Sedimentary Facies and Depositional Model of Wulabo Formation,Upper Permian Series in Bogeda Piedmont Depression, Junggar Basin

Key words: 
• sedimentary facies /
• depositional model /
• Upper Permian Series /
• Wulabo Formation /
• Bogeda piedmont depression

Abstract: The geologists have different opinions about the depositional environment of Wulabo Formation,Upper Permian series in the south margin of Junggar Basin.In this article,the depositional environment of Wulabo Formation,Upper Permian Series in Bogeda piedmont depression is analyzed based on the geochemical criteria in the sediments, including the content of equivalent boron,the ratio of B/Ga,Sr/Ba and the relationship among B?Rb?Ga,sandstone grain size distribution and clay mineral association of mudstone. It is considered that the Wulabo Formation was formed under marine regression background. The bottom of the strata was formed in shallow marine environment, and the middle to upper section was formed in terrestrial environment. By studies of rock types and their combination, the texture of fragmental rock, primary sedimentary structures and their evolution sequence, sedimentary rhythm, four kinds of sedimentary facies have been recognized in the strata. They are tidal flat, coastal subaqueous fan, braided stream and alluvial fan. The tidal flat and coastal subaqueous fan facies are distributed at the bottom,and braided stream facies in the middle,alluvial fan facies on the top of Wulabo Formation. The evolution of the sedimentary facies in this area was controlled by the formation and evolution of Bogeda intercontinental rift system.