Bolin Fm
Type Locality and Naming
It was named by Liang Dingyi in 1991. The naming section is located in the Bolicaga Gully, Zada County, Tibet (E 79°30′, N 31°20′), with its reference section being situated in the Caili area of Pulan County, Tibet (E 81°30′, N 30°10′).
Synonym:（波林组）
Lithology and Thickness
Lower and Middle parts of the formation represent black shales intercalated with argillaceous sandstones, yellow-grey marls. Upper part of the formation consists of yellow-grey medium, and thick-bedded limestone, ferruginous chamoisite-sandstone and phosphorite. The thickness of the formation is 10-50 m.
Relationships and Distribution
Lower contact
Being composed of yellow-grey marls, the basalt part of the formation is in a conformable contact with the grey bioclastic limestone of the top part of the underlying Youxiugou Fm
Upper contact
Meanwhile, the medium-bedded limestone of the top part of the formation is in a disconformable contact with the black silty shale of the basal part of the overlying Fangmachang Fm
Regional extent
The formation is distributed extensively in the Bolin and Mayang areas, and Zada-Nuba region of Zada County, as well as in Caili area of Pulan County, Tibet. Its lithology is consistent, yet in the Mayang area it consists already largely of argillaceous limestone, sandy limestone and oolitic limestone, with an increasing thickness.
GeoJSON
Fossils
In the Zada area of the formation yields abundant Callovian bivalves, ammonites, Belemnites and Brachiopods. From among the ammonites there occur the Choffatia sp., Macrocephalites sp., Xenocephalites sp., Oxycerites cf. oppeli; of the Belemnites there occur: Belemnopsis sp., B. mackayi, B. lalonglaensis, Hibolithes catlinensis; from the bivalves there occurs the Astarte hermanni-Homomya cf. hostulana assemblage.
Age
Depositional setting
Additional Information