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Nam Tham Formation
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Nam Tham Fm base reconstruction

Nam Tham Fm

Period: 
Triassic

Age Interval: 
Ladinian, T2, (7, 8, 9, 10, 11)


Province: 
West Bac Bo

Type Locality and Naming

Song Da – Tue Le Basin. The type section is located along the Nam Tham Stream, in the section from Na Ha Village upsừeam toward the southwest, Son La Province (N= 21° 1’; E= 104°05’). It was named by Nguyen Xuan Bạo 1969.

Synonym: Điệp Nậm Thẳm\ Nguyen Xuân Bao 1970; Phan Cự Tiến et al. 1977; Vũ Khúc, Trinh Thọ (in Trần Văn Trị et al.) 1977, (in Dương Xuân Hào et al. 1980; Bùi Phú Mỹ et al. 1978; Đinh Minh Mộng et al. 1978; Nguyễn Vĩnh et al. 1978; Nguyễn Xuân Bao et al 1978; Phan Sơn et al. 1978; Vũ Khúc 1989, 1990. - Hệ tầng Nậm Thẳm: Vũ Khúc 2000, (in Vũ Khúc et al..) 2000. - Hệ tầng Phà Lý (part.): Dovjikov A.E. et al.. 1965


Lithology and Thickness

Clayestone and Limestone: Stratotype is (1) Black-grey claystone with clayey limestone, 100 m; (2) Black-grey shale with interbeds of grey sandstone and siltstone, 200 m; and (3) White-grey massive limestone grading upwards into dark grey marl, 100 m thick. Total thickness in this section is about 400 m. In general, the massive limestone bands in the upper part are unstable in thickness.


Lithology Pattern: 
Sandy claystone


Relationships and Distribution

Lower contact

Confrmably upon the Dong Giao Fm. In Leo Cai – Yen Bai border region, underlain/partly coeval with the Nghia Lo Fm.

Upper contact

Not clear. Next younger unit is the upper Ladinian Muong Trai Fm.

Regional extent

In narrow bands closely connected to the underlying Dong Giao Fm. Extending from the Nam Ma Stream area (Lai Chau Province) through portions of Son La, Nam Tham, Moc Chau, Vu Ban and Hoa Binh provinces, Cue Phuong Preserve Forest to the Ba Sao (Ha Nam Province) and Bim Son (Thanh Hoa Province) areas.


GeoJSON

{"type":"Feature","geometry":{"type":"MultiPolygon","coordinates":[[[[103.62,22.85],[104,22.55],[104.21,22.34],[105.57,21.35],[105.57,21.11],[105.45,20.92],[105.18,20.72],[104.41,21.12],[104.09,21.41],[103.69,21.65],[103.24,22.26],[103.23,22.42],[103.62,22.85]]]]}}

Fossils

Bivalves Daonelỉa lommeỉi, D. paucỉcostata, D. cf. bulogensis, D. cf.moussoni, D. cf. bockhi, Posidonia wengensis.


Age 

This relation, together with its fossils allows us to date it as Ladinian, possibly Early Ladinian, due to its close connection with the underlying Anisian limestone

Age Span: 

    Beginning stage: 
Ladinian

    Fraction up in beginning stage: 
0.0

    Beginning date (Ma): 
241.46

    Ending stage: 
Ladinian

    Fraction up in the ending stage: 
0.5

    Ending date (Ma):  
239.23

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).