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Dashibao Formation
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Dashibao Fm base reconstruction

Dashibao Fm

Period: 
Permian

Age Interval: 
P3 (65), Lopingian Epoch (Late Permian)


Province: 
Sichuan

Type Locality and Naming

The type section is located in the area extending from the Toudao Village to the Dashipao area of Dongda River 50 km to the north of the Baoxing County Town, Sichuan Province.It was named by the West Sichuan Research Party under the Chinese Academy of Geological Sciences in 1965.


Lithology and Thickness

Volcanics and volcaniclastics. It is divisible into three parts: The Lower part is composed of dark-green and grey-purple pyroxene-basalt and porphyritic basalt, intercalated with tuffs and tuffaceous breccia. Within the basalt there are developed porphyritic structures, while the pillow structures are rare, containing crystals of pyrite, with a thickness of 47 m. The Middle part is composed of grey-black and grey-purple pillow basalt and dense massive basalt, intercalated with grey-green tuffaceous breccia, and tuffs, with a well-developed pillow structure being found within the basalt, with a thickness of 89 m. The Upper part is composed of interbeds of grey-green and dark-green tuffaceous sandstone, tuff and siltstone together with grey-white sericite phyllite, clayey limestone and slate, with a thickness of 4 m. The total thickness is 140 m.


Lithology Pattern: 
Volcanics


Relationships and Distribution

Lower contact

Disconformable contact with the underlying Sandaoqiao Fm

Upper contact

Disconformable contact with the overlying Bocigou Fm (early Triassic)

Regional extent

Distributed in the Xiaojin, Daofu to Jiulong and Mianning areas, Sichuan Province, with an unstable thickness, with its middle and lower parts thinning northeasterly with the Kangding area serving as a center. Until Wenchuan County their thicknesses reach as great as 150 m, but in the Tonghua County it is getting as thin as 5 m. The upper part of the formation is found to occur only in the Danba, Xiaojin, Baoxing and Wenchuan Counties of Sichuan Province, and with a thickness of 5-45 m.


GeoJSON

{"type":"Feature","geometry":{"type":"MultiPolygon","coordinates":[[[[102.1,30.51],[101.74,30.66],[101.3,30.99],[100.79,31.39],[100.3,31.78],[100.08,31.54],[100.24,30.57],[100.65,29.03],[100.82,28.33],[100.66,27.9],[100.42,27.55],[101.79,27.47],[102.18,28.43],[102.26,29.76],[102.58,30.39],[103.11,30.91],[103.45,31.26],[103.41,31.51],[102.47,30.74],[101.89,30.53],[102.1,30.51]]]]}}

Fossils

No fossils have been found in the particular section.


Age 

By inferring its overlying and underlying stratigraphic sequences, the middle part of the formation should be corresponding to the Basalt Fm in the Emei Mt., and the upper part of the formation should be corresponding to the Xuanwei Fm, belonging to late Permian Epoch in age.

Age Span: 

    Beginning stage: 
Wuchiapingian

    Fraction up in beginning stage: 
0.0

    Beginning date (Ma): 
259.55

    Ending stage: 
Wuchiapingian

    Fraction up in the ending stage: 
1.0

    Ending date (Ma):  
254.24

Depositional setting

It is interpreted as sea-bottom effusive volcanic-rock and deep-water flysch deposits.


Depositional pattern:  


Additional Information


Compiler:  

Fei Shuying, Zhu Zili

GeoJSON estimate by Can Cai and Xinyi Zhang (Chengdu Univ. Tech. students)