Machuan Fm
Type Locality and Naming
The type section is at area south of the Village Shuiquanwan in Machuan Township 17 km south of Pingliang City, Gansu.
The Xialingnangou Fm together with the overlying Qianzhongliangzi Fm (An et al., 1990) has generally a similar lithology to the Machuan Fm, and the former two formations should not be maintained.
Synonym: (麻川组）
Lithology and Thickness
The formation is dominated by dolomitic limestone, with interbedded dolomitic limestone and medium-bedded limestone in the upper part. In the type area, the Machuan Fm is 161.2 m thick.
Relationships and Distribution
Lower contact
It rests disconformably on the dolomitic limestone intercalated with shale of the Upper Cambrian Dataizi Fm
Upper contact
It is conformably overlain by the thick-bedded leopard limestone of the Shuiquanling Fm
Regional extent
With a persistent lithology, the Machuan Fm shows a diachronism. In the type area, it is 161.2 m thick, and is overlain by the Shuiquanling Fm yielding cephalopod Wutinoceras sp. and conodont Scolopdus eburnus. Northward to Tongxin, Ningxia, it is 312-429 m thick, and includes the sequence yielding Wutinoceras. Southward to Longxian-Qishan, Shaanxi, the Machuan Fm is dominated by the sequence yielding Wutinoceras, and is 60-178 m thick.
GeoJSON
Fossils
This stratigraphic unit yields cephalopod Parakogenoceras sp.; conodonts Drepanodus arcuatus diform, Scolopodus rex huolianzhaiensis, Ozarkodina joachimensis.
Age
Depositional setting
It is deposited on a closed platform environment.
Additional Information