Yundoutan Fm
Type Locality and Naming
The type section is located at Yundoutan 22.35 km to the southeast of the Zhen’an County Town of Shaanxi Province. It was named by the Xi’an Institute of Geology and Mineral Resources in 1965.
Lithology and Thickness
Limestone. Composed chiefly of dark-purplish red and grey-red massive limestone and clayey limestone, with its lower part being intercalated with pebbled clayey limestone and pebbled limestone, yielding Foraminifera, Fusulinida, corals, brachiopods and bryozoan fossils. Its basal part consisting of dark-purplish red and reddish brown pebble-rich clayey limestone. Thickness is 875 m.
Relationships and Distribution
Lower contact
Conformable contact onto the yellow and grass-green calcareous siltstones intercalated with limestone at the top of the underlying Xikou Fm.
Upper contact
Conformable contact with the white and grey-white thick-bedded massive limestone at the base of the overlying Longdongchuan Fm.
Regional extent
Distributed in the Yundoutan area, Xikou region, Zhenan County, Shaanxi Province and in the Yunxi County (705 m) of Hubei Province.
GeoJSON
Fossils
In the Xikou area the formation yields Fusulinids comprising Codonofusiella paradoxical, Reichelina turgida; Foraminifera represented by Colaniella minima, C. pulchra; brachiopods represented by the Edriosteges poyangensis, Strophalosiina tibetca assemblage zone, whose important molecular species comprise Costispinifera lopingensis, Edriosteges poyangensis, Semibrachythyrina zhenanensis and Uncinunellina limorensis; and corals such as Liangshanophyllum wengchengensis, Zhenanophyllum stereoseptatum, etc.
Age
Depositional setting
It is interpreted as a shallow-sea carbonate-platform
Additional Information