Periodic Characteristics of the Paleogene Tectonic Activity and Sedimentation Responses in the Deep-Water of Qiongdongnan Basin, South China Sea

In this study, the periodic evolution and characteristics of the Palaeogene tectonic activity in the deep-water area of the Qiongdongnan Basin were revealed through the identification and analysis of the regional angular unconformity and the characteristics of the periodic fault activity. In addition to a comprehensive analysis of the controls on sedimentary paleogeomorphologic background, sedimentary characteristics and evolution by periodic rifting are systematically discussed. The studies have shown that the tectonic activity of the Paleogene Qiongdongnan Basin underwent three separate rifting phases: Phase-I (T100–T80), Phase-II (T80–T70), and Phase-III (T70–T60). The early phase of rifting was dominated by strong differential block-fault settlement, while the later phase was gradually replaced by homogeneous settlement controlled by regional depressions and a small amount of fault activity, characterized by a weak-strong-weak evolution. From Phase-I to Phase-III, the paleo-geomorphology margin changed from a large gradient to a gentle gradient, the subsidence center moved from the initial basin margin to the later basin center, and the basin-marginal fans extended finitely before developing on a large lateral scale in the later Phase-III. Analyzing the characteristics of periodic tectonic evolution and sedimentation response is important for petroleum exploration in marine basins, such as locating economic reservoirs.