Sewa Fm
Type Locality and Naming
It was named by Wen Shixuan in 1979. The naming section is located on the northern slope of the Shaqiaomu Mts, Sewa region, Bange County, Tibet, with its reference section being situated in the Zhesong-Shaqiaomu area 5 km northwest of Sewa region, Bange County, Tibet.
Synonym: （色哇组）; Shaiwa Fm, Saiwa Fm (spellings)
Lithology and Thickness
The formation represents flyschoid deposits with a distinct rhythm composed of black, grey-black and yellow-grey shale, calcareous shale, silty shale, argillaceous siltstone, siliceous siltstone, poststone (=fine-grained sandstone), microcrystalline limestone and marl. It is 1330 m thick.
Relationships and Distribution
Lower contact
Its basal part consisting of yellow-green siltstone, and being in a conformable contact with the grey-black marl from the top part of the underlying Qushai Fm
Upper contact
The formation is lacking its top in the type section. Regionally, the schematic strat column indicates the next younger unit as the Shaqiaomu Fm.
Regional extent
The formation is distributed mainly in the Zesong, Shaqiaomu and Zhaxiagongma areas of Sewa region, with a consistent lithology, representing black and yellow-green sandy shales associated with siderite concretions, indicating that they are deposits of a fairly typical reduction environment.
GeoJSON
Fossils
It yields such as ammonites Witchellia sp. Dorsetensia sp., Sonninia (S.) propinguans, Zetoceras sp., Fontannesia sp., Pseudotoites sp., Megalytoceras sp., Stephanoceras sp., S. cf. wangen, Shirbuirnia cf. buokman, Kumatostephanus sp., Pelekodites sp. and Emileia sp.; as well as bivalves as represented by Parvamussium cf. pumilum, Camptonectes (C.) punctatus, Liostrea cf. acuminata and Pseudolimea duplicata?
Age
Depositional setting
Flysch; and deposits of a fairly typical reduction environment.
Additional Information