Petrology of basalts from DSDP Hole 83-504B

Basalts from Hole 504B, Leg 83, exhibit remarkable uniformity in major and trace element composition throughout the 1075.5 m of basement drilled. The majority of the basalts, Group D', have unusual compositions relative to normal (Type I) mid-ocean ridge basalts (MORB). These basalts have relatively high mg values (0.60-0.70) and CaO abundances (11.7-13.7%; Ca/Al = 0.78-0.89), but exhibit a marked depletion in compatible trace elements (Cr and Ni); moderately incompatible trace elements (Zr, Y, Ti, etc.); and highly incompatible trace elements (Nb, LREE, etc.). Petrographic and compositional data indicate that most of these basalts are evolved, having fractionated significant amounts of plagioclase, olivine, and clinopyroxene. Melting experiments on similar basalt compositions from the upper portion of Hole 504B (Leg 70; Autio and Rhodes, 1983) indicate that the basalts are co-saturated with olivine and plagioclase and often clinopyroxene on the 1-atm. liquidus. Two rarely occurring groups, M' and T, are compositionally distinct from Group D' basalts. Group T is strongly depleted in all magmaphile elements except the highly incompatible ones (Nb, La, etc.), while Group M' has moderate concentrations of both moderately and highly incompatible trace elements and is similar to Type I MORB. Groups M' and T cannot be related to Group D' nor to each other by crystal fractionation, crystal accumulation, or magma mixing. The large differences in magmaphile element ratios (Zr/Nb, La/Yb) among these three chemical groups may be accounted for by complex melting models and/or local heterogeneity of the mantle beneath the Costa Rica Ridge. Xenocrysts and xenoliths of plagioclase and clinopyroxene similar in texture and mineral composition to crystals in coarse-grained basalts from the lower portion of the hole are common in Hole 504B basalts. These suggest that addition of solid components either from conduit or magma chamber walls has occurred and may be a common source of disequilibrium crystals in these basalts. However, mixing of plagioclase-laden depleted melts (similar to the Costa Rica Ridge Zone basalts) with normal MORB magmas could provide an alternate source for some refractory plagioclase crystals found out of equilibrium in many phyric MORB. The uniformity of major element compositions in Hole 504B basalts affords an ideal situation for investigating the effects of alteration on some major and trace elements in oceanic basalts. Alteration observed in whole-rock samples records primarily two events - a high-temperature and a low-temperature phase. High-temperature phases include: chlorite, talc, albite, actinolite, sphene, quartz, and pyrite. The low-temperature phases include smectite (saponite), epistilbite or laumontite, and minor calcite. Laumontite may actually straddle the gap between the low- and high-temperature mineral assemblages. Alteration is restricted primarily to partial replacement of primary phases. Metamorphic grade, in general, increases from the top to the bottom of Hole 504B (Legs 69, 70, and 83) as seen in the change from a smectiteto- chlorite-dominated secondary mineral assemblage. However, a systematic progression for the interval recovered during Leg 83 is not apparent. Rather, the extent of alteration appears to be a function of the initial texture and fracture density. Variations in whole-rock major and trace element concentrations cannot be attributed convincingly to any differences in alteration observed. Compositional characteristics of the secondary minerals indicated that extensive remobilization of elements has not occurred; local redistribution is suggested in most cases. Thus, the major and trace element signature of these basalts remains effectively the same as the original composition prior to alteration.

