Shuanghechang Fm
Type Locality and Naming
It was named by Zhu Zaoling, Ge Meiyu et al in 1977. The type section is near the 76 km milestone, by the road from Shashuliang to Dayanmen in Tianba, 70 km west of the Chengkou County in northeastern Chongqing Shi.
Synonym: (双河场组)
Lithology and Thickness
The formation, about 450 m in thickness, consists of a Lower part of black carbonaceous shale and silty siliceous shale, and Middle and Upper parts of dark gray, green gray silty shale intercalated with thin-bedded siltstone.
Relationships and Distribution
Lower contact
It contacts conformably onto the underlying Wufeng Fm of the Upper Ordovician.
Upper contact
It contacts conformably with the overlying Tianba Fm
Regional extent
It is exposed restrictedly in the Chengkou area, northeastern Chongqing.
GeoJSON
Fossils
Almost all the fossils comprised in the formation, except extremely rare crinoid columnal in the middle and upper parts, are graptolites, which are preserved in the black carbonaceous shale of the lower part in gathering form with high abundance and disparity, in ascending order: the Diplograptus modestus-Glyptograptus gracilis zone, the Parakidograptus acuminatus zone，the Orthograptus vesiculosus zone，the Pristiograptus leei zone， the Pristiograptus leptotheca zone, the Petalolithus folium zone, the Rastrites maximus zone and the Spirograptus turriculatus zone.
Age
Depositional setting
Additional Information