Shigu Fm
Type Locality and Naming
It was named by Liu Yuanzhen, Yuan Zaishu as the “Shigu Horizon” in 1951. The naming section is located in the Shigu area, Sandu region, Zixing County, Hunan Province.
Synonym: （石鼓组）
Lithology and Thickness
Lower part represents an alternating layer of grey medium-grained arkosic quartz-sandstone in association with mudstone, gradating upwards into an alternating layer of grey-white argillaceous sandstone and mudstone. Upper part is composed of purple mudstone, with a thickness of about 140 m.
Relationships and Distribution
Lower contact
It overlies conformably the Maoxianling Fm
Upper contact
Regionally, the schematic strat column indicates the next younger unit as Baixiangdai Fm
Regional extent
The formation is distributed essentially in the Sandu region of Zixing County; Lishu’ao, Gaocun and Fanjia Villages of Rucheng County; Huangnitang and Baxi of Guidong County; Baji of Caling County, as well as Jiupujiang of Yuxian County. The strata of the formation in various regions are preserved incompletely, with the remnant thickness of the formation in the Sandu region being of 130 m; and with a better exposure of it being found in the Fanjia area of Rucheng County, with a thickness of 463 m. Meanwhile in the area of Chaling and Yongxing counties the thickness of the formation is less than one hundred meters.
GeoJSON
Fossils
It yields bivalve and plant fossils. Of the bivalve fossils there are found mainly the Pseudocardinia sp., Margaritifera isfarensis, Cuneopsis johannisboehmi; and of the plant fossils there occur the Equisetum sp., Cladophlebis sp., Pterophyllum sp. and Podozamites sp.
Age
Depositional setting
The formation belongs to shallow-lake deposits
Additional Information