Stratigraphy and structure of Liyue Basin and its implication for South China Sea break-up

Locating in the north of Nansha block, Liyue Basin departed from South China in middle Cenozoic. Experienced four tectonic phases, it is a complicated superimposed basin. Through seismic reflection profile interpretation and drilling as well as dredge sample analysis, we conjectured that there developed Mesozoic and Cenozoic marine deposits. The sedimentary strata are divided into three structural layers by two regional unconformities, which are Late Cretaceous interface and Mid-Miocene interface respectively. The bottom layer is thick Mesozoic sediment, where tilting fault-block and broad fold structures developed. The middle layer is thin rift stage sediment from Palaeocene to mid-Miocene. Absent in uplift area, it displayed typical half graben sediment filling. The top layer is post-rifting marine sediments, continuous and steady. The northeast-trending faults developed in early Cenozoic and controlled the early Cenozoic sediment filling in half graben. These faults indicated that Liyue basin underwent strong tensional tectonic movement above the Mesozoic sedimentary formation. Undergoing the Mesozoic and Cenozoic tectonic evolution, Liyue Basin recorded the transformation process from active margin to passive margin. Through physical and numerical simulation and comparision with Chaoshan depression, we made two conclusions. First,based on previous study results, the Liyue Basin was neighboring Chaoshan depression in Mesozoic, both developed NE-trending wide fold. There are some differences between them too. Reverse faults were revealed in Mesozoic Chaoshan depression but not in Liyue basin. During early Cenozoic, Liyue Basin rifted strongly with many tilt normal faults, while we don’t find rift fault in Chaoshan depression. Considering that the compression in Mesozoic came from the westward subduction of Pacific toward Eurasia, we conjecture that Liyue Basin may locate to the west of Chaoshan depression in Mesozoic, thus the Chaoshan depression underwent stronger compression than Liyue Basin. Second, Liyue Basin located above thinned continental crust before South China Sea opening. The existence of the rigid Reed Bank north of Liyue Basin may be an important factor for basin tectonic evolution. The slightly thinned Reed Bank may cause its northern neighbor areas thinned greatly and caused the cliffy faults developed toward the sea basin. Liyue Basin experienced weak extension and subsidence in Cenozoic.