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Bianmagou Formation
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Bianmagou Fm base reconstruction

Bianmagou Fm

Period: 
Neoproterozoic

Age Interval: 
Late Nanhuan (late Cryogenian), Nh （14）


Province: 
Gansu

Type Locality and Naming

Middle Qilian (north-central Gansu-Qinghai border region). The Bianmagou Fm was named by Qian Jiaqi et al. in 1986. The typical section is located in Bianmagou in Shulenanshan (mountains south of Shule River) in Middle Qilian Mountains, Gansu Province. Middle formation of the Duoruonuor Gr.

Synonym: （扁麻沟组）


Lithology and Thickness

Lower part of the Bianmagou Fm is composed of greenish gray sericite sandy slate interbedded with gray medium-to fine-grained and intermediate-acidic tuffaceous dolomitic lithic sandstone, which is intercalated with sandy conglomerate and pebbly gritstone. Upper part is composed of gray to gray-green phyllitic silty slate, phyllite sericite chlorite-slate, coarse-to fine-grained lithic sandstone, dolomitic quartzose sandstone intercalated with thin-bedded coarse-to medium-grained calcareous and tuffaceous lithic sandstone. Thickness of this formation is 784 m.


Lithology Pattern: 
Claystone


Relationships and Distribution

Lower contact

It conformably overlies the Shibandun Fm

Upper contact

It is conformably overlain by the Chaganburgas Fm

Regional extent

Middle Qilian (north-central Gansu-Qinghai border region). With a widespread distribution, the Bianmagou Formation is dominantly exposed in Shulenanshan and Bianmagou areas in Subei County.


GeoJSON

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Fossils

It yields microplants Asperatopsophosphaera sp., Margominuscula aff. tennela, Leiopsophosphaera pelucida etc.


Age 

Late Nanhuan (late Cryogenian) on schematic stratigraphic column

Age Span: 

    Beginning stage: 
Cryogenian

    Fraction up in beginning stage: 
0.3

    Beginning date (Ma): 
694.50

    Ending stage: 
Cryogenian

    Fraction up in the ending stage: 
1.0

    Ending date (Ma):  
635.00

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.