimentary sequence and tectonic environment in the CIB The sedimentary sequence in the CIB has been described elsewhere (Pimm, 1974; Denis-Clocchiatti, 1982; Fr6hlich, 1981). The oldest sediments collected during the MD14 and MD28 cruises are late Eocene carbonate oozes which are characterized by the presence of palygorskite (DenisClocchiatti, 1982). These sediments underlie a red clay of probable Miocene age (Pimm, 1974; Fr6hlich, 1981). Southeast of the study area, Oligocene deposits consist of calcareous nanno-oozes with phillipsite and clinoptilolite. These deposits are covered by 1 m of red clay. The Miocene(?) red clays are composed of an authigenic fraction (mainly Fe-smectite and phillipsite) and a detrital assemblage consisting of terrigenous material (quartz, kaolinite, iilite and chlorite) and biogenic debris. The red clay is unconformably overlain by the siliceous oozes (Fig. 3). In the northern part of this area (8°-10°S), the siliceous oozes were deposited after the Late Miocene/Early Pliocene (Pimm, 1974), whereas in the southern part the accumulation of siliceous ooze began during the Middle to Late Pliocene (Table 1). The biosiliceous deposits are composed mainly of diatoms and radiolarians at different stages of dissolution. The siliceous deposits may also contain amorphous Si-Fe complexes and, if so, the sediments change colour from white or beige to brown, indicating much dissolution of biogenic silica. The biogenic silica in oozes seems unstable and bottom water could enhance its dissolution, as suggested by the high concentration of dissolved silica in the interstitial waters (Nath and Mudholkar, 1989). To the south the siliceous sediments (Late Pleistocene/Recent) thin to a few centimetres above the red clays. Piston cores in the central deep area show that the siliceous sediments display significant differences in thickness related to submarine topography: the siliceous sediments are thinner on top of the topographic highs, and contain interstratified hydrogenetic nodules, presumably related to

253

breaks in deposition (Fig. 3 and Table 1). The complete biosiliceous series as well as part of underlaying red clays was sampled on these highs. Layers of altered ash are found within the red clays (Martin-Barajas, 1988). In contrast, the siliceous deposits in the deep-sea troughs are thick and contain diagenetic nodules and rhyolitic pumice in the upper 40 cm. This sedimentary pattern seems to be controlled by the topographic relief and by bottom-water circulation. Weissel et al. (1980) and Stein and Okal (1978) have provided the evidence for the tectonic deformation of the Indian plate. Recent data from north of the study area indicate that the oceanic plate has undergone south-north compressive stress which, since Late Miocene, has affected the overlying sediments (Wiens et al., 1985; Curray and Munasinghe, 1989). This deformation may have produced the bathymetric pattern of highs and lows which in part control the sedimentation in the CIB.

Manganese nodules The chemical and mineralogical analyses indicate that the manganese nodules from the CIB can be interpreted either as hydrogenetic or diagenetic types. These terms indicate the main processes involved in the formation of the nodules, although our results agree with those of other authors (Dymond et al., 1984; Calvert and Piper, 1984), and both types of the nodules are interpreted as resulting from growth by multiple accretionary processes.

Hydrogenetic nodules In our study, hydrogenetic deposits formed at the sediment/water interface are characterized by smooth, botryoidal textures, often with coalescing forms. The mean diameter of the nodules varies from 2 to more than 10 cm and systematic description shows that size and shape are related through nuclei shape and crust thickness (Fig. 4c-d). The hydrogenetic nodules have a 5-15 mm thick crust formed by compact layers of amorphous FeMn oxide phases or 6MnO2 Fe(OH)3 and amorphous silica. Amorphous silica is closely associated

254

A. MARTIN BARAJAS ET AL.

DEPTH u.

MD 5000

144 / ~ /

S ~

<--.4E N

IdD

MD 566

:373 I~- ~

MD , ~3. I '7 0 ~ ~,

MD 369

_~-~_

.oo

I

371

_,

-!

~,,=

=_-

- Z C -

"/

I

z_-z

MD .~-378//

~-~, z z-r-

MD

-~::3r:-

,____,,

MD 376

~_

~

~

Z-Z-

i

---

_

~-

/ z-z

• z-z z-z , z - _Z - z- . . - .Z -,

-5 -

Z-Z -z-"

,

\

-Z-

5 \

z-z-Z-

I

--

~

I~z~ ,.~

Z-Z

-z~_ ~ . -m - . i O

-

~

z

--:-

z

y

fo - , , - ~

----

--

--

2

---

-

z~z.

-

- --

z~_ ---

-----

~

--I0

Z-

Z

---

JZ- z Z H ° - ~ - ~ iO

~ ....

Z

-

Z-~: .... -

-

--

---

_zz~ iZ - :i 5 ---

z-z_ -

z-z- ~~I'~-

SILICEOUS OOZE

RED CLAY

~- ~

-~

.Z-Z-~

_z --

_z~_z

-'2-"C DETRITAL MUD

_

z-

PHILLIPSITE

_

BOUNDARY

PLIO/PLEISTOCENE

PALYGORSKITE O ALTERED ASH L A Y E R

HYDROGENETIC NODULE DIAGENETIC NODULE

15

Fig. 3. Sedimentarylogs from piston cores showing the lithological characteristics of sediments along a north-south transect in the studied area. Note that condensed sequences are located on the topographic highs. Vertical scale to the left is the depth to the top of the core. to the ferric hydroxide and often forms individual microlayers with it. The bulk and selected rind analyses indicate a Mn/Fe ratio of less than 2 and higher Fe, Co and Ti contents which inversely correlate with Mn, Ni, Cu and Zn (Tables 2 and 3).

The hydrogenetic deposits often show erosional disruptions of the layered structure. This can be interpreted as due to removal or erosion by sliding and/or bottom currents. Hydrogenetic nodules can also develop superficial dendritic (diagenetic) deposits on protected surfaces, mostly in lobate or mammillary forms (Fig 4c). In most cases the cores of hydrogenetic nodules are fragments of indurated sediments composed exclusively o f smectite or smectite-phillipsite with some associated feldspar. This indurated material is also found interstratified within the Late Miocene(?) red clays (Fig. 3), and represents layers of

altered ash from the Indonesian Volcanic Arc (Martin-Barajas, 1988; Martin-Barajas et al., 1988). These ash layers are 15-30 mm thick and the fragments exposed to the bottom water have acted as the main supply of nodule nuclei. In some cases this material shows intense bioturbation, which favours replacement by the F e - M n oxide and makes recognition in the cores difficult (Fig. 4c and d).

