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Bolila Formation

Bolila Fm


Period: 
Triassic

Age Interval: 
Middle Late Triassic (TJ33, TJ34. TJ35)


Province: 
Xizang (Tibet)

Type Locality and Naming

The type section is located at the Bolila Mountain, around the boundary between Chaya County and Gongjue County, Tibet Autonomous Region, which was named by the third survey team of Sichuan Geological Survey in 1974. This formation was once named as “Wangxia limestone” by geological team of Xizhang in 1974, but was renamed by the third team of Bureau of Geology of Sichuan, due to discovery of more well-exposed and complete sequence in Bolila.

Synonym: Fubolila Fm


Lithology and Thickness

The Bolila formation is predominated by carbonates. At the type locality, the Lower part of this formation consists of light grey or dark grey medium-bedded argillaceous limestone, with thickness of 26.7 m. Middle part is comprised of dark grey thick limestone with several bioclastic limestone interlayers, thickness of this member is 177.5 m. Upper part is represented by greyish medium-thick limestone. Tops of all these three parts is marked by limestone.


Lithology Pattern: 
Limestone


Relationships and Distribution

Lower contact

The Bolila Fm is conformable in contact to with both the Lower Triassic Jiapila Fm or Dongka Fm below.

Upper contact

Conformable in contact to Upper Triassic Bagong formation above.

Regional extent

This formation is mainly distributed around the Chaya, Gongjue, Jiangda and Changdu in Tibet Autonomous Region and Deqin in Yunnan Province.


GeoJSON

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Fossils

The Bolila formation contains diverse fossils. Lower part: Brachiopods: Rhaetinopsis ovata, Septalipharia sp., Aulacothyris sp. Middle part: Ammonoids: Ectolcites sp., E. pabdoensis; Brachiopod: Sanqiaothyris aff. elliptica, Rhaetina ovata, Robinsonella sp., Adygella sp., Amphiclina sp., Septaliphoria sp. Upper part: Brachiopod: Rhaetinopsis ovata


Age 

Tong et al. (2019, Triassic integrated stratigraphy and timescale in China, Science China: Earth Sciences, v. 62, no. 1) assign it as spanning lower Norian.

Age Span: 

    Beginning stage: 
Norian

    Fraction up in beginning stage: 
0.0

    Beginning date (Ma): 
227.30

    Ending stage: 
Norian

    Fraction up in the ending stage: 
0.5

    Ending date (Ma):  
216.52

Depositional setting

Marine facies


Depositional pattern:  


Additional Information


Compiler:  

Zhang Shunxin, Guo Wenwei and Tong Jinnan.