Sequence Stratigraphy And Lithofacies Palaeogeographic Research Of Carboniferous～Permian In Beishan And Its Surrounding Areas, Across Inner Mongolia Autonomous Region, Gansu Province And Xinjiang Autonomous Region

Beishan and its surrounding areas is located in intersectant area of Alashan and northern Xinjiang where the Carboniferous-Permian oil and gas drilling of the Tianshan-Inner Mongolia tectonic belt has won important discoveries. The study area is located in tectonic intersectant area of northern China plate, Tarim plate, Kazakhstan plate and Siberia plate; stratigraphic transition zone of the Carboniferous-Permian of Inner Mongolia and Tianshan; paleogeographic intersection area of Paleoasian Ocean and Paleo-Tethys Ocean. The research on Sequence Stratigraphy and Lithofacies palaeogeographic has important theoretical and practical significance about the correct analysis the tectonic setting and the basin evolution of the region and the whole structural belt and the objective understanding regional oil and gas geological conditions and its resource potential. This paper, for the first time, based on the project named "The Carboniferous-Permian contrast research in Tianshan-Inner Mongolia tectonic belt"; as the basis of fully digesting and absorbing others’data; as the guide of the paleontology and stratigraphy, sequence stratigraphy, sedimentology and lithofacies paleogeography theory and work method; as the main line of "the stratigraphic classification and correlation-stratigraphic sequence analysis lithofacies paleogeographic analysis ", carries out field geological survey and stratigraphic classification and correlation, establishes isochronous stratigraphic units, divides the sedimentary facies and sedimentary systems and reshapes the lithofacies palaeogeography. This thesis draws primary fruit as follows:1. The identification of sequence interface of Carboniferous-Permian mainly includes: unconformity surface, ancient weathering surface, lithofacies mutation, the transformation of parasequence superimposed style and trace element abundance face in the study area. The Carboniferous-Permian is divided into seven second-order sequences and eighteenth third-order sequences (including eight Type-I sequences and ten Type-Ⅱ sequences) and is divided into seven isochronous stratigraphic units.2. The transgressive systems tracts are the main part of the sequence for the Carboniferous-Permian. Lowstand system tract, shelf marginal systems tracts and highstand system tract account for a small proportion. TST is mainly composed of shallow sea shelf clastic facies, carbonate platform facies and restricted bay phase. SMST is mainly composed of open coast system. LST is mainly composed of alluvial fan system, braided delta system and fan delta system. HST is mainly composed of open coastal system, braided delta system and carbonate platform facies. The parasequence includes four kinds:coarsening-upward parasequence, fining-upward parasequence, interbeds of clastic rocks and carbonate rocks and interbeds of volcanic rocks and carbonate rocks parasequence.3. Both marine and continental sedimentary types are all developing for the Carboniferous-Permian in the study area, but the size and duration are different. By comprehensive analysis of geology and geochemical, combining regional sedimentary background with the spatial configuration of sedimentary facies, eight kinds of depositional systems and eighteen kinds of main sedimentary facies have been identified for the Carboniferous-Permian in this area. The distribution of continental sediment is limited, which is only identified in upper Permian and can be divided into alluvial fan and lake sedimentary system.The deposition of marine environment is the main part for the Carboniferous-Permian in this area, which can be divided into six kinds of sedimentary systems:bathyal environment, shallow sea shelf, open shores, limited coast, braided river delta and fan delta.4. Based on the study of sequence stratigraphy, depositional systems and sedimentary facies, this thesis reshapes the lithofacies palaeogeography of the seven isochronous stratigraphic units. The paleogeographic characteristics is that shallow sea shelf is the main part, open coast surrounds the land and carbonate platform and delta facies distribute scattered before the late Permian. The sea is extinctive gradually from Beishan area to east of Ejinaqi and to the west of Hami area after the late Permian. The evolution process of paleogeography is "chasmic initially formed-expanding-shrinking-expanding again-shrinking again until to die"...