Yen Duyet Fm
Type Locality and Naming
Lectostratotype: In the initial description of the formation (Dinh Minh Mong et al. 1976) its stratotype was not indicated, so the Thien Linh (Bui Village) section was selected as lectostratotype. It extends along the car road from Bui Village to Phuc Do Farm, situated 4 km southeast of the Yen Duyct coal mine (Cam Thuy District, Thanh Hoa Province) (N = 20° 09', E = 105° 33'), and can be supplemented by materials from the exploration borehole 2 of this mine.
Synonym: Điệp Yên Duyệt: Dinh Minh Mộng et al. 1976; Phan Cự Tiến et al. 1977; Đặng Trần Quần et al. 1980; Trần Xuyên et al. 1984; Phạm Xuân Anh et al. 1989; Ngô Quang Toàn et al. 1989; Trần Đăng Tuyết et ứ/. 1989; Vũ Khúc, Bùi Phú Mỳ et al. 1990 (P2); Dỗ Văn Chi et ứ/. 1992; Lê Văn Đệ, Nguyễn Đình Hợp et ứ/. 1994 (Hệ tầng)\ Phạm Đình Trưởng el al. 1999 (Hệ tầng). Hệ Per mi (part.) ; Hệ Trias (part.): Dovjikov A.E. et al. 1965. Hé« (part^: Bùi Phú Mỹ et al., 1971; Phan Sơnet al.1974; Lê Hùng (Triùi Văn Trị et al. 1977). Hệ tầng Bản cỏ: Phan Cự Tiến et al. 1977 (P2). Hệ tầng Chiềng Khừa: Nguyễn Xuân ỉ3ao et al. 1969 (P2 – T) Hệ tầng Đèo Sơn La'. Nguyẽn Văn Hoành et al. 2001(P1)
Lithology and Thickness
Characteristic section in Thien Linh area is 55-65 m thick: (1). Black clayey shale and cherty shale containing chocolate-colored lean ferrous ore (from some mm to 5 cm) in the lower part, and very thin beds of coal (from some mm to 10 cm) with poor plant remains in the upper part, 15 m thick. (2). Cherty shale and fine-grained limestone and siliceous limestone, 30-40 m thick; (3). Greenish-gray, calcareous shale, cherty shale; 10 m thick.
Relationships and Distribution
Lower contact
The Yen Duyet Fm rests conformably upon the volcanics of the Cam Thuy Fm and Vien Nam Fm.
Upper contact
Unconformably overlain by the Co Noi Fm of lower Triassic.
Regional extent
The exposures of the Yen Duyet Fm usually connect closely to the underlying Cam Thuy Fm. They occur southeast of the Song Ma Anticlinorium and west of the Song Da Anticlinoriuni, in Thanh Hoa (where Yen Dyuet is located, which has a coal mine), Hoa Binh, Lai Chau, Ha Tay, Son La and Lao Cai provinces.
GeoJSON
Fossils
Late Permian brachiopods Leptodus sp., Oldhamina cf. discipiens, Squamularia sp., Schellwienella sp., Chonetes sp., Actinọdesma sp., Spiriferella ex gr. vojnowskii, Neophricodothyris cf. asiatica. Abundant flora fossils such as Gigantopteris nicotiaefolia, Lobatannularia multifolia, etc.
Age
Depositional setting
Coal-bearing subcontinental sediments.
Additional Information