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Xu'an Formation
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Xu'an Fm base reconstruction

Xu'an Fm

Period: 
Neoproterozoic

Age Interval: 
late-Middle Qingbaikouan (middle Tonian)? Qb (62)


Province: 
Zhejiang

Type Locality and Naming

North-central Zhejiang. The Xu'an Fm was named by Kong Xiangsheng et al. in 1989, and published in 1995. The naming section is located in Xu'an, Dingjiawu Town, Chencai, Zhuji City, Zhejiang Province. Upper formation of the Chencai Gr.

Synonym: （徐岸组）


Lithology and Thickness

The Xu'an Fm is composed mainly of grey and dark grey to black leptite intercalated with hornblende-plagioclase gneiss, quartzite, locally migmatized. The formation is 240-1000 m thick.


Lithology Pattern: 
Volcanics


Relationships and Distribution

Lower contact

It is in conformable contact with underlying Xiawuzhai Fm.

Upper contact

The top is unconformably overlain by the Wuzao Fm [which seems to be late Triassic conglomerate.]. Regionally, the Chentangwu Fm would be the next older unit.

Regional extent

It is widespread in Zhuji, Longyou, Daishan counties, Zhejiang Province.


GeoJSON

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Fossils


Age 

late-Middle Qingbaikouan (middle Tonian)?

Age Span: 

    Beginning stage: 
Tonian

    Fraction up in beginning stage: 
0.5

    Beginning date (Ma): 
860.00

    Ending stage: 
Tonian

    Fraction up in the ending stage: 
0.6

    Ending date (Ma):  
832.00

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.