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Sijiagou Formation

Sijiagou Fm

Period: 
Ordovician

Age Interval: 
Katian, (21)


Province: 
Gansu

Type Locality and Naming

The type section is at Sijiagou in Xiehao, Wuwei, Gansu. The Sijiagou Fm was named by Mu Enzhi and Zhang Youkui in 1964.

Synonym: (斯家沟组）


Lithology and Thickness

The formation is dominated by argillaceous limestone, nodular limestone, limestone, shale, siltstone and line-grained sandstone. In the type area, the Sijiagou Fm is 397 m thick.


Lithology Pattern: 
Clayey limestone


Relationships and Distribution

Lower contact

It rests conformably on the sandstone and fine conglomerate at the top of the Tianzhu Fm

Upper contact

It is conformably overlain by the Xiehao Fm.

Regional extent

With a persistent lithology, the Sijiagou Fm is exposed at Qiqiaogou (225 m thick), Sijiagou (397 m thick), Zhigou (490 m thick) in Xiehao, Wuwei and Shichengzi in Dajing, Gulang (32 m thick), Gansu.


GeoJSON

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Fossils

The lower part yields trilobites Cyclopyge and Birmanites, and the upper yields graptolites of Orthograptus quadrimucronatus assemblage.


Age 

Katian. The Sijiagou Fm was named based on the correlation of graptolite Climacograptus geniculatus zone with the Dicranograptus clingani zone in Britain. In 1978, Zhao Fengyou renamed the Climacograptus geniculatus zone the Orthograptus quadrimucronatus zone, and correlated it with the D. clingani zone to the lower part of the Pleurograptus linearis zone.

Age Span: 

    Beginning stage: 
Katian

    Fraction up in beginning stage: 
0.2

    Beginning date (Ma): 
451.24

    Ending stage: 
Katian

    Fraction up in the ending stage: 
0.7

    Ending date (Ma):  
447.47

Depositional setting


Depositional pattern:  


Additional Information


Compiler:  

Jianpo Wang and Xiaofeng Wang