Song Da Fm
Type Locality and Naming
The Song Da Complex described by Dovjikov A.E. et al. (1965) from its distribution area in the upstream part of the Song Da River, hence its name, near the Viet-Chinese border.
Synonym: Song Da Complex Hệ tầngSôngĐà', Dovjikov A.E. et a1. 1965 (P - T1); Vù Khúc, Bùi Phú Mỹ et al, 1990(C 1-P1); Trần Đăng Tuyết et al. 1994; Nguyễn Văn Hoành et al. 2001(C3 – P1).
ĩndosinias ìn/érieurịpan): Fromaget J. 1934, 1952 (C2 - T).
Hệ Permi (part): Bùi Phú Mỹ et al. 1971.
Điệp Sông Đà (part.): Nguyễn Văn Liêm 1985 (P – T1).
Hệ tầng Bọ Lếch-. Trần Đăng Tuyết et al. 1994 (P3 - T1)
Lithology and Thickness
It is a unit of sedimentary - volcanic deposits composed of sandstone, shale, porphyrite, some rhyolite and tuff, tuffite, conglomerate, and limestone. Nam Keng Stream section: (1). Conglomerate with rounded pebbles of quartzite and sandstone; grading upwards to cherty shale and mafic volcanic flows; 300-350 m thick. (2). Fine-grained mafic volcanic flows and their tuffs with some interbedsof grey cherty shale, 200-300 m thick. (3). Siltstone, sandstone, marly shale and interbeds of light-grey limestone; 50 m thick. The total thickness is 550-700 m.
Toward the Southeast of its extent, the thickness of the andesite middle unit increases up to 500-700 m, and the total thickness of the formation reaches 2600 m.
Relationships and Distribution
Lower contact
Unconformable upon the "Devonian-age Huoi Nhi Fm" in type area [Not in Lexicon]. Regionally, the next older unit is the Bac Son Fm carbonate-platform.
Upper contact
Unconformable below the Suoi Bang Fm.
Regional extent
It occurs in the valleys of the Song Da upstream and of its tributaries located in extreme West Bac Bo. The lower part of the Song Da complex occurs also in the area of the upstream Nam Chim Stream, a southwest tributary of the upstream Song Da River. Extending through Muong Te to Muong Lay area, Dien Bien Province.
GeoJSON
Fossils
Upper part contains Permian fauna such as Anodontophora sp., and Neoschizodus sp. (?). Mỉsellỉna ovalis, M. minor, M.termieri, Pseudofusulina sp., Pseudoschwagerina sp. were found. 5 km below the mouth of the Nam Po there are the fusulinids Pseudofusulina cf. complícala, Parafusulina ex gr. japónica, Miseỉlina ovaỉis, M. cf. aliciae, and Cancellina (?) sp. 7 km northward Muong Toong - Pseudofusulina cf. complícala, Parafusulina aff, gigantea, Para.. ex gr.japonca, Pachyphloia sp.,
Age
Depositional setting
Based on the stratigraphic relationships and fossils, the Song Da Fm is referred to the Early-Middle Permian.
Additional Information