Geophysical Evidence for Carbonate Platform Periphery Gravity Flows in the Xisha Islands, South China Sea

High-resolution bathymetric and partial seismic data were utilized to determine the characteristics and distribution of masstransport deposits(MTDs) in the Xisha area, North of the South China Sea. Many isolated carbonate platforms are found in this area,providing mass-wasting materials as a sediment source for MTDs. The MTDs in the study area were divided into three types(slide,slump, and debris flow) based on their rheological properties. The MTDs were mostly distributed at the toe of the carbonate platform slope, where a large amount of carbonate debris accumulated. A total of 32 MTDs were identified on the carbonate platform slopes. A systematic assessment of the MTD morphometric parameters showed that their total area covered 2225.2 km~2, with the largest MTD covering 354.1 km~2. These MTDs differ largely from the MTDs of other areas, especially in terms of sediment compositions and deposit processes. Gullies and channels on the slope and reefs on the top of the platform act as sediment conduits and carbonate-producing sources, respectively, playing vital roles in the distribution and generation of gravity flow deposits. The development model proposed in this work states that reefs disintegrate into carbonate debris and mix with seawater to form gravity flows, which scour the seafloor and accumulate at the downslope, eventually resulting in failure. Sediments from these failures turn into gravity flows, flowing into submarine canyons and channels. The results of this research further our understanding of the development pattern of MTDs in a carbonate setting.