| dc.description.abstract | Considering the potential of elemental data in marine sediments as diagnostic tools of various geological and oceanographic processes, sediment geochemical data from the Indian Ocean region has been reviewed in this article. Emphasis is laid on the literature, where, the processes have been deciphered from geochemical studies and obviously avoiding the literature with mere description of spatial variation. Sediment geochemistry is primarily used in deciphering provenance. Therefore, a section is devoted to infer various sources of lithogenic sediments to the Indian Ocean region. Considering the size and very high discharge rates of rivers debouching northern Indian Ocean, studies involving clay mineralogical, major, trace elemental data, porewater chemistry, isotope geochemistry, rare-earth element fractionation and patterns to delineate the southern limits of influence of Ganges-Brahmaputra river system are described. Other sources of sediments to the northern and central Indian Ocean identified from geochemical and isotopic data are Indonesian volcanic arc, erosion of Crozet and Kerguelen Plateau, Indian sub-continent, Sri Lanka, West Burma, wind blown from Western Australia, Indus River and in situ weathering of Carlsberg and Central Indian Ridge systems. Monsoon is an important climatic feature in the region. Therefore, several geochemical and isotopic proxies such as calcium carbonate, organic carbon, stable isotopes of carbon and oxygen, inorganic elemental data used in interpreting the initiation, temporal variation and the controls on monsoonal variation on geological time scale are discussed. Barium data in DSDP drilled cores has been effectively used as a tool for determining paleoproductivity and also to infer the plate movement in the Indian Ocean region. However, it was suggested that caution has to be exercised in using Ba for paleoproductivity in view of the diagenetic remobilization, or sequestering of Ba with Mn oxides etc. Prevalence of anoxic conditions during last glacial cycle (stages 2, 3 and 4) has been inferred from geochemical proxies. However, it has been shown in the review that the changes shown by Sarkar et.al. could well be explained by invoking sub-oxic diagenetic processes. Other redox related events using Mn and Ce have been discussed. Geochemical studies were also used in studying the volcanogenic sedimentation in the Indian Ocean region including the seismic and aseismic ridges, Kerguelen Plateau, Indonesian volcanic arc, and those from the intraplate volcanoes. Hydrothermal activity as revealed by sediment geochemistry in various studies such as fish debris from Red Sea recording hydrothermal activity; 2) episodic hydrothermal activity in Thetis Deep; 3) hydrothermal activity at Rodriguez Triple Junction were reviewed. During the review, pitfalls in using some of the geochemical tracers in view of their susceptibility to sedimentary processes is also discussed. | |
