Amushan Fm
Type Locality and Naming
The type section lies along Amushan (Mt.), the Darhan Muminggan Joint Banner, Inner Mongolia. It was named by the No. 241 Geological Team of the former Ministry of Geology in 1955. In 1959, it was called “the Lalaotu limestone” by Sheng Jinzhang.
Synonym:
Lalaotu Limestone
Lithology and Thickness
Sandstone and limestone. It is characterized by interbedded clastic and carbonate rocks, in which the limestone bears an edgewise structure. The type section is composed mainly of yellow-brown polymineralogic sandstone, pebbled sandstone, quartzose sandstone, siltstone, purple-brown or red shale and light-gray limestone, locally containing volcanic rocks. The reference sections, Houtoumiao and Mihangao-qiaogaolu the West Ujimqin Banner, are dominated by gray white and dark-gray medium- to thick-bedded bioclastic limestone, intercalated with sandstone, conglomerate and clayey siltstone, with pebbled coarse-grained sandstone at bottom. Exposed thickness 875 m.
Relationships and Distribution
Lower contact
Conformable contact with the underlying Benbatu Fm; but locally is the Baoligmiao Fm volcanics
Upper contact
Faulted contact with the overlying Zhesi Fm; but next younger regional unit is the Xilimiao Fm volcanics (as displayed on Permian Lexicon chart)
Regional extent
Rocks of the formation are distributed in the Darhan Muminggan Joint Banner, Siziwang Banner, Sonid Left Banner, Sonid Right Banner, Abag Banner, southern West Ujimqin Banner as well as Ba League, Alxa League, etc. The lithology and thickness vary greatly. In the Uliji area of the western region, there occur intermediate-acid tuff and volcanic breccia intercalated with sandy mudstone, with an exposed thickness of 1671 m.
GeoJSON
Fossils
It is rich in Fusulinids, which can be divided in ascending order into the Triticites zone, the Pseudoschwagerina zone and the Eoparafusulina zone, consisting mainly of Rugosofusulina sp., Quaisifusulina sp., Schubertella sp., Paraschwagerina sp., Staffella sp., etc.; Corals, which are divided ascending into the Hilia-Antheria, Carinthiaphyllum-Akagophyllum and Empodesma-Tachylasma assemblages; Brachiopods Ella sp., Hustedia sp. and Stenoscisma sp.; Bryozoans: Fistulipora sp., Prismopora sp., etc.
Age
Depositional setting
It is interpreted as neritic facies intercalated with volcanic sediments.
Additional Information