Bang Ca Fm

Period:

Devonian

Age Interval:

Givetian-Frasnian; D₂gv –D₃frbe, (2, 3, 8, 9, 10)

Province:
West Bac Bo, East Bac Bo

Type Locality and Naming

Lower formation of the Trang Khang Gr. In both East and West Bac Bo. Holostratotype: Bang Ca - Lung Khoang Section, the part corresponding to the “Upper Bang Ca Subsuite”; Ha Lang area, Trung Khanh District, Cao Bang Province (N= 22° 46’, E= 106° 47‘).

Synonym: Ma La Fm (West Bac Bo; or merged as a or a component of the Ban Cao Fm (= Toc Tat Fm) or Da Nieng Fm), Diệp Bằng Ca: Phạm Đình Long 1973, 1974, 1975 (part., Middle Devonian, Givetian); Dương Xuân Hảo et al. 1980 (Late Devonian, Frasnian); Tổng Duy Thanh 1980 (Middle Devonian, Givetian). Lydienne; Bourret R. 1922 (Late Devonian/ Schìsíes en plaquettes: Bourret R. 1922 (Late Devonian). Các bậc Eifel - Givet (part.): Dovjikov A.E. el al. 1965. Bậc Giveti (part.).' Dương Xuân Hảo etaỉ. Ì9Ó8, 1973; Trần Văn Trị elal. 1977. Điệp Tốc Tải (part.): Dương Xuân Hào et al. 1973 (Late Devonian, Frasnian); Tống Duy Thanh 1980 (Late Devonian, Frasnian); Tổng Duy Thanh etai. 198Ố, 1988 (Late Devonian); Vũ Khúc, Bùi Phú Mỹ 1989 (Late Devonian); Trần Đức Lương, Nguyễn Xuân Bao 1994 (Late Devonian). Điệp Bàn Cài (part.): Nguyễn Xuân Bao et al. 1969 (D₂gv); Nguyễn Xuân Bao 1970 (D₃); Nguyễn VTnh et al. 1972 (D₂gv); Dương Xuân Hảo el at. 1975 (D₂gv?-D₃fr); Phan Cự Tiến, Nguyễn Vĩnh 1977 (part, D₂gv-D₃), Tống Duy Thanh 1979 (part., D₃); Duơng Xuân Hào ẽ/ ai. 1980 (Dr c t); Đoàn Nhật Trưởng 1980, Ì984 (Djfr- Cjt). Dá vôi Lũng Kki Cháo (part.): Dưưng Xuân Hào etaỉ. 1975 (Middle Devonian, Givetian). Tầng silic Bằng Ca: Phạm Huy Thông, Nguyễn Thế Dân 1984 (Late Devonian, Frasman). Hệ tầng Bằng Ca: Đoàn Nhật Trưởng, Tạ Hoà Phương 1999 (Late Devonian); Lê Vãn Giang, Tạ Hoà Phương 1999 (Middle - Late Devonian); Vũ Khúc (chù biên), 2000 (Late Devonian). Hệ tầng Ma La: Đoàn Nhật Trường, Tạ Hoà Phuơng 2003

Lithology and Thickness

East Bac Bo (Ha Lang), it is composed mainly of cherty shale and shale with limestone lenses; 200-220 m).

West Bac Bo, it is composed of dark-grey marl interbedded with cherty shale and limestone lenses.

[Figure: Bằng Ca Fm: Outcrop photo (images courtesy of Prof. Ta Hoa Phuong, Vietnam Natl. Univ. Hanoi)]

Lithology Pattern:

Shallow-marine marl

Relationships and Distribution

Lower contact

Conformably upon the Ban Pap Gr (West Bac Bo) or the Na Quan Fm (East Bac Bo)

Upper contact

Conformably beneath the Toc Tat Fm

Regional extent

The Bang Ca Fm occurs mainly in the Ha Lang area, situated in the West of Cao Bang Town, and in the Dong Van and Yen Minh areas of Ha Giang Province. (East Bac Bo). It is also in the lower course of the Da River in the Van Yen area, Son La Province (West Bac Bo).

GeoJSON

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Fossils

The Givetian age is based on the brachiopod Stringocephalus burtini discovered by Pham Dinh Long in the Ha Lang area (East Bac Bo), and by conodonts Polygnathus xylus xylus, Pol. varcus, Pol. linguiformis collected in the Ban Cai area (West Bac Bo) (Doan Nhat Truong, Ta Hoa Phuong 2003). The Frasnian age of the formation is based on foraminifera Eonodosaria evlanensis, Eogeinitziana aff. rara, Nanicella aff. uralica, and Tikhinella multiformis’, and conodonts of the Palmatolepis hassi and Pa. rhenana Zones.

[Figure: Bằng Ca Fm: Conodont species (images courtesy of Prof. Ta Hoa Phuong, Vietnam Natl. Univ. Hanoi)]

[Figure: Bằng Ca Fm: Tentaculites Homoctenus sp. (images courtesy of Prof. Ta Hoa Phuong, Vietnam Natl. Univ. Hanoi)]

[Figure: Bằng Ca Fm: Brachiopods Stringocephalus burtini (images courtesy of Prof. Ta Hoa Phuong, Vietnam Natl. Univ. Hanoi)]

Age

Givetian-Frasnian [Unconformable on Na Quan Fm in East Bac Bo that is also dated as Givetian; therefore base placed here as uppermost Givetian for graphics.]

Age Span:

Beginning stage:

Givetian

Fraction up in beginning stage:

0.8

Beginning date (Ma):

380.18

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