Unravelling submarine channel morphology in the lower Bengal Fan through ultra-high-resolution autonomous underwater vehicle (AUV) survey

The Bengal Fan, the largest submarine fan in the world, spanning the whole Bay of Bengal resulted from the India-Asia collision event and subsequent Himalayan orogeny. It is a significant depositional feature formed by the major river systems: the Ganges and Brahmaputra. Previous studies revealed the occurrence of an extensive channel-levee system in the Bengal Fan through various marine geoscientific investigations. In the present study, we have successfully mapped a submarine channel-levee segment in the lower Bengal Fan using hull-mounted multibeam bathymetry data collected for the first time. In addition, we conducted a pioneering study of a submarine channel segment using an Autonomous Underwater Vehicle (AUV) within the identified channel. The identified channel, characterized by moderate sinuosity, maintains a smooth morphology throughout its course, with the channel incision increasing towards the lower course. The microbathymetric observations revealed fine-scale features such as mass wasting, sediment waves and scour/depressions indicating the direct interaction between turbidity currents and the channel floor. The newly identified channel is proposed to result from the channel bifurcation of the previously identified channel W6 described by Curray et al. (2003). This study showcases the importance of near-bottom observations in complex submarine channel-levee systems for a better understanding of the formation processes involved in such systems.