Cenozoic Tectonic Characteristics and Evolution of the Southwest Bohai Sea, China

Based on the detailed description of the fault system and the regional dynamic background of the study area, the Cenozoic structural development and evolution characteristics of the southwest Bohai sea and the migration law of the sedimentary-subsidence center were studied by using 3D seismic data and drilling data.The results show that the NW, NNE, NE and EW trending faults were mainly developed in the study area. The NW-trending faults were Cenozoic revived faults, which control the development of the NW-trending structural belt. The NNE-trending faults control the formation of the uplift, including Kendong fault, Gudong fault and Changdi fault, which all belong to co-direction shear faults of the Tan-lu fault zone, and have obvious strike-slip characteristics. The NE-trending faults and EW-trending faults were extensional faults, which further complicate the tectonic pattern. Under the control of the NNE-trending faults and near EW-trending faults, the sedimentary thickness of the Paleogene strata in the study area changed from thick in the south and thin in the north in the early stage to thin in the south and thick in the north in the late stage. In the sedimentary period of Es₃, the uplift was highly segmented. The mountains were high and the surrounded lakes was deep, and the water bodies were connected between the depressions. During the sedimentary period from Es₂ to Es₁, the regional structure subsided and the lake area expanded. In the sedimentary period of Ed, it was high in the south and low in the north, and basically distributed regionally. After the Neogene, it finally became a unified whole to accept deposition. Generally, the overall evolution can be divided into four stages: ① Confined fault-depression stage of Ek to Es₄；② Strong fault-depression stage of  Es₃ to Es₂；③Weak fault depression stage of Es₁ to Ed；④ Weak extended depression stage of the Ng-Nm.