Diagenetic nodules. The diagenetic nodules are characterized by spherical or ellipsoidal shapes and granular surficial textures (Fig. 4a and b). Irregular and platy forms were also observed. Size varies from 2 to 5 cm mean diameter and the nodules are smaller than their hydrogenetic counterparts. The rounded shapes are generally associated with a well-devel-

MANGANESE NODULES AND SEDIMENTARYENVIRONMENT IN THE CENTRAL INDIAN BASIN

255

TABLE I CIB core description. A E T and SI = box core; M D = piston core Core

Depth (m)

Sample depth

Biozone NR"

Age (m.y.)

Thickness of Neogene biogenic deposits(m)

Sediment description

(m) MD215

5150

0.00 3.90

1 10-11

_<0.2 4.3-3.3

3.95

oxyhydroxide-rich siliceous ooze with hydrogenetic nodule on top

MD232

4525

0.00 2.80

I 8-7

0.2 2.9-2.5

4.80

diatom-bearing nanno-foram ooze, hydrogenetic nodules on top and interstratified at 4.30 and 6.30 m

MD370

5275

0.00 4.10

1 6

_<0.2 1.8-1.64

4.15

siliceous ooze with diagenetic nodules on top

MD371

5347

0.00

> 12.61

siliceous ooze

MD372

5314

0.00

> 17.61

siliceous ooze

MD373

5180

0.00 1.40 2.50 2.60

6 6 8

1.5-1.7 1.5-1.64 <2.6 Miocene?

2.70

hiatus on top, biosiliceous-rich red clay with hydrogenetic nodules on top and at 1.4 m, poorly preserved fauna at the base

MD374

5362

13.20

8

3.2-3.3

> 13.50

siliceous ooze with diagnetic nodules on top.

MD375

5279

0.00

>17.50

siliceous ooze

MD376

5190

0.70

3-4

0.4-0.7

0.78

oxyhydroxide-siliceous-rich red clay with hydrogenetic nodules on top

MD377

5230

0.00 0.25 0.57 0.65

4 6 5 9

0.85-0.80 1.5-1.6 1.1-1.5 3.3-3.5

0.55

biosiliceous-rich red clay

MD378

5229

0.10

3-4

0.7-0.4

1.0

biosiliceous-rich red clay with mixed-type nodules on top

AETI8

4430

0.00

<0.2

0.32

siliceous-calcareous-rich red clay with hydrogenetic nodule on top

AET19

4425

0.00

1

< 0.2

0.20

calcareous-rich red clay

AET21

5360

0.00 0.35

2 2

0.4-0.2 0.4-0.2

oxyhydroxide-rich siliceous ooze with diagenetic nodules in the upper 0.40 cm.

SI23

5080

0.00 0.18 0.45

1 2 5

<0.15 < 0.20 1.0-1.1

oxyhydroxide-rich siliceous ooze, hydrogenetic nodule on top, diagenetic nodules at 0.18 cm and 30 cm, 0xyhydroxide-rich siliceous ooze at the base

SI25

5152

0.00 0.25

1 3

_<0.15 _<0.40

oxyhydroxide-rich siliceous ooze, hydrogenetic nodules on top and at 0.05 m.

SI26

4925

0.00 0.27 0.65

1 1 1

<0.2 _<0.2 < 0.2

calcareous-bearing siliceous ooze, mixed nodule on top and diagenetic nodule at 0.28 m

"Radiolarian biozones after J o h n s o n et al. (1989)

256

A. MARTIN BARAJAS ET AL,

Fig. 4. (a) Thin section of diagenetic nodule (AET, 21-35 cm), showing typical dendritic internal structure. Nodule sampled 35 cm below sediment/water interface. (b) Diagenetic nodule within host sediment showing dendritic growth patterns. This nodule was collected 20 cm below the sediment/water interface (SI 26). (c) Thin section of a small hydrogenetic nodule. Note intense bioturbation and replacement of the nuclei. Nodule from dredge CP23. (d) Mixed type nodule showing internal compact hydrogenetic layer and external diagenetic patterns. Nodule from dredge CP30. oped crust and the irregular nodules are related to the nuclei shape and to less-developed crust. The platy nodules show an equatorial rind which shows preferential growth in horizontal directions within the sediment. In cross section, the crust is formed by concentric layers with dendritic or columnar structures disposed radially, producing a very porous texture (Fig. 4a-b). Crust thickness varies from 2 to 15 m m and this variation suggests that the nodules have different relative ages and that nuclei supply is continuous in time. The best developed nodules usually contain an altered core and could be oldest. In all cases, the nodule crust, which was analyzed using reflected light microscopy, reveals that the main component is a well-crystallized manganeseoxide which can be distinguished by a relatively high reflection index and by birefringence under polarized light. This well-crystallized phase is

mainly observed in botryoidal or dendritic structures as a primary deposit, but it does also occur as a late diagenetic product (Fig. 8a and b). Individual crystals can be observed with a high magnification lens ( > 8 0 × ). This material produces a 10 diffraction peak in X-ray difractogram, although in many cases a 7 A peak may be observed. The 7 A diffraction is more pronounced when the nodule has been exposed to air and dried at room temperature, while nodules preserved within the piston and box cores at 4°C and 80% humidity show only the 10 ~ pattern (Fig. 5). The bulk analysis of diagenetic nodules shows high C u + N i ( > 2 . 0 % ) with an Mn/Fe ratio of > 4 (Table 2). However the absolute metal content of the whole nodule depends on the crust/nuclei ratio and the stage of replacement of the core by the F e - M n oxide. During the systematic description of the nodule

MANGANESE NODULESAND SEDIMENTARYENVIRONMENTIN THE CENTRAL INDIANBASIN

257

TABLE 2

Chemical analysis of (bulk sample) nodules by atomic absortion (AA) in the soluble to 4N HC1 phase. *Data from bulk sample analysis by X R D spectrometry (quantitative analysis conducted with ZAF4 FLS program using standards). + D'Ozouville (1978). n.a. = not analyzed; bdl = below detection limit Sample

Mn (%)

Fe (%)

Ni (%)

Cu (%)

Co (ppm)

Zn (ppm)

(Mn/Fe)

