Shamu Fm
Type Locality and Naming
The type section is located at the Shamu Commanding Height 20 km to the northwest of the Deqin County Town, Yunnan Province, and the reference section is situated at Dajigong, Adengge Country, Deqin County, Yunnan Province. It was named by the Yunnan Regional Geological Reconnaissance Party in 1985.
Lithology and Thickness
Clastics and Volcanics. It is divisible into the upper and lower members. Lower member is composed of dark-grey and green-grey sandy shale and siltstone, intercalated with lithoclastic fine-grained sandstone, greywacke and a small amount of andesitic dacite or trachyte and tuff, intercalated locally with limestone, with a thickness of 328 m. The basal part of the formation is composed of dark-grey thin-bedded medium- and fine-grained calcareous greywacke. Upper member consists of grey-green and purple amygdaloidal andesite, trachyte, amphibole- andesite and andesitic lithoclastic tuff, with its middle part being intercalated with siltstone and constituting an interbed together with the conglomerate, with a thickness of over 207 m.
Relationships and Distribution
Lower contact
Conformable contact with the grey thick-bedded skeletal micrite and pure micrite of the underlying Jidonglong Fm
Upper contact
Unconformable contact with the overlying Xiapuotou Fm of the Middle Triassic Series
Regional extent
Distributed in the Deqin-Simao region, with the stratigraphic sequence in the Dajigong area of the Deqin County being fairly complete; southerly till the Nanpu Village and Yugong area there occurs only its Lower member which is composed of dark-grey shale and siltstone, intercalated with marl lenses, with a thickness of 320 m, yet in the Mojiang area there occurs only its Upper member, with a thickness of 200 m, and of 820 m up to the Weixi area, where the rocks are universally metamorphosed, representing clayey silty slate and calcareous sandstone, intercalated with intermediate-acidic volcanic rocks, with its top being composed of micritic limestone, intercalated with slate.
GeoJSON
Fossils
In the Deqin area the Lower member yields the Gallowayiinella sp. of Fusulinida; brachiopods such as Dielasma cf. dieneri, Martinia cf. mongolica and Dictyoclostus sp.; and plant fossils represented by Taeniopteris sp., etc. In the Mojiang area the limestone lenses in the Upper member yield Fusulinida represented by Palaeofusulina sp., etc., belonging to the Late Permian Epoch in age.
Age
Depositional setting
It is interpreted as a littoral shallow-sea facies with volcanics.
Additional Information
GeoJSON estimate by Runan Yong, Suxiao Li and Wen Li (Chengdu Univ. Tech. students)