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Tan Lap Formation

Tan Lap Fm

Period: 
Devonian

Age Interval: 
Late Devonian, (4)


Province: 
East Bac Bo

Type Locality and Naming

Mo Nhai (Bac Son District) and Pho Hoang (Chi Lang District) of Lang Son Province; named by Nguyen Huu Hung et al (1991).


Lithology and Thickness

Mo Nhai stratotype is 35 m of: (1) Feldspar-rich conglomerate and gritstone; 5 m thick. Pebbles are mainly compossed of chert and calcareous chert. Basal arkosic conglomerate took its source from granite bodies, which are widespread in these areas. (2) Medium-grained quartz sandstone interbedded with black-grey clayey limestone; 60 m thick.


Lithology Pattern: 
Coarse-grained sandstone


Relationships and Distribution

Lower contact

Disconformable upon the Na Quan Fm of Emsian-Eifelian. Regionally, the next older unit is also the Na Tuong Fm of similar age.

Upper contact

Conformably overlain by the Tan Lap Fm.

Regional extent

Mo Nhai (Bac Son District) and Pho Hoang (Chi Lang District) of Lang Son Province


GeoJSON

null

Fossils

Flora fossils of Lepidodendropsis cf. hirnesi of Late Givetian-Early Frasnian age.


Age 

Late Givetian-Early Frasnian

Age Span: 

    Beginning stage: 
Givetian

    Fraction up in beginning stage: 
0.5

    Beginning date (Ma): 
382.10

    Ending stage: 
Frasnian

    Fraction up in the ending stage: 
0.5

    Ending date (Ma):  
375.00

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).