Late Ordovician stromatoporoids from the Yingan Formation in northwestern Tarim Basin and their palaeobiogeographic implications

Abundant stromatoporoids have been found in the biostromal reef at the topmost Yingan Formation at the Arisu West Section in the Kalpin area, Xinjiang. Three species of stromatoporoids belonging to 3 genera are identified for the first time from the Yingan Formation, including Camptodictyon amzassensis (Khalfina, 1960), Simplexodictyon yavorskyi (Nestor, 1966) and Rosenella sp. These stromatoporoids serve as one of the main reef-building elements, and interact with associated corals to form the biostrome in the top part of the Yingan Formation. Among the occurred species, Camptodictyon amzassensis is widely distributed in the peri-Gondwanan regions during the Late Ordovician, and therefore its abundant occurrences in the Yingan Formation suggests a likely close paleobiogeographic relationship between Tarim and other peri-Gondwanan regions. The finding of Simplexodictyon in the Yingan Formation of Early Katian age represents the earliest occurrence of Stromatoporellida, suggesting a possible origination of the Simplexodictyon species in the Tarim and then spread into other regions like North China during the Katian