Abstract: Based on high-resolution 2D and 3D seismic data in Qiongdongnan basin, in northern South China Sea, the characteristics of mass turbidity depositions (MTDs) in different parts of the basin, from the slope system to abyssal plain, have been studied. The result shows that the characteristics of MTDs are different from the eastern to western part in Qiongdongnan basin. In eastern part, the head of MTDs is characterized by the slides, with little or no deformation, and the MTDs are of small scale. While in the western part, chaotic seismic facies and intense erosion are the main features of the head of MTDs, and the MTDs are of large scale, meanwhile, there is a series of parallel or sub-parallel thrusts in the strongly deformed strata in the toe of MTDs. There are mainly two reasons for the differences. Firstly, comparing to the eastern part, the western part of the basin has steeper slope gradient, which is favourable for the development of MTDs. The second lies in the morphology of the basin. The southern high stops the MTDs transporting along the slope. According to the relationship between the head of MTDs and the faults along the shelf margin, the earthquake related to reactivity of the faults is one of the triggers for the development of MTDs.

Key words: Qiongdongnan basin, MTDs, slope system, differences in morphology, sedimentology