Petrology and relict mineralogy of serpentinites at DSDP Leg 84 Holes

Eleven serpentine samples from DSDP Leg 84 and four serpentinized ultramafic samples from Costa Rica and Guatemala were described and their relict mineral compositions measured by electron microprobe to try to determine the origin of the Leg 84 serpentinites and their relationship to the ultramafic rocks of the onshore ophiolites. The Leg 84 samples comprise more than 90% secondary minerals, principally serpentine, with hematitic and opaque oxides, and minor talc and smectites. Four distinct textural types can be identified according to the distribution of opaque phases and smectite. Remnants of spinel, olivine, orthopyroxene, and clinopyroxene occur variously in the samples; spinal occurs in all the samples. Textural evidence suggests that the serpentinites were originally clinopyroxene-bearing harzburgites. Relict mineral compositions are refractory and relatively uniform: olivine, Fo90.6-90.9; orthopyroxene, En90-91; clinopyroxene, Wo47 En50 Fs3; spinels, Cr/Cr + Al = 0.4-0.6. 567A-29-2, 30-35 cm has slightly more magnesian olivines (Fo92) and orthopyroxene, and more aluminous spinels (Cr/Cr + Al = 0.3). These compositions are similar to those inferred for refractory upper-mantle materials and also fall within the range of compositions for relict minerals in abyssal peridotites. They could be of oceanic origin. The onshore samples include serpentinites, a clinopyroxene-bearing harzburgite, and a clinopyroxenite. They too have magnesium-rich silicate assemblages, but relative to the drilled samples have more iron-rich olivines (Fogo) and more aluminous and sodic pyroxenes; spinels which are clearly relicts are very aluminum-rich (Cr/Cr + Al = 0.1-0.25). These samples are most likely mantle materials, but significantly less depleted. Their relationship to the drilled samples is unclear. Serpentinites were the most common basement materials recovered during Leg 84, and there appears to be a bimodal assemblage (basalt/diabase and serpentine) of igneous rocks sampled from the trench slope. Diapirism of serpentine throughout the trench slope and forearc is suggested as an explanation for this distribution of samples.

Chemistry of peridotites of ODP Hole 103-637A

A ridge of peridotite was drilled off of the Galicia margin (Hole 637A) during ODP Leg 103. The ridge is located at the approximate boundary between oceanic and continental crust. This setting is of interest because the peridotite may be representative of upwelling upper mantle beneath an incipient ocean basin. The composition of the Galicia margin peridotite is compared with those of other North Atlantic peridotites. Hole 637A ultramafic lithologies include clinopyroxene-rich spinel harzburgite and lherzolite, as well as plagioclase-bearing peridotites. Variations in mineral modal abundances and mineral compositions are observed but are not systematic. The peridotites are broadly similar in composition to other peridotites recovered from ocean basins, but the mineral compositions and abundances suggest that they are less depleted in basaltic components than other North Atlantic peridotites by about 10%. In particular, the peridotites are enriched in the magmaphilic elements Na, Al, and Ti, as compared with other abyssal peridotites. The high abundances of these elements suggest that the Hole 637A peridotites had experienced, at most, very small amounts of partial melting prior to their emplacement. The presence of plagioclase rimming spinel in some samples suggests that the peridotite last equilibrated at about 9 kbar, near the transition between plagioclase- and spinel-peridotite stability fields. Temperatures of equilibration of the peridotite are calculated as 900°-1100°C. The relatively undepleted composition of the peridotite indicates that it was emplaced at a shallow mantle level under a relatively cool thermal regime and cooled below solidus temperatures without having participated in any significant partial melting and basalt production. This is consistent with the emplacement of the peridotite during incipient rifting of the ocean basin, before a true spreading center was established.

(Appendix 1-4) Geochemistry, desorption methods, TOC, TC, and mineral content of different settings

Sorption of volatile hydrocarbon gases (VHCs) to marine sediments is a recognized phenomenon that has been investigated in the context of petroleum exploration. However, little is known about the biogeochemistry of sorbed methane and higher VHCs in environments that are not influenced by thermogenic processes. This study evaluated two different extraction protocols for sorbed VHCs, used high pressure equipment to investigate the sorption of methane to pure clay mineral phases, and conducted a geochemical and mineralogical survey of sediment samples from different oceanographic settings and geochemical regimes that are not significantly influenced by thermogenic gas. Extraction of sediments under alkaline conditions yielded higher concentrations of sorbed methane than the established protocol for acidic extraction. Application of alkaline extraction in the environmental survey revealed the presence of substantial amounts of sorbed methane in 374 out of 411 samples (91%). Particularly high amounts, up to 2.1 mmol kg**-1 dry sediment, were recovered from methanogenic sediments. Carbon isotopic compositions of sorbed methane suggested substantial contributions from biogenic sources, both in sulfate-depleted and sulfate-reducing sediments. Carbon isotopic relationships between sorbed and dissolved methane indicate a coupling of the two pools. While our sorption experiments and extraction conditions point to an important role for clay minerals as sorbents, mineralogical analyses of marine sediments suggest that variations in mineral composition are not controlling variations in quantities of sorbed methane. We conclude that the distribution of sorbed methane in sediments is strongly influenced by in situ production.

