Submerged beach ridge lineation and associated sedentary fauna in the innershelf of Gopalpur coast, Orissa, Bay of Bengal

Detailed echosounding and side-scan sonar surveys coupled with SCUBA-diving operations in the innershelf region of Gopalpur, Orissa coast revealed the existence of a submerged NE-SW trending ridge lineation between the isobat hs of 25 and 35 m. Morphology of this ridge indicates parallel to sub-paral lel pinnacles with variable relief and widths. Very steep scarps in the lee ward side of the seabed at many places are attributed to large-scale seabed scouring. Diving operations recovered extensive live sedentary fauna such as sponges, gorgonians, soft and hard corals along with rock encrustations from the ridge features. X-ray diffraction analysis of the rock samples rev ealed the mineral composition of quartz, feldspars, and low and high magnes ium calcite, suggesting the morphological features to be of beach sandstone formation. High-resolution shallow seismic records indicate that the featu res are from the hard subsurface reflector, probably of Late Pleistocene. T he composition of sedentary fauna is discussed and its association over the features is attributed to the availability of porous beach sandstone which favours growth in euphotic zone.