Jiumenchong Fm

The type section is the Jiumenchong section lying 1.3 km southeast of Nangao Township or about 23 km northeast of Danzhai City (107°53’E, 26°24’N). It was measured by Zhang Zhenghua, Zhou Zhiyi and others in 1970. In the type section, the formation is 22.5 m thick. The formation was first published by Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences (1974). The name is derived from Jiumencun Village, Nangao Township, Danzhai County, Miao-Dong Autonomous Prefecture of Qiandongnan (Southeast Guizhou), Guizhou Province. It was originally appeared in a 1970 manuscript by Zhang Zhenghua, Zhou Zhiyi and others from the Institute of Geology, Guizhou Headquarter of Petroleum Exploration and the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences.

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The Jiumenchong Formation is a black organic limestone sequence with interbeds of greyish green, greyish black shale. In the type section, the formation is divided into three beds. The lower Bed is 4.5 m thick, consisting of dark grey, thin-bedded limestone in alternation with brown calcareous shale; the middle Bed, 3.8 m thick, consists of brown shale with interbeds of thin- to medium-bedded, dark grey limestone; and the upper Bed, 14.2 m thick, consists of dark grey, medium-and thin-bedded limestone with interbeds of dolomitic limestone in its basal part.

In the type section, the lower Bed of the formation contains sponge-spicule Protospongia sp.; the shale of middle Bed contains trilobite Hupeidiscus sp.; and the upper Bed contains trilobites Hupeidiscus orientalis, Metaredlichia sp., and Estaingia sp., and inarticulate brachiopod Lingula sp.