The Upper Cretaceous prototype basin of the Chaoshan depression in the northern South China Sea and its tectonic setting

Mesozoic strata of the Chaoshan depression revealed by well MZ-1 provides critical data for the analysis of the Late Mesozoic tectonic evolution of the northern South China Sea. Based on interpreting the seismic profiles calibrated through well log MZ-1, a systematical tectono-stratigraphic analysis has been carried out. A regional unconformity Tm30 was identified, and isotope dating determined that Tm30 formed during late Early Cretaceous to early Late Cretaceous. Accordingly, the distribution of the Upper Cretaceous in the Chaoshan depression was determined. In addition, a large-scale Xingning-Dongsha thrust-fold belt was recognized in the southwest of the research area, which consists of several NW-SE extending, westward dipping imbricate thrust faults and associated asymmetric folds, posing a significant impact during the deposition of Upper Cretaceous. Due to the lack of typical characteristics of a rift basin in the Upper Cretaceous sequence, it can be inferred that the transition of the northern margin of the South China Sea from an active margin to a passive margin postdates the end of the Late Cretaceous. Our research results suggest that in a general tectonic setting of the closure of the remnant Tethys oceanic basin about 80 Ma ago, a strong collision happened between the South China Sea and South China continental blocks. The fold and thrust system could develop near the collision zone, such as in the Reed Bank and southwest of the Chaoshan depression, and further controlled the development of the Late Cretaceous peripheral foreland basin of the Chaoshan depression.