(Ni/Mn) x 100

(Cu/Mn) x I00

(Co/Mn) x 100

No. of nodules analysed

ST.5+ ST.7+ ST.8+ ST.27 + DR2 DR3 CP17 CP18 CP23 CP25 CP26 CP27 CP28 CP29 CP30(1 ) CP30(2) BL2(I) BL2(2)*

17.5 27.7 24.2 22.0 22.2 25.2 20.7 13.9 21.4 27.4 23.3 19.8 18.7 28.9 25.2 28.8 24.2 26.0

13.00 7.10 7.80 12.30 5.60 3.60 n.a. 3.99 n.a. n.a. 5.40 n.a. 5.41 n.a. n.a. n.a. 5.21 10.03

0.64 1.22 1.16 0.86 1.00 0.58 0.39 0.71 0.81 1.35 1.06 0.98 0.82 1.37 1.14 1.32 1.10 1.08

0.40 1.30 0.90 0.59 0.96 1.20 0.28 0.50 0.59 1.29 1.06 0.94 0.67 1.43 1.22 1.47 1.01 1.05

1500 1400 1200 2000 1000 800 2000 490 1600 790 960 570 1160 1030 1240 1080 1060 bdl

700 1400 1200 1200 n.a. n.a. 280 1010 480 960 680 600 980 1211 750 1070 930 bdl

1.34 3.90 3.10 1.78 3.96 7.00 -3.50 1.78" 4.33* 4.30 4.54* 3.47 5.02* 2.95* 4.35* 4.64 2.60

3.65 4.40 4.79 3.90 4.50 2.30 1.88 5.08 3.78 4.92 4.54 4.94 4.38 4.74 4.52 4.58 4.54 4.15

2.28 4.69 3.92 2.68 4.32 4.76 1.35 3.59 2.75 4.70 3.73 4.74 3.61 4.94 4.48 5.10 4.17 4.03

0.85 0.50 0.49 0.90 0.45 0.31 0.96 0.35 0.74 0.28 0.41 0.28 0.61 0.35 0.49 0.37 0.43 --

5 13 5 9 1 1

TABLE 3 Mean values of chemical analyses in partial rind powders of diagenetic nodules

Core

Na20 AIzO 3 SiO 2 P205 $206 CI K20 CaO TiO 2 MnO 2 Fe20 3 NiO CuO Mn/Fe Si/AI Ni/Mn Cu/Mn

n=15

OLL n=12

ODL n=10

YLL n=26

YDL n=23

4.38 9.07 34.71 0.58 0.37 1.30 1.52 1.08 0.38 26.59 11.49 0.75 1.11 1.81 3.51 3.75 5.49

3.28 5.03 15.68 0.31 0.33 1.23 1.31 2.25 0.27 52.51 8.18 1.79 2.17 6.35 2.89 4.26 5.27

3.88 5.06 17.16 0.43 0.45 1.47 1.46 2.00 0.33 50.14 8.76 1.69 1.81 5.28 3.44 4.17 4.52

4.57 4.47 14.49 0.42 0.76 1.78 1.09 2.39 0.43 51.50 9.54 1.99 1.67 5.32 3.32 4.73 4.04

4.92 4.68 16.96 0.43 0.80 1.96 1.31 2.44 0.27 52.32 6.28 1.68 1.56 7.88 3.29 4.03 3.81

OLL = old laminated layer; ODL = old dendritic layer; YLL = young laminated layer; Y D L = y o u n g dendritic layer; n =

number of analyses.

crust 1 16 l 40 12 6 10 4 5 3 39

cores, it was found that rhyolitic pumice with different degrees of alteration and/or replacement by the Fe-Mn oxides constituted one of the most common nuclei in the diagenetic nodules (MartinBarajas, 1988). Indurated red clay sediments are also common as nuclei and may be related to the dissolution of the biosiliceous material during periods of non-deposition. This material was found at the base of, and interstratified with, the siliceous deposits. The mineralogical composition is a residual phase together with an authigenic assemblage similar to red clay sediments. M i x e d nodules

Mixed or intermediate nodules from the EEP have an external form and chemical composition intermediate between hydrogenetic and diagenetic nodules (Sorem et al., 1979; Halbach and Ozkara, 1979). The mixed nodules in the EEP have different top and bottom shapes, which are related to exposure to bottom water and sediment respectively.

258

A. MARTIN BARAJAS ET AL.

9.8 EARLY DIAGENETIC I0 .,~ MANGANATE

o

7..6 A f

Q Q I

9.6 ~

~

DRIED 24h-IIO*C

DRIED 24h-lfO°C

LATE DIAGENETIC I0 ,~ MANGANATE 9.77 ~,

O

DRIED 24h-I100 DR,ED

.

2e

(Cu k~)

Fig. 5. X-ray diffraction pattern of the 10 ,~. manganate, before and after heat treatment. (A) and (B) Manganate from the early diagenetic dendritic superficial layers. (C) Sample from the "old laminated zone" with late diagenetic replacement (Fig. 8b).

In the CIB, the mixed nodules are related to a change in the internal structure rather to morphological variation in the nodule between the top and the bottom. In most cases, the mixed types have an internal hydrogenetic crust which varies from 2 to 5 mm in thickness which is surrounded by a 1-4 mm thick outer crust of diagenetic material (Fig. 4d). These nodules may have a homogeneous diagenetic external shape, but internally the

diagenetic aspect changes gradually to hydrogenetic material. Observations under the microscope show that the contact between the two accretionary patterns is transitional, suggesting a progressive change in the sedimentary environment during growth. These nodules are larger than 50 ram. Chemically, the mixed nodules present an intermediate composition between diagenetic nodules and hydrogenetic ones (Fig. 2).

