Duong Dong Fm

Lower formation (landward) of the Do Son Gr. Hiep Son Ha Section. This section is situated to the south of Hiep Ha Village, 1.5 km northwest of Kinh Mon Townlet. The section base is exposed in a road fork (N = 20°59'22", E = 106°32’12"), with the northeastern branch extending to Hiep Ha Village. The Duong Dong Fm is synchronous with the Van Canh Fm in the more seaward sections.

Synonym: Tầng Dưỡng Động'. Nguyễn Quang Hạp 1967 (D 2C). Dévonien indéterminé (part.): Patte E. 1927; Saurin E. 1956. Bậc Eifel: Jamoida A.i. (in Dovjikov A.E. eí a i, 1965, 1972); Trần Văn Trị et al, 1975; Dương Xuân Hảo et al. 1975; Dương Xuân Hảo (in Trần Văn Tri et al. 1977). Điệp Yên Phụ-. Phạm Văn Quang 1971 (D₂e); Nguyễn Công Lượng 1980 (Dr D₂). lỉệ tầng Diỉõng Động: Tống Duy Thanh et al 1986; Vũ Khúc, Bùi Phú Mỹ et al. 1990 (Điệp) ; Tống Duy Thanh (ìn Vũ Khúc et al 2000; Tạ Hoà Phương eI aí.y 2004; Nguyễn Hữu Hùng (in Tống Duy Thanh eí a l, 2005); Tống Duy Thanh, Tạ Hòa Phương 2009 (Di-D₂e). Duong Dong Fm: 1988; Tong-Dzuy Thanh et al. 1995.

Claystone and Sandstone. (1). Greenish-grey shale, sericite shale containing poor remains of brachiopods and crinoids. In the middle and upper part of this member occur thin-banded quartz-rich sandstone beds. Thickness: 200 m. (2). White-grey, red-brown weathering, micaceous sandstone, siltstone, shale rhythmically interbedded with one another. Thickness; 170 m. (3). Brown-violetish clay shale interbedded with micaceous siltstone, containing poorly preserved brachiopods and bivalves. Thickness: 50 m. The total thickness of the Fm in this section reaches 420 m.

Include Schellwienella lantenoisi, Howellella sp., Aulacella cf zamoidai, Pseudoschizophoria sp., Spinulicosta sp., Eospirifer sp., Stropheodonta sp., Platyorthis cf. longi and Tulynetes hoabinhensis. They belong to a brachiopod assemblage usually met in sediments of the Mia Le Fm and Ban Nguon Fm in North Viet Nam and the Yujiang Fm in Kwangsi, China.