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

Abstract

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 isobaths of 25 and 35 m. Morphology of this ridge indicates parallel to sub-parallel pinnacles with variable relief and widths. Very steep scarps in the leeward 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 revealed the mineral composition of quartz, feldspars, and low and high magnesium calcite, suggesting the morphological features to be of beach sandstone formation. High-resolution shallow seismic records indicate that the features are from the hard subsurface reflector, probably of Late Pleistocene. The 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.