Tectono-Sedimentary Characteristic And Its Petroleum Geological Condition Of Permian-Triassic Of Southern Qilian Basin

Permian Triassic marine strata in Southern Qilian basin was an important part marine strata from late Paleozoic to early Mesozoic in the northwest of China, at the same time it was also an oil and gas exploration target strata in the northwest of China.The study area is located in the southwest margin of Qilian Mountains orogenic belt, which belongs to an important part of Qilian tectonic belt.Qilian orogenic belt was a typical Gary East tectonic belt inland areas of China, the Paleozoic tectonic position was very special, In different tectonic phases are controlled by the North China plate, Qilian plate, Qaidam-West Qinling plate,Bayankala plate and Yangtze plate et al, and the interaction among these plates.The study area was reformed and superimposed a period of tectonic system in Hercynian, Indosinian, Yanshanian, and Himalay,composition the Permian Triassic marine residual basin on the basis of the Gary East tectonic belt.The thesis is based on the theory of sedimentary basin geodynamics, regarded the Permian-Triassic structures-sedimentary characteristics as the object of study, regarded the measurement of the field geologic section, the geochemical testing of clastic and carbonate rock geochemical, organic elements testing of mudstone as the research method, comprehensive discussed the Mesozoic and Cenozoic structural styles of the basin, Permian-Triassic marine sedimentary characteristics and petroleum geological conditions.Based on the data of geolgy,geophysical and geochemical,according to the contact relation between strtum, the same era lithology of unconformity surface,the huge difference of facies metamorphic grade.magmatic activity,tectonic deformation,sediment thickness et al,revealed the stage of the tectonic experienced the intracontinental stable depression phase of Carboniferous, continental rifting phase of Permian, stable depression phase of Triassic and the intracontinental strong uplifting of Jurassic-Early Cretaceous, wide basin formed phase of Paleogene, strongly thrusting phase of Neogene and so on.According to the basement nature, the cap structure and composition, tactonic pattern and orientaion, regional large faults of the study area, combined to the actual geological features, the study area can be divided into eleven large tectonic units and some little tectonic units. The structural features of study area reveals:the northern uplift area is mainly composed of unilateral thrustnappe hemi anticlinal, opposed jet flow monoclinic and opposed jet flow synclinorium; central depression area is mainly composed of opposed jet flow synclinorium, back thrust synclinorium,back thrust anticlinorium and unidirectional thrust synclinorium; Southwest uplift area is mainly composed of opposed jet flow semi-slant, fault-uplift,unidirectional thrust synclinorium,unidirectional thrust anticlinorium and complex fault blocks; East area is mainly composed of opposed jet flow synclinorium, back thrust anticlinorium and opposed jet flow synclinorium.Based on the geochemical characteristic of sandstone and mudstone in study area in the research of sedimentary characteristics of Southern Qilian and explored Permian Triassic characteristics of paleosalinity, distance from the shore, hydrodynamic condition, deposition rate and characteristics of paleoproductivity with various parameters.The following conclusions can be drawn based on the evaluation:Influenced by land, Permian Triassic paleosalinity is overall low; Permian Triassic is mainly for littoral shelf sediment; That the greater water energy under transgression, the smaller under marine regression is has been pointed out in the hydrodynamic condition evaluation;In the Permian productivity is overall poor, it was obviously higher in Triassic than Permian; The Triassic paleoenvironment is oxygen deficit, and its reductive degree is general, tectonic pattern and orientation.There are three set of better source rocks, which is P2l, T2d carbonate rocks and T3g dark shale, P2l,T2d carbonate rocks are poor-secondary source rocks, T3g dark shale are better than the other two. Carbonate rocks of P2and dark shale of T3are the regional cap in the Southern Qilian basin.