Caodigou Fm
Type Locality and Naming
The type section is located in the Zhongshigong area to the southwest of Xiahuancang District, Tianjun County, Qinghai Province. It was named by Liu Guangcai in 1980. Upper formation in the Bayinhe Gr.
Lithology and Thickness
Sandstone. Dark-grey and dark-green thick-bedded and fine-grained feldspar-rich sandstone, quartz-sandstone and siltstone, intercalated with shale and thick-bedded bio-limestone. Its basal part consisting of grey, thick-bedded and fine-grained quartz-sandstone. Thickness is 184 m.
Relationships and Distribution
Lower contact
Conformable contact with the purplish red, medium- and fine-grained quartz-sandstone of the underlying Lemengou Fm.
Upper contact
Disconformable contact with the overlying Hajier Fm.
Regional extent
The formation is fairly developed commonly in the region to the north of the Buhar River, with its thickness generally of 132-212 m, while in the region to the south of the Buhar River it is short of grey-black and grey-green shales. To the west of the Zhongshigong section till the Dawashi area it has gradually changed facially into limestone, with a thickness of 114 m, and easterly clastic rocks are increasing in amount, with its thickness getting smaller. To the south of the Buhar River in the Huduologai trench of the Tuolongliang area, it turns into grey-white dolomites, with a thickness of 37-90 m.
GeoJSON
Fossils
Brachiopod fauna represented by the-Pygmochonetes minor assemblage, and Bryozoans of the Dyscritella sinensis-Pseudobatostomella abnormis-Maychella assemblage.
Age
Depositional setting
It is interpreted as marine deposits.
Additional Information