Hang Mon Fm

Song Da Basin. The type section is located in the Hang Mon coal mine, Yen Chau District, Son La Province (N = 21°00; E= 104°14’). It was named by Nguyen Xuan Bao.

Synonym: Điệp Hang Mon: Nguyễn Xuân Bao et al. 1969, 1978; Trịnh Dánh 1979, 1980, 1985; Trịnh Dánh (in Tổng Duy Thanh, Lê Hùng et al.) 1987. Hệ tầng Hang Mon: Trịnh Dánh (in Phan Cự Tiến et al.) 1989; (in Vũ Khúc, Bùi Phú Mỹ et al.) [990, (in Vũ Khúc et al.) 2000. Neogen: Dovjikov A.E. et al. 1965. Miocen: Trần Dinh Nhân (in Trần Văn Trị et al) 1977. Điệp Hang Mon và hệ tầng Phù Óc: Trịnh Dánh 1993.

Brown-coal bearing beds. Characteristic succession in the coal-mine section is: (1). Grey to dark grey, massive quartz conglomerate, gravelstone and sandstone interbedded with calcareous siltstone, lenses of calcareous sandstone and conglomerate, about 30 m thick. (2). Siltstone and claystone interbedded with brown coal seams and carboniferous shale, 20-30 m thick. (3). Interbedded marl, calcareous sandstone and calcareous siltstone, 60-70 m thick. The total thickness of the formation in this section is about 100-130 m.

Spores and Pollen of Na Duong Flora. Lycopodium sp., Asplenium sp., Pinus sp., Tsuga sp. Sinotalia sp., Rivularia sp.. Viviparus cf. margaryaeformis, V. aff. quadratus, Tulotoma sp., etc.. Cicatricosisporites dorogensis, Gothanipollis bassensis, Liquidambarpollenites minutus, Ephedripites sp., Proteacidites sp.. As in the member 3 - Cicatricosisporites dorogensis, Liquidambarpollenites minutus, Verrutricolporites pachydermus, Lycopodiumsporites neogenicus, Ephedra sp., Verrucatosporites usmensis, Proteacidites sp., Corsinipollenites sp.. Cicatricosisporites dorogensis, Gothanỉpoỉlỉs bassensis, Verrutricolporites pachydermus, etc. The uppermost beds of yield fossils of the lower jaw of the rhinoceros Chilotherium and Protocerothium cf. minutum of possible Early Miocene age.