Characteristics Of Paleostructure In The Mountain Front Region Of Southwestern Tarim Basin And Its Control Of Jurassic-Cretaceous Deposition

Basin and range is the uniform tectonic system which is closely linked in temporal and spatial development and formation mechanisms.The final closure of the Paleo-Asian Ocean along the northern margin of Tarim Basin in late Paleozoic and the formation of the late Triassic Paleo-Tethys orogenic belt in the Tibetan Plateau interior,had a significant impact on the Tarim Basin.Based on a detailed field survey of Mesozoic strata in the outcrops of the mountain front region of southwestern Tarim,the analysis of drilling data and the detailed interpretation of high quality seismic profiles.In order to reveal the pre-Jurassic paleo-structure and its control of deposition,this paper study the characteristics of paleo-structure and the sedimentary filling process of Jurassic-Cretaceous in the mountain front region of southwestern Tarim.The geological data and seismic profiles indicate that during the Latest Triassic epoch,paleo-uplifts were developed along the piedmont of South Tian Shan surround the north margin of Tarim Basin.The formation of paleo-uplifts was possibly due to the collision orogeny of South Tian Shan during the latest Paleozoic and the initial activity of Talas-Ferghana Strike Slip Fault during Early Jurassic epoch.A Late Triassic foreland fold and thrust belt was formed in piedmont of western Kunlun mountain with basement involvement structure developed in the root and imbricated structure developed in the front zone respectively,and the position of frontier fault is near the frontier fault of Cenozoic fold and thrust belt.Controlled by these thrust faults,the Paleozoic strata formed a series of anticline uplifts with steep north rim and gentle south rim.Affected by surface weathering and erosion,the paleo-uplifts in the core of anticline had the property with steep north slope and gentle south slope,but the depressions related to the fracture zone usually had the property with gentle north slope and steep south slope.During the Early-Middle Jurassic epoch,the mountain front region was controlled by dextral strike-slip and developed the rift basin group.However,four half graben rifts developed in the piedmont of western Kunlun mountain due to post-orogeny rifting extension mechanism.The characteristic of paleo-geomorphy caused by the Late Triassic deformation and the shape of Early-Middle Jurassic rift joint controlled the distribution of Jurassic-Cretaceous strata.The Early-Middle Jurassic strata was mainly controlled by the scale and shape of rift basins,while the Late Jurassic to Early Cretaceous strata was mainly controlled by the Late Triassic paleo-geomorphy,until the Late Cretaceous epoch.