Abstract: Previous studies regarded the glutenite of Baijiantan formation of the Upper Triassic in Baikouquan area in Junggar basin as deposits of the delta front, and the main basis was that the mudstone interbedded with glutenite was in reduction color which represents underwater reduction environment deposits. But the analyses of a large amount of core observation, well logs, logging data and seismic information indicate that the glutenite reservoir of Baijiantan formation is dominated by braided fluvial deposits, a few belong to delta front deposits. The colors of most mudstones interbeddedd with the glutenite are dark, because they contain a lot of fossils of many plant roots, rods, stems, leaves, and even have coal seam interbed. Also, the Baijiantan formation is a sedimentary cycle gradually becoming shallow from the top to the bottom, the lower part is lake deposit, the middle is delta deposit and the upper is braided fluvial one. The sands of braided fluvial deposits in the studied area are characterized by strip, coarse granularityand, low shale content and good reservoir quality, in which the main oil-bearing reservoirs have been formed and found; while sands of the delta front characterized by sheet, fine grain size, high shale content and poor reservoir quality, in which oil-bearing zone has not been found.

Key words: Junggar basin, Baikouquan, Triassic, Baijiantan formation, sedimentary facies