Abstract

The Nong Son coal basin is one of the 5 Late Triassic Nori-Ret coal- bearing sedimentary basins of Vietnam with a graben-type geological structure. The coal-bearing formation has a distinct characteristic: the sediments of the lower part are uncomformably upon the older formations, and in the upper part they are uncomformably covered by formations of the Jurassic sea-continental sedimentary group.
Late Triassic plant fossils in the coal-bearing sediments of the Nong Son basin were collected and studied a long time ago (Counillon H., 1903, 1908, 1914; Bourret R., 1925). Later Vietnamese geologists have cooperated with foreign geologists in the process of geological mapping as well as in-depth research, more plant fossils are discovered. (Trần V.T. và Vũ K., 2011; Cát Nguyên Hùng và nnk., 1996; Nguyễn C. H., 1983; Vũ Khúc và nnk.,1984 và Serra C.V. và Franceschi, D. D., 1999). Plant fossils are mainly distributed in sediments of the Suon Giua Formation (the upper part of the Nong Son group). Up to now, the number of species (including open nomenclature) of the plant fossil of Nong Son coal basin has reached about 60, is most of which belong to 2 taxon groups Pteridophyta and Cycadophyta and rich representatives of the Dipteridaceae family; it is also the third most abundant assemblage– after of Hon Gai and Suoi Bang assemblages) and it belongs to Hon Gai flora. The plant fossil assemblage of the Nong Son coal basin has a similar composition to that collected in other coal basins of the same age (Sam Nua, Song Da, Yen Chau, Quang Ninh). This plant fossil assembage represented by Hon Gai flora which is comparable with coeval floras of adjacent regions of Vietnam (such as: Soppong, Phong Sa Ly- Laos, Huổi Hin Lat – Thailand, Ypinlang- Yunnan- China) as well as those of the western margin of Pacific Ocean (such as: Primoria- Far East Russian, Deadong – Korea, Nariwa, Yamaguchi- Japan, Krusin- Malaysia, Bintan- Indonesia)

They have common characteristics of being a mixture of Southern Hemisphere elements (Gondwana: Glossopteris indica, Palaeovittar kurzii, Taeniopteris spatulata) and of Northern Hemisphere – Cathaysia floras). The presence of Gondwana ancient elements as well as the mixture of Gondwana and Cathaysia floras are inffered by the separation, dript, and assembly of the Sibumasu continent in its geological evolutionary history with Indochina terrane.

Sedimentary studies show that this ancient plant lived in sedimentary environments including premountains, alluvial plains, and the transition from lake facies to river-beds.
Along with the sediment containing the plant fossil assemblage of Nong Son coal basin, there are georesources that have been exploited (coal), have been researched (uranium) and building materials (sand, gravel, limestone, marble...).