259

M A N G A N E S E N O D U L E S A N D S E D I M E N T A R Y E N V I R O N M E N T IN T H E C E N T R A L I N D I A N BASIN

L a t e diagenetic e n r i c h m e n t

The late diagenetic enrichment of nodules is physically manifested in several ways. The replacement of the silicate phases by Fe-Mn oxides and the filled fractures in the crust and around the core are the clearest features (Fig. 8a and b). Chemically, the late diagenetic replacement shows a better correlation between Mn and Cu (Fig. 6). This produces a general increase in the Cu/Mn ratio from the outer to the inner part of the crust, while the Ni/Mn ratio remains essentially constant (Fig. 7 and Table 3). Furthermore, the microprobe analyses in the early diagenetic and late diagenetic deposits (Table 4) show that the higher values of Mn/Fe are better correlated with the Cu content whereas the Ni content decreases with high Mn/ Fe ratios (Fig. 6). The X R D analyses on the early diagenetic 10/~ manganate revealed a 7 A peak when the sample was dried to I I0°C for 24 hours (Fig. 5A) while the 10 A manganate diffractions of the late diagenetic deposits in the inner layers remain during the first few hours (Fig. 5B). After 24 hours, the crystal structure of this late diagenetic phase collapsed and no diffraction was recorded (Fig. 5C). The TEM analysis of both early and late diagenetic manganese-oxide phases shows that the early diagenetic 10/~ manganate is apparently a phyllomanganate (layered structure) of the buserite type (Giovanoli et al., 1975). In contrast, the late diagenetic 10 A manganate sampled in secondary structures showed the characteristic 120 ° fibrous twining

tO I0

O O

2O

30

40

50

,

,

C~

s 4

•

mean

(Ni/Mn)

x IO0

•

mean value

value

YOUNG DENDRITIC

Q

LAYER

• \

No. 23

\

\

\

--, '

'

, \

i

\

YOUNG LAMINATED LAYER

\ \

/

\

No. 26 +

'

,

+

I

'

/

'

"I

OLD DENORITIC LAYER

/

'

'

....

'

:

',

,

, \ , "4.

,

\

I . ,~,

,

i , ,

OLD LAMINATED LAYER / No. 12

/ /

/

,,

,,

I/

-

\

/

NO. I0

, ,,

I .....

• ~I '

i

•

i

:

/ CORE No. 15 .

.

.

.

i

3.s

.

.

.

.

i

4.0

.

.

.

45

i

so

.

.

.

.

:

ss

Fig. 7. Variation of the Cu/Mn and Ni/Mn ratios in samples obtained from the main internal structures in nodule cross section (after Marching and Halbach, 1982). Analysis with EDS and FRX in Martin-Barajas, 1988. No. 23=number of analysis.

of the todorokite (Fig. 8c and d) (Turner and Buseck,

1981; T u r n e r et

al.,

1982),

a l t h o u g h the

tunnel structure could not be revealed. However, this phase was unstable under weak temperature drying treatment. The systematic observation of the nodule struc-

,

0 _A 0

.r~.u

x IOO

I00 ,

o o~..~_

o

(Cu/Mn)

,

~ ~0"o~

,

200

300

400 5 0 0

,

0

I.O

•

o

O O

co

o

m N

3

A ¢=

C =E 2

Z

n U

•

o5 I0

• 5O

I

50 0

300

4OO

500

Mn/Fe Fig. 6. Relative Ni and Cu content versus Mn/Fe ratio in the 10 ,~ manganate showing the correlation between Cu and the higher Mn/Fe ratios which represent pure late diagenetic product. Data from microprobe analyses in Table 3.

26O

A. MARTIN BARAJASET AL.

TABLE 4

Microprobe analyses on 10 A manganate-rich material in thin sections (see Fig. 5). Remaining weight percent is assumed to be water, n.a. = not analyzed No.

K

Co2

Na

Ca/

Cuz

Mgz

Baz

Zn2

AI3

Ti4

Ni2

Si4

Fe3

Mn4

Total

Mn/Fe

oxide l 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

0.35 0.86 0,58 0.89 1,08 1,00 0,67 0.82 0.49 0,43 0,85 0.64 0.47 1.17 1.17 1,28 0.67 0.76 0.64 0.94 1.32 2,47 1.14 1.36 1,14 1,29 2.01 2.55

0.00 0.14 0.00 0.00 0.18 0.00 0.03 0.00 0.00 0.01 0.06 0.00 0.17 0.28 0.09 0,18 0.25 0.00 0.17 0.03 0.00 0.00 0.17 0.00 0.00 0.01 0.12 0.00

1.24 2.33 2.13 2.30 4.58 3.44 1,44 2.13 1.19 2.95 2.76 1,77 n.a, n.a. n.a, n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a.

0.85 2.07 1.05 1.33 2.54 1.62 1.50 2.06 1.81 2.07 2.00 2,41 n.a. 1.62 1.41 1.26 1.21 1.37 1.24 1.29 1.58 1.42 1.30 1.57 1.30 1.73 1.03 0.75

1.87 1.67 1,62 2.57 2.26 2.21 2.11 2.5! 1.81 1.98 2.13 2.77 2.90 2.02 2.61 2.75 2.86 2.62 2.19 2.56 2.82 2.13 2.63 2.76 0.84 2.12 2.13 1.37

6.31 2.04 4.42 2.16 2.91 2.47 5.68 4.45 3.33 5.50 3.27 4.02 n.a. 3.03 2.80 3.22 5.37 3.70 5,41 6.13 1.69 3.38 1.18 1,84 0.88 2.22 3.33 2.84

0.00 0.10 0.30 0.10 0.00 0.00 0.33 0.00 0.00 0.00 0.14 0.44 0.02 0.22 0.48 0.46 0.06 0.20 0.03 0.00 0.00 0.03 0.00 0.00 0.00 0.22 0.00 0.00

0.23 0.60 0,11 0.11 2.39 0.61 1.99 1.32 0.72 3.76 1.46 0.72 0.07 0.54 0.22 0.36 0.09 0.31 0.00 0.44 0.00 1.74 0,21 0.20 0.37 0.39 0.61 0.73

ture in thin section and the chemical data suggest that late diagenetic enrichment is continuous during nodule growth within the "accretionary level" in the upper 40 cm of sediments. Nodule-sediment relationship: stratigraphic constraints Dating of the radiolarian assemblage in selected samples served to define the timing of biosiliceous accumulation in the central deep area and the relative ages of the sediment and associated overlying nodules. From these data, in the piston cores qualitative accumulation rates and the presence of hiatuses (with hydrogenetic nodules) in the sedimentary sequence were inferred. Additional dates from box cores with nodules in the upper 40 cm

4.76 0.43 2.43 0.84 1.54 0.24 5.56 3.02 1.36 3.54 2.07 1.93 1.79 2.48 0.79 0.77 4.16 2.89 4.04 3.80 0.55 6,50 4,52 0.13 1.17 2.57 1.08 1.28

0.09 0.01 0.04 0.00 0.19 0.00 0.09 0.04 0.07 0.10 0.20 0.00 n.a. 0.00 0.00 0.00 0.00 0.00 0.03 0.08 0.00 0.03 0.00 0.00 0.00 0.03 0.03 0.02

