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Dong Hoi Formation

Dong Hoi Fm

Period: 
Neogene

Age Interval: 
Late Miocene, N13, (18)


Province: 
North Trung Bo

Type Locality and Naming

Quang Binh and Quang Nam provinces. The type section is located borehole GK.273 drilled in the Bac Ly kaolin mine, near Dong Hoi Town (N = 17°30’; E = 106°35’). It was named by Komarova N.I., Pham Van Hai.

Synonym: Điệp Dồng Hồi : Komarova N.I., Phạm Vãn Hải 1980; Trịnh Dánh 1984, 1985, 1993; Trịnh Dánh (in Tống Duy Thanh, Lê Hùng et al.) 1987. Hệ tầng Dồng Hớt: Trịnh Dánh (in Phan Cự Tiến et al.) 1989; (ìn Vu Khúc, Bùi Phú Mỹ et al.) 1990, (in Vũ Khúc et al.) 2000; Nguyễn Quang Trung et al. 1996. Hệ tầng Ải Nghĩa: Nguyễn Văn Trang et al. 1985.


Lithology and Thickness

Kaolin-bearing continental beds. Characteristic section in the Bac Ly kolin mine: (1). Thick-bcdded conglomerate and gritstone with some interbeds of motley-colored sandstone, 30-160 m thick. (2). Kaolin-bearing silty claystone, 50-120 m thick. (3). Interbeddcd claystone and siltstone with interbeds of conglomerate, 50-100 m thick. The total thickness of the formation in this scction is 130-380 m.


Lithology Pattern: 
Claystone


Relationships and Distribution

Lower contact

Unconformably rests upon the Upper Silurian Dai Giang Fm in type area. Regionally, the next older unit is the Mu Gia Fm (late Jurassic-early Cretaceous red beds).

Upper contact

Not given. Regionally, the next younger unit is the Pliocene Sam Son Fm.

Regional extent

This formation includes Neogene sediments occurring in the Dong Hoi, Le Ninh, Ba Don (Quang Binh Province), Hue Plain and Ai Nghia (Quang Nam Province) areas.


GeoJSON

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Fossils

Containing a palynological assemblage with Polypodiaceae gen. indet., Cystopteris sp., Ginkgo sp., Pinus sp., Magnolia sp., Araliaceae gen. indet., Castanea sp., Rhus sp., Castanopsis sp., Myrtus cf. communis and the leaf impression Ficus tingeri., collected leaf impressions include Diospyros brachysepala, Phragmites oeningensis, Ficus aff. liliaeformis, Benzoin sp. and a relatively abundant and diversified palynological assemblage including 10% ferns and 85- 90% angiospcrms with the following characteristic forms: Selaginella selaginoides, Lygodium japoniciformis, Polypodium serratum, Cycas sp., Ginkgo sp., Podocarpus sp., Dacrydium sp., Magnolia sp., Hamamelis sp., Liquidambar sp., Moms sp., Castanea sp., Castanopsis sp., Myrica carolinensifonnis, Carya sp..

Containing a poor, monotonous palynological assemblage with Cycas sp., Taxodium sp., Quercus sp., Castanea sp., Carya sp., etc..


Age 

Late Miocene from the palynology.

Age Span: 

    Beginning stage: 
Tortonian

    Fraction up in beginning stage: 
0.0

    Beginning date (Ma): 
11.63

    Ending stage: 
Messinian

    Fraction up in the ending stage: 
1.0

    Ending date (Ma):  
5.34

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).