Yanchiwan Gr
Type Locality and Naming
The type section is at Wuligou in southern mountain, Danghe, Gansu. The Yanchiwan Gr is derived from the Yanchiwan Fm proposed by No.2 Gansu Party of Regional Geological Survey in 1975 and published by Gansu Compiling Group for Regional Stratigraphic Scale (1980). Gansu Bureau of Geology and Mineral Resources (1989) renamed the Yanchiwan Fm the Yanchiwan Gr.
Synonym: (盐池湾群）
Lithology and Thickness
The group is divided into three parts. Lower part is dominated by greyish green feldspathic-quartzose greywacke and slate intercalated with muddy siltstone, sandstone, with a thick-bedded boulderstone intercalated with greywacke and slate at the base. Middle part is characterized by slate. Upper part is represented by interbedded grayish green greywacke and slate intercalated with pebble-bearing coarse sandstone and conglomerate. In the type area, the Yanchiwan Gr recorded an incomplete thickness of 3349 m.
Relationships and Distribution
Lower contact
The Yanchiwan Gr rests conformably on the Wuligou Gr
Upper contact
Upper boundary is covered in the type section. Regionally, the next younger unit is the Xiaoshihugou Fm of early Silurian.
GeoJSON
Fossils
The middle part of the formation yields trilobites Lonchodomas yohi, Remopleurides cf. latus, Birmanites sp., Telephina sp., Ampyx sp., Illaenus sp., Cyclopyge sp., Vodesia sp. and cephalopod Discoceras sp.
Age
Depositional setting
Additional Information