Mineral composition of 0.1-0.05 mm grain size fraction from the surface layer of bottom sediments in the West European province of the Atlantic Ocean

Rock material sampled from the Mir manned deep-sea submersibles and by dradges, grabs, and sediment cores over a vast area of the North Atlantic was analyzed to show that this material is of continental origin, unlike original rocks of the ocean floor. It is proved to be related to iceberg rafting during Quaternary glaciations. Independent data on distribution and composition of sandy and silty grains in sediment cores also support this relation to the recent glaciation. New criteria for identification of iceberg rock matter in pelagic sediments are presented on the base of analysis of all available data.

Chemistry of peridotites from ODP 109-670A

During Leg 109 of the Ocean Drilling Program, about 100 m of serpentinized peridotites were drilled on the western wall of the M.A.R. axial rift valley, 45 km south of the Kane Fracture Zone. The present study reports petrological and mineralogical data obtained from 29 small pieces of these ultramafic rocks, including about 60% serpentinized harzburgites, 26% serpentinized lherzolites, 14% serpentinized dunites, and one sample of olivine websterite. Modal analyses show that all these rocks are plagioclase-free four-phase peridotites equilibrated in the spinel lherzolite facies. The estimated average modal composition of the sample set is about 80% olivine, 14% opx, 5% cpx, and 1% spinel, that is, a cpx-poor lherzolite. The well developed porphyroclastic structures and mineralogical characteristics of these rocks indicate their affinity with the group of residual mantle tectonites, among the abyssal peridotites. Features typical of magmatic cumulates are lacking. The high contents in Al2O3 of the cpx (average 5.4%) and of the opx (average 4.3%) porphyroclasts, the low Cr# of the spinels (average 22.9%), and the rather high content in modal cpx (about 5%), indicate a moderate percentage of melting, of the order of 10%-15%. Site 670 peridotites plot close to the least depleted mantle rocks collected in the oceans in most diagrams used to define the average trend of the ocean-floor peridotites. Microprobe traverses across the cores of the exsolved opx and cpx porphyroclasts permitted the recalculation of the magmatic compositions of these pyroxenes: the 'primitive' opx were equilibrated at about 1300°C, probably at the end of the main melting episodes, whereas the 'primitive' cpx show lower equilibration temperatures, at about 1200°C, reflecting a more complex thermal history. The subsolidus evolution is well recorded, from 1200°C to about 950CC, by the exsolved pyroxenes and the olivine and spinel phases. Unusually high blocking temperatures, close to 1000°C, indicate that the peridotite body was cooled very rapidly between 1000°C and the beginning of serpentinization. Oxygen fugacities, calculated for 10 kb and at the blocking temperatures indicated by the olivine/spinel geothermometer, are close to the usual fugacities calculated in oceanic peridotites and basalts (of the order of 10**-10 to 10**-11, on the QFM buffer). Site 670 peridotites have compositions close to those of the peridotites collected in the Kane Fracture Zone area, and obviously belong to the moderately depleted mantle peridotites which characterize abyssal peridotites collected away from mantle plumes and oceanic islands. In particular, they differ from the highly residual harzburgites collected along the M.A.R. over the Azores bulge.

Platinum-group, major, and trace element abundances in ODP Leg 183 basalts

Seventeen basalts from Ocean Drilling Program (ODP) Leg 183 to the Kerguelen Plateau (KP) were analyzed for the platinum-group elements (PGEs: Ir, Ru, Rh, Pt, and Pd), and 15 were analyzed for trace elements. Relative concentrations of the PGEs ranged from ~0.1 (Ir, Ru) to ~5 (Pt) times primitive mantle. These relatively high PGE abundances and fractionated patterns are not accounted for by the presence of sulfide minerals; there are only trace sulfides present in thin-section. Sulfur saturation models applied to the KP basalts suggest that the parental magmas may have never reached sulfide saturation, despite large degrees of partial melting (~30%) and fractional crystallization (~45%). First order approximations of the fractionation required to produce the KP basalts from an ~30% partial melt of a spinel peridotite were determined using the PELE program. The model was adapted to better fit the physical and chemical observations from the KP basalts, and requires an initial crystal fractionation stage of at least 30% olivine plus Cr-spinel (49:1), followed by magma replenishment and fractional crystallization (RFC) that included clinopyroxene, plagioclase, and titanomagnetite (15:9:1). The low Pd values ([Pd/Pt]_pm < 1.7) for these samples are not predicted by currently available Kd values. These Pd values are lowest in samples with relatively higher degrees of alteration as indicated by petrographic observations. Positive anomalies are a function of the behavior of the PGEs; they can be reproduced by Cr-spinel, and titanomagnetite crystallization, followed by titanomagnetite resorption during the final stages of crystallization. Our modeling shows that it is difficult to reproduce the PGE abundances by either depleted upper or even primitive mantle sources. Crustal contamination, while indicated at certain sites by the isotopic compositions of the basalts, appears to have had a minimal affect on the PGEs. The PGE abundances measured in the Kerguelen Plateau basalts are best modeled by melting a primitive mantle source to which was added up to 1% of outer core material, followed by fractional crystallization of the melt produced. This reproduces both the abundances and patterns of the PGEs in the Kerguelen Plateau basalts. An alternative model for outer core PGE abundances requires only 0.3% of outer core material to be mixed into the primitive mantle source. While our results are clearly model dependent, they indicate that an outer core component may be present in the Kerguelen plume source.

