Research On The Structural Characteristics And Genetic Mechanism Of The DACHIGAN Structural Belt In The Eastern Sichuan Basin

The DACHIGAN structure is located in the east of the Sichuan Basin.It is a typical high-steep anticline structure in the NNE-trending barrier fold belt in eastern Sichuan.The main body of the anticline is located in the Zhongxian to Fuling area.It is a large gas-bearing structure that has been proven so far.Based on the analysis and summary of the regional geological background,this paper discusses the structural characteristics,formation,evolution and genetic mechanism of the DACHIGAN anticline through geological surveys,seismic profile fine structure interpretation,structural evolution history analysis,and structural physical simulation experiments.the following main understandings can be drawn:1.The DACHIGAN structure is a long and narrow asymmetrical anticline in the SW-NE direction,about 70 kilometers long and 10 kilometers wide.The north-west flank is gentle,with an inclination angle of about 20-30°,and the south-east flank is steep and the inclination is up to at 84°,the Middle Triassic Leikoupo Formation and the Upper Triassic Xujiahe Formation are exposed in the core of the anticline.The two wings are from the Lower Jurassic Zhenzhuchong Formation to the Upper Jurassic Suining Formation,in Longtou-Diaozhongba,A reverse fault about 23km long is exposed in the area.2.According to the analysis of drilling and seismic profile deformation characteristics,there are mainly two sets of detachment in the Middle Triassic Jialingjiang Formation and Middle Cambrian Gaotai Formation in the study area.They divide the sedimentary caprocks in the study area into upper,middle and lower sections,three sets of structural deformation layers.The upper structural deformation layer is the stratum?T₂l?J?above the gypsum salt rock of the Jialingjiang Formation of the Middle Triassic.The faults in this deformation layer are basically not developed,and the faults break through the surface only in the northern section of the anticline,Obliquely closed and high and steep;the middle structural deformation layer refers to the stratum??₂g?T₁j?between the gypsum salt rock of the Middle Cambrian Gaotai Formation and the Middle Triassic Jialingjiang Formation.The faults are extremely developed in this deformed layer.In the section,there are developed inverse faults with a southwest trend and a northeast trend in a"Y"shape;the lower structural deformation layer refers to the strata?An Z??₁?below the gypsum salt rock of the Middle Cambrian Gaotai Formation.The deformed layer has almost no wrinkles,is almost horizontal,and the substrate is not involved.3.The evolution process of DACHIGAN anticline can be divided into three stages.?a?.Caledonian to Hercynian,it is the dynamic background of extensional basin formation,which mainly accepts stratigraphic deposits from Early Paleozoic to Late Paleozoic;?b?.Indosinian to early Yanshanian,transition from extension to compression,stress from southeast to northwest spread;?c?.From the late Yanshan to the Himalayas,the southeast-northwestward compression stress continued to act,forming a southeast trend thrust structure in the deep,and with the further action of the stress,a northwest trend recoil structure was formed in the shallow part,The Himalayan Movement transformed the rudimentary folds formed in the early stage to form the current structural style.4.Through structural physical simulation experiments and previous research results,it is believed that the formation of the current structure of the DACHIGAN anticline was due to the early Yanshan period,the Xuefengshan-West Hunan-Hubei structural belt continued to uplift.The SE-NW compression dynamics environment was formed in eastern Sichuan,and the DACHIGAN anticline formed an embryonic form under this continuous compression structure environment.After the strong folds of the Himalayan period,the early structure was transformed and finally formed.