Youxiugou Fm
Type Locality and Naming
It was named by Liang Dingyi in 1991. The naming section is located at the Polinchaga Gully of Zhada County, Tibet.
Synonym: （优秀沟组）
Lithology and Thickness
Lower part is composed of dark-grey medium-bedded-massive limestones, intercalated with argillaceous limestones. Upper part is composed of grey, dark-grey and violet-grey medium-, and thick-bedded bioclastic limestones, argillaceous limestones and shelly limestones with hexacorals reef. Its thickness is of over 550 m.
Relationships and Distribution
Lower contact
No base of the formation has been found, and no clear relations between it and the underlying strata have been known. No base of it having been found in most regions, and only in the Mayang region the formation has been found to be in a disconformable contact with the underlying upper Triassic Series or still older strata.
Upper contact
In all regions except the type locality the formation is in a conformable contact with the overlying Polin Fm
Regional extent
The formation is distributed essentially in the Polin, Mayang Nubar and Pulancaili regions of Zhada County, with a consistent lithology and a thickness of 25-1100 m.
GeoJSON
Fossils
It yields corals, Brachiopoda and bivalve fossils in the Zhada region, with the corals being represented by the Callignonastrea jumavenensis-Protethmos blanfordi assemblage; with the bivalves being represented by the Pracexogyra acuminata assemblage and the Costamussium multicostatum-Meleagrinella bulingensis assemblage; and with the Brachiopoda being represented by the Homoseorhynchia-Lacunalrhynchia assemblage.
Age
Depositional setting
Additional Information