The discovery of Silurian graptolites from the Kepingtage Formation in Sepabayi area, Xinjiang

The Kepingtage Formation in Sepabayi area of Xinjiang is mainly composed of schistosity shale and feldspathic quartz sandstone with few fossils and very insufficient age data. At the bottom of the middle Kepingtage Formation well-preserved graptolite fossils were discovered, which included five graptolite genera with five species and two analogous species with eight indeterminate species. These fossils indicate an age of the Glyptohraptus perscuptus Biozone. Thus, the Kepingtage Formation in Sepabayi area is probably latest Rhuddanian to Aeronian (Landovery) in age. According to the characteristics of graptolite combination and rock association, the sedimentary environment of the middle member of Kepingtage Formation should be continental shelf facies, and its water energy was low and beneficial to the preservation of graptolite fossils. The upper member was near shore facies unfavorable for the preservation of graptolite fossils due to its high water energy.