Abstract：The post-rifting subsidence characteristics of the Pearl River Mouth Basin,located in the northern margin of the South China Sea,are different from those of typical intracontinental rift basins,and have distinguishing feature of the South China Sea. The results show that there are four stages of orderly differential subsidence in post-rifting stage: (1)During the early Oligocene(~ 33~27 Ma),the basin was dominated by slow subsidence and characterized by large-scale transgression;(2)During the late Oligocene(~ 27~23 Ma),the basin characterized by the strong subsidence of Zhu IV depression,adjacent to the northwest sub-basin of the South China Sea. Differential subsidence controls the development of shelf-slope break zone and the distribution of shallow-water and deep-water sedimentary environment respectively in shelf and slope during this period;(3)During the early and middle Miocene(~23~10 Ma),the strong subsidence area extended northward to Zhu II depression,especially the Baiyun sag,which resulted in the northward transition of continental shelf slope break and established the present sedimentary environment pattern of shallow-water and deep-water respectively in shelf and slope;(4)From late Miocene to present(~10~0 Ma),the tectonic subsidence of the continental margin gradually weakened. The continental slope changed from a depositional area to a bypass area, and a large number of sediments entered the northwest sub-basin. The initial time of rapid subsidence in Oligocene corresponds to the transition of the spreading ridge in the South China Sea. Post-rift subsidence of continental margin expands northward with the southward transition of spreading ridge,accompanied by early strength and late weakness of magmatism. The amount of subsidence is positively related to the thinning degree of the crust during the rift stage. It reflects that the continental margin lithosphere experienced the evolution process of early balanced adjustment of flexure and the orderly evacuation of mantle materials to the south,because of the transition of spreading ridge in the South China Sea. The orderly differential settlement of the Pearl River Mouth Basin controls the development of the shelf slope break zone,and then controls the distribution of the shallow water and deep water sedimentary systems. Different depression zones in the basin have different tectonic subsidence history,which shows that their thermal evolution history must have the same zoning differences,thus having different hydrocarbon generation and diagenesis laws. It provides reference for the exploration and research of continental margin rift basins.
Zheng Jin-Yun,Pang Xiong,Liu Jun et al. Staged differential subsidence and its genetic mechanism in post-rifting stage of Pearl River Mouth Basin[J]. JOPC, 2022, 24(1): 85-98.
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