Characteristics and genetic development of a low-angle boundary normal fault in Xijiang Main Sag, Pearl River Mouth Basin, China

The Xijiang Main Sag, located in the west-central Zhu-1 Depression, is one of the most important hydrocarbon-rich sags in the Pearl River Mouth Basin, China.To recognize the properties of the boundary fault (Fxj33) in the Xijiang Main Sag, we comprehensively analyze the geometry and kinematics of Fxj33, using high-resolution 3-D seismic data under the constraints of well data.The results show that the boundary fault Fxj33 of about 55 km long and up to 9.5 km displacement at most, is a NEE-trending low-angle normal fault with a dip of 5°-36°.During the evolution of multistage rifting, the fault Fxj33 is characterized by differential activities of different segments along the strike, and jointly controls the evolution of the sub-sags in the Xjiang Main Sag together with the two lines of EW-trending high-angle normal faults.Various structures developed in the Mesozoic basement, including imbricate structures, residual hills and pre-existing fault planes, indicate that the boundary fault Fxj33 was developed by the inversion of the pre-existing Mesozoic thrusting system in the Cenozoic, and subsequently reformed by the EW-trending high-angle fault planes cutting into it during the middle-to-late rifting stage.The research results are expected to be of referential meaning to the study of the boundary faults during rifting in passive margin faulted basins. © 2020, OIL & GAS GEOLOGY Editorial Board. All right reserved.