Yixibaila Fm

Junggar Basin NW. Named by Zhu Xia et al. in 1955 and reported in 1975. The naming section is located near Sangequan (i.e. Uqbulak in Uygur) ~100 km south of the Ulungur River on the northern margin of the basin and the reference section is located at the Huashigou >20 km northwest of Sangequan.

Synonym: Uqbulak Fm, Ulungurhe Fm; maybe also Sangequan Fm (?; Han name for the Uqbulak town))

Lower part is grayish white and grayish green sandstone with brownish red and variegated mudstone. Upper part is alternating beds of grayish white, grayish yellow and grayish green sandstone and conglomerate and grayish brown or brownish red sandy mudstone and mudstone. The thickness is ~80 m.

The formation has three fossil beds in Huashigou: bed A contains Hyopsodus huashigouensis, Mesonychidae and Coryphodontidae; bed B contains Mesonyx uqbulakensis, Metacoryphodon sp., Breviodon minutus, Schlosseria magister etc.; bed C at the top contains Rhodopagus sp. The lower part of the formation near Sangequan contains the charophytes Stephanochara kiangsuensis, Nemegtichara prima, Maedlerisphaera nana, Gobichara deserta etc. and the mammals Mesonyx, Metacoryphodon and Schlosseria. From the features of the fauna, this fauna is quite similar to those of the early-middle Eocene Ashantou Fm in Inner Mongolia and the Dacangfang Fm in Henan and is not equivalent to that of the Anjihaihe Fm (or called the Lower Green Fm) on the southern margin of the basin.