Thac Ba Fm
Type Locality and Naming
The type section is located in the Thac Ba Hydroelectric Dam (N = 21° 45'; E = 105° 02'). It was named by Hoang Thai Son. Exposed along the road from Tan Quang to Hoang Su Phi, West of Luc Yen.
Synonym: Hệ tầng Thác Bà (Neoproterozoic- Lower Cambrian): Hoàng Thái Son et al. 1999. Hệ tầng Nà Hang (Proterozoic) (part): Dovjikov A.E. et al. 1965. Hệ tầng Sông Cháy (Upper Proterozoic- Lower Cambrian) (part.): Trần Văn Trị et al 1977, Trần Xuyên et al, 1987.
Lithology and Thickness
The total thickness of the Fm in this section is 1430 m; original composition was medium- to thick-bedded terrigenous clastics. (1). Quartz - two-mica schist interbedded with mica schist, thin lenses of marble, quartzite and quartz-epidote-calcite schist; over 1100 m thick. (2). Quartzite, micaceous quartzite interbedded with quartz-mica schist; 330 m thick.
Relationships and Distribution
Lower contact
Not given (tectonic relations)
Upper contact
Conformably underlies the An Phu Fm. It was penetrated by the pre-Devonian Song Chay Granite Complex Gr.
Regional extent
Distributed in the Lo-Gam Anticline, situated in the external south margin of the Song Chay Granite Massif, in the Thanh Thuy and Tan Quang areas (Ha Giang Province) and Luc Yen Anticlinate (Yen Bai Province) in a band lying between the Song Chay (Chay River) and the Song Lo (Lo River) faults (which are just north and parallel to the Red River Fault) extending southeastward to Hanoi, then plunging beneath Quaternary deposits of the Red River Delta.
GeoJSON
Fossils
No fossils.
Age
Depositional setting
Primitive composition was medium- to thick-bedded terrigenous sediments of neritic and littoral facies, formed in a relatively stable tectonic setting. The An Phu Fm and Thac Ba Fm were formed in a basin of terrigenous and carbonate sediments having similar composition with the Sa Pa Gr in West Back Bo and equivalent formations in the West of South China.
Additional Information