Geochemistry of vein rocks of ODP Hole 118-735B

Rock samples from Hole 735B, Southwest Indian Ridge, were examined to determine the principal vein-related types of alteration that occurred, the nature of fluids that were present, and the temperatures and pressures of these fluids. Samples studied included veined metagabbro, veined mylonitic metagabbro, felsic trondhjemite, and late-stage leucocratic diopside-bearing veins. The methods used were standard petrographic analysis, mineral chemical analysis by electron microprobe, fluid inclusion petrography and analysis by heating/freezing techniques and laser Raman microspectroscopy, and oxygen isotopic analyses of mineral separates. Alteration in lithologic Units I and II (above the level of Core 118-735B-3OR; approximately 140 meters below the seafloor) is dominated by hydration by seawater-derived fluids at high temperature, up to about 700°C, and low water/rock ratio, during and immediately after pervasive ductile deformation. Below Core 118-735B-30R, pervasive deformation is less common, and brittle veining and brecciation are the major alteration styles. Leucocratic centimeter-scale veins, often containing diopside and plagioclase, were produced by interaction of hot (about 500°C) seawater-derived fluid and gabbro. The water/rock ratio was locally high at the veins and breccia zones, but the integrated water/rock ratio for the lower part of the hole is probably low. Accessory hydrous magmatic or deuteric phases formed from magmatic volatiles in some gabbro and in trondhjemite. Most subsequent alteration was affected by fluids that were seawater-derived, based on isotopic and chemical analyses of minerals and analyses of fluid inclusions. Many early-generation fluid inclusions, associated with high-temperature veining, contain appreciable methane as well as saline water. The source of methane is unclear, but it may have formed as seawater was reduced during low water/rock interaction with ultramafic upper mantle or ultramafic and mafic layer 3. Temperatures of alteration were calculated on the basis of coexisting mineral chemistry and isotopic values. Hydrothermal metamorphism commenced at about 720°C and continued to about 550°C. Leucocratic veining took place at about 500°C. Alteration within brecciated horizons was also at about 500° to less than 400°C, and the trondhjemite was altered at about 550° to below 490°C. Pressures calculated from a diopside-bearing vein, based on a combination of fluid inclusion and isotopic analysis, were 90 to 100 MPa. This pressure places the sample, from Core 118-735B-70R in Unit V, at about 2 km below the seafloor.

Sandstone and siltstone beds overlying conglomerate at DSDP Hole 59-439

Massive sandstone and siltstone beds with many shallow-water megafossils overlie acidic volcanic conglomerates at DSDP Site 439. Smear-slides, thin sections from coarse fractions, and heavy minerals of the sandstone and siltstone beds were analyzed. The sandstones and siltstones are very rich in lithic fragments and are classified as lithic arenite and (or) lithic wacke. Hornblende and clinopyroxene are abundant, and zircon is present in most of the examined samples. The proportions of sandstone, chert, and volcanic rock in the coarse fraction are variable, but fragments of clastic rocks and cherts are predominant. Plagioclase crystals of volcanic-rock origin, such as highly zoned plagioclase and very fine, euhedral, lath-shaped plagioclase, are frequently observed. Metamorphic-rock fragments and metamorphic minerals are also observed. Thus, the provenance of the sandstone and siltstone beds appears to have been a slightly mature island arc, the Oyashio ancient landmass, consisting of clastic sediments and metamorphic and volcanic rocks.

