The Sedimentary Facies And Sequence Stratigraphy Of Middle-Later Jurassic Epoch In Easten Qiangtang Basin, Qingzang Plateau

This paper centers on two questions, namely sedimentary evolution and sequence stratigraphy in eastern Qiangtang Basin. And Middle-Upper Jurassic is selected as object of study. A thorough and all-round study is carried on Middle-Upper Jurassic series sedimentary geology and sequence stratigraphy in the studied area. The main fruits of study are as follows:(1) A complete stratigraphic framework of Middle-Upper Jurassic series is set up through systematic stratigraphic study of Middle-Upper Jurassic by the analysis of lithostratigraphy , biostratigraphy and chronostratigraphy on five groups of Middle-Upper Jurassic series in the studied area.(2) Based on the two important sections of Yanshiping and Yicangma, a study is conducted on the sedimentary features and facies of Middle-Upper Jurassic series, it is suggested that Quemo Formation is river-delta facies deposit, Buqu Formation is chiefly carbonate ramp facies deposit, Xiali Formation is delta-tidal flat facies deposit, ?Suowa Formation is mixed shelf-lagoonal facies deposits and Xueshan Formation is river-delta facies deposit.(3) On the basis of study of sedimentary thickness change of each formation, analysis of provenance a nd p aleo-current d irection, s tudy o f d istribution o f s edimentary facies b elt a nd analysis of vertical phase sequence, lithofacies and paleogeography are analyzed and the sedimentary history of five stages of Middle-Upper Jurassic series is renewed in the studied area.(4) Based on the above-mentioned studies, the tertiary sequence of Middle-Upper Jurassic series is identified, divided and compared . And Middle-Upper Jurassic series is divided into two I typed sequence and three II typed sequence, and divided each sequence for systems tract. The emphasis of the study is on the sedimentary characteristic response of sequence stratigraphy.(5) The study indicated that the formation and evolution of five tertiary sequence of Middle-Upper Jurassic series correspond to five rise and fall cycles of sea level, and finally ends in marine deposits. The formation and evolution of sequence stratigraphy of Middle-Upper Jurassic series is affected by change of global sea level, tectonic uplift and subsidence, sedimentary supply and climate conditions.(6) The comparative study of stable isotope respond between Qiangtang Basin and Middle-Upper Jurassic epoch section in the central Italy indicated that the global sea level presented a general rising trend in five rise and fall cycles in Middle-Late Jurassic epoch, whereas it presented a general falling trend of sea level in five rise and fall cycles in the studied area. Regional tectonism and global sea level change play a controlling role in the relative sea level change of the studied area.