Abstract
Recently, in the Yên Tử Mt, a spores and pollens assemblage containing the Jurassic genera Coniopteris and Classopollis has been found in coal-bearing sediments belonging to the Hòn Gai Formation of Late Triassic, Norian-Rhaetian age.
The sediments containing the above spores and pollens consist of siltstone interbedded with coarse-grained beds, mainly of conglomerate, about 300 m thick, distributed from Bảo Sái to Đồng Pagodas, lying in the summit of the Yên Tử Mt. They belong to the uppermost part of the coal-bearing section of this locality. They have been described as “Chùa Đồng Conglomerate, of Early Jurassic age”. So, the Hòn Gai Formation in the Yên Tử Mt has a thickness of 1150-1300 m and has an age of Late Triassic - Early Jurassic (T3n-J1 hg).