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Cam Duong Formation

Cam Duong Fm

Period: 
Cambrian

Age Interval: 
Early to early-Middle Cambrian, Cm1 cd, (7, 8)


Province: 
West Bac Bo

Type Locality and Naming

Lectostratotype: the Ngoi Dum section, extending from Coc San to Ta Turn villages, situ¬ated about 5 km southwest of Lao Cai Town (N= 22°25f; E= 103°50'). Described by Tran Huu Dan during Project KT 01.05 (Tong-Dzuy Thanh et al. 1995).

Synonym: •报 /石坂 C■卿 Dovjikov A^E•过 aA 1965 (S?); Tr^n H(?u D&Wn T6ng buy Thanh 扨 a/. 1995 - Si; Nguyln Dinh Hgp 扨 d 1998 (£【);T6ng Duy Thanh w Vfi KMc 扨 d 2000; Nguyln VSn Hoinh 咨 a/. 2001. -Serie de Coc-xan (part.): Jacob C. 1921 (Algonkian); Saurin E. 1956 (t - 0). -Di?p CSc San (part.): Kalmykov 1959,1970 (Sinian). -Di^p Cam fhcdng ch^a phosphorit: TrSn V5n Trj et al 1967 (£]). -Di^p Cam Dudng: Bui Phu et at. 1971, 1972, 1978, 1988 (part. - €,); Tran V&1 Trj et al 1973, 1975, 1977 (£2- 〇i)； V5 Nang L^c 1974 (part. - D〇; Ho^ag Hoa Cuong, Ho^tig Luong 1976 (part. - Riphean); Ph^m KinfNgan, Lirong H6ng Hugfc 1976 (PRr ^i)> Kim Ng§n 1982, 1986, 1994 (£j); Tran Hflu D^n in Vu Kh6c et al. 1984 (PR3 - Lucmg H6ng Huge in Le H^ag, T6ng Duy Thanh et al 1987 (PR3 - tx); Tr^n Xuyea et al. 1988 (part. - £,); VQ KhQc, Bi^i Ph6 My et al. 1990 (£).


Lithology and Thickness

Claystone (Schist): The Cam Duong Fm is characterized by phosphorite-bearing fine-grained terrigenous sediments. The thickness of the forrmation varies inconsiderably in the distribution area and averages about 500 m. The Ngoi Dum Section (Lectostratotype) spans 575 m: (1) Polymictitic conglomerate with clasts mainly of quartz and chet, som schist; grading upward into quartz-mica schist with some interbeds of quartzite; 95 m thick. (2) Gray calcareous siltstone with some interbeds of marl and micritic-limestone; 90 m thick. Containing Early Cambrian acritarchs (Protosphaeridium tuberculiferum, etc.) (3) Phosphorite-bearing Quartz-mica-carbonate-apatite schist; 150 m, containg same acritarch assemblage. (4) Manganese-bearing quartz-mica schist with interbeds of quartzite and sericite schist; 95 m thick.


Lithology Pattern: 
Sandy claystone


Relationships and Distribution

Lower contact

Rests unconformably upon the dolomite of the Da Dinh Fm (NP3 dd); this relation can be followed along the contact between these two formations extending from Lang Phoi to Da Dinh villages. It clearly differs from the carbonate beds of the underlying Da Dinh Fm.

Upper contact

It clearly differs from the weakly metamorphosed terrigenous sediments of the overlying Devonian formations.

Regional extent

Right bank of the Red River from Lao Cai to Yen Bai Province in two bands. The first extends from Lung Po Ho through Cam Duong to Ban Ban areas; and the second is discontinuously exposed in Gia Ho, Sa Pa and Ta Phinh areas.

Correlated to phosphorite-bearing formations in Yunnan, China, which contain trilobites of Early Cambrian.


GeoJSON

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Fossils

Early Cambrian acritarchs.


Age 

Early Cambrian age on the basis of the acritarch assemblage collected from the middle part of the formation. [But correlation of upper part to Yunnan phosphorite-bearing formations with trilobites implies includes part of "middle" Cambrian in international usage.

Age Span: 

    Beginning stage: 
Fortunian

    Fraction up in beginning stage: 
0.0

    Beginning date (Ma): 
538.80

    Ending stage: 
Cambrian Stage 4

    Fraction up in the ending stage: 
1.0

    Ending date (Ma):  
509.00

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