Structural Characteristics Research Of Zhanhua Sag In Bohai Bay Basin

The Zhanhua sag is located in the northern part of the Jiyang depression and is a secondary structural unit of the Jiyang depression in the Bohai Bay Basin.This dissertation studies the structural geometry,kinematics and dynamic characteristics of Zhanhua sag by means of cross-integration studies of structural geology,sedimentary geology,and seismic stratigraphy based on previous researches.The basin grids and the geometrical characteristics of the faults were clarified on the basis of accurately identifying the unconformity of the study area.The development features of the faults and the evolution of the basin are clarified by the analysis of the tectonic evolution.In combination with the regional tectonic geological background and the interactions of the surrounding plates,the fault development and the mechanism of basin evolution in the Zhanhua sag are discussed.Through the above research and analysis methods,this paper has some understanding of the structural features of Zhanhua sag:(1)According to the scale of the fault,the study area mainly develops controlled faults and controlled belt faults and each different level of fault in the plane has a variety of different combinations of styles.Due to different fault combinationin in the study area,different fault zones are formed(Rifty fault depression?Half-Ground Composite fault depression?Barrier composite failure).(2)The structure of the study area is complex,the NW-trending fault is cut by faults in the northeast and north-north-east faults,which reflects the characteristics of multi-phase faults of fault activities,and ultimately complicates the structural features of the study area.(3)There are multiple tectonic movements in the study area,where the strata undergo multiple uplifts and erosions,and multiple sets of unconformities are developed.The structural evolution of the NW-trending and NW-trending seismic profiles reveals an ordered sequence of extrusion-tensioning.(4)The fracture mechanism of the study area:the extrusion and splicing of the North Triassic North China plate and the Yangtze plate resulted in the formation of the NW thrust fault in this area.The reversion of NW-trending faults in the late Jurassic and Cretaceous was the result of sinistral shear of Tanlu fault zone under the level stretching background caused by the ascending of mantle,which was the result of subduction of Pacific plate.A fault basin was formed.In the Paleogene,the transition from sinistral to dextrorotation of Tanlu fault zone resulted in the transition of faults from NW-trending to NE?NEE-trending in Zhanhua Sag.