Xishanbulak Fm

The type section of Xishanbulak Formation is the Mohershan section, situated on the north slope of the Mohershan Mountain in the border area between the Yuli and Heshuo counties, Bayingolin Prefecture, Xinjiang Uygur Autonomous Region (88°21’05” E, 41°24’20” N). The section lies 35 km southeast of Qinggir Village or about 40 km northeast of Xingdi Village in Yuli County, and was measured by Zhang et al. (1959). The Xishanbulak Formation was first published by Zhang and Gao (1984). It is the lowermost portion of the same section shared by the overlying Xidashan and Mohershan formations. The name is derived from the Xishanblak Spring, which lies between the north slope of Mohershan Mountain and the Xidashan Mountain in Yuli County, Bayingolin Mongolian Autonomous Prefecture, Xinjiang Uygur Autonomous Region. Originally the unit was proposed as Xishanbulak series in a 1957 manuscript by the No. 722 Team of Xinjiang Geological Buruea.

Synonym: (西山布拉克组)

The Xishanbulak Formation is a composed sequence of siliceous and volcanic rocks. Lower part consists of black chert or phosphoric chert with a layer of phosphorite at its top. Middle part consists of volcanic rocks, mainly basic eruptive rocks with gas leaks and almond-shaped structures, and is greatly variable in thickness; upper part consists of black chert. In other sections, this part usually bears andesitic porphyrite, andesitic tuffaceous agglomerate and tuffaceous sandstone in its lower part. In the type section, the formation is more than 130 m.

So far only trilobite fragments, brachiopoda Lingelella and sponge spicule Protospongia are known from the formation.