Research Progress on Carboniferous Strata in Bogda Area, Eastern Tianshan

The project of geological survey in 1:250000 Sandaoling Sheet made some research progresses on carboniferous stratigraphic redivision, including the unconformity interface found in Tuckerbasstao Formation. According to the fossils of lower strata in Jiangbasstao Formation, it's thought that the geological age of this lower strata is the middle and late period of Early Carboniferous.Some brachiopod fossil elements of late carboniferous have been found in the higher strata of Jiangbasstao Formation, such as Brachythyria, Cancrinella, Choristite, Ella, Paramuirwoodia and Wellerella, the further analysis showes that these brachiopod fossils can be grouped into Choristites-Paramuirwoodia fossil assemblage zones in North Xinjiang region and the geological age of the higher strata is early period of Late Carboniferous. Based on contact relationship between these strata, fossils and zircon U-Pb age, the geological age of Qijiaojing Formation has been revised as early period of Late Carboniferous. The results suggest that the Liushugou Formation, Qijiaojing Formation, Qijiagou Formation and Ashenkala Formation belong to different sedimentary facies with same geological age.