Muc Bai Fm
Type Locality and Naming
The section along Muc Bai Stream, 6 km northwest of the Chuc A area (Huong Khe District, Ha Tinh Province) (N = 18° 07'; E = 105° 40').
Synonym: Série de Xom Con Giau: Fromaget J. 1927 (D2 - Dj). Frasnien, Famennien (part.): Saurin E. 1956. Các bậc Givet - Frasni (part.): Marcichev A.M., Trần Dức Lương (Dovjikov A.E. et al. 1 965); Dương Xuân Hào 1968, 1973. Giveti'. Dương Xuân Hảo 1965, 1977; Tống Duy Thanh 1967. Tầng vị Thanh Lụng: Dương Xuân 1 láo 1965 (D2g - Djfr). Hệ tầng Qui tìại: Dương Xuân Háo et al. 1975; Đặng Trần Huyên. Nguyễn Đình Hồng 1981 (Djgv); Tống Duy Thanh 1978; Tống Duy '1‘hanh et al. 1986, 1988 (D2gv - D3fr); Nguyễn Dức Khoa 1984; Nguyễn Hữu Hùng et al. 1995 (D2gv). Diệp Mục Bãi: Trằn Tính 1979; Nguyễn Quang Trung 1983; Nguyễn van Hoành, Phạm Huy '1'hông 1984 (D2gv); Nguyễn 1Iữu Hùng (Tổng Duy Thanh et al. 1995. Hộ tầng); Nguyễn Hữu Hùng 1996 (Hộ tầng); Tống Duy Thanh, Nguyễn Đức Khoa (i« Vũ Khúc et al.2000 - Hệ tầng); Phạm Huy Thông 2001 (Hộ tầng D2gv)
Lithology and Thickness
Marly limestone and claystone (700 m total): (1). Dark grey marl grading upward into black limestone and clayey limestone interbedded with siltstone and shale; contains the brachiopods Desquamatia kansuensis, Gypidula biplicata, Spinatrypa aff. quydatensis, Stringocephalus sp., Spinatrypa asperaeformis, Desquamatia ventricosa, corals Thamnopora cf. nicholsoni, Alveolites cf. admirabilis, Coenites sp., Scoliopora cf. denticulata, and Heliolites sp.; 235 m thick. (2). Medium-grained sandstone interbedded with clayey shale, 250 m thick. (3). Black marly shale and calcareous siltstone interbedded with gray limestone; with abundant fossils including brachiopods Schizophoria sp., Spinatrypa vassinensis, Sibiratrypa sp. and coral Thamnopora sp.
Relationships and Distribution
Lower contact
A conformable relation with the underlying Ban Giang Fm is observed in almost all sections where they are exposed.
Upper contact
A conformable relation with the overlying Dong Tho Fm is observed in almost all sections where they are exposed.
Regional extent
The Muc Bai Fm occurs mainly in Ha Tinh and Quang Binh Provinces, in the Chuc A area (Ha Tinh Province). The formation occurs in two NW - SE bands on the east slope of the Giang Man Mt range with a 2 - 5km width and 50 - 60km length. In Quang Binh Province it also occurs in NW - SE bands, exposed in the south bank of the Rao Nay River, from Thanh Lang (Minh Hoa District) through the Quy Dat, Dai Du, Lam Xuan areas to the west of Bo Trach District
GeoJSON
Fossils
Fossils (see lithology description) include stromatoporoids, brachiopods and corals.
Age
Depositional setting
The lithology and faunal assemblages indicate that the Muc Bai Fm developed in the shallow marine environment. It was possible that the marine level varied many times during deposition, which is shown by the intercalation of the coarse sandstone containing the nearshore shallow marine fauna and offshore shallow marine sediments containing corals.
Additional Information