Sand-rich Pleistocene deep-water channels and their implications for gas hydrate accumulation: Evidence from the Qiongdongnan Basin, northern South China Sea

Abstract

Deep-water turbidite channels are conduits for transporting terrigenous clastic sediments into the ocean, and channel deposits can also act as high-quality hydrocarbon reservoirs. In this study, based on high-resolution 3D seismic data and logging-while-drilling data, four Pleistocene turbidite channels are identified and characterized in the deep-water area. These deep-water channels are sinuous with V- or U-shaped on the seismic profiles, and their evolutionary history can be divided into Unit 1 (Erosion-dominated stage), Unit 2 (Erosion-Deposition stage), Unit 3 (Erosion-Deposition stage), and Unit 3 (MTDs-dominated stage). The internal fillings of these channels are almost basal lags with high-amplitude reflections at the bottom, pelagic sediments with low-amplitude reflections, and mass transport deposits with translucent/transparent seismic facies. Since sand-rich sediments dominate the deep-water channel-levee systems in Unit 3 in the study area, they could act as shallow gas reservoirs and facilitate the accumulation of gas hydrates. By analyzing the source-to-sink systems around the basin, the source of the sediments within the deep-water channels is discussed, which are mainly from the Truong Son Belt. Floods, sea level fluctuations, and earthquakes are the most likely triggering mechanisms of turbidity currents in the Qiongdongnan Basin. This study provides new insights into the Quaternary deep-water sedimentary process, gas hydrate exploration, and source-to-sink systems in the northwestern South China Sea.