Tongziyan Fm
(90-93), mid-Middle Permian
Type Locality and Naming
The type section is located at Tongziyan 5 km to the west of the Liancheng County Town of Fujian Province, while its reference section is situated at Maotaokeng 7 km to the southeast of Longyan City, Fujian Province. It was named by Wang Shaowen in 1930.
Synonym: Tongtseyan Fm
Lithology and Thickness
Clastics and Coal. It is divisible into three members, namely the Lower and Upper Coal-bearing Members, and the Middle Marine siltstone Member. Lower Coal-bearing Member is composed of siltstone, intercalated with fine-grained sandstone, carbonaceous siltstone and coal seams yielding ammonoid, brachiopod, Fusulinids and plant fossils (phytolites), with a thickness of 188 m. The basal part of the formation is composed of thick-bedded medium- and fine-grained sandstones. Middle Marine Siltstone Member is composed mainly of siltstone, intercalated with limestone and fine-grained sandstone, containing pyrite and calcareous concretions, yielding Fusulinids, ammonoid and brachiopod fossils in a fairly great amount, with a thickness of 114 m. Upper Coal-bearing Member is composed of sandstone and siltstone, intercalated with coal seams, with the brachiopod and bivalve fossils decreasing in amount and with the plant fossils (phytolites) increasing in amount in ascending order, with a thickness of 243 m. Total thickness of 200-600 m in southern Jufian and Guangdong provinces.
In the southern part of Fujian Province the formation is divisible into three coal-bearing belts. Among them the eastern belt had been coalified earlier than the western belt, with the coal layers in them showing a tendency of being uplifted. The central belt is characterized by its best coal-bearing capacity and the greatest thickness of the coal layers. The grains of clastics are getting finer in a direction from east to west, with the marine-facies strata are increasing in amount.
Relationships and Distribution
Lower contact
Conformable contact with the thin-bedded siltstone of the underlying Wenbishan Fm. Or in Zhejiang with chert of Gufeng Fm
Upper contact
Disconformable contact with pebbled sandstone of the overlying Cuipingshan Fm or the Shahu Fm. Or in Zhejiang with coal-rich Longtan Fm
Regional extent
Distributed in the southwestern part of Fujian Province, as well as in Guangdong Province, with a thickness of 200-600 m, and with the greatest thickness being found in an alignment from the Jiafu area of Yongan City (620 m) and through the Maotaokeng area (555 m) to the Yongding area (880 m) of Longyan City. But it is thinning to both flanks of the alignment. The thickness of the formation is of 380 m in the Tianhu Mt. of the Yongchun area on its eastern flank, of 226 m in the Meixian County, and of 154 m in the Taishan County on its western flank. In the western part of Zhejiang Province the Lixian Coal Series has been assigned for the time being to the Tongziyan Fm, with the Lixian Coal Series being subdivided into a lower Shimentang Member consisting main of siltstone and an upper Lengwu Member consisting of bioherm limestone, with a total thickness of about 200 m.
GeoJSON
Fossils
The Fusulinid fossils occurring in the Lower member of the Tongziyan Fm should be incorporated into the Eopolydiexodina-Metadoliolina zone; the Ammonoid fossils occurring in the Middle member are known as the Shouchangoceras-Altudoceras assemblage. The Upper and Lower members yield Brachiopods of the the Neoplicatifera huangi-Uncilirata assemblage and the Pygmochonetes jingxianensis-Tenuichonetes tenuilirata assemblage. The Upper member yields also Plant fossils (phytolites) represented by the Gigantonoclea fukienensis-Asterophyllites assemblage.
Age
Depositional setting
It is interpreted as delta-facies coal-bearing deposits.
Additional Information