Discovery of the Zhesi brachiopods fauna in Bolgensume area, Xilinhot, Inner Mongolia, and its biogeographical division

Lots of brachiopods which include 18 genera and 23 species were discovered in Zhesi Formation, Wulejitu section, Bolgensume, Xilinhot, Inner Mongolia.The brachiopod community is mainly composed of Productida and Spiriferida, which show typical Zhesi fauna characteristics.It can be divided into two assemblages from bottom to top: Ⅰ Yakovlevia mammata -Anidanthus rugousa assemblage; Ⅱ Anidanthus ussuricus- Rhombospirifer zhesiensis assemblage.The geological age of assemblage Ⅰ is assigned to the Kungurian to Roadian, with the characteristic of cool water facies-differentiation type.The geological age of assemblage Ⅱ is assigned to the Wordian, with the characteristic of cool water facies-micro-osmosis type.A comparison of Zhesi brachiopods fauna from other regions shows that the Zhesi brachiopods fauna evolved from the cold water type to the mixed type mixed type from Kungurian to Wordian.The cause of this change may be the tectonic movement between the Siberian plate and the North China plate or the Late Paleozoic glaciation.