Xiaoerbulak Fm
Type Locality and Naming
The type section of Xiaoerbulak Formation (not named) is located close to the 3082 elevation point in the north of Wushi County, Xinjiang Uygur Autonomous Region (79°53’36”E, 40°54’30”N). The section lies about 45 km southwest of Aksu City, and was measured by the No. 9 Brigade of No. 13 Geological Team of Geological Ministry of China in 1957. In the type section, the formation is about 211 m thick. The Xiaoerbulak Formation was named by the Compiling Group for Xinjiang Regional Stratigraphical Scale (1981). The name was originally appeared in a 1958 manuscript by the joint team of No. 3 and 9 brigades of No.13 Geology Team of Ministry of Geology of China 1958. The name is derived from Xiaoerbulak in the south of Wushi County, Aksu Prefecture, Xinjiang Uygur Autonomous Region. The name originally appeared in a 1958 manuscript by Zhang Zhenghua and Wang Jinbing. Originally the formation was proposed as Xiaoerbulak Series, and was subsequently renamed Xiaoerbulak Formation by Compiling Group for Regional Stratigraphical Scale of Xinjiang Uygur Autonomous Region (1981).
Synonym: （肖尔布拉克组）
Lithology and Thickness
The Xiaoerbulak Formation is essentially a shallow-water carbonate sequence, dominated by limestone, marlstone, dolomitic limestone with siliceous lumps and bands, and intercalated with dolomite occasionally. The thickness of the formation varies between 26 to 247 m.
Relationships and Distribution
Lower contact
The Xiaoerbulak Fm is in conformably contact with the underlying Yurtus Fm. The lower boundary is marked by disappearance of dolomite or appearance of limestone.
Upper contact
The Xiaoerbulak Fm is in conformably contact with the overlying Awatag Fm. The upper boundary is defined by the appearance of the purplish red, argillaceous dolomite of the Awatag Fm.
Regional extent
The Xiaoerbulak Formation is exposed in the Bachu-Kalpin Area of Tarim Region, distributed, as known from outcrops and exploratory borings, in Aksu, Kalpin, Qipan, Subexi, Wensu, Wushi, and Zanbile cities and counties etc.
GeoJSON
Fossils
The Xiaoerbulak Formation yields trilobites Kepingaspis kepingensis, Jingyangia sp., Meitanella xinjiangensis, Paokannia sp., Shizhudiscus sugaitensis, Tianshanocephalus tianshanensis, and Ushbaspis kalpinensis; and brachiopods Archaeooides? sp., Lingulella sp., Linnarssonia sp., and Obolella? sp.
Age
Depositional setting
Shallow-water carbonate
Additional Information
Cheng (1979) named the lower part of the overlying Awatag Formation as Wusongger Fm by the presence of certain trilobite assemblage. This newly erected formation is obviously of lithostratigraphic form with biostratigraphic meaning. Cai (1999) merged the Wusongger Fm with Xiaoerbulak Formation to form an expanded Xiaoerbulak Formation because both formations are similar in lithology. The concept of expanded Xiaoerbulak Formation, as revised by Cai (1999), is followed in this book.