Eastern Ordos Basin Shanxi Formation Depositional Systems And Lithofacies Palaeogeography

By multipurposly using outcrop, core, well log data and sedimentary geochemistry data and so on, drawing lessons from the research of forefathers, based on the theory of sedimentology, this paper analyses the types of depositional system and its temporal and spatial evolution in Shanxi Formation,East Ordos.Firstly, according to region sedimentary frame and sedimentary action, Shanxi Formation in East Ordos Basin are devided into three groups of sedimentary systems, five kinds of sedimentary systems, fifteen kinds of sedimentary subfacies, and the spatio-temporal distribution and characteristics of all kinds of facies, subfacies and microfacies are summarized detailly and embeddedly. Furthermore, facies association, lithologic composition, deposition sequence, sectional structure, sedimentary structure and grain size probability are analysed in detail. According to abundant evidence of sedimentology, paleontology and geochemistry datas, the author first puts forward and studies systemicly the sedimentary characteristics of marine and fluvial-tide delta, and respectively builds river-tide delta and river-lake delta sedimentary facies models.Based on these, the author puts forward a new cognition that distributary channels of delta plain belong to braided river during earlier Shanxi period and meandering river during later Shanxi period.Based on the analysis of sedimentary systems, taking S₂ as importance of study and exerting research methods of sequence stratigraphy and lithofacies palaeogeography, 14 pieces of sequence paleogeographic map have been drawned up on condition of middle-time cycle sequence as drawing unit, then discussing the distribution of depositional systems on different phases, paleogcographic spread and evolution have been disclosed.On studying of them , the author detailedly analyses sourse of matter and roudly summarizes the relationship between congeries of gas and evolution of basin, sedimentary systems, and points out that great aeration massed distributes in sandstones of distributary channels of delta plain, underwater distributary channels of delta front, estuarine dam and tide sand-dam .For father reservoir, cap, source rock and oil gas expiortion.