The Late Cretaceous Arman Flora of Magadan Oblast, Northeastern Russia

The Arman flora from the volcanogenic-sedimentary beds of the Arman Formation is systematically studied using materials from the Arman River basin and the Nelkandya-Khasyn interfluve (Magadan oblast, Northeastern Russia). Seventy-three species of fossil plants belonging to 49 genera are described. They consist of liverworts, horsetails, ferns, seed ferns, cycadaleans, bennettitaleans, ginkgoaleans, czekanowskialeans, conifers, gymnosperms of uncertain systematic affinity, and angiosperms. The Arman flora shows a unique combination, with relatively ancient Early Cretaceous ferns and gymnosperms occurring alongside younger Late Cretaceous plants, primarily angiosperms. The similarity of the Arman flora to the Penzhina and Kaivayam floras of northwestern Kamchatka and the Tylpegyrgynai flora of the Pekul'nei Ridge allows the Arman flora to be dated as Turonian and Coniacian (Late Cretaceous), which is corroborated by isotopic (U-Pb and 40Ar/39Ar) age determination for the plant-bearing layers.