Liudaogou Fm

The type section of the Liudaogou Formation is the Donggou (Liudaogou section). It is located at Liudaogou Village, about 9.5 km southeast of Gucheng Town, Ping’an District, Haidong City or 12 km north of Nangdoi Town, Hualong Hui Autonomous County, Haidong City, Qinghai Province. (102°04’E, 36°16’N). The section was measured by Qinghai Regional Geological Survey Team in 1964. The name is derived from Liudaogou Village in Gucheng Hui Autonomous Township, Ping’an District, Haidong City, Qinghai Province. The Liudaogou Formation was named by Qinghai Regional Geological Survey Team (1966a, b) in the explanatory text for 1:200 000 scale geological map of both Xi’ning and Ledu sheets, which are published simultaneously in the same month and same year (January 1966). The erecting date has been often cited as 1994 or 1995 (e.g. Zhou et al., 1996; Sun, 1997; Compiling Committee for Chinese Stratigraphic Lexicon et al., 1999), which are incorrectly informed. Originally the unit was called Liudaogou Group and was lowered in rank as Liudaogou Formation by Sun (1997).

Synonym: （六道沟组）

The Liudaogou Formation is basically a volcanic sequence with interbeds of carbonate and clastic rocks. It is divided into two parts. The lower half of the lower part of the formation consists of grey, crystalline limestone and light green tuffaceous slate, intercalated with carbonated andesite and with a layer of greyish green calcareous breccia, 27.2 m thick, at the base; the upper half of the lower part consists of basalt, basaltic andesite, and andesite intercalated with basic tuff, volcanic breccia, and minor phyllite and crystalline limestone. Upper part consists of tuffaceous and siliceous slate, intercalated with basic and intermediate volcanic rock, calcareous sandstone and arkose. In the type section the formation is over 1095.4 m thick with no upper part exposed. A secrion nearby shows the total thickness of the formation is 2074 m thick.

Near its base, just above the basal breccia bed in the type section, the formation yields trilobites Pseudagnostus sp., Changia [=Quadraticephalus]？sp., Saukidae. In a section at Nidanshan, Hualong County, which is close to the Liudaogou Village, the type locality, the lower part of the formation yields diverse agnostoid trilobites including Acmarhachis quasivespa, A. typicalis, Clavagnostus sp., Hadragnostus modestus, Idolagnostus agrestis, Nahannagnostus nganasanicus, Oedorhachis sp., Proagnostus bulbus sinensis, Pseudagnostus Dubius, P. josepha, and Tomagnostella cf. sulcifera. The lower part also contains diverse polymerid trilobites, including Adelagonus ablongus, Angsiduoa lajishanensis, Fuchouia cf. bulba, Hualongia typica, Interalis serena, Nidanshania pandacta, Fatocephalus chytrus, F. sp., Hebeia conica, Iniotoma porosus, Jimachongia lata, Maotunia sp., Meteoaspis qinghaiensis, Neosolenopleurella sp., Paracoosia? sp., Paranomocarella dingmaoshanensis, Placosema qinghaiensis, Proashaphiscus? sp., Wanshania wanshanensis, Xintaia? sp., and Zhalangtania valleaculata. The middle part of the formation yields trilobites Acrocephalaspina insueta, Idamea sp., Probilacunaspis cf. nasalis, Prochuangia sp., Proceratopyge cf, grabaui, and P. sp. (Lin et al., 2013, 2015).