Growth And Evolution Of Faults During Fault-Depression Transition Period And Their Control On Deposition

The characteristics of fault activity and its control over sedimentary stratigraphic sequence and sand body distribution are one of the research hotspots in sedimentary basin analysis.Taking Xinzhao area in the south of Qijia Gulong sag in Songliao Basin as an example,using seismic,drilling and logging data,under the guidance of sedimentology,stratigraphy and seismic sedimentology,this paper finely depicts the geometric characteristics of synsedimentary faults in the area,quantitatively analyzes the kinematic characteristics of synsedimentary faults by fault drop method,and further restores the structural evolution history of the study area by using equilibrium section method.On this basis,through seismic facies Based on the analysis of logging facies,stratigraphic division and correlation are carried out,and the influence of faults on the distribution of sedimentary sand bodies is discussed.The understanding is as follows:Most of the faults developed in the study area are near north-south synsedimentary faults.During the sedimentary period of the first member of Qingshankou Formation and the second and third member of Qingshankou formation,the tectonic activity is strong.At the end of the second and third member of Qingshankou formation,the regional tectonic pattern is basically formed,and the profile combination styles of "graben type" and "Horst type" are mainly developed,with occasional "cabbage type","ladder type","Y-type" or "anti-y-type".As a whole,it has a structural pattern of alternating distribution of "graben Horst".In addition,during the sedimentary period from the first member of Qingshankou formation to the second member of Nenjiang Formation,the study area mainly experienced the tectonic evolution stage of "from the end of fault depression transition to depression period".The period from the first member of Qingshankou formation to the second and third members of Qingshankou formation is the end of fault depression transition,and the period from the first member of Yaojia formation to the second member of Nenjiang Formation is the depression period.The fault activity in the area has the episodic characteristics of "from strong to weak and then strong",that is,the fault activity is the strongest in the sedimentary period of the second and third members of Qingshankou Formation and the weakest in the sedimentary period of the second and third members of Yaojia formation.From the sedimentary period of the first member of Nenjiang Formation,the fault activity becomes stronger.Four subfacies,including shore shallow lake,semi deep lake,turbidite fan and braided river delta front,are mainly developed in the study area,with a total of seven microfacies.From the superposition map of sand body thickness isoline,sand ground ratio isoline and fault,it can be found that during the sedimentary period from the first member of Qingshankou formation to the second and third member of Qingshankou formation with strong fault activity,the sand body has the trend of "enrichment" to the descending side of the fault,and often forms "shore shallow lake beach bar sand" or "gravity flow rosette sand".During the sedimentary period from the first member of Yaojia formation to the second and third member of Yaojia formation with weak fault activity,the distribution of sand bodies in the area is basically not affected by faults.