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Bulun Formation

Bulun Fm

Period: 
Triassic

Age Interval: 
Early Triassic (TJ71)


Province: 
Yunnan

Type Locality and Naming

The type section is located in Bulun Village, Zhongdian County (now called "Shangri-La" County), Yunnan Province, which was named by regional Geological Survey Team of Yunnan Geological and Mineral Resource Bureau in 1985.

Synonym: Xibulun Fm


Lithology and Thickness

This formation is mainly consisted of reddish mudstone and siltstone, which are interbedded with bioclastic limestone and oolitic dolomite in the Lower part and limestone and marlstone in the Upper part. Bottom and top of this formation was marked by reddish purple clastics. Total thickness is 1078 m.


Lithology Pattern: 
Shallow-marine marl


Relationships and Distribution

Lower contact

The Bulun Fm is in an unconformable contact with the underlying Lower Permian strata

Upper contact

Conformable upper contact to either the Niru Fm or Jiedi Fm (both are coeval, but in different parts of Zhongdian County).

Regional extent

Mainly distributed around Zhongdian of Yunnan Province, including Jidi, Dongju, Geza and Xiaguimuchang.


GeoJSON

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Fossils

Bivalve: Claraia and Eumorphotis; Ammonoid: Tirolites spinosus; Conodont: Pachycladina sp.


Age 


Age Span: 

    Beginning stage: 
Induan

    Fraction up in beginning stage: 
0.0

    Beginning date (Ma): 
251.90

    Ending stage: 
Olenekian

    Fraction up in the ending stage: 
1.0

    Ending date (Ma):  
246.70

Depositional setting

Shallow marine


Depositional pattern:  


Additional Information

Comparable strata of Bulun Formation were described as Cigang Formation in the 1:1000000 <Changdu> geological map.


Compiler:  

Zhang Shunxin, Guo Wenwei and Tong Jinnan.