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Kaijianqiao Formation
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Kaijianqiao Fm base reconstruction

Kaijianqiao Fm

Period: 
Neoproterozoic

Age Interval: 
Early Nanhuan (latest Tonian), Nh (44, 45)


Province: 
Sichuan

Type Locality and Naming

South-central Sichuan. The Kaijianqiao Fm was named by the Sichuan No. 1 Party of Regional Geological Survey in 1960 and was formally published by Zhang Shengshi in 1963. The typical section is situated in Kaijianqiao, in Ganluo County, Sichuan Province.

Synonym: （开建桥组）


Lithology and Thickness

The Kaijianqiao Fm is a suite of acidic volcaniclastic rock. Basal part is dominated by grayish green intercalated with grayish purple tuff, which is interbedded with tuffaceous sandy conglomerate. Lower part is dominated by purple red, gray purple and brick red sandy tuff intercalated with greenish gray rhyolite vitric tuff, grayish green sandy conglomerate, volcanic lithic sandstone and tuffite with cross-bedded and ripple mark. Upper part consists of purple gray, greenish gray pebbly sandy tuff, tuffaceous breccia, rhyolitic vitric tuff and tuffaceous feldspathic lithic sandstone intercalated with tuffaceous siltstone and tuffite. The total thickness is 500 to 3000 m.


Lithology Pattern: 
Volcanic ash


Relationships and Distribution

Lower contact

It rests disconformably on the dark gray to green compact massive basalt in the uppermost part of the Suxiong Fm (South-central Sichuan; column 45) or overlaps on the older rock mass (Dengxiangying Gr; Jiupanying Fm?). Or maybe a discontinuity onto Zhagu Fm (upper Yanbian Gr) in southernmost Sichuan (column 44)?

Upper contact

The uppermost part with a bed of red purple fine-to medium-grained feldspathic lithic tuffite is bounded by the overlying Lieguliu Fm.

Regional extent

South Sichuan. It is distributed in Xichang, Ganluo, Dechang and Hanyuan area in Sichuan Province.


GeoJSON

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Fossils

It yields Leiopsophosphaera minor, L. solicroplants, L. aperta, L. densa, Trachysphaeridium simplex, T. minor, T. planum, Trachyminuscula sp., Trematosphaeridium minutum, etc.


Age 

Early Nanhuan (latest Tonian-early Cryogenian) on schematic stratigraphic column, but radioisotopic date of ca. 720 Ma on the overlying Lieguliu Fm implies only latest Tonian (used here for graphic purposes).

Age Span: 

    Beginning stage: 
Tonian

    Fraction up in beginning stage: 
0.8

    Beginning date (Ma): 
776.00

    Ending stage: 
Tonian

    Fraction up in the ending stage: 
1.0

    Ending date (Ma):  
720.00

Depositional setting

The Kaijianqiao Formation was considered to be a terrestrial deposit in river fan facies.


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.