Hon Gai Fm

Period:

Triassic

Age Interval:

Norian-Rhaetian, (T3n-r hg) (5)

Province:
East Bac Bo

Type Locality and Naming

Hon Gai Coal Basin in Quang Ninh basin is famous as the main source of coal for the Vietnamese industry. Named by Pavlov A. (1960).

Synonym:

Lithology and Thickness

Coal-rich. Composite section based on position of main industrial coal seams is ca. 2100-3400 m thick. Interbedded coarse-grained sandstone, conglomerate, grey siltstone, coal seams (industrial-quality in the lower and middle parts) and coaly shale. Coal beds in Vang Danh Mine are up to 60 m thick (Day [= "Thick"] Seam, of which 30-40 m is pure coal).

Lithology Pattern:

Coal

Relationships and Distribution

Lower contact

Unconformable upon Paleozoic sediments (such as Bai Chay Fm). Regionally, the next older unit is the Kong Lang Fm volcanic-sediment suite.

[Figure: Hòn Gai Fm resting unconformably on the Bai Chay Fm (images courtesy of Prof. Ta Hoa Phuong, Vietnam Natl. Univ. Hanoi)]

Upper contact

Unconformably underlies the Jurassic age Ha Coi Fm.

Regional extent

Quang Ninh Basin

GeoJSON

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Fossils

Han Gai Flora consists of 195 species, of which 62 are endemic and 50 are not yet fully studied.

[Figure: Hòn Gai Fm: Plant fossils (images courtesy of Prof. Ta Hoa Phuong, Vietnam Natl. Univ. Hanoi)]

Age

Dated as Norian-Rhaetian on the basis of the flora.

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, 2^nd edition; 2011; English edited by A. Boucot).