1.68 0.52 1.36 2.08 1,45 0.26 2.57 3.01 1.66 2.60 1.73 0.79 1.51 1.48 0.73 1.37 2.14 1.49 2,06 2.90 1.01 2.44 0.70 0.41 0.41 1.78 3.05 2.71

5.30 0.84 1.30 0.43 2.40 0.42 5.98 1.33 0.65 0.68 2.80 1.65 0.68 3.81 1.28 0.13 2.35 2.57 3.59 0.45 1.54 9.37 16.73 0.26 9.92 3.14 1.43 1.97

2.46 1.10 0.78 0,91 2,49 0,53 2.93 1.11 1.63 1.62 1.68 2.31 2.72 2.35 2.29 0.77 1.40 1.89 2.23 1.80 0.31 4.83 1.06 0.31 0.37 2.55 3.06 1.12

42.7 65.7 51.4 53.2 61,3 68.9 58.4 63,4 64,5 58.5 57.0 71.5 51.1 50.8 56.0 56.4 48.2 52.3 45.7 54.6 54.0 43.5 43.5 57,3 53.5 49.4 55.9 51.8

67.0 78.1 67.2 66.7 84.6 81.6 88.4 84.8 78.8 83.2 77,6 90.2 61,5 69.8 69.8 69.0 68.8 70.0 67.3 75.1 64.9 77.9 73.1 66.1 69.9 67.5 73.8 67.2

18.6 66.9 73.4 65.2 28.6 142.7 22.2 67.4 44.0 40.4 38,0 34.6 38.5 48.0 54.2 161.8 76.2 61.3 45.4 67.2 380.5 20.0 91.0 403. l 318.6 43.0 40.5 102.9

of sediment permit qualitative estimates of the growth rates of nodules. In box cores and piston cores, the hydrogenetic nodules were observed on top and/or interstratified within condensed sequences of biosiliceous sediment as well as associated with red clays. Nodules with less-developed crusts are interstratified within the underlying red clays (Fig. 3). The condensed succession sampled on the topographic highs represents a post-Late Miocene/Early Pliocene sedimentary record corresponding to the period when the hydrogenetic accretion in the nodules was active. The condensed series contains hydrogenetic nodules associated with a hiatus, suggesting that periods of non-deposition or erosion by bottom currents promote nodule nucleation (e.g. MD373, MD377 and AET19). Furthermore, the data imply

MANGANESE NODULES AND SEDIMENTARY ENVIRONMENT IN THE CENTRAL INDIAN BASIN

261

Fig. 8 (a) Typical dendritic structure with high 10 ~ manganate content. Arrow shows late diagenetic replacement of the silicate phase by Mn-oxides. Scale b a r = 1 mm. (b) Imaging of Mn distribution in thin section showing late diagenetic crack filling in the "old laminated layer" near the contact between nucleus and crust (DIGIMAP imaging treatment coupled with SEM). Scale bar = 0.1 mm. (c) High-resolution TEM view of 10 A layered manganese oxide (buserite). The sample is from young dendritic structures like those in Fig. 4a. (d) High-resolution TEM view of 10 ~ tectomanganate or todorokite showing the typical 120° twinning. Sample from late diagenetic structures (Fig. 4b).

that significant biogenic deposition in the central deep area (11-15°S) began in the Late Pliocene, as dated with the radiolarian assemblage (Table 1). This also implies that younger accretionary processes were mainly of hydrogenetic origin. From Late Pliocene times the biosiliceous sedimentation increased, producing the favourable conditions for diagenetic nodule growth observed in the studied area. The diagenetic nodules were found exclusively in the upper 40 cm of the recent siliceous-diatomaceous sediments in areas where the sedimentary sequence is thick (Fig. 3 and Table 1). Some piston cores sampled more than 12 m of siliceous deposits in the deeper areas. Diagenetic nodules were also sampled by dredge at the same site (CP24, CP25, CP26 and CP27). Late Pliocene fauna were found at the base of these thick biosiliceous deposits

(MD371, MD374 and MD375). In-situ observations of box cores and bottom photographs show that the diagenetic accretion of nodules occurs below the sediment/water interface, within the upper 40cm of the recent siliceous oozes. No diagenetic buried nodules were sampled below 40 cm, suggesting that dissolution of nodules takes place at deeper levels. In some cases, "abnormal" nodule-sediment relationships were observed in box cores with hydrogenetic nodules on top. If we assume that hydrogenetic accretion is slower than diagenetic accretion (Halbach et al., 1983; Reyss et al., 1982; Finney et al., 1984), hydrogenetic nodules sampled on top of recent siliceous oozes might be considered as occurring in a "foreign" location or as being the result of rapid growth (e.g. SI23 and SI26). In addition, in a few cases diagenetic nodules

262

below the sediment/water interface were observed in the same core with hydrogenetic and mixed nodules on top (SI23 and AET20). Discussion

With reference to metal content, relationship between metals, nodule abundance, morphological variation and the correlation of these factors with local topography, our results are in agreement with the published data (Jauhari, 1987; Ahmad and Husain, 1987; Kodagali, 1988; Mukhopadhyay, 1987). Nodules associated with siliceous oozes are smaller, less abundant, and richer in Mn, Ni and Cu (diagenetic nodules) than nodules of hydrogenetic origin found in red clays. The hydrogenetic nodules show smooth textures, compact-laminated layers mainly formed by amorphous Fe-Mn oxide, and are relatively richer in Fe, Co and Ti. The published data are mainly descriptive however. Based on our results, the accretionary processes for nodule growth in the CIB are similar to those described in the EEP (Halbach et al., 1981; Dymond et al., 1984; Calvert and Piper, 1984). However, the nodules of the CIB can be considerably younger, representing the first generation; the relationship between sedimentary environment and nodule growth is direct. This means that in the CIB the nodules still reflect the sedimentary environment where they were found and, in the case of the more evolved nodules (mixed and hydrogenetic nodules), the growth process is linear with the sedimentary evolution of the basin and reflects the temporal transition between the red clay and the biogenic depositation in the southern part of the studied area. To the north, local accumulation rates and nodule type are controlled by bottom currents and relief. According to the proposed model of Martin-Barajas et al. (1988), the origin of manganese nodules in the CIB can be related to successive sedimentological and geodynamic processes occurring since the Late Miocene. The nodule formation depends first on the avaibility of seeds, or nuclei. Our results show that the Indonesian Volcanic Arc constitutes the main source of nodule nuclei in the CIB (Martin-Barajas, 1988). The activity of the Indonesian Volcanic Arc has been recorded in the deep-sea sediments

