Geomorphology and geology of the Bay of Bengal and the Andaman Sea

Abstract

Marine geological studies in the Bay of Bengal were initiated by the Andhra University in early 1950's and have subsequently become widespread during the International Indian Ocean Expedition (IIOE - 1962-65). Geomorphological studies indicate that the continental shelf is relatively wide in the northern Bay of Bengal and in the northern and eastern Andaman Sea and narrow in the western Bay of Bengal. The depth at which shelf break occurs also varies. Several submarine canyons/valleys cut across the shelf-slope region. The 'Bengal Fan' is a major physiographic feature. The Andaman Sea consists of several seamounts, valleys and fracture zones. Reefal structures occur around the Andaman Islands and on the outer shelf off Visakhapatnam. Lithogenic sediments (clayey silts/silty clays) are predominant on the continental margins and Bengal Fan. Relict carbonates of late Pleistocene age are exposed as small patches on the eastern Indian shelf, off Irrawady and on Mergui terrace. Pelagic carbonates are abundant on the Ninety-East Ridge. Authigenic green grain facies at places is associated with outershelf and upper slope sediments on the western Bay of Bengal. Pleistocene phosphorites on the shelf-slope of Chennai serve as analogs of ancient phosphorites. Prospects of oil and gas in the sedimentary basins of the major peninsular rivers and evidences of gas hydrates in the continental slope sediments off Krishna and Godavari are reported. Although the composition of the turbidites differs at certain times, the radiogenic (Sr, Nd) and stable isotopes (C, O, H) indicate that the source sediments are predominantly the Himalayas. Studies on palaeooceanography of the eastern Bay of Bengal and Andaman Sea reveal intense northeast monsoon and higher productivity during the glacial times. The processes influencing sea level changes have to be identified.