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Jiangkou Formation
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Jiangkou Fm base reconstruction

Jiangkou Fm

Period: 
Neoproterozoic

Age Interval: 
Early to middle Nanhuan (late Tonian-middle Cryogenian), Nh (54, 59)


Province: 
Hunan, Henan

Type Locality and Naming

Southwest-central Hunan. The Jiangkou Fm was named by the Hunan Party of Regional Geological Survey in 1965 (published on the Guidebook of 1: 200 000 Scale Geological Map of Wandongkou Sheet). The typical section is situated south of Jiangkou village in Dongkou County, Hunan Province.

Synonym: （江口组）


Lithology and Thickness

In ascending order, the Jiangkou Fm is subdivided into four members. The lower part of the First member is composed of dark green pebbly sandstone and sandy slate, and the upper part, sandy slate. The lower part of the Second member consists of pebbly slate and upper part, feldspathic quartzose sandstone, calcareous quartzose sandstone. Third member composed of chlorite-slate, sandy slate and lenses of limestone and iron ore. Fourth member is feldspathic quartzone sandstone, slate and manganiferous limestone. It is over 2000 m. [Other papers imply it is a glacial deposit.]


Lithology Pattern: 
Glacial till


Relationships and Distribution

Lower contact

Its base is incomplete in the typical area; but in Yuexi of Dongkou and Shibao of Qianyang, the Jiangkou Fm rests disconformably on the underlying Banxi Gr.

Upper contact

The Jiangkou Fm is overlain conformably or disconformably by the Nantuo Fm tillite. However, schematic stratigraphic column of this region places the widespread Datangpo Fm (middle Cryogenian interglacial) above this Jiangkou Fm.

Regional extent

Southwest-central Hunan to northwest Hunan.


GeoJSON

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Fossils


Age 

A SHRIMP U-Pb data of 743.8 ±4.1 Ma (Gao Linzhi et al., 2015). The first and second members correspond to the Chang'an Fm (early Nanhuan = early Cryogenian glacial), and the third and fourth members to Fulu Fm (early to middle Cryogenian) of SE Guizhou and North Guangxi (columns 56, 57). According to Gaoyuan Song et al. (2017. New U-Pb age constraints on the upper Banxi Group and synchrony of the Sturtian glaciation in South China. Geoscience Frontiers, 8: 1161-1173; https://doi.org/10.1016/j.gsf.2016.11.012), the deposition of the underlying Wuqiangxi Fm ended at ca. 715 Ma (LA-ICPMS, 714.6 ±5.2 Ma from the top of the Wuqiangxi); just before the Jiangkou Fm (Sturtian) glaciation. [However, schematic stratigraphic column of this region places the widespread Datangpo Fm (middle Cryogenian interglacial) above this Jiangkou Fm, implying upper members do not really correspond to the lower part of the Fulu Fm? – used here for graphic column.]

Age Span: 

    Beginning stage: 
Cryogenian

    Fraction up in beginning stage: 
0.0

    Beginning date (Ma): 
720.00

    Ending stage: 
Cryogenian

    Fraction up in the ending stage: 
0.7

    Ending date (Ma):  
660.50

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.