Geophysical studies of mass transport deposits on the slope canyon floor with high-resolution autonomous underwater vehicle (AUV) in the Shenhu area and its implications for sediment transportation

Submarine canyons are important pathways for terrestrial sediment moving to the deep water far away from the land, and turbidity current is considered as the primary agent. Detailed sedimentary features of the canyon floor are not clear so far due to the low resolution of conventional geophysical data and complicated operating setting in deep water. Here, in this program, high-resolution autonomous underwater vehicle (AUV) based multi-beam bathymetry data, side-scan sonar data and chirp sub-bottom profiles are jointly used to map the floor of a canyon and image its shallow strata in the Shenhu area. The canyon floor looks quite flat. However, the underlying shallow strata are composed of widespread mass transport deposits (MTDs) which are a little less than 8.4 meters with weak and chaotic acoustic reflections. They are distributed along the canyon floor in an elongated shape and show little direct links with adjacent steep canyon ridges at the middle and lower segments of the canyon. Thus, we suggest the repeated mass wasting downslope on the canyon floor is an effective mechanism for sediment transportation in addition to turbidity currents. The AUV based geophysical exploration is a efficient tool for further studies of marine sedimentation and seabed installation under deep water.