Yangjiawan Fm
Type Locality and Naming
The type section of the Yangjiawan Formation is the Sandu section lying on the riverside of the Duliujiang River. It was measured between Zhalagou and Sanhe Town, about 2 km east of Sanhe Town. Except for the thickness no lithology was described by Qian (1961) when he first publishes the formation. A better section measured at the Yatang Village in Sandu County was selected as representative section of the formation (117°55’E, 26°03’N) by Guizhou Bureau of Geology and Mineral Recourses (1987). The Yatang section lies 5 km north of the Sanhe Town, and was measured by Cai Ying, Yin Gongzheng and others from Guizhou Regional Geological Survey Team in 1983. In this section, the formation is 371.89 m thick. The Yangjiawan Formation was first published by Qian (1961). The name is derived from Yangjiawan in the outskirts of Sanhe Town, the seat of Sandu Shui Autonomous County, Qiannan Buyi-Miao Autonomous Prefecture, 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: （杨家湾组）
Lithology and Thickness
The Yangjiawan Formation is a carbonate sequence, consisting of grey, thick-bedded to massive brecciated limestone, brecciated dolo-rudite, and brecciated dolomite in the Lower part; and grey, thin-bedded limestone and marlstone with minor interbeds of shale in the Upper part. The thickness of the formation varies from 77 to 370 m.
Relationships and Distribution
Lower contact
The Yangjiawan Fm is in conformable contact with the underlying Duliujiang Fm. The lower boundary is marked by lithological change from the highly-carbonaceous shale in the top of Duliujiang Fm to brecciated limestone or brecciated dolomite.
Upper contact
The Yangjiawan Fm is in conformable contact with the overlying Sandu Fm. The upper boundary is defined by the appearance of massive brecciated limestone at the base of the Sandu Fm.
Regional extent
The Yangjiawan Formation is exposed in the west part 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 Jinaghe County and Shahe Town of Sandu County).
GeoJSON
Fossils
In the Yatang section, the basal part of the Yangjiawan Formation yields trilobites l.isania sp., Fenghuangella sp. and Hypagneostus sp.; the lower part yields trilobites Corynexochus sp., Lejopyge sp., Proceratopyeg sp., Pseudagnostus sp., Sanduspis sp., and Yakutiana sp.; the middle part yields trilobites Olenus sp., Onchonotina sp., Proceratopyge fenghwangensis, Prochuangia sp., Pseudagnostus cf. communis, P. sp., Pseudoyuepingia modesta, Sanduspis gracilis, and S. sp., and graptolites Dictyonema sp. and Dendrograptus sp.; and the upper part yields trilobites Lotagnostus americanus, Jegorovaia expansa, and Sanduspis sp.
Age
Depositional setting
Additional Information