The Study On The Evolution And Genetic Mechanism Of Fault System In The Middle-shallow Formations In Northern Daqing Placanticline

Based on the whole structure of the study area,this paper makes a comparative analysis of the fault geometry characteristics of different structural belts in northern Daqing Placanticline,the structure units of the study area are divided.and make a detail analysis on the fault developmental characteristics of different structure units.The formation and evolution of faults in northern Daqing Placanticline are determined by means of fault plane depth contour map of fault distance and contours map of throw on fault surface,combined with member precise correlation in well profiles and growth index profile after defining the entire structure of the study area.Then the fault system is divided.Finally,the formation mechanism of different fault systems are analyzed and discussed combining with the regional stress field.Based on that,physical simulation experiments are designed to simulate the formation process of type I faults,type V faults and the fault type inversion anticline focussing on the Saertu inversion anticline.The faults in study area are divided into 5 sets of fault system according to their geometry and kinematics characteristics: type I faults,which trend NEE,break through the layers of T11 to T06 or T11,formed in the end-of-Nenjiang formation-the end-of-Ming formation-the end of Paleogene period of inversion stage;type II faults,trend NNW-NWW,break through the layers of T11,active in Yaojia formation to member 1or member 2 of Nenjiang formation;type III faults,whose strike are NNW-NWW,break through the layers of T11-T06,active in Yaojia formation to member 1or member 2 of Nenjiang formation and reactive in inversion period;type IV faults,trend NW-NNW,break through the layers of T2-T06,which are segmented faults in vertical direction,active at the Qingshankou formation,Yaojia formation-member 1or member 2 of Nenjiang formation and inversion period.Type V faults,NNE trend faults,break through the layers of T5-T06,formed in rift stage and reactive at the inversion stage.The formation of the positive inversion fault and the fault type inversion anticline,which results from the activity of central uplift of the ramp-flat normal fault during the inversion stage,is controlled by the inversion pattern of the ramp-flat normal fault.The positive inversion fault is controlled by the NWW tensile stress field during the depression period,forming the pre-existing normal fault,inversed during the inversion stage affected by the pre-existing ramp-flat normal fault.Type IV fault,which formed during the depositional period of Qingshankou formation,are controlled by WE directional tension stress field,then transformed into NW-NNW strike faults by sinistral rotation and compressive shearing stress field during the inversion stage.type II and type III fault formed resulting from the reversal of the NEE-SWW stretching component of the sinistral rotation and compressive shearing stress field of the inversion period.Type I faults are controlled by the local tensile stress field at the top of the inversion anticline,the strike of faults are controlled by the NNW compressional stress component of the inversion stage.