Tectonic-depositional Environment And Proto-type Basin Evolution Of The Carboniferous And Permian Ordos Area

Proto-type basin refers to the result of geodynamic environment in a period of geological time.The research of protro-type basin contributes to reveal the tectonic-depositional environment and its evolution during the formation of basins.Carboniferous-Permian is the key period to the evolution of Ordos region and it is the key stratum for increasing oil and gas storage and production in Ordos Basin.The recovery of Carboniferous-Permian proto-type basin in ordos region is not only have important theoretical significance to reveal the tectonic-depositional environment evolution,but also have important guiding significance to oil and gas exploration in this period.According to the latest drilling,logging,field outcrop and geochemistry data,Carboniferous-Permian stratigraphic system was rebuilt.Combined with the research achievements of orogenic belt and ancient plate,this paper recovers the peripheral tectonic environment of the basin.Through the analysis of single well,well tip,paleontology,paleo-salinity,paleo-climate and paleoredox environment,we recovery the tectonic-depositional environment and filling evolution in each period of Carboniferous-Permian in Ordos area.finally,the basin-mountain coupling relationship was also revealed.This study has achieved the following understandings:(1)During the Carboniferous-Permian,the North China plate continued to move northward from the equator,with small Angle clockwise.Paleo-Asian Ocean's continuing subduction of northern North China plate make Ordos basin suffered strong compression.The Mian-Lue ocean's expansion and northern subduction lead to compression to southern of north China plate.(2)The Ordos region experienced a large transgressive regressive cycle from Late Carboniferous to early Permian.In the late early Permian the sea quickly withdrew from the Ordos region.During middle-late Permian Ordos region through offshore lake basin and inland lake basin evolution stage.(3)The proto-type basin of Ordos in the late carboniferous to the early Permian taiyuan period can be divided into four tectonic units,including Shangluo-Danfeng passive continental margin,Bayan Obo-Chifeng active continental margin,Eastern craton inner depression and Western craton marginal depression.In the early-late Permian period can be divided into seven tectonic units,including Shangluo-Danfeng passive continental margin,Bayan Obo-Chifeng active continental margin,Wuzhong depression,Wuqi depression,Mizhi-jixian depression,south provenance supply area and the north provenance supply area.Weastern cratonic marginal depression chasmic die inner depression,and atrophy to Wuzhong depression.Eastern Ordos craton depression is decomposed into Wuqi depression and Mizhi-jixian depression.In the late Permian the eastern of north China plate is uplifted into land.(4)The Carboniferous-Permian Basin pattern in Ordos area has experienced the transformation from East-West differentiation to North-South uplift-depression differentiation.The basin evolution has a good coupling relationship with the evolution of peripheral orogenic belt,especially Qinling and Central Asia orogenic belt has played an obvious role in controlling the evolution of Ordos Basin.