Song Hien Fm
Type Locality and Naming
Song Hein Basin. The type section is located on the dirt road from Pac Giai to Ma Phuc, on the left side of the Song Hien River, to the west of Cao Bang Town (N = 22°35’; E = 106° 14’).
Synonym: Schistes de Song-hiem (part.): Bourret R. 1922 (Anthracolithique moyen - Triassique moycn). Điệp Sông Hiếh (part.): Vasilevskaia E.D. 1962, (in Dovjikov A.E. et al. 1965.); Vũ Khúc 1989, 1990 (Trias hạ - trung), (in Vũ Khúc et al. 1965, 1986) (Trias trung-thượng); Nguyễn Kinh Quốc (in Vũ Khúc, Bùi Phú Mỹ et al. 1990) (Trịas hạ - trung). Hệ tầng Sông Hiến: Vũ Khúc, Đặng Trần Huyên 1995; Đặng Trần Huyên 1996; Vũ Khúc et al. 2000 (Trias hạ). Điệp Sông Hiến (part.): Phạm Đinh Long 1975 (Anísi); Trịnh Thọ (in Trần Văn Trj et al. 1977 (Trias trung). Các irầm tích Ânisi: Vũ Khúc (in Dương Xuân Hảo et al. 1980). Điệp Bình Gia: Nguyễn Kinh Quốc, Đặng Trần Huyên (in Nguyễn Kinh Quốc et al. 1991).
Lithology and Thickness
Terrigenous with thick intervals of volcanics in lower parts of some sections. Section from Binh Gia Townlet to BanHuan Village (Lang Son Province; 760 m thick): (1). Polymictic conglomerate and gravelstone containing some boulders of limestone, and tuffaceous gritstone shale containing some coaly matter; 100 m thick; containing Induan bivalve Claraia gervilliaeformis. (2) Dacite, rhyolite, rhyolitic tuff with lenses of greenish-grey andesite-basalt and basalt; 100 m thick. (3) Rhyolitic tuffs, tuffaceous sandstone and gritstone, yellowish-grey tuffaceous sandy siltstone; grading upward into rhyodacite, dacite and their tuffs; 250 m thick. (4) Greyish fine-grained sandstone, siltstone and shale; 110 m thick, containing Claraia species.
Relationships and Distribution
Lower contact
This formation rests unconformably upon Upper Paleozoic limestone (Bac Son Fm; although uppermost Permian Dong Dang Fm is also in this region), as has been observed in the sections west of Cao Bang Town and in the Binh Gia area.
Upper contact
Unconformably underlies the Anisian-age Lan Pang Fm, as observed only in the Lan Pang area.
Regional extent
The Song Hien Fm is widely distributed and occupies almost all the Song Hien Depression. It extends from the Pho Bang, Yen Minh, Cao Bang areas in the north, southeastward to the Binh Gia, Diem He and That Khe areas of Lang Son Province.
GeoJSON
Fossils
Fossils are rare in the formation. In its extensive distribution area only some fossil localities have been found in the above-described sections. They can be subdivided into two levels: 1) that with Lytophiceras and Claraia, collected from the lower part of the formation, belonging to the Claraia-Eumorphotis Assemblage, known in Viet Nam as an Induan fauna, 2) that with Olenekian ammonoids Anakashmirites and Dieneroceras, collected from the upper part.
Age
Depositional setting
Additional Information