Tanchi Fm

The type section of the Tanchi Formation, measured from Pingkou to Yanxi (old site) along Zijiang River by Wang and Bian (1949). The section does not exit longer as it was submerged by a reservoir after a dam was built downstream on the Zijiang River. For this reason, a new section, the Langlinchong section, was proposed as representative section of the formation by Zhang (1997). The section is located at Langlinchong Village (which now has been incorporated into to Shimen Village), Anhua County, Yiyang City, central Hunan Province (111°53’E, 28°16’N). The section lies about 5.8 km southwest of the seat of Gulou Township or about 70 km east of the seat of Anhua County. The Tanchi Formation was named by Wang and Bian (1949). The name is derived from Tanchi (spelled Tanxi in Hanyu Pinyin) Village, Gulou Township, Anhua County, Yiyang City, central Hunan Province. Originally it was called Tanchi Limestone by Wang and Bian (1949) and was renamed Tanchi Formation by Hunan Bureau of Geology and Mineral Resources (1988).

Synonym: （探溪组）

The Tanchi Formation is a carbonate sequence. In the new section, the formation consists mainly of dark grey, carbonaceous and argillaceous dolomitic limestone, interbedded with laminated argillaceous limestone, dense and microcrystalline limestone, and argillaceous striped limestone, and with a layer of dark grey argillaceous limestone, 25.9 m thick, at the base. In this section, the formation is 199.9 m thick.

In the new section the formation yields trilobites Hedinaspis sp., Homagnostus sp., Lejopyge sp., Lotagnostus sp., Pseudagnostus sp. Yakutiana sp., and Yuepingia sp. In other sections, the formation yields additional trilobites Acrocephalina cf. armata, Charchagia norini, C. sp., Diceratopyge sp., Pseudagnostus communis, P. cf. douvillei, and Westergaardites sp.