Cenozoic faults evolution of Wenchang 9/8 area in Pearl River Mouth Basin, and the response to clockwise rotation of regional extension stress in northern margin of South China Sea

As the most important hydrocarbon-rich area of Wenchang A sag of Pearl River Mouth Basin, the Wenchang 9/8 area has attracted more scientific attention in fault-related hydrocarbon reservoirs. Here, we employ 2D and 3D seismic data and syn-rifting fault maps to analyze the fault characteristics and evolution of Wenchang 9/8 area, and its response to clockwise rotation of regional extension stress in northern margin of South China Sea. The results demonstrate that three NE- and NW-striking fault belts developed in Wenchang 9/8 area during Cenozoic, respectively. The pre-existing NE- and NW-striking basement faults and clockwise rotation of regional extension stress influenced the evolution of fault system in this area. During Paleocene to Eocene, the NE-striking sag-controlling faults activate intensively, under the control of NW-SE-directed extension. The extension was derived from the NW-direction subduction retreat of Pacific Plate, and the extension direction is perpendicular to pre-existing NE-striking faults, which resulted in the reactivation of the pre-existing NE-striking faults and the formation of the new NE-striking secondary normal faults. During Oligocene to early Miocene, the fault activity of the NE-striking sag-controlling faults weaken rapidly, resulting in segment activate and generate three NE-striking fault belts. These NE-striking fault belts were consisted of a series of new E-W-striking secondary transtensional faults. And the three NW-striking fault belts were started to reactivate in the form of abundant E-W-striking secondary transtensional faults, which were influenced by oblique extension. The characteristics of fault system indicated that N-S-directed extension worked on the study area, and the extension stress shifted clockwise from NW-SE to N-S during this stage. The clockwise rotation of the extension was believed related with the India-Eurasian collision and southern ward subduction of the Proto-South China Sea block. During middle Miocene to present, the NE-striking fault belts stopped. While the NW-striking fault belts activate continually, and each fault belts were consisted of a series of newly-formed NWW-striking secondary transtensional faults distributed in en-echelon. The NWW-striking secondary transtensional faults were formed under the control of NNE-SSW-directed extension, which influenced by regional extension stress further clockwise rotate to NNE-SSW direction. This extension was derived from the Philippine Sea Plate NWW-direction obduction, which leading to arc-continent collision at Taiwan Island, while giving rise to the NNE-SSW-directed extension at Pearl River Mouth Basin. Cenozoic evolution of fault system in Wenchang 9/8 area, Pearl River Mouth Basin revealed by this study not only provides guidance for petroleum exploration, but also affords implication for the research on tectonic stress field in northern margin of South China Sea.