Na Duong Fm

Cao-Lang Basin. The type section is located in southward of Na Duong Village, along Tong Da stream and at Na Duong Coal Mine, Loc Binh District, Lang Son Province (N = 21°42’; E = 106°58’). It was named by Tran Dinh Nhan.

Synonym: Điệp Nà Duong: Trần Đình Nhân, Trịnh Dánh 1975; Trịnh Dánh 1979,1980.1985, 1986,1993. Điệp Nà Củp: Trần Đình Nhân, Trịnh Dánh 1975. Hệ íầng Nà Dương: Trịnh Dánh (in Vù Khúc et al.2000); Đoàn Kỳ Thụy et al. 2001. Neogcn (part.): Dovjikov A.E. et al. 1965. Miocen: Trần Đình Nhân ịin Trần Vãn Trị et al.1977). Hệ tầng Nà Dương (part.): Trịnh Dáiih (in Phan Cự Tiến et al. 1989; ;in Vũ Khúc; Dùi Phú Mỹ et al. 1990);Phym Đình Long 2001. Hệ tầng Phan Lương (part.): Trịnh Dánh (in Vù Khúc et al. 2000), Phạm Đình Long et al. 1969, 2001. Hệ tầng Tuyên Quang (part.): Trần Đinh Nhân, Trịnh Dánh 1975.

Brown-coal bearing facies, mainly clayey sandstone. Characteristic section exposed in the Na Duong Coal Mine area is 250 m of (1) Rhythmic intercalation of sandstone, mudstone, carbonaceous shale and 4 coal seams; 130 m; with fresh-water bivalves. (2) Rhymthic interbedding, but more fine-grained than the lower part, of sandstone, mudstone, clayey shale, and 5 coal seams, 120 m thick. Industrial coal production.

Containing freshwater bivalves Unio sp., Anodonta sp., leaf impressions of the Quercus parceserrata - Laurophyllum and Quercus - Castanea complexes including characteristic forms such as Quercus aff. parceserrata, Fagus antipofi, Laurophyllum sp., Cinnamomum polymorphism, Phoebe pseudolanceolata, Dryophyllum relongtanense, etc. Fossils include leaf impressions of the Graminỉphyỉlum - Phragmites oeningensis, Quercus lobbii - Diospyros brachysepala, Nelumbo protospeciosa - Craminiphyllum complexes, in which characteristic species are Quercus cf. lobbii, Q. glaucay Phragmites oeningensis, Betula prisca, Litsea cf. pontica, Acer trilobatum, Magnolia mirabilis, Ainus smalhauseni, Arbutus elegans, Diospyros brachysepala, Pterocarya ezoana, Sporomorphs and palynomorphs of Sabal, Phoenix, Salix, Juglans, Carya, Coryh is, Quercus, Fagus, Castanea, Liquidambar, Rhus, Aralia, etc. Leaf impressions include known species such as Laurus mansuyi, L. cf. vetusta, Cinnamomun polymorphum, Phoebe pseudolanceolata, Litsea cf. magnified, L. doumeri, Ulmus longifolia, Ficus beauveriei, Dryophyllum relongtanense, D. yunnanensis, Quercus lantenoisi, Q. neriifolia, Q. bonnieri, Q. parceserrata, Q. lobbii, Betula cf. cuspidens, B. cf. alnoides, Carpinus vimina fossil is, Diospyros brachysepala, Rhamnus goepperti. Sporomorphs and palynomorphs are also abundant and close to those of the Na Duong Fm, consisting of representatives of Quercus, Castanea, Carya, Juglans, Plaiycarya, Acer, Ilex and other genera such as Sabal, Phoenix, Salix, Ginkgo, Castanopsis, Menispermum, Magnolia, Aralia, Alnus, etc.