Shuanglungtan Fm
Type Locality and Naming
The type section of the Shuanglungtan Formation is Longwangmiao section. The Longwangmiao is a temple built near Shuanglongtan Lake. The type section lies about 6 km south of the seat of Qujing City (103°45’E, 25°27’N), and was measured by Jiang et al. (1964). The formation was named by Jiang et al. (1964). The name is derived from Shuanglungtan (spelled Shuanglongtan in Hanyu Pinyin) Lake, Qilin District, Qujing City, eastern Yunnan Province.
Synonym: （双龙潭组）; Shuanglongtan Fm
Lithology and Thickness
The Shuanglungtan Formation is a carbonate sequence with interbeds of clastic rocks. In the type section, the formation is consisting of grey limestone and argillaceous and dolomitic limestone, intercalated with thin-bedded shale and fine-grained sandstone. In the type section, the formation is 265.6 m thick.
Relationships and Distribution
Lower contact
The Shuanglungtan Fm rests conformably on the underlying Toupossu Fm. The lower boundary of the Shuanglungtan Fm is defined by the appearance of limestone at its base and the disappearance of yellow siltstone or shale of the underlying Toupossu Fm.
Upper contact
It is in disconformable contact with the overlying formations of Ordovician, Silurian or Devonian systems from place to place. In the type locality it is overlain by the Guandi Fm of the Silurian System.
Regional extent
The Shuanglungtan Formation is exposed in the southwest of Yangtze Area of South China Region, restricted to the central part of eastern Yunnan Province. The formation is basically stable in lithology in the area east of Kunming and increases argillaceous limestone and dolomitic limestone in the area around Kunming City and in the area west of Kunming as well, such as in Wuding and Lüquan counties. The residual thickness of the Shuanglungtan Formation is different from place to place because of various erosion extent, varying from 79 m to about 300 m.
GeoJSON
Fossils
The middle part of the Shuanglungtan Formation yields trilobites Kuetsingocephalus kuetsingensis, Proasaphiscus sp. and Solenoparia sp., and the top part yields trilobites Manchuriclla sp., Potohedinia sp. and Szeaspis sp.
Age
Depositional setting
Additional Information
The formation represents deposits in tidal flat environment.