Source-sink analysis based on dynamic provenance evolution: taking Lingshui Formation in Songnan area of Qiongdongnan Basin as an example

Qiongdongnan Basin, a key oil-bearing basin in China, has been gradually expanded the exploration to the deep-water area. The Songnan area, an important provenance in the basin, has typical slope control characteristics in tectonic geomorphology, which is obviously different from the basin margin fault-control area. Due to the sea level fluctuation, the existence of early local provenance was often neglected during oil and gas exploration, which restricts the search for large-scale reservoir in the Songnan area. Based on the dynamic evolution of provenance, we found that two dynamic provenance systems, “dynamic multi-phase type” and “dynamic submergence type”, were mainly developed in the area. During the deposition period of Lingshui Formation (LF) (Oligocene), the effective material supply area of actual fan decreased, and the near-source fan delta deposition was formed in the low and high stages of the third member of LF and the low stage of the second member of LF. The latter had large-scale local provenance with well-developed fan delta sedimentary system in the lower area of the third member of LF. The dynamic provenance system in the Songnan area was influenced by the sea level fluctuation and paleo-geomorphology. The uplift area as a whole evolved from a material supply source forming fans in early period, to an underwater high as a dam in late period. Quantitative analysis on the source-sink components of the dynamic provenance system showed that the size of the source area, the depth of the channel, and their combination pattern were the main controlling factors of sand body formation in the dynamic provenance system in the Songnan area. Therefore, the large-scale provenance in low water level period, the strong downcut channel in the high and steep terrain, and the multiclass complex water system in a gentle terrain background are conducive to the large-scale fan development in the catchment of the study area.