Marine geophysical investigations across the submarine canyon (Swatch-of-No-Ground), northern Bay of Bengal

Abstract

Multibeam swath bathymetry, gravity and magnetic investigations were conducted across the major deltafront canyon known as Swatch-of-No-Ground in the northern Bay of Bengal. The study reveals that the canyon is a 300 m deep and 18 km wide depression with step-like micro-terraces running in NNE-SSW direction. The depth to the seafloor topography varies from 900 to 1459 m with 100-150 m thick levee sediments deposited on both the edges of the canyon as seafloor swells spreading over a distance of 10-20 km. In the area north of the 20°07'N lat., the canyon is characterized by a gentle step-like slope towards the western flank and a steep slope towards the eastern flank, while in the area south of the 20°07'N lat., the morphology of the canyon is vice versa. The anatomy of the canyon suggests that the turbidity sediments flow in a semi-circular manner within it. When the muddy sediments strike the flank within the canyon, a part gets bounced-off in an orthogonal direction to the semicircular turbidity flow leading to the formation of step-like small terraces on the other flank of the canyon. The canyon is associated with a low gravity field of about 15 mGal and weak magnetic field of the order of 30-40 nT. The model study revealed that the submarine canyon is not associated with any structural discontinuities such as faults and folds. Hence, it is surmised that the submarine canyon is a morphological feature formed by major river flow and underwater currents in the northern Bay of Bengal.