Sequence stratigraphy and sedimentary evolution of the Middle Jurassic Toutunhe Formation on the eastern margin of the Junggar Basin,Xinjiang

The present paper deals, on the basis of high-resolution sequence stratigraphic theory, outcrops and well logs, with the sequence stratigraphic division and correlation, sedimentary facies distribution and sedimentary environmental evolution of the Middle Jurassic Toutunhe Formation, aiming at revealing the sequence stratigraphic characteristics and sedimentary evolution of the Middle Jurassic Toutunhe Formation on the eastern margin of the Junggar Basin, Xinjiang. The Middle Jurassic Toutunhe Formation consists of one third-order, three fourth-order and nine fifth-order depositional cycles, and comprises the deepening-upward symmetric and asymmetric types of sequence architectures. The sediments are mainly composed of sandy conglomerates and mudstones. The sedimentary environments are separated into braided river, braided delta, and littoral and shallow lake with the lake transgressive evolution spanning from the depositional period of the first member of the Middle Jurassic Toutunhe Formation (J₂t¹) to the depositional period of the second member of the Middle Jurassic Toutunhe Formation (J₂t²). The sedimentary model is proposed herein showing the sedimentary evolution of the braided river facies, braided delta facies and lacustrine facies in the Middle Jurassic Toutunhe Formation in the study area.