GEOCHEMISTRY OF DEEP-SEA SEDIMENT CORES FROM THE CENTRAL INDIAN-OCEAN BASIN

Four 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.