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Van Lang Formation
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Van Lang Fm base reconstruction

Van Lang Fm

Period: 
Triassic

Age Interval: 
Norian-Rhaetian, (T3n-r vl), (4)


Province: 
East Bac Bo

Type Locality and Naming

An Chau and Song Hien basins. Named after Van Lang Coal Mine (Thai Nguyen Province); described by Ta Hoang Tinh and Pham Dinh Long (1966).

Synonym:


Lithology and Thickness

Coal-bearing. Van Lang Coal Mine has 170-230 m of: (1) Basal conglomerate, 20-80 m. (2) Black-grey calcareous sandstone and siltstone, thin-bedded clayey limestone; and in the upper part, interbeds of coaly shale and coal seams (20 cm to 9 m, with thickest being 16 m!); 100 m; with bivalves and leaf imprints. (3) Light-grey, medium- to coarse-grained quartz sandstone, conglomerate and gritstone, grading upward into dark-grey siltstone and shale, 55 m.


Lithology Pattern: 
Coal


Relationships and Distribution

Lower contact

Unconformable on the Mau Son Fm of Carnian.

Upper contact

Unconformably underlies the Ha Coi Fm of Early-Middle Jurassic.

Regional extent

Change in facies and coal-bearing levels from the west eastward: The section n the west, such as in the Van Lang, Lang Cam, Phan Me, Ba Son and Quan Trieu (Thai Nguyen Province) and Khao Que and Luc Ra (Tuyen Quang Province) areas has the lower part of marine facies and the upper part containing fat coal of industrial significance. But in the west, such as in the Chu and Deo Chinh areas (Bac Giang Province), the section belongs mainly to the brackish to marshy facies and has not coal-bearing significance. Besides, this formation still occurs in the Song Hien Basin in small areas formed along faults.


GeoJSON

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Fossils

Bivalves include Unionites species.


Age 

Attributed to Norian-Rhaetian on the basis of fossils and correlation with other Triassic coal-bearing formations.

Age Span: 

    Beginning stage: 
Norian

    Fraction up in beginning stage: 
0.0

    Beginning date (Ma): 
227.30

    Ending stage: 
Rhaetian

    Fraction up in the ending stage: 
1.0

    Ending date (Ma):  
201.36

Depositional setting


Depositional pattern:  

Additional Information


Compiler:  

Tran Van Tri and Vu Khuc (Editors; Geology and Earth Resources of Viet Nam, General Dept. of Geology and Minerals of Viet Nam; completed in Dec., 2011), with additional details from Tong-Dzuy Thanh and Vu Khuc (Editors; Stratigraphic Units of Viet Nam, 2nd edition; 2011; English edited by A. Boucot).