Abstract

The eastern margin of the Indian subcontinent is a passive type of continental margin. Phanerozoic sedimentary rocks ranging from Permian to Neogene are intermittently exposed along the coastal plains. There are five sedimentary basins along the eastern margin viz., the Cauvery basin, the Palar basin, the Godavari-Krishna basin, the Mahanadi basin and the West Bengal basin. They are mainly clastic basins. Their formation was initiated around late Jurassic times by taphrogenic movements associated with the break-up of the Gondwana land. At the outset these basins were differentiated into ridges and depressions trending parallel to the Archaean structural grain. These ridges and depressions controlled sedimentation during the Mesozoic They had a subdued influence during the Palaeogene and almost none in the Neogene. There was late Mesozoic-early Tertiary basaltic volcanism to a varying extent in all the basins except the Palar where the subsurface information available is scanty.

The Godavari-Krishna and West Bengal basins show great thickening of the Neogene across a hinge zone associated with growth faults and rollover structures. High pore-pressures were encountered in the argillaceous sequences underlying relatively coarse normally pressured regressive sequences. However, shale diapirism is clearly seen only in the Godavari-Krishna basin. Spectacular channel-cut-and-fill features are seen in the West Bengal basin and to a minor extent in the Godavari-Krishna basin.