Shihwengtzu Fm
Type Locality and Naming
The type section of Shihwengtzu Formation is the Shiwengzi section. It is located at east bank of the Qianyouhe River in the north of Shiwengzi Village, about 0.2 km north of Shiweng Town, or about 12 km southwest of the seat of Zhashui County, Shangluo, Shaanxi Province. (109°10’05” E, 33°37’45” N). The section was remeasured by Shaanxi Regional Geological Team in 1985. The Shihwengtzu Formation was named by Zhao and Huang (1931). The name is derived from Shihwengtzu (spelled Shiwengzi in Hanyu Pinyin) Village in Shiweng Township, Zhashui County, Shangluo City, southeastern Shaanxi Province.
Synonym: （石瓮子组）; The unit was originally called Shihwengtzu Limestone by Zhao and Huang (1931), which was renamed Shihwengtzu Limestone by Ma (1998).
Lithology and Thickness
The Shihwengtzu Formation is a carbonate sequence. It consists of light grey, thick-bedded to massive dolomite, intercalated interbeds of thin-bedded limestone, which varies in number from where to where. The dolomite contains chert nodules or bands, which increase in number upwards in section. Thickness of the formation at type section is unkown. It is 336 m in a section nearby at Guanyinbian, Zhashui County, Shangluo City, southeastern Shaanxi Province.
Relationships and Distribution
Lower contact
The Shihwengtzu Fm rests conformably on either the underlying Yuejiaping Fm in the area east of Shanyang Town, Shanyang County or the underlying Shuigoukou Fm in the area of west to Shanyang Town. The lower boundary of the formation is defined by the appearance of the thick-bedded dolomite of Shihwengtzu Fm on the red dolomite at the top of the Yuejiaping Fm in the area east of Shanyang Town or on the dark grey limestone at the top of the Shuigoukou Fm in the area west of Shanyang Town.
Upper contact
It is in conformable contact with the overlying Bailongdong Fm of Ordovician System or in disconformable contact with overlying Dafenggou Fm of Devonian System. The upper boundary is defined by lithological change from thick bedded dolomite of the formation to the thin-bedded limestone at the base of the Bailongdong Fm in the area east of Shanyang Town or by unconformable plane from the overlying Dafenggou Fm of Devonian System in the area west of Shanyang Town.
Regional extent
The Shihwengtzu Formation is exposed in the Jiangbei Slope Area of South China Region, restricted to southeastern Shaanxi Province (Zhashui, Ningshan Shanyang, Shangnan counties). The thickness of the formation varies significantly from 4 to 1045 m. In the area east of Shanyang Town, Shanyang County, the Shihwengtzu Formation deposited conformably on the Yuejiaping Formation. Because the latter formation tapered out westward, the Shihwengtzu Formation therefore deposited directly, also comfortably, on the older Shuigoukou Formation in the area west to Shanyang Town.
GeoJSON
Fossils
The top part of the formation yields gastropod Eotomaria sp.
Age
Depositional setting
Additional Information