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A Vuong Formation

A Vuong Fm

Period: 
Cambrian, Ordovician

Age Interval: 
Middle Cambrian to early Ordovician, Cm2-O1 av, (20)


Province: 
North Trung Bo

Type Locality and Naming


Lithology and Thickness


Lithology Pattern: 
Clayey sandstone


Relationships and Distribution

Lower contact

The A Vuong Fm rests unconformably upon the Kham Duc-Nui Vu Complex Gr, that has been observed in the Khe Huong section, situated 5 km northwest of the Hiep Due District center (Koliada A.A. et al. 1991, Nguyen Van Hoanh et al. 1994).

Upper contact

It underlies unconformably the Long Dai Fm (O1-S3 Id) that has been observed in the Con Tom Stream, A Luoi area, Thua Thien Hue Province (Vu Manh Dien et al. 1993).

Regional extent

Distributed in the Thua Thien Hue and Quang Nam provinces. The A Vuong Fm occurs in 3 main bands: 1) Huong Hoa - A Luoi - Ban Nau band, with a NW-SE direction, 130 km in length and 3-10 km in width; 2) Da Nang - Song Vang River - A Vuong band sub-latitudinally directed, about 80 km in length and 4-10 km in width, and 3) Tam Ky - Hiep Due - Song Tranh River band latitudinally directed, about 100 km in length and 2-10 km in width.


GeoJSON

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Fossils

The A Vuong Fm is very poor in fossils; only acritarchs have been collected in two localities as follows: 1) in black clayey shale situated in the northeast and east of the Ba Na Summit with Archaeohystrichosphaeridium sp., Protosphaeridium sp., Tasmanites sp., Ballesphaeridium brevispinosum. 2) in cherty shale at Tra Bong - Protosphaeridium gibberosum, P. torulosum, P. densum, Favosphaeridium sp., Kildinella hyperboreica, Trematosphaeridium sp., Acanthodiacrodium sp., Laminarites sp..


Age 

These fossils are widespread in Cambrian and Ordovician sediments in many places in the world (Vu Khuc, Bui Phu My et al. 1990).

Age Span: 

    Beginning stage: 
Cambrian Stage 3

    Fraction up in beginning stage: 
0.0

    Beginning date (Ma): 
521.00

    Ending stage: 
Darriwilian

    Fraction up in the ending stage: 
1.0

    Ending date (Ma):  
458.18

Depositional setting

Based on stratigraphic relations of the A Vuong Fm with underlying and overlying formations and the above-cited fossils, the A Vuong Fm has been refereed to Cambrian - Lower Ordovician.


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).