Sedimentary differences between different segments of the continental slope-parallel Central Canyon in the Qiongdongnan Basin on the northern margin of the South China Sea

Submarine canyons have been the subject of intense studies in recent years because of their academic significance to studies of climate signals, eustasy and tectonic movement of the neighbouring area and their economic significance for hydrocarbon exploration in deep-water areas. The Central Canyon in the Qiongdongnan Basin runs parallel to the continental slope, and has a length, width and depth of 520 km, 2-15 km and 270-800 m. Using seismic and well log data, we analyses the sedimentary differences and controlling factors of the sediments in the different segments of the Central Canyon. The sediments within the Central Canyon can be subdivided into five phases of the secondary canyon filling. The most typical features of each phase of the secondary canyon are high- and low-density turbidity currents developed in the phase 1-2 of the secondary canyon, the muddy debris flows, turbidity currents and mass transport deposits in the phase 3, the high-density turbidity currents in the phase 4, the hemi-pelagic mudstone and mass transport deposits in the phase 5. There are four depositional models corresponding to the head area, upstream segment, middle reaches and downstream segment of the Central Canyon were established. It is characterized by muddy matrix-supported conglomerates and thickly massive sandstones with the feature of upward fining and thinning deposited in the head area, the thickly high net to gross sandstone infilled in the upstream segment, the thinly interbedded sandstones and mudstones and muddy mass transport deposits developed in the middle reaches, and the extensive hemi-pelagic mudstone infilled in the downstream segment. The transformation of the debris flows into turbidity currents and high-density turbidity currents into low-density turbidity in the head and upstream segment, supersaturated filling in the upstream segment, extensive development of mass transport deposits in the middle reaches, under-compensation filling and widely development of canyon wall collapse in the downstream segment are the main reasons contributing to the sedimentary differences between different segments of the Central Canyon.