Chau Thoi Fm

The type section is located a composite scction whose lower part occurs in the Buu Long Hill area, and upper part - in the Chau Thoi Mt area. Hypostratotype - Buu Long Hill towards Bien Hoa Airport (N10°50’; E 106°50’). It was named by Bui Phu My et al. 1994.

Synonym: Complexe érupii/du Nui Chau Thoi: Saurin E., Tạ Trần Tấn 1962 (Permi); Tạ Trần Tấn 1963 (Pr Tị}. - Compíexe voìcano-sédimentairedu Chau Thoi: TạTrần Tấn, Nguyễn Văn Vân 1967 ựurà). - Hệ tầng Châu Thới: Bùi Phú Mỹ, Vũ Khúc 1980; Vũ Khúc 1980, 1986, 1990, 2000, (in Vũ Khúc et al. 1986, 2000); Bùi Phú Mỹ et at. 1994; Nguyễn Ngọc Hoa ei al. 1996; Ma Công Cọ et ai. 2000,2001- - Hệ tầng Măng Giang (part.): Nguyễn Kinh Quốc (in Vũ Khúc, Bùi Phú Mỹ et al. 1990). - Hệ tầng Bửu Long: Nguyễn Ngọc Hoa et al. 1996.

Silty sandstone, Sandstone with volcaniclastics, and Conglomerate. Volcanogeno-sedimentary formation containing Middle Triassic ammonoids. Hypostratotype is: (1). Heterogenous conglomerate; the observed thickness is 37 m, but based on drilling material it can reach up to 150 m. (2). Greenish-grey, medium-grained feldspar-rich sandstone, containing many felsic tuffaceous breccias, with some interbeds of polymictic conglomerate, 100 m thick. (3). Grey, thin-bedded silty sandstone, dark grey silty clayey shale and siltstone, sometimes calcareous siltstone, 150 m thick; silty clayey shale yields the ammonoids Bulogites multinodosm, and Gymnotoceras cf. blackei of Middle Anisian age as at Chau Thoi Mt. The total thickness of the formation in this section is about 400 m.

Ammonoid Balatonites cf. balatonicus, the bivalves Daonella lindstroemi, Posidonia sp., some plants Podozamites sp., Ferganiella sp., Asterotheca sp., and Pecopteris sp., and palynomorphs Classopoỉlis sp., Cyclogranisporites sp., Hymenozonotriletes sp. etc. These fossils date their host sediments as Anisian