Abstract

Volcano-sedimentary formations in the Đồng Văn Karst Plateau were formed from Cambrian to Middle Triassic. They have been regularly studied for over a century. Up to now, 13 stratigraphic units have been described, namely: Chang Pung, Lutxia, Si Ka, Bắc Bun, Mia Lé, Si Phai, Tốc Tát, Lũng Nậm, Bắc Sơn, Đồng Đăng, Sông Hiến, Hồng Ngài, and Yên Bình Formations. They were formed in different geological settings and sedimentary environments. The formations in shallow-water marine environment are: Chang Pung, Lutxia, Bắc Bun, Mia Lé, Bắc Sơn, Đồng Đăng, Hồng Ngài, and Yên Bình ones; the formation interbedded with effusives in intracontinental rift conditions are: , Sông Hiến one; the formations in deep-water troughs in shallow-water environments are: Si Phai, Tốc Tát and Lũng Nậm; the formation in littoral continental conditions: Si Ka one. These formations contain fossil groups with diversity and abundance in varied environments: - Fossil groups in littoral continental facies: vertebrates, flora, ostracods, and gastropods; - Fossil groups in shallow-water marine facies: trilobites, brachiopods, bivalves, anthozoans, fusulinids (foraminifera), crinoids; - Fossil groups in deep-water marine facies: tentaculits, conodonts, and some species of bivalves and ammonoids.