Grain sizes and mineral composition of the basement of ODP Site 206-1256

Hole 1256C was cored 88.5 m into basement, and Hole 1256D, the deep reentry hole, was cored 502 m into basement during Ocean Drilling Program Leg 206. Hole 1256D is located ~30 m south of Hole 1256C (Wilson, Teagle, Acton, et al., 2003, doi:10.2973/odp.proc.ir.206.2003). A thick massive flow drilled in both holes, Units 1256C-18 and 1256D-1, consists of a single cooling unit of cryptocrystalline to fine-grained basalt, interpreted as a ponded lava, 32 m and at least 74.2 m thick, respectively. This ponded flow gives us a unique opportunity to examine textural variations from the glassy, folded crust of the lava pond recovered from the top of Unit 1256C-18 through the coarse-grained, thick massive lava body to the unusually recrystallized and deformed base cored in Unit 1256C-18. Some detailed descriptions of the textures and grain size variations through the lava pond (Units 1256C-18 and 1256D-1), with special reference to the recrystallization of the base of Unit 1256C-18, are presented here.

Conglomerate and sandstone petrography at DSDP Hole 58-445

Conglomerates and sandstones in lithologic unit V at DSDP Site 445 comprise lithic clasts, detrital minerals, bioclasts, and authigenic minerals. The lithic clasts are dominantly plagioclase-phyric basalt and microdolerite, followed by plagioclase-clinopyroxene-phyric basalt, aphyric basalt, chert, and limestone. A small amount of hornblende schist occurs. Detrital minerals are dominantly plagioclase, augite, titaniferous augite, olivine, green to pale-brown hornblende, and dark-brown hornblende, with subordinate chromian spinel, epidote, ilmenite, and magnetite, and minor amounts of diopside, enstatite, actinolite, and aegirine-augite. Bioclasts are Nummulites boninensis, Asterocyclina sp. cf. A. penuria, and some other larger foraminifers. Correlation of cored and dredged samples indicates that the Daito Ridge is mainly composed of igneous, metamorphic, ultramafic, and sedimentary rocks. The igneous rocks are mafic (probably tholeiitic) and alkalic. The metamorphic rocks are hornblende schist, tremolite schist, and diopside-chlorite schist. The ultramafic rocks are alpinetype peridotites. Mineralogical data suggest that there were two metamorphic events in the Daito Ridge. The older one was intermediate- to high-pressure metamorphism. The younger one was contact metamorphism caused by a Paleocene volcanic event, possibly related to the beginning of spreading of the west Philippine Basin. The ultramafic rocks suffered from the same contact metamorphism. During the Eocene, exposed volcanic and metamorphic rocks on the uplifted Daito Ridge may have supplied pebble clasts to the surrounding coast and shallow sea bottom. The steep slope offshore may have caused frequent slumping and transportation of the pebble clasts and shallow-water benthic organisms into deeper water, forming the conglomerates and sandstones treated here.

Chemistry of serpentinized peridotites from ODP Hole 109-670A

In this paper we describe textural relationships in hydrated upper mantle peridotites emplaced at a nonconstructive ridge segment. Development of serpentinites and partially serpentinized peridotites takes place in four main stages: (1) pervasive serpentinization forming mainly lizardite, (2) a tensional stage forming chrysotile + talc + chlorite, (3) a deformational stage forming antigorite + tremolite, and (4) a late local tensional stage forming another generation of chrysotile veinlets. Mineral chemistry of serpentine pseudomorphs reflects in part primary mineral compositions. Olivine pseudomorphs are typically nickeliferous and depleted in aluminum and chromium. Orthopyroxene pseudomorphs have lower nickel contents and relatively high iron, aluminum, and chromium contents. Clinopyroxene pseudomorphs have very low nickel contents and relatively high aluminum and chromium contents. These chemical patterns in the serpentinites can be used to help discriminate between harzburgitic and lherzolitic protoliths. Oxygen isotopes and mineral parageneses suggest serpentine is derived from circulation of hydrothermal (200?C) fluids through the peridotite body. Crystallization of tremolite, talc, and chlorite may have occurred at temperatures up to 525?C if C02/H20 ratios were less than 0.25. Open fissures developing in aging upper mantle provide paths for important seawater circulation through a thin basaltic carapace down to shallow mantle rocks.

