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Tongchang Formation
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Tongchang Fm base reconstruction

Tongchang Fm

Period: 
Neoproterozoic

Age Interval: 
middle-Early Qingbaikouan (early-middle Tonian), Qb (52, 53, 56)


Province: 
Guizhou

Type Locality and Naming

East Guizhou. The Tongchang Fm was named by the Party of Regional Geological Survey, Guizhou Bureau of Geology in 1974. The type section is at Tongchang, Jiangkou County, central Fanjing Mountain, Guizhou Province. Middle formation in the Fanjingshan Gr.

Synonym: （铜厂组） , Tongchangkou Fm


Lithology and Thickness

The Tongchang Fm is composed of rhythmic thin-bedded interbedding of meta-sandstone, siltstone, metamorphosed tuffaceous sandstone, sericite phyllite and slate. Lower part is dominated by grey, grey-green and dark-grey phyllite and slate, sandwiched with meta-siltstone, sandstone and minor volcanic lava. Upper part consists of greyish dark-grey and minor grey green metamorphosed fine-grained sandstone, tuffaceous sandstone, intercalated with phyllite, slate and minor metamorphosed diabase and spilite. The clastic rock in the middle- and upper-part bears microplants. The formation is 860-1204 m thick.

[Figure: The stratigraphic column of the Fanjingshan Gr (the group is about 1000 m thick). a. Pillow lava of the Huixiangping Fm.; b. The boundary between the underlying Fanjingshan Gr and the Furongba Fm (= lower Jialu Fm?) which is the basal formation of the Xiajiang Gr.]

[Figure: The Tongchang Fm in Heiwan River of Jiangkou, Guizhou Province (photos by Zhang Jianshu)]


Lithology Pattern: 
Fine-grained sandstone


Relationships and Distribution

Lower contact

It is in conformable contact onto the underlying Huixiangping Fm

Upper contact

It is conformably overlain by the Waxi Fm

Regional extent

East Guizhou. Southeast of Fanjing Mt Guizhou Province.


GeoJSON

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Fossils

Protosphaeridium, Protoleiosphaeridium, Polyporata.


Age 

LA ICP MS U-Pb date on zircon is 832±9 Ma (Wang Min et al., 2012). middle-Early Qingbaikouan (early-middle Tonian) – the seven formations of the Fanjingshan Gr spanning the early Qingbaikouan (early Tonian) are given semi-equal durations.

Age Span: 

    Beginning stage: 
Tonian

    Fraction up in beginning stage: 
0.21

    Beginning date (Ma): 
941.20

    Ending stage: 
Tonian

    Fraction up in the ending stage: 
0.27

    Ending date (Ma):  
924.40

Depositional setting


Depositional pattern:  


Additional Information


Compiler:  

Extracts from The Neoproterozoic Erathem (chapter in Stratigraphic Lexicon of China, draft of 2022) by Gao Linzhi, Ding Xiaozhong, Zhang Chuanheng, Zhang Heng.