Shuangyingshan Fm

The type section of the Shuangyingshan Formation is the Shuangyingshan section, located between the south of Shuangyingsha hills and east of Dahuoluojing Village in Mazongshan Township, Subei Mongolian Autonomous County, Jiuquan City, Gansu Province (96°35’E, 41°28’N). The section was measured by the Institute of Geology, Ministry of Geology of China in 1964. In the type section the formation is 12 m thick. The Shuangyingshan Formation was first published by Gansu Bureau of Geology (1976). The name is derived from Shuangyingshan hills in Mazongshan Township, Subei Mongolian Autonomous County, Jiuquan City, western Gansu Province, and was originally appeared in a 1964 manuscript by Xiu Zelei, Zhao Xiangsheng, and colleagues from the Xi’an Institute of Geology and Mineral Resources. Originally the formation was called Shuangyingshan Group, and was lowered in rank as Shuangyingshan Formation by the Gansu Bureau of Geology, 1976.

Synonym: （双鹰山组）

The Shuangyingshan Formation is mainly an epimetamorphic clastic sequence with siliceous and carbonate rocks, dominated by greyish black siliceouss slate, grey phyllite, black siliceous rock, and light grey bioclastic limestone with a layer of greyish purple, medium- to thin-bedded ferruginous calcirudite, 0.6 m thick, at the base. In some localities the formation contains phosphoric or baritic nodules

The Shuangyingshan Formation yields trilobites Bonnia sp., Dinesus sp., Calodiscus sp., Serrodiscus sp. and Subeia sp., and monoplacophora Scenella cf. reticulata and brachiopod Lingulella sp. and hyolithid Hyolithes sp.