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

Mineralogical (X-ray diffraction, differential thermal analysis), geochemical [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 Pleistocene sediments from the Central Indian Basin. The samples were taken from five giant cores recovered between 1-degree and 10-degrees-S on a transect along 80-degree-E. The clay assemblages are homogeneous and characterized 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 material. Temporal clay mineralogical fluctuations in the depositional basin reflect environmental changes in the provenance. On the basis of spectral analyses of a mineralogical parameter (peak height ratios), the fluctuating smectite-illite clay sedimentation is controlled by periodic Late Miocene climatic changes. During the Late Pliocene, an irregular, probably tectonic, control appeared.