Longtou Fm
Type Locality and Naming
The type section is located at near Longtou, Huaxi, Guizhou. It was named by the Eighth Geological Survey Group of the Ministry of Geology in 1977. And it was first publicly cited by the Guizhou District Survey Brigade in 1980. The original "Longtou Formation" represents the deposits dominated by reef (shoal) facies during the middle Ladinian period in Guizhou. In 1987, the Guizhou Bureau of Geology and Mineral Resources revised the meaning of the Longtou Formation to only represent the lower layer of the original "Longtou Formation", and the upper part was called the Gaicha Fm. This lexicon follows it. In addition, Wang Zunzhou et al. (1992) maintained the original meaning of the named "Longtou Group", but incorrectly cited "Longtou Group" as "Gongtou Group".
Synonym:
Lithology and Thickness
Lower part is dominated by dolomite. Middle and Upper part is composed of light gray to gray-white thick-bedded lamina dolomite, cohesive dolomite, dolomitic limestone, sparry algal clastic limestone, and sparry oncolite limestone. And they are in forms of rhythmic interbeds. The thickness is 174 to 1254 m.
Relationships and Distribution
Lower contact
Its bottom with the thick dolomite is conformable in contact with the underlying Poduan Fm of the reef (shoal) facies limestone.
Upper contact
Its top with the oncolite limestone is in conformable contact with the overlying Gaicha Fm
Regional extent
It is mostly well developed in Tongmuling of Qingyan, Bazichang of Guanling, Pochanmawodang of Guanling, Zhenfeng, and Nidang of Xingyi, Guizhou.
GeoJSON
Fossils
Bivalves: Entolium cf. lavaredanum, Pteria cassiana, Halobia cf. subcomata. Daonella indica; Brachiopods: Lissorhynchia pygmaea, Mentzelia sp., Rhaetina sp.; Ammonoids: Flexoptychites sp., Protrachyceras sp.; as well as corals, crinoids and algae.
Age
Depositional setting
This formation is a carbonate reef (shoal) facies.
Additional Information