Yanwugou Fm

The type section of the Yanwugou Formation is the West Hill Ridge section. It is located on the hill ridge west of Fengjia’ao Village, about 7 km north of the Xijiadian Town, Danjiangkou, Hubei Province (111°12’58”E, 32°50’52”N). It is the lower portion of the same section shared by the overlying Fengjia’ao and Xijiadian formations. The section was measured by Zhu and Tao (1988) from Hubei School of Geology (now Hubei University of Geological Staff). The Yanwugou Formation was named by Zhu and Tao (1988). The name is derived from Yanwugou Village in Xijiadian Township, Danjiangkou City (County), northwestern Hubei Province. In following the revision by Yang et al. (1991) and Chen and Jin (1996), the Yanwugou here is an expended one with inclusion of the Siliceous Slate Member (Bed 5) of Zhu and Tao (1988).

Synonym: （岩屋沟组）; Chen and Jin (1996) named Zhuangzigou Fm for the expanded Yanwugou Formation. Although the Zhuangzigou Fm appeared first in a 1975 manuscript by the No.5 Hubei Geological Team, it was published as late as 1997 by Chen and Jin (1996). Therefore the Zhuangzigou Fm should be regarded as an invalid synonymous of Yanwugou Formation for its later publication (see also the remark of the entry of Yangjiabao Fm).

The Yanwugou Formation is an epi-metamorphic clastic sequence, consisting of greyish black, vanadic carbonaceous slate, carbonaceous silty slate, carbonaceous siliceous slate, and siliceous silty slate. Lower part of the formation also contains thin-bedded siliceous concretions, bone coals, phosphoric nodules, and upper part contains thin-bedded argillaceous limestone lenses. In the type section, the Yanwugou Formation is 39 m thick.

No fossil was reported from the type section. However, in a section at Yujiachong, Jingshan County, northern Hubei Province the upper part of the formation yields trilobites Hupeidiscus sp., Sinodiscus duchuanensis and Tsunyidiscus tingi.