Genesis and evolution of the mass transport deposits in the middle segment of the Pearl River canyon, South China Sea: Insights from 3D seismic data

Abstract

Abstracts Utilizing newly acquired 3D seismic data, piston core, bathymetry and wells, this study investigated the geomorphological characters, genesis and evolution of two main phases of Quaternary mass transport deposits (MTDs) in the Pearl River canyon's middle segment. The older MTDs_1 almost covers the whole trough zone of Pearl River canyon's middle segment with an area of 1570 km2, which is sourced from north, west and south. Whereas the younger MTDs_2 has a much smaller coverage area of 840 km2 and is mainly from the northern slope. These MTDs could be divided into western and northern slope-attached MTDs and southern slope-detached MTDs based on their source areas. Within the MTDs-dominated study area, coarse sediments are presented at the area connecting to the slope channels and canyons. These two phases of MTDs probably occurred at ∼0.79 Ma and ∼0.54 Ma according to a published dating result. The homogeneous, organic-rich fine-grained sediments have high compressibility, preconditioning the generation of weak layers for submarine failures on the low gradient slope in the Pearl River canyon's middle segment. Our results showed that slope canyon types, variations of sediment supply and the regional tectonic evolution exerted important controls on the generation and evolution of these MTDs. The eastern slope canyons with little slope fans have a steeper slope at the canyon mouths, resulting the northeastern MTDs to be prone to retrograde landwards. The change of shelf-channel system from un-incised type to incised type increased the sediment delivery efficiency, resulting in larger scale MTDs_1 in the Pearl River canyon. While the subsequent decrease in the number of incised shelf channels cut down the sediment delivery into the deep-water and reduced the younger MTDs' scale as well. The variation of sediment supply had a greater impact on the development of slope-attached MTDs. The rapid subsidence of Baiyun Sag and tectonic activities of Dongsha Rise during the Quaternary favored the occurrence of the submarine landslides on low gradient slopes in the study area. However, the weakening of the tectonic activities resulted the Quaternary MTDs’ scale to be decreased upwards, especially for the southern slope-detached MTDs. The complex topography formed by the slope-attached MTDs has a greater potential to capture the subsequent turbidity currents from the shelf-edge deltas, bringing the generation of potential good turbidite reservoirs in the deep-water region.