Dazhai Fm
Type Locality and Naming
The type section of Dazhai Formation is located at Dazhai Village in Zhicun Township, Mengzi, southern Yunnan Province (103°30’E, 23°16’N). It lies 8.5 km southwest of the seat of Zhicun Township, or about 20 km southeast of the seat of Mengzi City. The section was measured by the Guangxi Bureau of Geology and Guangxi Regional Survey Team in 1965. The Dazhai Formation was published by Liu Yuanzheng et al. (1965) from Geological Bureau of Guangxi Zhuang Autonomous Region. The name is derived from Dazhai Village in Zhicun Township, Mengzi City (county level), Honghe Hani-Yi Autonomous Prefecture, southern Yunnan Province, and was originally appeared in a 1964 manuscript by the No. 4 Brigade of Yunnan Regional Geological Survey Team.
Synonym: （大寨组）
Lithology and Thickness
The Dazhai Formation is a clastic sequence. The formation mainly consists of yellowish green, yellow, and yellowish red silty shale with minor interbeds of micaceous siltstone or minor bands and lenses of sandstone. In the type section, the Dazhai Formation is 190.5 m thick.
Relationships and Distribution
Lower contact
The Dazhai Fm is in conformable contact with the underlying Chongzhuang Fm. The lower boundary of the formation is defined by appearance of sandy shale at the base of the formation and by the disappearance of arkose-quartzose sandstone of the underlying Chongzhuang Fm
Upper contact
The Dazhai Fm is in conformable contact with the overlying Tianpeng Fm. The upper boundary is defined by appearance of limestone and argillaceous striped limestone of overlying Tianpeng Fm.
Regional extent
Like the underlying Chongzhuang Fm, the Dazhai Formation is exposed in the southwestern corner of the Yangtze Area of South China Region, restricted to merely in the area belonging to the Honghe Hani-Yi Autonomous Prefecture, mid-southern Yunnan. The formation is rather stable in lithology except for adding minor limestone bands or lenses at Chongzhuang, Pingbian County, and minor ferro-manganiferous siltstone at Dayakou, Mongzi City. The formation varied in thickness, being 251.7 m at Chongzhuang, 190.5 m at Dazhai, and only 23.4 m at Dayakou.
GeoJSON
Fossils
In the type section, the Dazhai Formation yields trilobites Kaotaia magna, K. sp., Kunmingaspis sp., Mengzia mengziensis, M. sp., Probowmaniella dazhaiensis, “Ptychoparia” sp., Redlichia chinensis, and R. murakamii. In other localities, the formation yields trilobite Hoffetella sp.
Age
Depositional setting
Additional Information