A. MARTIN BARAJAS ET AL.

throughout the Northeastern Indian Ocean since the Late Miocene (Ninkovitch, 1979; Vallier and Kidd, 1977; Von der Borch et al., 1974). In the study area, volcanic material is found in the form of altered ash layers within Miocene(?) red clays and as rhyolitic pumice. This ash material was transported by surface currents and deposited in deep-sea troughs. In Late Miocene times the central deep area saw red clay sedimentation which could induce only hydrogenetic Fe-Mn oxide deposits. At this time, the high productivity belt developed southward, producing biogenic sedimentation which favoured the diagenetic mobilization of the manganese within sediments and the diagenetic growth of nodules. This has been demonstrated by the temporary increase in the silica flux registered in the Late Miocene and middle Pliocene (Caulet, 1978), which seems to have been related to changes in the intensity of the water circulation produced by the seasonal inversion of the Monsoon (Leclaire, 1974; Johnson et al., 1989). South of 12°S, the oldest siliceous sediments are from the Early to middle Pliocene (NR9) (Table 1) and correlate with the late pulse of silica flux (Caulet, 1978). Southward, the siliceous deposits thin and are younger. Pure diagenetic nodules have only been observed in the deep areas with higher sediment accumulation rates, and within the upper 40 cm of recent siliceous sediments (< 400,000 yrs B.P.). This sedimentological pattern may be related to the bottomwater circulation and to the relief. The relief in the CIB is the result of the southnorth compressive stress (Weissel et al., 1980), which affects the Indian plate and the post-Late Miocene sedimentary sequence of the CIB (Curray and Munasinghe, 1989). The bottom-water circulation is related to Antarctic water, which is reported to cross the Ninety East Ridge at 10°S from the Warton Basin. It flows west and southward in the CIB (Warren, 1982), and it may have been responsible for producing the hiatus recorded in the condensed series on the bathymetric highs and the thicker biogenic deposits in the deep-sea trough. In deep-sea troughs, higher deposition rates of sediment result in the diagenetic mobilization of the manganese-oxides by the consumption of oxidants during organic matter decomposition. The

MANGANESE NODULES AND SEDIMENTARY ENVIRONMENT IN THE CENTRAL INDIAN BASIN

study of nutrients in porewaters in the CIB shows that oxic and anoxic processes are active over the upper 50 cm of sediment (Nath and Mudholkar, 1989). Nodules sampled within host sediments show growth structures 20 cm below the sediment/ water interface (Fig. 4b) and two nodules collected 35 cm below the interface show no evidence of dissolution, suggesting stable conditions for FeMn oxides in the nodule at that burial depth. Growth rate is one of the most controversial aspects of nodule formation. However, some agreement has been established (Finney et al., 1984)--diagenetic nodules grow faster than hydrogenetic nodules. In the EEP several mechanismes have been invoked to account for the maintenance of nodules at the sediment/water interface. Bioturbation and gravity sliding are the most frequently cited, two processes which result in nodules being positioned in "foreign" locations in the host sediment (Von Stackelberg, 1979). In the CIB, nodule characteristics correlate well with the sedimentary environment, suggesting that the nodules of this area have not been introduced from elsewhere. The mineralogical analyses indicate that early diagenetic 10 A manganate is an unstable phase out of in-situ conditions. This phenomenon has been discussed by several authors (Glasby, 1972; Burns and Burns, 1977; Giovanoli et al., 1975). Our data suggest that the early diagenetic 10 .~, manganate is a phyllomanganate with linked [MnO6] octahedra, forming a wall of parallel sheets, similar to the synthetic buserite layered structure (Giovanoli et al., 1975). Within interlayer sites this phase could include H20 and OHmolecules and divalent cations such as Cu 2 ÷ and Ni 2 + which give stability to the mineral structure (Arrhenius et al., 1979; Giovanoli and Arrhenius, 1983). The stability seems enhanced in the internal, older deposits by metallic uptake in a post-depositional enrichment process. The late diagenetic 10 A manganate shows a tectomanganate (todorokite) feature. Todorokite is described in terms of [MnO6] octahedra forming a tunnel structure which can accommodate large cations such as Ba and K (Turner and Buseck, 1981; Turner et al., 1982; Burns et al., 1983). Both todorokite-like and buserite-like phases have been recognized in marine manganese deposits (Burns

263

et al., 1985; Turner et al., 1982; Usui et al., 1989). Usui et al. (1989) has proposed a structural model for marine manganates in the form of two continuous series of increasing stability--the buseritelike series of diagenetic origin and the todorokitelike series of hydrothermal origin. In the later, the stability increases with increasing temperature. In the EEP the natural occurrence of todorokite has been pointed out as being related to diagenetic nodule-forming processes (Turner et al., 1982; Chukhrov et al., 1982; Siegel and Turner, 1983). Our data agree with the late diagenetic occurrence of todorokite in manganese nodules, which induces metallic enrichment in the nodules and a preferential increase of Cu over the Ni content. Published analyses of marine todorokite (Siegel and Turner, 1983) support this explanation and are interpreted here as showing a Cu increase from the outer to the inner part of the crust. Conclusions The history of manganese nodule genesis from the CIB is related to the sedimentary and geodynamic evolution of that basin since the Late Miocene. This can be supported as follows: (1) The favourable environment for metal-rich nodule formation appears only since the Late Pliocene; indeed most of the diagenetic nodules sampled in the deep-sea troughs in thick siliceous sediments are probably much younger than this ( < 400,000 yrs). (2) Late diagenetic enrichment was continuous during nodule growth within the upper 40 cm and produced a metallic uptake (Cu > Ni), mineralogical stability of the 10 ~, phyllomanganate, and formation of diagenetic todorokite. (3) The hydrogenetic nodules are found on deepsea hills and slopes. They are associated with red clays and with thinner condensed biosiliceous sediments which result from deep-water circulation and the influence of bathymetric relief. (4) The favourable conditions for the hydrogenetic growth of nodules began in Late Miocene/ Early Pliocene, which means that the hydrogenetic nodules are older than the diagenetic nodules in the basin. (5) All the nodules of the CIB are first generation

264

A. M A R T I N B A R A J A S ET AL.

n o d u l e s a n d c o n s i d e r a b l y y o u n g e r t h a n the n o d u l e s f r o m the E E P .

