THE BRAIDED FLUVIAL DELTAIC DEPOSITS IN THE 3RD MEMBER OF BADAOWAN FORMATION AND THEIR DEPOSITIONAL CHARACTERISTICS, BAIKOUQUAN AREA, JUNGGAR BASIN

Previous studies suggested that the 3_rd Member of Badaowan Formation of the Lower Jurassic in the Baikouquan area of Junggar Basin be a meandering fluvial delta. According to the texture, sedimentary structure and distribution pattern of the sandstones, the authors believed that it is the product of a traction current with fairly strong hydrodynamic conditions and belonging to a braided fluvial delta. Three subfacies and six microfacies were recognized, including subfacies of distributary channel, flood plain and swamp, subaqueous distributary channel, interdistributary bay, mouth bar and prodelta clay. Based on the distribution pattern of sedimentary facies and its evolution, it is revealed that the braided fluvial deltaic system was formed during a water level falling period. In the early stage, the study area was occupied by the braided delta front and braided delta plain; and in the middle stage, the water level continued to fall, the study area was covered by a braided deltaic plain. The northwest Halaalate Mountains, Delun Mountains and Zhayier Mountains were the main provenance of sediments.