Pliocene seismic stratigraphy and deep-water sedimentation in the Qiongdongnan Basin, South China Sea: Source-to-sink systems and hydrocarbon accumulation significance

Abstract

This study uses high-quality two-dimensional (2-D) seismic and well data to analyse seismic stratigraphy and deep-water Pliocene sediments in the Qiongdongnan Basin (QDNB), South China Sea. Eight major seismic facies were identified based on the amplitude, continuity, configuration, and external geometry of seismic reflections. Among them, sigmoid progradational configurations, oblique progradational configurations, mound-shaped chaotic configurations, and mound-shaped hummocky configurations are newly identified seismic facies indicative of provenance and water system significance. They were interpreted as a Pliocene-aged eastern shelf-edge delta, a western shelf-edge delta, and eastern and western submarine fans in QDNB. Consequently, two sets of Pliocene shelf-edge delta-continental slope canyon-submarine fan systems were established in the QDNB. From the approximately NNW–SSE progradation of the shelf-edge delta, the characteristics of the approximately ENE–WSW distributed continental slope system, and the definition of a source-to-sink system, as well as previous heavy mineral research, we conclude the existence of two Pliocene sources from Hainan Island in the northern QDNB, corresponding to the Lingshui River and Wanquan River. Two independent and complete source-to-sink systems (S2S-2, S2S-3) were distinguished from the northern Hainan Island to the basin area. S2S-2 is located in the western QDNB, which includes the Lingshui River-western shelf-edge delta-continental slope canyon-submarine fan. This source-to-sink system has more sand-rich material and better reservoir conditions than S2S-3 in the eastern basin, predominantly due to a higher quality granite parent rock, abundant provenance, and a large-scale delta and submarine fan.