Zhalagou Fm
Type Locality and Naming
The type section of the Zhalagou Formation is the Sandu section, located on the riverside of the Duliujiang River. It was measured between Zhalagou and Sanhe Town and lies about 2 km east of Sanhe Town, the seat of Sandu Shui Autonomous County. Except for the thickness no lithology was described by Qian (1961) when he first publishes the formation. A better section on the south bank of Duliujiang River at Zhalagou was selected as representative section of the formation (107°54’E, 25°58’N) by Guizhou Bureau of Geology and Mineral Recourses (1987). The Duliujiang south bank section lies about 3.5 km east of the seat of Sandu County and was measured by No. 5 Brigade of Guizhou Regional Geological Survey Team in 1965, which was published by the Guizhou Bureau of Geology (1965a, b). The Zhalagou Formation was first published by Qian (1961). The name is derived from Zhalagou Ditch in the Sandu Shui Autonomous County, Guizhou Province. The name was originally appeared in a 1959 manuscript by Yang Jingzhi, Qian Yiyuan and colleagues from Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences.
Synonym: （渣拉沟组）
Lithology and Thickness
The Zhalagou Formation is a clastic sequence, dominated by black carbonaceous shale and phosphoric and bituminic shale with rich nodules of pyrite and with phacoidal sandy shale in upper part. In the Sandu section, the formation is 91 m thick.
Relationships and Distribution
Lower contact
The Zhalagou Fm is in conformable contact with underlying Liuchapo Fm. The lower boundary is marked by lithological change from the black chert of the Liuchapo Fm to the black carbonaceous shale of the Zhalagou Fm.
Upper contact
The Zhalagou Fm is in conformable contact with overlying Duliujiang Fm. The upper boundary is marked by the disappearance of the black shale of the Zhalagou Fm, and the appearance of yellow argillaceous shale at the base of the Duliujiang Fm.
Regional extent
The Zhalagou Formation is exposed in the west of Jiangnan Basin Area of South China Region, distributed in southeastern corner of Guizhou Province (in the area east of the line connecting Nanmin and Gedong towns of Jianhe County and Sanhe Town of Sandu County). The formation is thickening northward with thickness varying from 94 to 248 m.
GeoJSON
Fossils
Only sponge spicule Protospongia sp. is known from the middle and upper parts of the formation.
Age
Depositional setting
The formation belongs to deposits in anoxic-reducing environment with very rare fossils collected.
Additional Information