CHARACTERISTICS AND STRUCTURAL EVOLUTION OF FAULT SYSTEMS IN NORTHERN QIONGDONGNAN BASIN, SOUTH CHINA SEA

The Qiongdongnan Basin is located in the northern passive continental margin of the South China Sea. Since the Cenozoic, the Qiongdongnan Basin has undergone complex tectonic evolution processes, resulting in fault systems comprising normal faults, reverse faults, and strike-slip faults. Although there has been a lot of studies focusing on the Qiongdongnan Basin, the control of fault evolution on the spatial and temporal geometric variation have not been well documented. In this research, by employing 3D seismic interpretation and seismic attributes analysis, the stratigraphic contacts and fault systems in Cenozoic were interpreted with high-resolution. The temporal deformation rates of four key fault zones were analyzed by calculating the fault offsets versus geological time intervals. The various deformation rates along strikes suggest high level of lateral variation of faulting deformation. By integrating the fault distribution maps, the key fault zones were then subdivided into four segments from east to west. Five representative seismic profiles were restored in 2D MOVE, with extension amounts and deformation rates calculated to reveal the Cenozoic structural evolution occurred in the Qiongdongnan Basin. The balanced profile restoration and statistics indicated that the Qiongdongnan Basin experienced a multi-staged evolution, including the Oligocene rifting stage, the middle Miocene weak compression stage, and the late Miocene depression stage. As the fault systems dominated the distribution of the paleo-highs and lows, it is critical to reconstruct the paleo-geomorphology and understand its impacts on sedimentation patterns in the Qiongdongnan Basin. The erosion amounts of the three key horizons were calculated by considering both the structural trend and thickness variation. The paleo-geomorphology maps were then constructed, indicating that the general structural framework of the Qiongdongnan Basin was generated in late Oligocene and was subsequently altered in Miocene. The characteristics and structural evolution of the fault systems may provide important hints for the petroleum exploration in the northern Qiongdongnan Basin.