Characteristics of StructuralHSequence and Evolution of Tectonic and Sedimentary of Wan'an Basin in South China Sea

The Wan'an basin is one of the most important sedimentary basins in the southwestern South China Sea. Based on 2D seismic data covering the whole basin, combined with the latest research results, this study analyzes the characteristics of tectonic-sequence and evolution of tectonics-sedimentary infillings of the Wan'an basin. In this study, 8 major 2nd and 3rd order sequence boundaries have been identified in the Wan'an basin. Further subsidence simulation shows that the overall feature of subsidence rate of the basin shows a high-low-high process, with rough characteristics of higher in the east and lower in the west, higher in the north and lower in the south. Combined tectonic-sequences and simulation results of subsidence, evolution of tectonic-sedimentary infillings of Wan'an basin since Cenozoic can be divided into five stages, which are early rifting stage, late rifting stage, rifting-post rifting transitional stage, thermal subsidence stage and accelerated thermal subsidence stage. Since the formation of the basin, the subsidence has mainly been affected by the deep faults caused by the extension of the East Asian continental margin. In Pliocene, the Wan'an fault became the main influencing factor of the basin subsidence, which resulted in the early migration of the basin subsidence center from the middle to the west, and then gradually to the east. From Oligocene to Early Miocene, the basin was in rifting stage, which was dominated by terrigenous clastic deposits. In Middle Miocene, the basin was in rifting-post rifting transitional stage and thermal subsidence has begun since Late Miocene. In these two stages, except for clastic deposits, carbonate deposits were also developed. In addition, compared to transitional stage, carbonate deposits in the thermal subsidence stage were relatively reduced, and the terrigenous clastic deposits were relatively expanded. © 2021, Editorial Department of Earth Science. All right reserved.