Sigang Fm
Type Locality and Naming
The type section is at Sigang in Neixiang County, Henan. The Sigang Fm was named by Pei Fang and Cai Shuhua in 1987. The Sigang Fm had previously been referred to the metamorphosed mudstone intercalated with micrite in the lower part of the Shiyanhe Fm proposed by Yan Guoshun et al. (1983), and was thought to be Middle Ordovician in age. In 1991, Liu Yinhuan confined the Sigang Fm to be the nodular mudstone intercalated with limestone yielding abundant marine fossils, and named the underlying strata the Yangzhuang Fm. Considering the similar lithology of the Yangzhuang Fm of Liu et al. (1991) with the Sigang Fm, the present book includes it in the Sigang Fm.
Synonym: (寺岗组）
Lithology and Thickness
The formation is divided into two parts. Lower part is dominated by quartz siltstone and quartz-bearing silty mudstone intercalated with sandy dolomite and limestone. Upper part is represented by nodular mudstone intercalated with limestone and dolomitic limestone. In the type area, the Sigang Fm is 318 m thick.
Relationships and Distribution
Lower contact
The Sigang Fm rests disconformably on the volcanic and volcaniclastic rocks of Zuoxiu Fm
Upper contact
It is conformably overlain by the mudstone and dolomitic limestone yielding corals of the Shiyanhe Fm.
Regional extent
With a persistent lithology, the Sigang Fm is exposed at Shiyanhe (255 m thick) in Xichuan, Sigang (318 m thick) in Neixiang, Henan.
GeoJSON
Fossils
The upper part is fossiliferous, and yields conodonts of Aphelognathus neixiangensis assemblage and trilobites of Neseuretus (Neseuretinus) assemblage.
Age
Depositional setting
Additional Information