Riwanchaka Fm
Type Locality and Naming
The type section is located at Riwanchaka of Chabug District, 220 km north of Gêrzê County, Tibet. It was named by Yao Zongfu, Chen Fuquan et al. in 1981.
Lithology and Thickness
Clayey Limestone. Dominated by carbonate rock intercalated with fine-grained clastic rock. Lower part is dominated by gray thin- to moderately thick-bedded clayey limestone, intercalated with yellow-brown brecciated limonitized micrite limestone and calcareous sandstone, and strongly silicified organic limestone; 119 m thick. Upper part is composed of gray thin- to moderately thick-bedded clayey limestone, crystalline limestone, organic limestone intercalated with thin-bedded green siltstone, shale and purple-red, gray-green shale and sandstone intercalated with clayey limestone; 292 m thick.
Relationships and Distribution
Lower contact
Unconformably over the siliceous brecciated trachybasalt of unknown age
Upper contact
Conformable contact with the Talilai Fm of the early Late Carboniferous
Regional extent
Distributed along Gangmaco-Chasang, etc. of Gerze County
GeoJSON
Fossils
Lower part yields Corals Thysanophylloides minor, Gerzenophyllum longiseptatum, Actinocyathus berthiaumi, Diphyphyllum platiforme, Kueichouphyllum sinense, K. heishihkuanense, Yuanophyllum sp., Arachnolasma sinens; and brachiopods Echinoconchus elegans, Balakhonia yunnanensis, etc.
Upper part yields Corals Aulina rotiformis, Yuanophyllum kansuense, Parahexagonaulina xizangensis, Slimoniphyllum multiseptatum and Kueichouphyllum sinense; as well as Brachiopods Datangia gerzenensis, Striatifera anqusta, Gigantoproductus protvensis, Balakhonia yunnanensis, etc.,
Age
Depositional setting
It is interpreted as typical neritic carbonate platform deposits under a warm-water environment, same as that of the Shangsi Fm of Guizhou
Additional Information