Study On The Middle-lower Triassic Sedimentary Characteristics In The Southern And Eastern Margin Of Junggar Basin

This dissertation relies on the project The Research of Geological Investigation and Sedimentary Characteristics of Permian-Jurassic in the Southern and Eastern Margin of Junggar Basin, which was entrust to China University of Geosciences(Beijing) to finish the technical services by the Xinjiang exploration management department of Sinopec Shengli Oilfield Branch Company. Basing on the collection of the previous stratigraphic data and the research and laboratory analysis of the field outcrop, the dissertation has studied the sedimentary characteristics of the middle-lower Triassic system of the southern and eastern margin of the Junggar Basin and the division and contrast of the high resolution sequence stratigraphic. Then the dissertation establishes the early-middle three superimposed lithofacies paleogeographic map. The achievements can be listed as followed: 1. Through the in-depth study of the four measured stratigraphic section, the dissertation establishes middle-lower three stacking sequence of strata of the southern and eastern margin of the Junggar Basin. 2. According to the analysis of four measured sections of rock types, sedimentary structures and combination characteristics of system, the dissertation divides types of the middle-lower three superimposed sedimentary facies, subtfacies and microfacies of the southern and eastern margin of the Junggar Basin. There are 2 main sedimentary facies types, which are braided river delta facies and lacustrine facies, and are divided into 5 kinds of sedimentary subfacies and 9 kinds of microfacies. 3. The dissertation implements the theory and research methods of high resolution sequence stratigraphy, which is based on the stratigraphic base level cyclic analysis, such as Cross, etc. It discusses the identification of the sequence of each level in detail and then makes the high-resolution sequence strtigraphic division of each stratum. The middle-lower three Triassic system is divided into 2 long-term base level cycles, several intermediate datum cycles and short-term base level cycles. 4. According to the contrast of the profile stratigraphic and sedimentary facies, the middle-lower three Triassic system paleogeography and palaeoenvironment of the southern and eastern margin of the Junggar Basin are recovered. The dissertation discusses the possible reason and the environmental differences between the southern margin and eastern margin of the basin in different period. Then it reveals the characteristics of the evolution of the basin, based on which, 2 lithofacies paleogeographic maps are established.