Choushui Fm
Type Locality and Naming
The type section is in Yunxian Village, Pu'er County, Yunnan Province.
Synonym: The established Yibi Fm based on the Yiwuxiang section in Mengla County, Yunnan by second regional geological survey group of Yunnan bureau of geology and mineral resources in 1976, was proposed to replace the Choushui Fm. But it was not adopted herein.
Lithology and Thickness
This formation is consisted of interbedded grey calcareous mudstone, silty mudstone and limestone, argillaceous limestone, which have been subdivided into three parts. Lower part is dominated by mudstone, siltstone interbedded with argillaceous limestone and marlstone, which is 88.6 m. Middle part is mainly argillaceous limestone and siliceous banded limestone intercalated with silty mudstone, with thickness of 271.4 m. Upper part is comprised of siltstone, calcareous siltstone interlayered with bioclastic limestone, and is 295.8 m.
Relationships and Distribution
Lower contact
The mudstone at the base of Choushui Fm was conformable in contact with the dolomite blocks that dominate the underlying Dashuijingshan Fm
Upper contact
It is unconformity in contact with the overlying Upper Triassic Weiyuanjiang Fm
Regional extent
This formation is mainly distributed around Simao, Yunnan, with consistent lithology. Thickness of this formation decreased from Choushui-Qingtou-Taozishu of Simao County northwards and eastwards.
GeoJSON
Fossils
Diverse bivalve, ammonoid, coral and brachiopod fossils. Bivalves: Posidonia wengensis, P. gemmellaroi, P. bittneri, Costatorta maequicostata, Daonella cf. lommeli, D. indica, D. aff. Reticulata, Leptochondria cf. paradoxica. Ammonoids: Protrachyceras sp., Celtites cf. epolensis
Age
Depositional setting
Shallow marine
Additional Information