The South China Sea continental slope morphology and its relation to the anomalous gravitational field

Abstract

The bottom topography of the studied area of the South China Sea is characterized by an uneven distribution of depths, their sharp variations and the presence of a large number of seamounts. As a result of the research conducted, bathymetric profiles, a bathymetric map and a scheme of Faye anomalies were compiled. Geomorphological zoning was conducted. Sections of bottom distinguished by morphology were identified: 1) weakly dissected slope, steep (angles up to 15°) in the upper part and more gentle (5–7°) to the bottom of the deep-water step, 2) slope eroded by fluvial processes, 3) stepped slope, 4) chains of mountains and flat-topped hills, 5) accumulative bottom of the deep-water plain. It was established that the gravitational field as a whole reflects the complex structure of the bottom, and the local forms of the underwater relief are expressed in Faye anomalies. For elevations, zones of positive anomalies of Faye are marked, and sections of canyon-like valleys were mapped by an intense negative anomaly of the gravitational field to -60 mGal. In the process of endogenous evolution of the region, the relief became more complex. The primary endogenous continental slope was almost everywhere transformed by exogenous processes. Within the shelf, the filling of the basin led to the unification of all its projections into a single raised base. A significant role in the formation of the modern relief was played by large-scale repeated sea regressions, as a result of which the formation of the sedimentary cover was interrupted by periods of its erosion with the formation of planation surfaces. The Late Pleistocene peak of the regression (16–18 thousand years BP), which caused the complete drainage of the shelf areas of the region, caused the erosion of the shelf and the movement of coarse clastic material through submarine canyons and valleys.