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Sandaoqiao Formation
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Sandaoqiao Fm base reconstruction

Sandaoqiao Fm

Period: 
Permian

Age Interval: 
P (65), Guadalupian Epoch (Middle Permian)


Province: 
Sichuan

Type Locality and Naming

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


Lithology and Thickness

Limestone. Composed mainly of grey-black brecciated limestone, with its top being a layer of 1.7-m-thick black thin-bedded limestone. Thickness is 47 m.


Lithology Pattern: 
Limestone


Relationships and Distribution

Lower contact

Disconformable contact with the underlying Dongdahe Fm whose top part consists of a layer of thin- and medium-bedded limestone intercalated with shale

Upper contact

Disconformable contact with the basic volcanic rocks at the base of the overlying Dashibao Fm

Regional extent

The lithology of the formation is variable. It is distributed in the Kangding (303 m), Baoxing (50 m), Wenchuan (40 m). In the Songpan area (200 m) there are found dolomitic limestone and dolomite, yielding Fusulinida represented by Neoschwagerina craticulifera, Neomisellina, as well as corals.


GeoJSON

{"type":"Feature","geometry":{"type":"MultiPolygon","coordinates":[[[[103.48,31.43],[103.28,31.47],[103,31.21],[102.14,30.45],[101.69,29.93],[101.82,29.75],[102.28,30.08],[102.91,30.68],[103.26,31.07],[103.48,31.43]]]]}}

Fossils

Fusulinida fossils represented by Neoschwagerina simplex and Verbeekina crassispira.


Age 

Corresponding to the Maokou Fm, belonging to the Maokou’an Subepoch of the Middle Permian Epoch = Guadalupian Epoch (Middle Permian)

Age Span: 

    Beginning stage: 
Roadian

    Fraction up in beginning stage: 
0.0

    Beginning date (Ma): 
274.37

    Ending stage: 
Capitanian

    Fraction up in the ending stage: 
0.5

    Ending date (Ma):  
261.94

Depositional setting

It is interpreted as a shallow-sea carbonate-platform.


Depositional pattern:  


Additional Information


Compiler:  

Fei Shuying

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