Large-scale scours formed by supercritical turbidity currents along the full length of a submarine canyon, northeast South China Sea

Abstract

High-resolution multibeam bathymetric and seismic data enables a detailed morphological investigation of a submarine canyon (West Penghu Canyon) on the northeastern South China Sea margin, where twenty-three (23) scours are observed along the canyon thalweg. These scours form narrow topographic depressions in plan view and show asymmetrical morphologies in cross-section. The identified scours can be further divided into two groups (Types A and B) based on their sizes and relative locations. They are separated by a slope break at a water depth of ~2850 m. Type A scours (S1-S18) occur upslope from the slope break, whereas Type B scours (S19-S23) lie downslope from this same break. The scours are interpreted as net-erosional cyclic steps associated with turbidity currents flowing through the West Penghu Canyon; the currents that form Type A scours reflect higher V, Q, and Δel compared to the currents forming Type B scours. A change in slope gradient and loss of lateral confinement are proposed to control the change from Type A to Type B scours. Furthermore, Coriolis force influences the flow direction of turbidity currents, leading to the preferential development and larger incision depths of scours towards the southwestern flank of the West Penghu Canyon. Our results contribute to a better understanding on the origin of scours in submarine canyons across the world.