New Insights into the Distribution and Evolution of WNW-Directed Faults in the Liaodong Bay Subbasin of the Bohai Bay Basin, Eastern China

WNW-directed faults are widespread in eastern China, but debates regarding their distributions and evolutionary processes remain unsettled. Based on the latest 3-D seismic data, a series of WNW-directed faults south of the Liaodong Bay subbasin was identified, for which the evolution and formation mechanisms were discussed. The results show that four WNW-directed faults are characterized by poor continuity and nearly parallel orientations. Vertically, they exhibit listric geometries and cut through Paleozoic and Mesozoic formations. Since the late Triassic, these faults began as reverse faults under nearly S-N horizontal compression. In the Jurassic, those faults maintained their reverse-faulting activities with dramatically decreased intensities. In the Early Cretaceous, the WNW-directed faults were changed into normal faults under regional extension and were influenced by the sinistral strike-slip movement along the Tan-Lu fault zone. In the Late Cretaceous, the WNW-directed normal faults probably stopped moving due to a regional compressional event. During the Paleogene, the WNW-directed faults were reactivated with decreased intensities and were cut by NNE-directed faults. Here, we emphasize that the evolution of the WNW-directed faults could shed light on the regional tectonics. The WNW-trending faults that developed in the Liaodong Bay subbasin are closely related to the faults in the Yanshan orogenic belt. Therefore, investigating the characteristics and origin of WNW-induced faults will provide evidence for the tectonic evolution of the North China Block. In addition, the development of WNW-directed faults in the southern Liaodong Bay subbasin was conducive to the formation of buried Mesozoic and Paleozoic hills and hydrocarbon accumulations. In addition, we suggest that the compressional segment of the conjugated strike-slip transition zone that was formed by the interaction of the WNW- and NNE-directed strike-slip faults was conducive to hydrocarbon accumulations.