Multifactorial Controls on the Dongdaobei Submarine Canyon System, Xisha Sea, South China Sea

The submarine canyons system is the most widely distributed geomorphic unit on the global continental margin. It is an important concept in the field of deep-water sedimentation and geohazards. Based on high-resolution multibeam bathymetry and two-dimensional seismic data, the dendritic canyon system north of Dongdao island is studied at the eastern Xisha area of the South China Sea. The Dongdaobei submarine canyon is distributed in water depths between 1000 and 3150 m. The main source area in the upper course of the canyon originates from the northwest of Dongdao platform and the Yongxing platform. The sediments from the source area are transported to the main canyon in the form of various gravity flows. Landslides on the slope significantly impact canyon evolution by delivering sediment to the canyon head and causing channel deflection through substrate failure and flow-path reorganization. A large number of pockmarks are distributed around the north slope of the main canyon. The small-scale channels, which are formed as a result of the continuous erosion of the pockmark chains, are connected to the canyon sidewalls. The seamounts are distributed along the south bank of the canyon, exerting a controlling influence on the directional changes in the main canyon’s downstream segment. The formation and evolution of the Dongdaobei submarine canyon are primarily influenced by several factors, including tectonic activity and inherited negative topography, erosion by sedimentary gravity flows, sediment instability, and the shielding effect of seamounts.