Xiaoba Fm
Type Locality and Naming
Southernmost Sichuan. The No.508 Geological Team under the Southwest Bureau of Geology erected the Xiaoba bed in the report on the Cretaceous in Huidong and Huili (unpublished). The section for the designation is at Xiaoba of Jiangzhou of the Huidong County of Sichuan.
Lithology and Thickness
The Xiaoba Formation is represented by a set of purple red calcareous siltstone and mudstone, which is roughly divided into two parts. Lower part is built up by purple gray and purple red massive sandstone, intercalated with purple gray thin marl beds. It is 134.50 m thick.
Relationships and Distribution
Lower contact
The unconformable base of the formation marked by purple gray and purple red sandstone and conglomeratic sandstone is distinguished from the Upper Jurassic Guangou Fm marked by purple red mudstone with marl. Regionally, its base is in disconformable contact with a purple red conglomerate overlying the Feitianshan Fm.
Upper contact
The disconformable top is bounded by the appearance of light purple gray massive sandstone with gravels at the base of the Paleocene Leidashu Fm.
Regional extent
The formation occurs in the Panxi area and mainly on the Mishi syncline and in Huile and Huili of west Sichuan. It is quite persistent in lithology. Copper mineralization is common. Mudstone is often intercalated with gypsum. The formation is 860-1430 m thick and up to 1900 m at maximum. In the northeast Huili area, it is in unconformable contact with the Feitianshan Fm.
GeoJSON
Fossils
The formation yields ostracods Cypridea-Talicypridea-Candona- Eucypris-Cyprois-Cypris-Cyprinotus-Harbinis assemblage; Charophyte Obtusochara- Grambastinchara-Mesochara-Charites assemblage; and estheria Orthestheria sp.
Age
Depositional setting
Additional Information