Diagenetic remobilization of rare earth elements in a sediment core from the central Indian basin

341-344Rare earth elements (REE) distribution in a 36 cm long sediment box core from the Central Indian Basin is studied. REE concentration is generally higher in the upper oxic zone than in intermediate suboxic zone suggesting REE diffusion upwards the sediment column and subsequent incorporation in the oxyhydroxide phase. The similarity in depth distribution of bulk REE concentration, solid Mn phase and micronodule abundance from the coarse fraction suggest that micronodules are one of the major component controlling the REE distribution in a sediment column

Ferromanganese oxides from Mid-Indian Ridge, seamounts and abyssal plains from the Indian Ocean

11-15Mineralogical and chemical investigations show that todorokite is the only Mn mineral in the Mid-Indian Ridge ferromanganese, coatings, delta δ MnO2 in the seamount crusts, and well crystallised todorokite and minor amounts of delta δ MnO2 in the abyssal nodules. Enrichment of Mn, Cu, Ni and Mn/Fe ratio is in the sequence, abyssal nodules > seamount crusts > Mid-Indian Ridge samples. Fe is highest in the Mid-Indian Ridge samples followed by seamount crusts and abyssal nodules. Co is enriched (up to 0.47 %) in the seamount crusts. The ferromanganese oxides from the Mid-Indian Ridge, seamount crusts and abyssal nodules appear to be of hydrothermal, hydrogenous and early-diagenetic in origin respectively

Geochemistry of deep-sea sediment cores from the Central Indian Ocean Basin

241-246Four sediment cores from the Central Indian Ocean Basin (CIOB) were studied to characterise the coarse fraction (<63 mu), transition metal and major oxide contents. Transition metals (Mn, Cu, Ni, Zn) show enrichment towards the surface, thought to be of diagenetic origin. Metals are supplied by upward migration from a suboxic to anoxic zone at an intermediate depth of 12-35 cm below the sediment-water interface in all the cores. Buried maxima in transition metal concentration at depth of 26-55 cm below the sediment-water interface may represent relict enrichments formed prior to the formation of suboxic to anoxic zone. R-mode factor analysis suggests that detrital and diagenetic/hydrogenous components are the two main sources of elements in these sediments. The terrigenous index factor [Al/(Al+Fe+Mn)] showed its maximum influence as far south as 14 degrees S from approximately 140 to 100 ky BP (last interglacial maxima). This might be related to discharge of large quantity of sediments by Ganges and Brahmaputra rivers during intensive monsoon in the Asian sub-continent during that period

Size, surface texture, chemical composition and mineralogy interrelations in ferromanganese nodules of central Indian Ocean

201-203Fiftyseven ferromanganese nodules, classified into 3 size class ( 4 cm diam.) class. These observations suggest that the smaller nodules appear to have been influenced more by diagenetic processes that the larger nodules

Biogenic silica in space and time in sediments of Central Indian Ocean

116-120Biogenic silica content in 50 surface sediments and in 7 sediment cores from Central Indian Ocean shows a variation from 1.88 to 35.76%, while radiolarian abundance (number.g-1 dried sediment) ranges from 500 to 345000. Biogenic silica accumulation rate averages 2.25 X 10(-5)g.cm-2.y-1 and it is contributed from 33 to 50% of the total silica. Higher biogenic silica content of the surface sediments is well correlated with Mn, Cu and Ni concentration of the overlying manganese nodules. Higher biogenic silica (30-35%) in the surface sediments from 11-degrees to 13-degrees-S, may be due to higher productivity and better preservation of siliceous tests. The lowest biogenic silica at approximately 100 to 140 x 10(3) y BP is suppressed with higher terrigenous input into the Central Indian Ocean sediment cores