Anshun Fm

It is derived from the “Anshun Freshwater Snail Bed” named by Le Senxun 1929. Hsu Deyou renamed it the “Anshun Limestone” in 1943, and Zhao Jinke renamed it the “Anshun Group” in 1962. Guizhou Petroleum Geological Team renamed it the “Anshun Formation” in 1960. The type locality is located at Hill Luoshishan, Toupu, in the southeast to the Anshun City, Guizhou Province.

Synonym:

It is mainly composed of dolomite, argillaceous dolomite and evaporate solution breccia, and it is divided into two members. Lower member consists of grayish yellow and gray dolomite, occasionally containing barite masses in the lower part and oolitic and bioclasts in the upper part, often intercalated with yellowish-green dolomitic shale or marlstone, 151-266 m thick. Upper member is of yellowish gray, grayish white, and purplish red thin- to thick-bedded dolomite, argillaceous dolomite, and oolitic dolomite intercalated with evaporate solution brecciated dolomite, often containing gypsum pseudocrystals or gypsum beds, 195-371 m thick.

This formation is well-known in its rich gastropod fossils, as well as bivalves, ammonoids, foraminifers, calcium algae and other fossils. The Entolium disites microtis-Pteria cf. murchisoni bivalve assemblage zone can be established. The lower part contains ammonoid Tirolites spinosus at Anshun whereas the upper part yields ammonoid Proptychitoides sp. and foraminifer Glomospira sinensis and Glomospirella shengi.

It deposited on the nearshore shallow carbonate bio-bank.