Structural Evolution of Tongcheng Fault Zone in Jinhu Sag,North Jiangsu Basin

The faults in the Jinhu sag,North Jiangsu Oilfield,have strong activities. Faults with different size,different properties and different periods interweave together to control the formation and distribution of hydrocarbon resources in the sag. The Tongcheng fault zone is located in the south of the Jinhu Sag and is a structural uplifting belt. It has mainly experienced the Wubao and Sanduo tectonic movements during the sedimentation in Palaeogene,which formed the complicated fault system and made it into a complex fault-nose and fault-block reservoirs. In the plane,Tongcheng fault is a nearly SN-trending linear belt and the dip of southern part is east and northern part is west. There are many lower-order faults on both sides of the main fault. The strike of the secondary normal fault in the east plate is NE and the dip is NW. The strike of the secondary normal fault in the west plate is nearly E—W and the dip is NNW. These lower-order faults intersected Tongcheng fault with acute angle and formed en echelon structure. There are different views about its characteristics of structural evolution.Based on the analysis of structural evolution section and the tectonic stress field modeling,the Tongcheng Fault zone experienced a evolutionary process from simple to complex in Palaeogene. In the Funing period,controlled by Yangcun fault,the secondary faults in the east plate of Tongcheng fault formed first under the NW—SE tensile stress. In the late of Sanduo periods,anticlines formed and the thrust fault developed by the extrusion press in near E—W. At the end of Sanduo period,Tongcheng fault is considered as a typical Pshear strike-slip normal fault.