Tongzi Fm
Type Locality and Naming
The type section is at Honghuayuan 7 km south of Tongzi City, Guizhou. The Tongzi Fm is derived from the Tongzi Bed proposed in 1940 and published in 1958 by Zhang (Chang) Mingshao and Sheng Xinfu. In 1962, Zhang Wentang renamed the Tongzi Bed the Tongzi Fm, and lowered its base 8.5 m to the base of the dolomitic limestone at the top of the previously defined Loushanguan Gr on the trilobite and brachiopod found from the Tongzi Fm, a suggestion accepted widely for long time till present.
Synonym: (桐梓组)
Lithology and Thickness
The Tongzi Fm is divided into three parts. The lower and upper parts are dominated by grayish green clay and silty shale intercalated with thin-bedded limestone and bioclastic limestone, and the middle part is composed dominantly of light gray, dark gray medium-bedded intercalated with thin-bedded micritic to fine-crystalline dolomite, bioclastic limestone and shale intercalations, with local dolorudite, oolitic and pisolitic dolorudite and common chert nodules.
Relationships and Distribution
Lower contact
The Tongzi Fm rests conformably on the medium-bedded dolomitic limestone at the top of the Loushanguan Gr (Maotian Fm ). In most below mentioned areas, the Tongzi Fm is in conformable contact with the underlying strata. But at Dalianghui and Rentao to Wusheng, it rests disconformably on the Middle Cambrian.
Upper contact
It is conformably overlain by the thick-bedded limestone at the base of the Honghuayuan Fm, with a variable lower and upper boundary in different areas. In most below mentioned areas, the Tongzi Fm is in conformable contact with the overlying strata. But at Dalianghui and Rentao to Wusheng, it is disconformably overlain by the Upper Permian Liangshan Fm.
Regional extent
The Tongzi Fm is generally 100 m thick, with a persistent lithology, and is seen at Dalianghui (12 m thick) in Wangcang, northern Sichuan, northern Guizhou and southern Sichuan (105 m thick), southern Guizhou (70-110 m thick) and eastern Sichuan (87-115 m thick). From drilling data, at Rentao to Wusheng in the central Sichuan basin also exists about 12 m thick Tongzi Fm. The Banhe Series (Wang, 1945a) or Yangjiaba Fm (Zhang et al., 1982) in eastern Sichuan have a similar lithology and fauna with the Tongzi Fm.
GeoJSON
Fossils
In northern Guizhou, the Tongzi Fm yields trilobites of Dactylocephalus-Asaphellus assemblage, Tungtzuella range-assemblage and conodonts of Acanthodus costatus assemblage, Scolopodus quadraplicatus assemblage, Scolopodus barbatus range-assemblage, and is equivalent to Rhabdinopora flabelliformis zone to Clonograptus-Kiaerograptus zone.
Age
Depositional setting
Additional Information