Age of the Upper Ordovician Koumenzi Formation in the Lenglongling area of the North Qilian Mountain: The evidence from conodonts

Conodonts from the Upper Ordovician Koumenzi Formation in the Lenglongling area of the North Qilian Mountains are reported for the first time. Five genera and nine species of conodonts have been identified, including two undetermined species. On the basis of the characteristics of conodont fossil succession, a conodont assemblage has been established: the Aphelognathus grandis - Panderodus gracilis assemblage. We compared the conodont assemblages of the Koumenzi Formation with those at the same stratum at home and abroad. Combined with other fossil data for the Koumenzi Formation, the author concluded that the age of the Koumenzi Formation is the Kaidi-Middle Hernandian period, which is equivalent to the Late Aijiashan-Middle Qiantangjiang stage in the Chinese stratigraphic chronology.