Zhoujieshan Fm

Type section of Zhoujieshan Formation is the Quanjishan section, located at Heitupo at the Hongtiegou Village in the Quanjishan Mountain, Da Qaidam, Haixi Prefecture, Qinghai Province (95°51’E, 37°25’N). The section lies about 60 km southeast of Da Qaidam Town, and was remeasured by Wang Yunshan and Chen Jiliang in 1983. It is the upper portion of the same type section shared by the underlying Hongtiegou Fm and Heitupo Fm, which embrace the Bed 1‒3 and Bed 4‒6 respectively, while the Zhoujieshan Formation embraces the Bed 7‒10 of the section. In the type section, the formation is 56.0 m thick. The Zhoujieshan Formation was named by Wang et al. (1980). The name is derived from Zhoujieshan Hills to the west of Hongtiegou Village in Quanjishan Mountain in Da Qaidam Township, Haixi Mongolian and Tibetan Autonomous Prefecture, Qinghai Province.

Synonym: （皱节山组）

The Zhoujieshan Formation is mainly a clastic sequence with minor interbeds of carbonate rocks. The formation includes the upper four beds of the Quanjishan type section (Bed 7 to 10), from bottom up: 7, light pink to greyish white, thick-bedded dolomite with a layer of pebbly dolomite, 0.5 ‒1 m thick, at the base (7.20 m thick); 8, purplish red, platy ferriferous siltstone, quartzose sandstone with interbeds of brownish yellow, sandy and calcareous dolomite (11.30 m); 9, greyish green and purplish red, platy siltstone and find-grained sandstone (23.50 m); 10, grey thin-bedded, find-grained sandstone with a layer of platy siltstone, 50 cm thick, at the top (14.00 m).

In the type section, the Bed 9 yields micro-paleoplant fossils Microhystridium sp., Osilatorites sp., Trematosphaeridium cf. holtedahlii and T. minutum, and fragments of worms.