Mineralogy of ODP Site 105-645

Cores from the upper 70 meters below seafloor (mbsf) (upper Pleistocene) at Ocean Drilling Program (ODP) Site 645 in Baffin Bay show dramatic meter-scale changes in color and mineralogy. Below this interval, mineralogical changes are more gradual to the top of the Miocene at about 550 mbsf. The Pliocene-Pleistocene section can be divided into five facies: Facies 1 - massive, poorly sorted, gravel-bearing muds; Facies 2 - gray silty clays and silty muds; Facies 3 - laminated detricarbonate silty muds; Facies 4 - silty sand and sandy silt; and Facies 5 - poorly sorted muddy sands and silty muds. Facies 4 and 5 are restricted to the Pliocene section below depths of about 275 mbsf. The mineralogical/color cycles in the upper 70 mbsf are the result of alternations between Facies 2 and three lithotypes of Facies 1: lithotype A - tan-colored, carbonate-rich, gravel-bearing mud; lithotype B - weak, red-colored, gravel-bearing mud rich in sedimentary rock fragments; and lithotype C - gray, gravel-bearing mud. A fourth lithotype, D, is restricted to depths of 168-275 mbsf and is dark gray, carbonate-poor, gravel-bearing mud. We believe that all lithotypes of Facies 1 and the sand and gravel fractions of Facies 2 and 3 were deposited by ice rafting. Depositional processes for Facies 4 and 5 probably include ice rafting and bottom- and turbidity-current transport. Data from petrographic analyses of light and heavy sand-sized grains and X-ray analyses of silt- and clay-size fractions suggest that tan-colored sediments (lithotype A of Facies 1; Facies 3) were derived mainly from Paleozoic carbonates of Ellesmere, Devon, and northern Baffin islands. Weak red sediments (lithotype B) contain significant red sedimentary clasts, reworked quartzarenite grains and clasts, and rounded colorless garnets, all derived from Proterozoic sequences of the Borden and Thule basins, and from minor Mesozoic red beds. Other sediments in the upper 335 mbsf at Site 645 contain detritus from a heterogeneous mixture of sources, including Precambrian shield terranes around Baffin Bay. Sediments from 335 to 550 mbsf (Facies 5) are rich in friable sedimentary clasts and detrital micas and contain glauconite and, in a few samples, reworked diatoms. These components suggest derivation from poorly consolidated Mesozoic-Tertiary sediments in coastal outcrops and beneath the modern shelves of northeastern Baffin Island and western Greenland. For the upper Pleistocene section (about 0-100 mbsf), marked mineralogical cyclicity is attributed to fluctuating glacial margins, calving rates, and iceberg melting rates, particularly around the northern end of Baffin Bay. Tan-colored, carbonate-rich units were derived at times of maximum advance of glaciers on Ellesmere and Devon islands, during relatively warm intervals induced by incursion of warm Atlantic surface water into the bay. At the beginning of these warmer episodes, most icebergs were contributed by glaciers near sea level around the Arctic channels, which resulted in deposition of weak red, ice-rafted units rich in Proterozoic sedimentary clasts.

Ages, lithologie descriptions and mineral analyses from different DSDP holes in the Indian Ocean

The present work is based on mineralogical studies of sand and silt layers from a number of Deep Sea Drilling Project sites in the Indian Ocean belonging to different physiographic provinces of different ages. The minerals can be grouped into two major associations: a hornblende-opaque association with varying amounts of pyroxene, garnet, epidote, zircon, etc. and a biotite-chlorite-muscovite assemblage. The dominance of unstable minerals indicates a first generation, though evidence of reworking is reflected in the zircon and tourmaline grains at some sites. A large variety of minerals at some sites indicates a complex source. The mineral composition is nearly homogeneous at different sites for the entire length of the core, indicating that they have been derived from the same source during the deposition of that interval. However, the provenance changed by tectonic activity, the effect of which has been reflected in the mineralogy of some sites. An attempt was made to describe the mineralogic characteristics and their tectonic interpretations in the Pliocene and Miocene periods in the Ganges and Indus fan sites and also in the Wharton and Mozambique basin sites. Similar attempts could not be made for other ages in other physiographic provinces as the numbers of samples were too few. Within the limited scope, some idea about the mineralogical character of different basins and different physiographic provinces can be obtained from the present study. Mineralogical evidence also suggests very long transport of sediments in the deep sea. Regional variation of mineralogy has resulted due to source, sea-floor configuration, selective removal, reworking by different agencies and the processes operating in the ocean. There is no relation between a particular age and a set mineral assemblage for the Cenozoic sediments of the Indian Ocean.