Verdine and Glaucony Facies from Continental Margin Off Chennai, Bay of Bengal

Green and brownish green grains associated with surficial sediments of outer continental shelf and subsurface sediments of upper slope off Chennai have been investigated for their distribution. The green and brownish grains account for 40% of the sediments in the outer continental shelf while in the upper slope the green grains account for 20-90% of the sediments. X-ray diffractograrns reveal that the grains from outer shelf are mainly composed of Phyllite V clay mineral of the verdine facies and a mixture of detrital clays. The grains from the upper slope constitute glauconitic slnectite and glauconitic mica of the glaucony facies. The ferric oxide and potassium oxide contents of the grains confirm their verdine and glaucony facies respectively. Their distribution pattern signifies the palaeobathymetric and palaeoenvironmental conditions of the area. Glaucony facies in upper continental slope apparently belong to the period of Last Glacial Maximum (LGM) and verdine facies in outer continental shelf to subsequent transgression.