Ben Khe Fm
Type Locality and Naming
Ban Chanh - Ban Khua Section, along the Song Da River, 1 km southeast of Ben Khe Village, Moc Chau District, Son La Province (N = 20°58', E = 104°55'); the formation name was taken from Ben Khe Village, where it is well exposed and was first studied by Dovjikov A.E. et al. (1965).
Synonym: Hệ tầng Bến Khế (part.): Dovjikov A.E et al. 1965 (£j - 0); Điệp Bến Khế: Nguyễn Xuân Bao et al. 1969 (e 2 - O 1); Bùi Phú Mỹ et al. 1971 (Cm 3 - O); Nguyễn Văn Hoành et al. 1974 (Cm2 - O1); Nguyễn Đình Hợp et al 1989 (Cm 2 – O1); Vũ Khúc, Bùi Phú Mỹ et al. 1990 (Cm - O1); Nguyễn Công Lượng et al, 1992 (Cm2 - O1). Điệp Bển Khế (part): Trần Văn Trị et al. 1970, 1975, 1977 (Cm2 - O1). Điệp Bến Kế: Phan Cự Tiến et al. 1977 (Cm2 - O1); Nguyền Xuân Bao et al. 1978 (Cm2 – O1); Nguyễn Vĩnh et al. 1978 (E2 - O1); Bùi Hữu Lạc et al. 1983 (Cm2 - O1); Trần Đăng Tuyết et al. 1989 (Cm2 - O1). Hệ tầng Bến Khế: Phạm Kim Ngân et al. 1986,1995 (£2 -O1), 1998 (£? - O); Nguyễn Văn Hoành et al. 2001 (£ - O)
Lithology and Thickness
Sandstone, Claystone, Limestone: Stratotype (1100 m thick): (1). Quartz conglomerate, gravel and thickly bedded coarse sandstone, thickness 140 m. (2). Banded calcareous shale, and mudstone interbeds, 150 m thick. (3). Light grey limestone, thickness 150 m. (4). Fine-grained quartzite, mudstone and shale, claystone in the top, thickness 700 m.
Relationships and Distribution
Lower contact
Unconformably rests on the Da Dinh Fm (Ediacaran) and Sin Quyen Fm (Neoproterozoic).
Upper contact
Unconformity between the Ben Khe Fm and the overlying Sinh Vinh Fm.
Regional extent
The formation is exposed in two different bands, the first in the downstream basin of the Song Da River, from Suoi Khoang Stream through Ben Khe Village (Son La Province) to Hoa Binh, and then northward to Thanh Son (Phu Tho Province). The second distributed in the upstream basin of the Song Da River, extending from the Pa Ham area through the Sin Ho Plateau to Pa Tan (Lai Chau Province).
GeoJSON
Fossils
Trematosphaeridium sp., Orygmaiosphaeridium sp.
Age
Depositional setting
Additional Information