Origin of pre-existing basement faults and their controls on new fault formation in Gaoyou Sag, Subei Basin

The Zhenwu and Wubu faults are two major pre-existing basement faults in the Gaoyou Sag, Subei Basin. They were formed during the Indosinian period when the Lower Yangtze plate collided with the North China plate, and strike NEE in the west and NNE in the east. The regional stress field and 3D seismic data showed that the controls of the two faults on the development of the southern terrace can be divided into four periods as follows. (1) Tectonic compression. The north of the Lower Yangtze plate collided with the southeast of the North China plate, developing a series of thrust slip, thrust-motion and complicated dislocation. (2) Tectonic reverse. The Zhenwu fault reversed from a normal fault to a reverse fault. (3) Orthogonal rifting. The Zhenwu fault diffe-rentiated into the Zhen① and Wu① faults which controlled the formation of Zhenwu and Wubu terraces. (4) Oblique rifting. The Zhenwu and Wubu terraces were controlled by NS oriented extensional environment instead of the Zhenwu fault. Tectonic deformations were different in the Zhenwu and Wubu terraces. According to the activity of pre-existing basement faults in new faults, they were classified into four types from strong to weak in turn: inherited, variable, adjusted, and induced. Pre-existing basement faults were the foundation of the southern terrace formation and evolution, and strongly influenced the development of new faults.