Rinh Chua Fm

Cao-Lang Basin. The type section is located along the left bank of the Ky Cung River, from South Po Mo to Rinh Chua Villages, Loc Binh District, Lang Son Province (N = 21°44’; E = 106°59’), and reference section can. be observed in the Luc Dau section, from Ban Be to the Ky Cung River .

Synonym: Điệp Rinh Chùa: Trần Đình Nhân, Trịnh Dánlì 1975; Trần Đinh Nhân (in Trần Văn Trị et al. 1977); Trịnh Dánh 1979,1980, 1985, 1993;Nguyễn Địch Dỹ 1987. Hệ tầng Rinh Chùa: Trịnh Dánh (in Phan Cự Tiến et ai. 1989; in Vũ Khúc, Bùi Phú Mỹ et al 1990; in Vũ Khúc et al. 2000); Đoàn Kỳ Thụy et al. 2001. Neogen (part.): Dovjikov A.E. et al. 1965. Miocen (part.): Trần Đình Nhân (in Trần Văn Trị et al. 1977).

Mainly lacustrine facies of sandy claystone. Lower part includes fine- and medium-grained, horizontally bedded sandstone, which usually is undulated on the bed surface, interbeds of mudstone and thin siderite lenses, 140 m thick. Upper part is characterized by interbedded brown clayey shale, mudstone with conchoidal fracture, and thin siderite lenses, yielding leaf impressions, molluscs, and fragments of coleoptcrids, 160 m thick. The total thickncss of the formation is about 300 m.

Abundant leaf impressions are composed of Magnolia sp., Laurus mansuyi, L. similis, Cinnamomum cf. obovatum, Litsea cf. maghifolia, Nelumbo sp., Ficus beauveriei, Fagus antipofi, Dryophyllum relongtanense, Quercus lantenoisi, Qu. neriifolia, Betula prisca, Juglans acuminata, Salix elongata, Arundo sp. Sporomorph and palynomorph assemblage includes the reprentatives of Sabal, Phoenix, Salix, Juglans, Quercus, Castanea, Castanopsis, Rhus, and Acer. Freshwater molluscs are also abundant such as Viviparus cf. margaryaeformis, Tulotoma sp., Cuneopsis sp., Chamberlainia sp., Sinanodonta ex gr. wodiana.

Among leaf impressions there are Phoebe pseudolanceolata, Ficus beauveriei, Nelumbo sp., Fagus antipofi, Quercus lantenoisi, Qu. zeilleri, Qu. neriifolia, Qu. cf. lobbi, Nelumbo sp., Atnus kefersteini, Betula cf. prisca, Juglans acuminata, Myrtus minor, Eugenia sp., Graminiphyllum sp., etc. Sporomorph and palynomorphs include representatives of Sabal, Phoenix, Salix, Juglans, Quercus, Carya, Fagus, Castanea, Castanopsis, Rhus, Acer, Platanus, Sterculia. Among remains of coleoptcrids there are representatives of Dityscidae, Cerambicidae, and Hydrophyllidae.

Lycopodiumspórites neogenicus, Cicatricosisporites dorogensis, Liquidambarpollenites minutus, Crassoretitriletes nanhaiensis, Cr. sp., Pinuspollenites sp., Ephedripites sp., Tsugapollenites sp., Corsinipollenites sp., Verrutricolporites pachydermus, Caryapollenites sp., Gothanipollis bassensis, Pentapollenites maomingensis, Oculopollis sp., Momipites triletipollenites, Alnipollenites sp., Alangiopollis sp., etc.

Mainly lacustrine