Song Mua Fm

Period:

Devonian

Age Interval:

Lochkovian, D₁sm, (9, 11)

Province:
West Bac Bo

Type Locality and Naming

Along the upper course of the Song Mua River, near Nga Hai Village (Son La Province)

Synonym: Hệ lầng Sông Mua: Dovjikov A.E. et al. 1965 (D₁?-D₂c); Dương Xuân 1 lào et al. 1968 (D₁?-D₂c); Nguyễn Vĩnh et al. 1972 (D₁-D₂c); Dương Xuân l lào 1973 (D₁-Djc); Dương Xuân Háo el al. 1972 (Điệp, D₁); Tống Duy Thanh 1967 (assise, D₁); 1975 (Điệp - D₁); Tống Duy Thanh et al 1986, 1988 (Điệp - D₁); Vũ Khúc, Bùi Phú Mỹ 1990 (Diệp - D₁); Vù Khúc et al. 2000. Devon hạ (part.): Nguyễn Xuân Bao et al 1969, Dương Xuân Hào et al. 1975; Nguyền Vĩnh 1977. Điệp Suối Tra: Dương Xuân I lão 1975 (D₁), Phan Cự Tiến etai 1977 (D₁), Dương Xuân Mào et al. 1980(D₁)

Lithology and Thickness

Claystone with minor sandstone and quartzite. In the stratotype (2300 m total thickness), the formation is composed of two parts: Lower part includes mainly black monotonous clay shale with some interbeds of greenish-grey sandstone and quartzite. Upper part is marly shale and sandy limestone.

Lithology Pattern:

Claystone

Relationships and Distribution

Lower contact

The lower black clay shale of the Song Mua Fm rests conformably upon the limestone and clayey limestone of the Bo Hieng Fm of upper Silurian.

Upper contact

Conformable below the overlying Ban Nguon Fm

Regional extent

It is widespread in the lower basin of the Song Da River, West Bac Bo. Better exposures are in the Hoa Binh – Tu Ly section. . [Note: coeval Ta Khoa Fm is in parts of the lower (SE) Son La Province portion of the same area.]

GeoJSON

null

Fossils

such as Mesodouvillina aff. subinterstrialis, Iridistrophia aff. praeumbracula, Howellella sp., Schellwienella sp., Camarotoechia sp., Platyorthis sp. together with some bivalves Pteria sp„ Sphenotus? sp., Posidonia sp.. The second contains abundant fossils with a predominance of brachiopods, such as Howittia wangi, Howellella sp., Pugnacina sp., Strophochonetes sp., Pugnacina aff. baoi, Tulynets hoabinhensis; the bivalves Sphenotus? cf. spatulata, Mytilarca sp., Paracyclas ? sp., Pteria (Actinopteria) subdecusata, Pt. (A.) sp.,

[Figure: Sông Mua Fm: Brachiopod and Bivalve fossils (images courtesy of Prof. Ta Hoa Phuong, Vietnam Natl. Univ. Hanoi)]

Age

Early Devonian according to the fossils. [Assigned ages to conformable overlying and underlying formations constrain it as early Early Devonian.]

Age Span:

Beginning stage:

Lochkovian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

419.00

Ending stage:

Lochkovian

Fraction up in the ending stage:

0.5

Ending date (Ma):

415.70

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).