Study On The Cenozoic Extensional Transition Structure In Lin Qing Depression

Linqing depression is a secondary structural unit in the southwest of Bohai Bay Basin,which has a good prospect for oil and gas exploration.However,the area is large and the geological conditions of oil and gas are complex,so the degree of research and exploration in different areas is quite different.In order to have a better understanding of the Cenozoic extensional structure in this area,this paper chose the extensional transition structure zones as the perspective of research,in order to provide a certain reference for oil and gas exploration and extensional structure research in this area.Based on the comprehensive analysis of oil and gas exploration data and previous research results,this paper systematically analyzes the tectonic characteristics of the pre-Cenozoic basin,the Cenozoic fault tectonic activities and the characteristics of the controlled half grabens.The distribution,order and structural type of the Cenozoic extensional transition tectonic zones are further studied,and the causes,controlling factors and the formation and evolution process of the transition tectonic zones are analyzed.At last,the relationship between oil and gas and the direction of further oil and gas exploration are discussed.There are five stages of basins with different properties in the pre-Cenozoic in this area,namely,Early Paleozoic,Late Paleozoic,Triassic,Early-Middle Jurassic and Cretaceous.The complex geological structure of the pre-Cenozoic basin was formed by the movement of the Indosinian,early Yanshanian and late Yanshanian.The extensional structures of the Cenozoic basin are mainly controlled by NNE,NE trend?and?order normal faults.The period of activity was mainly concentrated in the Paleogene.The fault activity of Linqing area in the north was earlier(beginning in Ek),and the fault activity of Dongpu sag and Tangyin sag in the south was later(beginning in Es₄).The intensity of fault activity is strong in the south and weak in the north,strong in the east and weak in the west,among which the activity is strongest in Dongpu depression,second in the east of Linqing area,and weaker in Tangyin depression and the west of Linqing area.The activities of large normal faults are segmented,which control a series of extensional half grabens of different scales.The Cenozoic extensional transition structure zone in this area can be divided into three?order transverse transition structure zones(Fengqiu-Lankao,Maling-Huilongzhen,Xiajin-Yaozhan),seven?order transition structure zones and several secondary transition structure zones.Its genesis may be mainly controlled by NW,NWW and nearly EW trend faults and basement structure of Indo-China and Yanshanian.Its formation and evolution can be divided into three stages:Ek-Es₄,Es₃and Es₂-Ed.The extensional structure zone controls the formation of hydrocarbon generating sags,the distribution of source rocks,the development of reservoirs and the accumulation of oil and gas.In the future,the direction and target of further oil and gas exploration in this area is the secondary transformation structure belt in Dongpu depression which has not yet been broken through by oil and gas,and the potential transition structure zones in the east of Linqing area can be explored.