Ritang Fm
Type Locality and Naming
It was named by Wang Yigang, Sun Dongli, He Guoxiong in 1980. The naming section is located in the Duosong (Dusuo) Township, Ritang Region, Longzi County, Tibet, with its reference section being situated at the Xiongre Mts south of the Ritang region, Longzi County, Tibet.
Synonym: （日当组）, Ridang Fm
Lithology and Thickness
The Xiongreshan Member (Hettangian) is composed of grey-black and black shales and silty shales, containing siliceous concretions, with no base having been found, and with a thickness of about 300 m; the Duosong Member (Sinemurian) is composed of grey-black shales and calcareous shales, intercalated with siliceous stripes and concretions, with a thickness of 62 m; and the Duobashan Member (Pliensbachian; and Toarcian?) represents grey-black and grey shales and calcareous shales, intercalated with siliceous and argillaceous limestones, poststones (= fine-grained sandstone), siliceous and chert concretions. The formation is more than 1000 m thick.
Relationships and Distribution
Lower contact
No base has been found. Regionally, the schematic strat column indicates the next older unit as Xiajiabula Gr
Upper contact
The formation is lack of its top and base, with only a disconformable contact between it and its overlying grey-white and white medium-bedded quartz-sandstones of unknown age being seen in the North Mts of the Dusuo region, where the formation is 450 m thick. Regionally, the next younger unit is indicated as the volcanics of the Binhu Fm.
Regional extent
The formation is distributed mainly in the area south of the Ritang region extending to the Zaxikang area, Longzi County, with a consistent lithology of it and a changeable thickness varying in a range from 66 m to about 1000 m.
GeoJSON
Fossils
The Xiongreshan Member yields ammonites as represented by Psiloceras psilonotum, Wachneroceras latum and etc.; and the Duosong Member yields ammonites such as Ectocentrites lengziensis and Arnioceras arnouldi. In the North Mts of the Dusuo region, the formation yields ammonites such as Prodactylioceras enodem, Hantkeniceras cf. hantkeni, Oxynoticeras sp., Juraphyllites spp., Jytoceras cf. fimbriatum, and Galaticeras cf. harpoceratoides.
Age
Depositional setting
Additional Information