On the Stratigraphic Setting and Composition of the Ayanka Flora from the Upper Cretaceous of Okhotsk-Chukotka Volcanogenic Belt, Northeastern Russia

Three floristic assemblages from the Upper Cretaceous volcanogenic deposits of the Bolshaya Ayanka River basin (Okhotsk-Chukotka volcanogenic belt (OChVB), Northeastern Russia) are described for the first time. The flora includes about 60 species of fossil plants. Conifers and angiosperms dominate; ferns are less diverse; horsetails, liverworts, ginkgoaleans, and cycads occur as single specimens. The Ayanka flora is similar to the Santonian–Campanian floras of Northeastern Russia and Northern Alaska (with Barykov, Late Bystraya, Ust-Emuneret, and, to a lesser extent, with the Ola and Early Kogosukruk floras), which allows to conclude the most probable Santonian–Campanian age of the studied flora. Floristic assemblages of the Ayanka flora reflect both slope vegetation dominated by conifers and vegetation of lowlands—river or lake banks—dominated by angiosperms. These assemblages demonstrate the penetration of plant communities dominated by advanced angiosperms from the coastal lowlands of the Anadyr–Koryak subregion to the territory of the volcanic highlands, where ferns and conifers are often found in the Late Cretaceous, and the relict plants of the Early and beginning of the Late Cretaceous are still preserved.