Structural Features of the Jinhu Sag in the Subei Basin and its Petroleum Geological Significance

From Late Cretaceous to Cenozoic, the Jinhu sag (south-west part of the Subei Basin) developed a complex fault system. The fault system includes extensional faults,strike-slip faults and reverse faults which were controlled by the unified regional stress field. The Fault system experienced four stages of evolution:initial extension, inheritance extension, intense extension, and superimposed strike-slip stages. The sag extended weakly in the initial extension stage and the faults had weakly controls on sedimentation except the major fault. In the inheritance extension stage, the basin experienced continual extension; some of the earlier faults were inactive. The major faults such as the Shigang fault and Yangcun fault strongly active and formed the main sags in the intense extension stage. The faults experienced dextral strike slipping and extension in superimposed strike-slip stage. And consequently, the structural pattern of the Jinhu sag was established. The Yangcun and Shigang faults are persistence active faults controlled by the pre-existing basement faults. The Tongcheng fault, a transfer fault which accommodated the strike-slip stress between the Shigang and Yancun faults, was formed in the late stage. The activity of fault system was mainly controlled by the pre-existing faults and region stress filed. Under the influence of the two stage tectonic movements, the Jinhu sag formed the hydrocarbon traps.