Abstract: In the Ashelekuoerlesi area, West Junggar, the Lower Carboniferous Jiangbasitao Formation unconformably overlies the Heishantou Formation and underlies the Lower Permian Haerjiawu Formation.The youngest detrital zircon clusters from three sandstone samples yielded U-Pb ages of 328 Ma (Serpukhovian Stage) for the top of the Heishantou Formation, 318 Ma (Bashkirian stage) for the bottom of the Jiangbasitao Formation and 297 Ma (Asselian stage) for the bottom of the Haerjiawu Formation, respectively.Therefore, the Jiangbasitao Formation is Late Carboniferous in age, rather than Early Carboniferous, and is equivalent to the Upper Carboniferous Molaoba Formation in the West Junggar area.The Heishantou Formation is a set of fossil-bearing marine deposits.The Molaoba Formation is a retrograding filling sequence from fan delta facies to shallow marine facies, but there is no preservation of the progressive filling sequence above, which may have resulted from the denudation after the tectonic uplift of the Junggar residual ocean basin in the Late Carboniferous.The Haerjiawu Formation is continental alluvial fan facies.The provenances of the Carboniferous and Lower Permian strata were confined to a neighboring area, and the youngest detrital zircons were derived from the contemporaneous volcanic rocks.