Wulanbulag Fm

Central-Eastern Inner Mongolia. The naming section is located in an area from Huji’ertu to the Yikenbulage Gully in the Qianli Mountains, Ih Ju League, Inner Mongolia. Named by Wang Banyue in 1981.

Synonym: Ulan Bulag Fm

This formation is divided into two members: Lower member is dark red-purplish red, moderately thick-bedded mudstone, muddy sandstone and sandy mudstone with orange yellow, medium-coarse to medium-fine sandstone. Upper member is grayish white-light orange-yellow, medium-coarse sandstone and locally fine sandstone. The total thickness exceeds 200 m.

The formation contains abundant mammal fossils, mainly including about 30 species such as Desmatolagus gobiensis, Parasminthus tangingoli, Cyclomylus lohensis, Karakoromys decessus, Tataromys sigmodon, Cricetops dormitor, Cadurcodon ardynense and Lophiomeryx gobiae. Of these up to 10 species such as Desmatolagus gobiensis and Karakoromys decessus are found in the Hsanda Gol Formation of the People’s Republic of Mongolia or the Ulantatal Fm (Wulantataer Fm) of China. It is conformably overlain by the Late Oligocene Yikenbulage Fm; therefore its age should be Early Oligocene. However, it is noteworthy that Cadurcodon ardynense and Lophiomeryx gobiae are also found in this formation. The two species were never found in post-early Oligocene strata previously. This suggests that if the identification is correct, there will be two possibilities: one is that there are possibly early Oligocene strata at the base of the formation, and the other is that the living period of the two species extend to later times.