NEOGENE TO QUATERNARY CLAY MINERAL FLUXES IN THE CENTRAL INDIAN BASIN

The late Cenozoic clay sedimentation in the Central Indian Basin was investigated by mineralogical analyses of five very long cores (33-49 m long), which were recovered between 1-degrees and 10-degrees-S along a transect at about 80-degrees-E and compared with data from adjacent ODP and piston cores. Progressive changes occur from North to South, and are especially marked by a decrease of illite and chlorite amounts balanced by increased contents of smectite and kaolinite. These changes arc attributed to a southwards reduction of Himalaya-derived detrital fluxes, and to a correlative augmentation both of smectite reworked from coastal Indian, Indonesian and volcanic submarine sources, and of kaolinite supplied from Australia and blocked by the equatorial divergence. The stratigraphic changes are more diversified than the geographic changes and develop discontinuously. High fluxes of illitic and chloritic materials during the middle-late Miocene reflect major activity of the Himalayan Main Central Thrust. A tectonic relaxation developed during the latest Miocene-early Pliocene, allowing alternating supply of illite-rich and smectite-rich sediments, which suggests periodical changes from distant to more local supply partly controlled by climate and by Indian intraplate deformations. The more abundant and constant amounts of smectite in late Pliocene-early Pleistocene sediments are chiefly attributed to erosion of Indian coastal zones favored by a worldwide sea-level drop. The middle to late Quaternary increase of the illite group resulted from the resumption of the tectonic activity in the Himalaya-Tibet range associated with a general climatic cooling.