Xiahuancang Fm
Type Locality and Naming
The Northwestern Region Marine Triassic, Jurassic Fault dating conference named this formation in 1976. Yang Zunyi et al. first public citation in 1983. The named section is located at Caodigou, Xiachangxiang Township, Tianjun County, Qinghai Province. The Early Triassic marine strata in the Qilianshan area, Qinghai Province, have been successively called the Lower Xiajunzihe system (Yang Zunyi et al, 1962) and the Jialige Fm (Qinghai coalfield 705, 1974). The Yangkang Gr was named by Conference on Marine Triassic and Jurassic strata in Northwestern Region in 1976, and was divided into the Xiahuancang Fm and the Jianghe Fm from bottom to top, representing the early and late early Triassic sediments respectively. Yang Zunyi et al (1983) followed the scheme and divided each formation into two members.
Synonym: Xiahuancanggou Fm.
Lithology and Thickness
It is medium-coarse quartz sandstone, feldspar sandstone with siltstone and silty shale, and can be divided into lower purple sandstone member and upper grey-green sandstone member according to its color. The bottom boundary is marked by the appearance of purple sandstone, and the top boundary is marked by the disappearance of gray-green sandstone. Thickness is 23-260 m.
Relationships and Distribution
Lower contact
It is in disconformable contact with the underlying Nuoyinhe Gr of Upper Permian.
Upper contact
It is in conformable with the overlying Jianghe Fm
Regional extent
It is mainly distributed in the middle of Junzi river and Xiariha river in the south of Qilian Mountains of Qinghai Province.
GeoJSON
Fossils
Ammonoids: “Vishunites” decipiens-Glyptophereras polore at the lower part. Bivalve: Claraia aurita, C. yangkangensis is the main species at the lower part., and Eumorphotis multiformis is abundant in the upper part.
Age
Depositional setting
This formation is a shallow water deposit.
Additional Information