The Baogutu Formation, located in the southern margin of the West Junggar accretionary orogenic belt, constitutes a significant Mississippian sedimentary record. A comprehensive understanding of its lithostratigraphic sequence, lithology, and contact relationships with overlying and underlying strata is paramount for unraveling the Late Paleozoic tectonic evolution of the Junggar basin. A newly measured stratigraphic section at Hongshanliang, located in northern Baijiantan, reveals two distinct lithostratigraphic units, each characterized by unique lithological assemblages and marked color differentiation. The upper unit, composed of gray- black carbonaceous fine clastic rock, exhibits a conformable contact with the underlying bright red unit comprised of chert, silty chert, and tuffaceous chert sandwiched with basic to intermediate volcanic rocks. These units are assigned to the Baogutu Formation and Hongshanliang Formation, respectively. LA- ICP- MS zircon U- Pb dating, conducted on samples from the bottom of the Baogutu Formation and the top of the Hongshanliang Formation, yielded ages of 345. 1 Ma and 365. 9 Ma, respectively. These ages firmly establish the Mississippian and Late Devonian depositional ages for the respective formations. This new discovery unequivocally confirms the Baogutu Formation as the oldest Carboniferous lithostratigraphic unit in the region, further establishing its precedence over the Xibeikulasi Formation. The establishment of this complete Lower Carboniferous lithostratigraphic sequence provides invaluable insights into the sedimentary construction and rock assemblage at the bottom of the Carboniferous system within the region.These findings contribute significantly to theunderstanding of the sedimentary characteristics and tectonic evolution of the Junggar basin during the critical Devonian- Carboniferous transition.