Acknowledgements S p e c i a l t h a n k s to J.P. C a u l e t f o r the r a d i o l a r i a n d a t i n g a n d for f r u i t f u l d i s c u s s i o n o f the stratig r a p h i c c o n s t r a i n t s . P.J. G i a n n e s i n i ( M N H N ) ,

P.

T r e m b l e y ( O r s a y ) a n d C. C l i n a r d ( O r l e a n s ) p r o vided valued analytical support. This research was partially 84/769!

supported by I F R E M E R contract a n d c o n t r a c t 40169 o f C O N A C Y T ,

Mexico. In m e m o r y o f P r o f . L. L e c l a i r e w h o sadly p a s s e d a w a y last A p r i l a n d w h o m a d e significant c o n t r i b u tions to t h e g e o l o g y o f the I n d i a n O c e a n .

References Ahmad, S.M. and Husain, A., 1987. Geochemistry of ferromanganese nodules from the central Indian Basin. Mar. Geol., 77: 165-170. Aplin, A.C. and Cronan, D.S., 1985. Ferromanganese oxide deposits from Central Pacific Ocean, II. Nodules and associated sediments. Geochim. Cosmochim. Acta, 49: 427-436. Arrhenius, G., Cheung, K., Crane, S., Fisk, M., Frazer, J., Mellin, T., Nakao, S., Tsai, A. and Woolf, G., 1979. Counter ions in marine manganates. In: La Gen6se des Nodules de Manganese. Colloq. Int. CNRS, 289: 333-356. Bezrukov, P.L. and Andrushchenko, P.F., 1974. Geochemistry of the iron-manganese nodules from the Indian Ocean. Int. Geol. Rev., 16: 1044-1061. Burns, G.R., Burns, M.V. and Stockman, W., 1893. A review of the todorokite-buserite problem: implications to the mineralogy of marine manganese nodules. Am. Mineral.. 68: 972 980. Burns, G.R,, Burns, M.V. and Stockman, W., 1985. The todorokite-buserite problem: further considerations. Am. Mineral., 70: 205-208. Burns, R.G. and Burns, V.M., 1977. Mineralogy. In: G.P. Glasby (Editor), Marine Manganese Deposits. Elsevier, Amsterdam, pp. 185-248. Calvert, S.E. and Piper, D.Z., 1984. Geochemistry of ferromanganese nodules from DOMES, site A. Northern Equatorial Pacific: Multiple diagenetic metal sources in the deep-sea. Geochim. Cosmoehim. Acta, 48: 1913-1928. Caulet, J.P., 1978. S6dimentation biosiliceuse n6og~ne et quaternaire darts l'ocOan Indien. Bull. Soc. G~ol. Fr., S6r. 7, XX(4): 577-583. Caulet, J.P., Clement, P., Milleliri, P., 1984, GEOCORES: Inventaire informatis6 des roehes et s~diments matins conservOs au Museum d'Histoire naturelle. Bull. Mus. Natl. Hist. Nat., Paris, S&. 4, 6, Sect. C, 3: 215-243. Chukhrov, F.V., Gorshkov, A.I., Sivtsov, A.B. and Berezov-

skaya, V.V., 1978. Structural varieties of todorokite. Int. Geol. Rev., 22: 75-83. Chukhrov, F., Gorshkov, A., Yermilova, L., Berezovskaya, V. and Sivtsov, V., 1982. Mineral forms of manganese and iron in oceanic sediments. Int. Geol. Rev., 24 (4): 466-480. Cronan, D.S. and Moorby, S.A., 1981. Manganese nodules and other ferromanganese oxide deposits from the Indian Ocean. J. Geol. Soc. London, 138: 527-539. Curray, J.R., and Munasinghe, T., 1989. Timing of intraplate deformation, northeastern Indian Ocean. Earth Planet. Sci. Lett., 94: 71-77. Denis-Clocchiatti, M., 1982. S6dimentation carbonat6e et pal6oenvironnement dans l'oc6an Indien au Cenozoi'que. Th~se Doct, Etat. (M~m. Soc. G6ol. Fr., Nouv Ser., LX(143): 192 pp.) D' Ozouville, 1978. Rapport de mission MD14. CNEXO, 12 pp. (Unpubl.). Dymond, J., Lyle, M., Finney, B., Piper, D.Z., Murphy, K., Conrad, R. and Pisias, N., 1984. Ferromanganese nodules from MANOP Sites H, S and R. Control of mineralogical and chemical composition by multiple accretionary processes. Geochim. Cosmochim. Acta, 48: 931-949. Emmel, E.J. and Curray, J.R., 1984. The Bengal Submarine Fan, Northeastern Indian Ocean. Geo-Mar. Lett., 3: 119-124. Finney, B., Heath, R.G. and Lyle, M., 1984. Growth rates of Mn rich nodules at MANOP site H (Eastern North Pacific). Geochim. Cosmochim. Acta, 48:911-919. Fr6hlich, F., 1981. Les silicates dans l'environnement pdlagique de l'Ocean Indien au Cenozo/'que. Mere. Mus. Natl. Hist. Nat., Paris, S6r. C, XLVI: 206 pp. Giovanoli, R. and Arrhenius, G., 1983. Structural chemistry of marine manganese and iron minerals and synthetic model compounds. In: P. Halbach, Marine Mineral Deposits: New Research Results and Economic Prospects. Gluckauf. Giovanoli, R., Bfirki, P., Giuffredi, M. and Stumm, W., 1975. Layer structured manganese oxide hydroxides. IV: The buserite groups. Structure and stabilization by transition elements. Chimia, 29: 110-113. Glasby, G.P., 1972. The mineralogy of manganese nodules from a range of marine environments. Mar. Geol., 13: 57-72. Halbach, P. and Ozkara, M., 1979. Morphological and geochemical classification of deep-sea Fe-Mn nodules and its genetical interpretation. In: La Gen6se des Nodules de Manganese. Colloq. Int. CNRS, 289. Halbach, P., Sherhag, C., Hebich, V. and Marchig, V., 1981. Geochemical and mineralogical control of different genetic types of deep-sea nodules from the Pacific Ocean. Mineral. Deposita, 16: 58-84. Halbach, P., Segi, M., Puteanus, D. and Mangini, A., 1983. Co fluxes and growth rates in ferromanganese deposits from central Pacific sea-mount areas. Nature, 304: 716-719. Jauhari, P., 1987. Classification and inter-element relationships of Central Indian Ocean Basin. Mar. Min., 6: 419-429. Johnson, D.A., Kent, D.V., Schneider, D.A., Nigrini, C.A. and Caulet, J,P., 1989, Pliocene-Pleistocene radiolaria events and magnetostratigraphic calibration for the tropical Indian Ocean. Mar. Micropalentol., 14: 33-66. Kodagali, V., 1988. Influence of regional and local topography

