Bayankarashan Gr

Qinghai geological bureau the first area survey team was named in 1970. The named section is located in the Bayan Kala (Bayan Hala) Mountains at the border of Qinghai and Sichuan.

Synonym: Bayanharashan Gr (spelling)

It is divided into three subgroups: Lower sandstone subgroup consists of medium-coarse arenaceous feldspar sandstone, feldspar sandstone, feldspar quartz sandstone, etc., interbedded with silty slate, and interbedded locally. It is further divided into the lower sandstone unit and the upper sandstone slate interbedded unit. The upper part of the lower sandstone unit is dark grey-green argillaceous and calcareous cemented feldspar sandstone, and the hard sandy feldspar sandstone is interbedded with black and yellow-green silty slate. The lower part is gray-green, green argillaceous, calcareous cemented pebbled feldspar sandstone, feldspar sandstone interbedded with gray limestone and interbedded conglomerate, and the bottom is gray-green conglomerate. Lower part thickness of 977 m. The upper sandstone and slate interbedded unite consists of gray-green medium-thick medium-fine grained hard sandy feldspar sandstone, interbedded quartz feldspar sandstone and gray-black slate interbedded with gray-black thin crystalline limestone with thickness of 1561 to 4600 m. Middle subgroup is composed of a set of medium-fine grained feldspar sandstone, feldspar quartz sandstone, siltstone and silty slate with distinct rhythm and a total thickness of more than 3510 m. Upper subgroup is characterized by a large number of argillaceous clastic rocks, and can be roughly divided into five rock units from bottom to top. The interbedded sandstones and slates at the bottom are medium-fine grained quartz sandstone, gray-green, gray-black, interbedded feldspar greywacke, interbedded sandy feldspar sandstone and gray-black slate, interbedded silty slate with thickness of 1056 to 3500 m. The lower slate unit is composed of dark gray slate, gray black slate, sandy slate and gray green mixed sandy feldspar sandstone with thickness of 1053 to 3500 m. In the lower part of the interbedded sandstones and slates, there are gray, gray green thick to very thick layers of medium coarse feldspar graystone and sandy feldspar sandstones interbedded with gray-black slate. The upper layer is interbedded with thin limestone. The upper layer is interbedded with gray-black silty slate and gray-black feldspar sandstones with thickness of 643 to 2100 m. Upper sandstone unit is composed of grayish or grayish green medium-thick medium-fine grained feldspar greywacke, grayish sandy feldspar sandwiched with black millenite slate and a small amount of purplish gray sandstone. The upper sandstone is sandwiched with thin-bedded limestone with thickness of 756 to 2300 m. The lower part of the interbedded sandstone and slate at the top is interbedded with gray and grayish green medium thick medium-fine grained feldspar graystone, grayish sandy feldspar graystone and gray silty slate, interbedded with limestone lens occasionally. The upper part is grayish green thick grayish sandy feldspar graystone, interbedded with gray slate, with the thickness of 1996 to 3322 m.

The lower subgroup produced ammonoids "Vishnuites" decipiens, Gyrophiceras vermiforme, Acanthophiceras cf. gibbosum, Anotoceras costatum, Flemingites muthensis, Cordillerites sp. and so on. Upper ammonoid Meekoceras cf. infrequens, Iculitoides globosus, Procarnites kokeni, etc.; Bivalves, such as Entolium cf. sichuanensis, Posidonia baiyushiensis, et al. Lenotropites debilis, Danubites sp.; bivalve Leviconcha orbicularis and gastropod Tuosuohuthyris sulcus, etc. The upper subgroup is rich in marine bivalves, but the species are monotonous. There are 12 species of Halobia. The important representatives were Halobia cordillerana, H. cf. dissecsecta, Myophoria subvestita, Nuculana perlonga, N. yunnanensis, Pachycardia subrugosa, Pteria aff. annamitica, Gervillia praecursor, etc. There are also crinoids, corals and plant fossils.