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Yushas Formation
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Yushas Fm base reconstruction

Yushas Fm

Period: 
Neoproterozoic

Age Interval: 
Early Qingbaikouan (Early Tonian), Qb (10)


Province: 
Xinjiang

Type Locality and Naming

Tieklik region (SW Tarim Basin). The Yushas Fm was named by Ma Shipeng, Wang Yuzhen et al. (1989). The type section is located in Yushas Valley near Sukuluok village, Halastan River, Yecheng County, Xinjiang Weiwuerzhu Zizhiqu (Xinjiang Uygur Autonomous Region). Lower formation of the Sukuluok Gr.

Synonym: （玉沙斯组）


Lithology and Thickness

The Yushas Fm consists of gray-green, purple fine-grained clastic rock, which is subdivided into three members. There is an unstable basal conglomerate in the bottom. Lower member of interbedded purple and gray-green mudstone-limestone, consists mainly of purple silty calcareous mudstone and purple brown ferruginous shale, with stromatolitic limestone, siltstone and green sandstone. Middle member of gray sandstone and black mudstone consists of dark gray platy fine-grained sandstone and medium- to coarse-grained feldspathic quartz sandstone and uneven interbedding with gray black thick-bedded argillaceous chert, mudstone, with large- and medium-scale oblique bedded sandstone. Upper member is purple fine-grained clastic rock, consisting of light gray interbedded with purple banded mudstone. There is an unstable layer of kaolinton (kaolin clay) at the top, and light-gray, gray sandstone, siltstone interbedded with gray limestone and thin-bedded siliceous mudstone with horizontal and oblique bedding. It is over 100 m in thickness.


Lithology Pattern: 
Pelagic marl


Relationships and Distribution

Lower contact

The basal conglomerate is disconformable onto the underlying Sumalan Fm of the Jixian System.

Upper contact

The top is disconformably overlain by the Aqikbaxi Fm; and in some locations, the formation is overlapped (mostly unconformably) by other younger strata (Sinian, Devonian and Carboniferous).

Regional extent

Tieklik region (SW Tarim Basin). The Yushas Formation is developed north of the Halastan River and west of Xinjiang-Tibet highway.


GeoJSON

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Fossils

The Yushas Formation is developed north of the Halastan River and west of Xinjiang-Tibet highway.


Age 

Early Qingbaikouan (Early Tonian)

Age Span: 

    Beginning stage: 
Tonian

    Fraction up in beginning stage: 
0.0

    Beginning date (Ma): 
1,000.00

    Ending stage: 
Tonian

    Fraction up in the ending stage: 
0.4

    Ending date (Ma):  
888.00

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.