Wufeng Fm
Type Locality and Naming
The type section is at Yuyangguan 30 km east of Wufeng City, Hubei. The Wufeng Fm is derived from the Wufeng Shale proposed by Sun Yunzhu (Y.C. Sun) in 1931. The Wufeng Shale had previously been referred to as the Ashgill yielding graptolites at Yuyangguan in Wufeng. Mu Enzhi (1954) studied in detail the Wufeng Shale. In 1958, Zhang Mingshao and Sheng Xinfu first found a several centimeters-thick marl yielding abundant brachiopods at the top of the Wufeng Shale in the roadcuts along the Sichuan-Guizhou Highways, 2 km south of Guanyinqiao in Qijiang, Sichuan. In 1959, Lu Yanhao renamed the Wufeng Shale the Guanyinqiao Bed, which includes the above mentioned marl. In 1962, Zhang Wentang redefined Lu's Guanyinqiao Bed the Wufeng Shale Fm which is the present Wufeng Fm in broad sense. Sheng Xinfu (1964) renamed “Guanyinqiao Bed” the “Guanyinqiao Member”. Guizhou Bureau of Geology and Mineral Resources (1987) divided the Wufeng Fm in broad sense into “Wufeng Fm” (in narrow sense) in the lower part and “Guanyinqiao Fm” in the upper part. Mu et al. (1979) and Zeng Qingluan et al. (1983) renamed the Wufeng Shale Fm the Wufeng Fm. At the same time, Zeng et al. (1983) further divided the Wufeng Fm into Graptolite Shale Member in the lower part and the Guanyinqiao Member in the upper. Reference Section: The reference section is at Huanghuachang, 42 km northwest of Yichang City, Hubei, where the Wufeng Fm is 5.6 m thick.
Synonym: (五峰组)
Lithology and Thickness
The formation is divided into a lower Graptolite Shale Member and an upper Guanyinqiao Member. The Graptolite Shale Member is composed dominantly of yellowish green, light purple or brown micro- to thin-bedded organic, quart-sandy hydromica claystone intercalated with dark grey micro- to thin-bedded chert. The Guanyinqiao Member is dominated by hydromica claystone. The Wufeng Fm is 5.6 m thick in the reference section.
Relationships and Distribution
Lower contact
In most areas, the Wufeng Fm is in conformable contact with the underlying strata. The Wufeng Fm rests conformably on the nodular limestone yielding trilobite Nankinolithus of the Linxiang Fm (Ordov columns 44, 49). However, at Xihe in Nanzheng and Qiaoting in Nanjiang, it rests disconformably on the Jiancaogou Fm (not in Lexicon). In north-central Guizhou (Ordov column 43) it directly overlies the Baota Fm (Pagota Fm) with no intervening Linxiang Fm. At Nanjing (Ordov column 45), it overlies the Tangtou Fm. At Taojiang (Ordov column 50), it overlies the Nanshichong Fm.
Upper contact
It is conformably overlain by the black shale at the base of the Longmaxi Fm. Generally, a 0.01-0.02 m thick clay bed exists between the Wufeng and overlying Longmaxi Fm. In most areas above mentioned, the Wufeng Fm is in conformable contact with the overlying strata. However, at Sinianpan in Hexian of Anhui, Village Shiyu in Yangxin and Yangloudong in Puqi of Hubei, northwestern Hunan and Changyang-Enshi in western Hubei, the Wufeng Fm is disconformably overlain by the Longmaxi Fm. The boundary between the black Graptolite Shale Member and the Guanyinqiao Member shows diachronism (Rong, 1979).
Regional extent
It is very widespread in the Yangtze region of South China. With a persistent lithology, the Wufeng Fm is generally several meters, and is widely distributed in northeastern Yunnan (3-3.4 m thick), northern Guizhou and north part of northeastern Guizhou (4-8 m thick), northwestern Hunan (0.3-3.7 m thick), eastern Sichuan (1-16.2 m thick), western Hubei (5-5.7 m thick), eastern Hubei (2.8-6.8 m thick), southern Anhui (3.1-11.5 m thick), Tangshan in Jiangsu (5.2 m thick), southern Shaanxi (0.15-4.8 m thick) and northwestern Sichuan (8.5-15 m thick). In southern Shaanxi, the Wufeng Fm had previously been referred to as the Nanzheng Fm (Lu Yanhao, 1959; Zhu Zhaoling et al., 1986).
GeoJSON
Fossils
At eastern Gorge areas, the Wufeng Fm yields an abundant graptolite fauna, which includes Dicellograptus complexus assemblage, Tangyagraptus typicus assemblage, Diceratograptus mirus assemblage and Diplograptus bohemicus-C. ? extraordinarius assemblage, in ascending order; the Guanyinqiao Member yields abundant Hirnantia-Dalmanitina fauna; the Graptolite Shale Member yields conodonts of Amorphognathus ordovicicus assemblage (Zeng et al., 1983, 1987). Additionally, ostracods and chitinozoans have also been found from the Wufeng Fm. At Xinkailing, north of Wuning City, Jiangxi, exists a 1-m thick black carbonaceous or siliceous mudstone yielding shells and graptolites at the top of the Wufeng Fm, and is equivalent to the Normalograptus bohemicus-N. extraordinarius zone. This black mudstone was named the Xinkailing Bed by Yu Jianhua (1976).
Age
Depositional setting
Additional Information
Wang Xiaofeng and Chai Zhifang (1989) reported the iridium and carbon isotope anomalies in the Guanyinqiao Member, and suggested that the extinction of the some faunas at the end of Ordovician was probably caused by some extraterrestrial factors.