Redefinition of Carboniferous lithostratigraphic units in the Kumtag sand-ridge area, East Tianshan, based on new fossil evidence

The stratigraphic division in the Kumtag sand-ridge, East Tianshan, has long been in dispute. During 1∶50,000 regional geological and mineral survey, the conodonts Streptognathodus suberectus and Idiognathoides sinuate and the corals Pelalaxis intermedia, Lithostrotionella rarivesicula and Fomichevella kiaeri were found in two sequences of carbonate rocks in the Kumtag sand-rigde area north of the Kanggurtag deep fault, East Tianshan. The two sequences of strata are Late Carboniferous Luosuan-Dalaanian and Dalaanian-Xiaodushanian in age respectively, assigned to the Dikan'er Formation and Qishan Formation in the Karlik stratigraphic area respectively. Two suites of volcanic rocks are separated by the two sequences of sedimentary rocks. They are very easy to recognize and distinguish in the field and correlate at a regional scale because their spatial distributions are relatively fixed and the features of rock associations are distinct. Their ages are Early Carboniferous and Late Carboniferous respectively. The Qi'eshan Group can be further divided in ascending order into the Xiaorequanzi, Dikan'er, Qi'eshan and Qishan formations.