MANGANESE NODULES AND SEDIMENTARY ENVIRONMENT IN THE CENTRAL INDIAN BASIN

on the distribution of polymetallic nodules in the central Indian Ocean Basin. Geo-Mar. Lett., 8: 173-178. Kolla, V., B+, A.W.H. and Biscaye, P.E., 1976. Calcium carbonate distribution in the surface sediments of the Indian Ocean. J. Geophys. Res., 81: 2605-2616. Leclaire, L., 1974. Late Cretaceous and Cenozoic pelagic deposits. Paleoenvironments and paleoceanography of Central Western Indian Ocean. lnit. Rep. DSDP, 25: 481 512. Leclaire, L. and Perseil, E.A., 1979. Min6ralogie, composition chimique et milieux de s+dimentation de concr+tions polym6talliques dans l'oc6an Indien. In: La Gen6se des Nodules de Mangan6se. Colloq. Int. CNRS, 289: 23-27. Marchig, V. and Halbach, P., 1982. Internal structures of manganese nodules related to conditions of sedimentation. Tschermaks Mineral. Petrogr. Mitt., 30: 81-I 10. Martin-Barajas, A., 1988. Gen~se des champs de nodules polym6talliques dans le Bassin Indien central. Thbse Doct., Univ. Paris-Sud, 192 pp. Martin-Barajas, A., Leclaire, L. and Lallier-Verges, E., 1988. Origin of manganese nodule fields related to the geodynamic evolution of the central Indian Basin. C.R. Acad. Sci. Paris, S~r. II, 307:1259 1264 (in French with abridged English version). Mukhopadhyay, R., 1987. Morphological variations in the polymetallic nodules from selected stations in the central Indian Ocean. Geo-Mar. Lett., 7:45 51. Nath, B.N. and Mudholkar, A.V., 1989. Early diagenetic processes affecting nutrients in the pore waters of central Indian Ocean cores. Mar. Geol.,.86: 57-66. Nath, B.N., Rao, V.P. and Becker, K.P., 1989. Geochemical evidence of terrigenous influence in deep-sea sediments up to 8 S in the Central Indian Basin. Mar. Geol., 87: 301-313. Ninkovitch, D., 1979. Distribution, age and chemical composition of tephra layers in deep-sea sediments of Western Indonesia. J. Volcanol. Geotherm Res., 5: 67-86. Pautot, G. and Hoffert, M., 1984. Les nodules du Pacifique Central dans leur environnement g6ologique. R6sultats des campagnes fi l a m e r n ~' 26. CNEXO, 202 p. Perseil, E.A. and Jehanno, C., 1981. Sur les caract+res min6ralogiques et g6ochimiques des nodules polym6talliques du bassin Indien Central. Mineral. Deposita, 16: 391-407. Pimm, A.C., [974. Sedimentology and history of the northeastern Indian Ocean from late Cretaceous to Recent. lnit. Rep. DSDP, 22:717 804. Rao, P.V.. 1987. Mineralogy of polymetallic nodules and

265

associated sediments from the central Indian Basin. Mar. Geol., 74: 151-157. Reyss, J.L., Marchig, V. and Ku, T.L., 1982. Rapid growth of a deep-sea ferromanganese nodule. Nature, 295: 401-403. Siegel, M.D. and Turner, S., 1983. Crystalline todorokite associated with biogenic debris in manganese nodules. Science, 219: 172-174. Sorem, R.K., Fewkes, R.H., McFarland, W.D. and Reinhart, W.R., 1979. Physical aspects of the growth environment of Mn nodules in the "Horns Region", East Equatorial Pacific Ocean. In: La Gen6se des Nodules de Manganese. Colloq. Int. CNRS, 289. Stein, S. and Okal, E.A., 1978. Seismicity and tectonics of the Ninetyeast Ridge area: evidence for internal deformation of Indian plate. J. Geophys. Res., 83:2233 2245. Turner, S. and Buseck, P.R., 1981. Todorokites, a new family of naturally occurring manganese oxides. Science, 212:1024 1027. Turner, S., Siegel, M.D. and Buseck, PR., 1982. Structural features of todorokite intergrowths in manganese nodules. Nature, 296:841 842. Usui, A., Mellin, A.T., Nohara, M. and Yuasa, M., 1989. Structural stability of marine l0 ,~ manganates from the Ogasawara (Bonin) Arc: Implication for low-temperature hydrothermal activity. Mar. Geol., 86: 41-56. Vallier, L.T. and Kidd, R.B., 1977. Volcanogenic sediments in the Indian Ocean. In: Heirtzler et al. (Editors), Indian Ocean Geology and Biostratigraphy. Am. Geophys. Union, Washington, D.C., pp. 87-118. Von der Borch, C.C., Sclater, J.G., Gartner, S., Hekinian, R., Johnson, D.A., McGowran, B., Pimm, A.C., Thompson, R.W., Veevers, J.J. and Waterman, L.S., 1974. Init. Rep. DSDP, 22. Von Stackelberg, U., 1979. Sedimentation hiatuses and development of manganese nodules: Valdivia site VA-13/2. Northern Central Pacific. In: Bischoff and D.Z. Piper (Editors), Marine Geology of the Pacific Manganese Nodule Province. Plenum, pp. 559-586. Warren, B.A., 1982. The deep water of the Central Indian Basin. J. Mar. Res., 40: 823-860. Weissel, K.J., Anderson, N.R. and Geller, A.C., 1980. Deformation of the Indo-Australian plate. Nature, 287: 284-291. Wiens, A.D., DeMets, C., Gordon, G.R., Stein, S., Argus, D., Engel, F.J., Lundgren, P., Quible, D., Weintein, S. and Woods, F.D., 1985. A diffussive plate boundary model for Indian Ocean tectonics. Geophys. Res. Lett., 12: 429-432.