Angzanggou Fm
Type Locality and Naming
The unit was named by Yin et al. (1957) and published by Mu (1962). The type locality is at Angzanggou about 40 km west of Yumen City, Gansu Province. The type section is at Shimenzi- Quannaogoushan- Hanxia Section, 2 km to the south of Jiyingongtai, west of the Yumen City, Gansu Province. Its coordinate is 39°49′N, 97°08′E.
Synonym: （肮脏沟组）
Lithology and Thickness
The formation is dominated by black grey and blue grey sandy shale and siltstone, intercalated with black grey shale and conglomerate in its middle and lower parts. The thickness is up to 2315 m at the type section (Wang Ruiling, 1983).
Relationships and Distribution
Lower contact
It is conformable contact with the underlying Xiaoshihugou Fm
Upper contact
It is conformable contact with the overlying Quannaogoushan Fm
Regional extent
It is widely distributed in an area from Changma, Yumen City, Gansu Province in west to Mengyuan County, Qinghai Province in east.
GeoJSON
Fossils
Three graptolite zones such as Spirograptus turriculatus zone, the Streptograptus crispus zone and the Monoclimacis griestoniensis zone, are found in the formation.
Age
Depositional setting
The formation shows typical features of turbidite deposit. The environment is from deep-sea fan to proximal pluvial basin and distal pluvial basin (Xu Weidong et al., 2006).
Additional Information
The Xiaoshihugou Fm was rejected and included in the Angzanggou Fm by the Gansu Bureau of Geology and Mineral Resources in 1997, for the reason that the subdivision of the formations is based on the biostratigraphy rather than the lithology. However, we tentatively keep the name of Xiaoshihugou Fm until more works to definite the stratigraphic units in high resolution in this area, although the opinion of GBGMR in 1997 is worthy to be considered.