The segmentations and the significances of the Central Canyon System in the Qiongdongnan Basin, northern South China Sea

Abstract

The submarine canyons as the important element of the source to sink have attracted the widespread interests in studying their morphologic features, stratigraphic frames, depositional architectures, as well as the related depositional model, hydrodynamic simulation, and hydrocarbon exploration. The Central Canyon System, a large axial submarine canyon, in the Qiongdongnan Basin is developed in Neogene passive continental margin of northern South China Sea, which is paralleled to the shelf break with an “S-shaped” geometry and an NE–NEE orientation. Based on the integrated analysis of high-resolution 2D/3D seismic data and well log data, the whole canyon could be divided into three segments from west to east through its distinct morphological and depositional architecture characteristics, the head area, the western segment and the eastern segment. The canyon shows the classical U-shaped morphology in seismic profiles, and the infillings are composed of a suit of turbidite channel complex in the head area. In the western segment, the canyon demonstrates the sinuous geometry and multiple-shaped morphology in seismic profiles. Four complexes of turbidite channel and mass transport complex (MTC) are observed, which could constitute into two stratigraphic cycles. The canyon in the eastern segment shows V-shaped morphology with steep flanks and a narrow and straight course, which is composed of collapse deposits in the flanks and the sheet sand-MTC complex. The sediment supply, northern continental slope system, paleo-geomorphic characteristics and tectonic setting in the Qiongdongnan Basin are considered as the controlling factors on the development and evolution of the Central Canyon System, each of them have different influences in the three segments. The turbidite channel in the head area was triggered by the abundant sediment supply from western source together with the fault activity at 5.7Ma of the Red River Fault. The evolution of the canyon in the western segment should be the combined effects of the turbidite channel from western source, the mass transport complex from the northern continental slope, and the paleo-seafloor geomorphology. In the eastern segment, the canyon should be constrained by the semi-closed subbasin in eastern Qiongdongnan Basin corresponding to the tectonic transformation at about 11.6Ma. This unique submarine canyon in the Qiongdongnan Basin is suggested to be characterized by axial gravity flow, ascribing to different gravity deposits originated from different sediment supplies and the tectonic activities.