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Lancang Gr
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Lancang Gr base reconstruction

Lancang Gr

Period: 
Neoproterozoic

Age Interval: 
mid-Qingbaikouan through Sinian (mid-Tonian through Ediacaran), Pt3 (38?)


Province: 
Yunnan

Type Locality and Naming

Southwest Yunnan. The Lancang Gr was named by Yunnan Party of Regional Geological Survey in 1965 (Guidebook of 1: 1000000 Scale Geological Map of Pu'er Sheet). The typical section is situated around Lancang County and Menghai, Manlai, Xiding and north of Daluo, Yunnan Province.

Synonym: （澜沧群）


Lithology and Thickness

The Lancang Gr consists of the Nanmuling Fm, Mengjingshan Fm, Manlai Fm, Huimin Fm and Nankenghe Fm. The Group is dominated by intermediate- basic to intermediate-acidic pyroclastic rock, which suffered multiple progressive deformation and metamorphism, locally to high greenschist facies. The Lancang Group is dominantly composed of greenish gray and greenish yellow sericite schist, sericite quartz schist, dolomitic quartz schist, phyllite intercalated with carbonaceous chert, hornblende schist and quartz keratophyre. The total thickness is more than 1500 m.


Lithology Pattern: 
Volcanics


Relationships and Distribution

Lower contact

Unconformable onto the underlying Damenglong Gr (Mesoproterozoic underlying all of West Yunnan)

Upper contact

The Huimin Fm is obducted onto the Lancang Group.

Regional extent

Southwest Yunnan. The Lancang Gr is mainly exposed in Xiqianjie, Shuangjiang and Shangyun of Fengqing County and in Manlai, Xiding of Menghai County in Yunnan Province.


GeoJSON

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Fossils

Microplants: Lophominuscula sp., Margominuscula uerrucosa, Leiominuscula minuta, Leiopsophosphaera minor, Baulinella faueolata, Microconcentrica aff. induplicate.


Age 

Entire mid-Qingbaikouan through Sinian (mid-Tonian through Ediacaran) span given on schematic stratigraphic column – dotted. The age of the Lancang Group has given rise to much controversy. The assigned age was based on a Sm-Nd isochron date of 1438.0±17.7 Ma from the unconformably underlying Damenglong Gr. However, the Lancang Group has also been inferred to belong to Ordovician (462-454 Ma), according to detrital zircon, which yields two major age peaks at 530 Ma and 930 Ma (Wang Fang et al., 2017)..

Age Span: 

    Beginning stage: 
Tonian

    Fraction up in beginning stage: 
0.4

    Beginning date (Ma): 
888.00

    Ending stage: 
Ediacaran

    Fraction up in the ending stage: 
1.0

    Ending date (Ma):  
538.80

Depositional setting


Depositional pattern:  


Additional Information

As the Huimin Fm is obducted onto the Lancang Group and was attributed to the Lancang Group, a tectonic block, it was removed from the Lancang Group


Compiler:  

Extracts from The Neoproterozoic Erathem (chapter in Stratigraphic Lexicon of China, draft of 2022) by Gao Linzhi, Ding Xiaozhong, Zhang Chuanheng, Zhang Heng.