Research On Structural Characteristics Of Carboniferous- Triassic Period In Lunnan Area

Located in the north of Tarim Basin in Xinjiang,the Tabei Uplift is a pre Jurassic paleo uplift that runs east to west and presents as a north-facing arc-shaped line.Besides,it is a long-term area of oil and gas migration in Tarim Basin as well as an important area for oil and gas exploration in Tarim Basin.Lunnan low uplift is a secondary tectonic unit in Tabei uplift of the North Tarim Uplift which is mainly located in the middle of Tabei uplift,with Caohu sag to the East,Halahatang depression to the West,manjiaer sag to the South and Luntai uplift to the North.This paper takes the Carboniferous to Triassic as the research object.The research area is Lunnan Oilfield and the surrounding areas which is in Tabei uplift Lunnan low uplift.In this area,we mainly use core,logging,seismic and chemical analysis data of the layer section to study layer division,seismic interpretation,structural features and evolution law.Six geological layers are discussed in this research.They are top surface of the Triassic,the top surface of TI oil group,the top surface of TII oil group,the top surface of TIII oil group,the bottom surface of Triassic and the bottom surface of Carboniferous.Based on the Seismic-geological interpretation of seismic survey lines in research area,the plane structural features,fault distribution characteristics and the formation mechanism of the tectonic belt are studied.According to the tectonic unconformity recognition and sedimentary cycle,the construct pattern of Lunnan Oilfield is divided into stages.Interval transit time method is used to restore the erosion thickness of Carboniferous and Triassic bottom unconformity surface.And then combining the analysis of fault activity with the history of regional tectonic evolution to make the regional tectonic evolution profiles.Based on the above results,the relationship between the tectonic activity and oil and gas is studied and analyzed.From the results,we can see that the Carboniferous and lower strata,because of the uplift in the northern and central areas,are higher in the north and lower in the south.But because a slight stratigraphic inversion started in Triassic,the stratigraphic above of Triassic strata is low in north and high in south.The studied area has experienced several tectonic movements,the development of Lunnan fault zone,Sangtamu fault zone,Lungudong strike slip fault zone and Lunxi strike slip fault zone.These fracture zones have differences in the formation mechanism,direction,the degree of development and the formation of the same time,secondary faults in the fault zone and the development of different nature.The round of the South and Sangtamu fault zone were mainly the inverse fault caused by extrusion stress,nearly east-west,Lungudong and Lunxi strike slip fault zone were echelon strike slip fault caused by tensile stress and formed after Lunnan and Sangtamu fault belt,near the north east direction.The inherited uplift of the studied area resulted in the general erosion of Silurian,Devonian and Permian,the formation of two angles of unconformity surface in the bottom of the Triassic and Carboniferous.According to the above characteristics,the studied area is divided into four stages: relatively stable period,weak extrusion uplift erosion stage,strong extrusion uplift and denudation and low profile forming period.According to the distribution of oil and gas in the structural belt,it is found that the structural features are closely related to the migration and distribution of oil and gas.