Sanduo Fm
Type Locality and Naming
The naming section is located in the wells of northern Jiangsu. Named by the Jiangsu Petroleum Party in 1958.
Lithology and Thickness
Brownish red mudstone and siltstone, containing gypsum concretions and locally black mudstone and several beds of basalts; the top is dominated by grayish green mudstone and the base is sandstone and conglomerate. The thickness is ~550 m.
Relationships and Distribution
Lower contact
This formation has a disconformable or unconformable contact with the underlying Eocene Dainan Fm.
Upper contact
Unconformable contact with the overlying Neogene Yancheng Fm.
Regional extent
The Sanduo Formation is widespread in northern Jiangsu, being only absent at northern Xuyi, Hongze, Baoying, Jianhu and Yancheng, as well as at Zhongbao and Wubao of Xinghua County, Taizhou and Xiaohai of Dafeng.
GeoJSON
Fossils
The formation is rich in fossils. Member II contains the ostracods Cyprinotus hubeiensis-Cyprois xiangensis assemblage and Member I contains the Echinocypris jingshanica-Limnocythere posterocosta assemblage. Charophytes are represented by the Obtusochara jianglingensis-Gyrogona qianjiangica assemblage, and in addition there are the mammals Rhombomylus sp. and sporopollen.
Age
Depositional setting
The formation is fluvio-lacustrine (predominantly lacustrine) deposits.
Additional Information