CLAY SUPPLIES IN THE CENTRAL INDIAN BASIN SINCE THE LATE MIOCENE - CLIMATIC OR TECTONIC CONTROL

Mineralogical (X-ray diffraction, differential thermal analysis), geoc hemical [microprobe, inductively coupled plasma (ICP)-atomic emission spectrometry, ICP-mass spectrometry] and Sr-Nd isotopic analyses have been carried out on the clay size fraction of Late Miocene to Pleistoc ene sediments from the Central Indian Basin. The samples were taken fr om five giant cores recovered between 1-degree and 10-degrees-S on a t ransect along 80-degree-E. The clay assemblages are homogeneous and ch aracterized by an alteration of illite- and smectite-rich levels. Most of the clays are detrital and were derived from a unique source: the weathering of the Indo-Gangetic Plain supplied most of the eroded mate rial. Temporal clay mineralogical fluctuations in the depositional bas in reflect environmental changes in the provenance. On the basis of sp ectral analyses of a mineralogical parameter (peak height ratios), the fluctuating smectite-illite clay sedimentation is controlled by perio dic Late Miocene climatic changes. During the Late Pliocene, an irregu lar, probably tectonic, control appeared.