“Source to sink” analysis of a sea basin: The Quaternary deepwater turbidite fan system in Pearl River Valley-Northwest subbasin, Northern South China Sea

Using high resolution seismic profiles and multi-beam echo-sounding data acquired in recent years, a large complicated Quaternary deepwater gravity flow depositional system is identified in the Pearl River Valley (PRV) and Northwestern subbasin (NW subbasin) of the northern South China Sea (SCS). It runs through the whole continental slope along a channel in NW-SSE direction, discharged in the NW subbasin to form a deepwater turbidite fan system. Extending from the northern valley to the southern sea basin, it is more than 320 km long longitudinally. From the aerial view, the turbidite fan shows different features on continental slope and in sea basin. In the slope area, it may be divided into three sections, the north, middle and south sections respectively. The north section is mainly an incised channel under erosion. The middle section shows channel filling and natural levee, while the southern section is composed of the channel-levee complexes and lobes. In the NW subbasin, it is characterized by lobes with large scale of fan-shaped sand bodies, extending for 70 km towards the south direction. The Pearl River Valley, which goes through the continental slope of northern South China Sea, is the main passage for sediments to be transported from the continental margin into the abyssal plain. Vertically, the turbidite fan could be subdivided into three phases and the depocenters of the three phases are not consistent. The first phase of the fan or the oldest deposit is the largest in scale comparing to the other two. The three fans migrate along the slope, suggesting a retrogression towards continent owing to the rising of relative sea level during Quaternary. The regional pattern of the PRV-NW subbasin turbidite fan system has recorded a rather completed process for a gravity flow moving from continent erosion to sediment unloading and provided a perfect example for a “source-conduit-sink” system. This paper carefully described the system and has provided a reference for the depositional model of the deepwater fan in early Neogene in the northern South China Sea, which is significant to prospecting of deepwater oil and gas resources.