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Song Ma Formation
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Song Ma Fm base reconstruction

Song Ma Fm

Period: 
Cambrian

Age Interval: 
Middle Cambrian, Cm2 sm (9, 11)


Province: 
West Bac Bo

Type Locality and Naming

Holostratotype: the Hoi Xuan - Lang Bai Section, lying along Road No.217, Quan Hoa District, Thanli Hoa Province (N= 20°22', E= 105°06'). Tran Huu Dan (in Pham Kim Ngan et al.) 1998, 2000

Synonym: -H4 tang Song Ma: Ph^m Kim Ng^n in Tran Van Trj et aL 1973, 1975, 1977 (£2)» ^ Ducfng XuSn Hao el al 1980 (£2)； Ph?un Kim Ng^a et ai 1986, L991, 1994, 1995, .1996, 2000 (£2)； Luong H6ng Hu(?c in Le Himg, T6ng Duy Thanh et al 1987 (£2)； Nguyln Dinh K<^p et al 1993 (£J; Nguyln VSn Hoanh et al 1994 (£2)； Luofng H6ng Hir^c

et aL 1996 (£2); Tr^n Hiiu Dk\ in Ph^m Kim Ngan et al 1998 (£ 2)； Ph^m Dinh Tru6ng et at. 1999 {£2)； Nguyin Van Tru^t et al L999 (£2)； T<Sng Duy Thanh in Vu Khuc et al 2000; Dinh C6ng Hung et al 2001 (£2)- -D'4p Song Md: Vu Khuc, Bui Phu My et al. 1990 (£}; Phan C\r Tien et al. 1989 (£); Ph^im Xuan Anh et al, 1989 (£2); D§ Van Chi et al. 1992 (e2). -tdng BdThu&c (partly.]>lgayh\TriVziet al. 1963 {£3). -ff^ tang Bin Khe (part.): Nguyin Tri VM et al 1963 (£3). -H4 tang Dong San (part.); Jamoida A.I. in Dovjikov A.E. et al. 1965 (£r〇). -H4 tdngBen Khi (part.): Dovjikov A. E. et ai) 1965 (£3-0). -Middle Cambrian: Ph^m Kim Ngan 1972, 1975, 1976; Phan Cyr Ti^n et al. 1997, 1978; Bui Phu My 1978; Tr4n Dang Tuylt e, “/• 1978; Trin Nghla d 1980; D^ng TrAn Qudn 以 “/_ 1980; Luong H6ng Hugrc 1980.

-H$ tdng Diin Lu (pari.): Ph$m Van Quang et ai 1973 (£2); Tong Duy Thanh et ai 1995 (E2)*

-Di^p BoXinh (part.): Phan Scm etal 1974, 1978 (&2-0). Di^p Lan^Khuong (part.): Dinh Minh Mpng et al. 1976, 1978 (£2)- tdng Ha Giang: Ph^un Kim Ngan 1982 (£2); Luomg H6ng Hu<?c 1986, 1987. (£2)


Lithology and Thickness

Characteristic sequence along the Lo River from Hoi Xuan to Bai Villate (Quan Hoa District) is 600-700 m of mainly schist with interbeds of limestone. Luong River section is 330 m: (1) Sericite-shale and cherty shale; 180 m. (2) Thin-bedded recrystallized limestone with some interbeds of sericite shale; 40 m. (3) Banded quartzite interbedded with carbonate-bearing schist and light-grey limestone; 60 m; with trilobites of Middle Cambrian. (4) Dark-grey recrystallized limestone interbedded with sericite-quartz schist; 50 m.


Lithology Pattern: 
Shallow-marine marl


Relationships and Distribution

Lower contact

Unconformably upon the Nam Co Fm (PR3 - Cm1 nc),

Upper contact

Conformable below the carbonate sediments of the Ham Rong Gr (Cm2 - Oi)

Regional extent

Two narrow and discontinuous bands in NW-SE direction (Same extent as the overlying Ham Rong Gr). First band extends from the Pha Din Pass (Lai Chau Province) to Ban Mo through Na Vien (Son La Province) through Laos to Quan Hoa, Ham Rong Bridge and Ba Trieu Temple (Thanh Hoa Province). Second band is from Co Ma, Chieng Dong (Son La Province) through Laos to Luong and Lo Rivers (Thanh Hoa) areas.


GeoJSON

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Fossils

Middle Cambrian trilobites characterize the adjoining beds between Middle and Upper Cambrian, such as: Cyclolorenzella sp.? Damesellidae and Agnostidae, found in sericite schist, on Road No.217 about 2 km S-SE of Ta Lang Village.


Age 

Middle Cambrian age of the Song Ma Fm has been determined with the inarticulate brachiopods Lingulella sp., Obolus sp. and oncolites found generally in the upper part of the formation. In addition, limestone of the overlying Ham Rong Fm containing trilobites of transitional Middle - Upper Cambrian age is also evidence of the Middle Cambrian age of the Song Ma.

Age Span: 

    Beginning stage: 
Cambrian Stage 3

    Fraction up in beginning stage: 
0.0

    Beginning date (Ma): 
521.00

    Ending stage: 
Drumian

    Fraction up in the ending stage: 
1.0

    Ending date (Ma):  
500.50

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).