A New Discussion on the Sedimentary Characteristics of Shawan Formation in Chepaizi Area, Junggar Basin

Key words: 
• Chepaizi area /
• Shawan Formation /
• exposed environment /
• alluvial fluvial system

Abstract: A big controversy about the sedimentary environment of Shawan Formation in Chepaizi area, of Junggar Basin is still existed in the previous views, the main view about that is considered most likely braided river delta or beach bar sand deposition. A further analysis based on the borehole, paleontology data and physical geography data was deemed that rather than the previous sedimentary model,the Chunguang block was likely exposed, alluvial fan and fluvial deposition. The alluvial fan system developed from the northern part of the study area and fluvial system was found in the south central area. Moreover, in different sedimentary period, the sedimentary system was changed: in member 1 of the Shawan Formation, alluvial-braided river sedimentation was formed and in member 2 of the Shawan Formation, alluvial-meandering river deposit existed,however,in member 3 of the Shawan Formation, Chunguang area lack of typical fluvial deposits,mainly alluvial fan system and the flood plain deposited. All in all,in the shawan sedimentary period, Chunguang block has the character whith multi-source deposition and multiple sedimentary system.In the vertical profile,two different alluvial-braided river sedimentary model have been built up.