Sedimentary characteristics and evolution of Badaowan Formation of Lower Jurassic in northwest margin of Junggar Basin

The sedimentation of Badaowan Formation in the 8th block in northwest margin of Junggar Basin is regarded as braided river facies. Based on the analysis of the rock type, features and sedimentary facies marks, it is believed that Badaowan Formation is braided river delta and lacustrine sedimentation. The sedimentary distribution and evolution of Badaowan Formation are systematically studied. The result shows that the lake level descended since Late Triassic and swamp deposit widely developed in Badaowan Formation by the extinction of the lake basin, with the inputting of alluvium and the shrinking of swamp, strata overlapped from east to west and braided river developed; shallow lacustrine and braided river delta developed well with the ascending of the lake level in sub-stage of J1b51; the lake level descended swiftly since the sub-stage of J1b4, which resulted in the extinction of the shallow lacustrine in thestudy area; during the sub-stage of J1b2+3, lake transgression emerged once more, and it was characterized by a large scale of shallow lacustrine; the lake level descended again since the sub-stage of J1b1, shale increased with the attenuation of fluviation, and swamp widely developed at the last stage of Badaowan Formation.