Ban Diet Fm

Holostratotype: the section along a small stream extending from Muong Lang (Ban Mo village) to the Song Mua River, 200 m southeast of Ban Diet Village, Phu Yen District, Son La Province (N = 21°15'; E = 104°44'30")

Synonym: In some works, it is considered to be a lenticular body within the Bac Son Fm. Điệp Bàn Diệt: Phan Cự Tiến et al. 1977 (C₃). Carbon trung, thượng và hệ Permi (part.): Dovjikov A.E. et al. \ 965. Tầng Vạn Yên: Nguyễn Văn Liêm 1968 (Pi). Thống dưới hệ Permi: Nguyễn Xuân Bao et al. 1970; Lê Hùng 1969, 1973, 1975; Lê Hùng (in Trần Văn Trị et al.) 1977. - Hệ Permi (part.): Bùi Phú Mỹ et al. 1971. Hệ Carbon, thống trên - Hệ Permi thống dưới: Trần Đăng Tuyết et al. 1977. Hệ tầng Mường Lang (part.): Lê Hùng, Tổng Duy Thanh et al 1987 (C₃ - P₁). Hệ tầng Bàn Diệt (part.): Vũ Khúc, Bùi Phú Mỹ et al. 1990 (C - p); Lê Hùng, Trần Thị Ninh, 1990 (C₃ - Pị); Đoàn Nhậl Trưởng (in Tống Duy Thanh et al.) 1995. Hệ tầng Si Phay: Tô Vãn Thụ et al. (1997); Nguyễn Vãn Hoành et al. 2001 (Pi-2>.

The Ban Diet Fm consists of terrigenous sediments with interbeds of mafic volcanics and carbonate rocks, which clcarly distinguish it from the overlying and underlying carbonate formations. Holostratotype is 210 m of: (Ỉ). Black clayey shale containing small mica flakes interbedded with sandstone, 50 m thick. (2). Sandstone interbedded with clayey shale, calcarcous shale and mafic volcanics, 160 m thick.

Neoschwagerina craticulifera, N. sp., Verbeekina ex gr. Verbeeki

The Ban Diet Fm was deposited during the beginning of the sedimentary differentiation, when the faulting and extension responsible for the Song Da Depression appeared.