On the Age of the Buor-Kemus Flora of Northeast Asia Based on the Data on the Nonmarine Cretaceous in Eastern Chukotka

On the basis of the analysis of literature and cartographic materials, our field observations, results of U–Pb isotope dating of zircons, and examination of paleobotanical collections, it was established that the “Mesophytic” Buor-Kemus fern–gymnosperm flora existed in Eastern Chukotka in the Late Cretaceous longer than in other regions. The volcanics of the Nyrvakinot sequence are partly facially replaced by the sedimentary deposits of the Olkhovaya Formation. Both units contain plant remains of the Buor-Kemus flora. The Amgen volcanogenic sequence lies conformably and without any hiatus on the Nyrvakinot sequence and contains “Cenophytic” plant assemblages with a significant amount of angiosperms, ascribed to the Turonian–Coniacian. These three units were previously considered as the three major constituents of the Etelkuyum Formation. The U–Pb isotope ages of zircons from volcanogenic and tuffaceous sedimentary rocks of the Nyrvakinot sequence show that they accumulated in the Late Сretaceous in the age range of 93–87 Ma (Turonian–Coniacian). Taking into account all data available, it is evident that the Buor-Kemus flora (at least within the Eastern Chukotka segment of the Okhotsk–Chukotka Volcanogenic Belt) existed in the Albian, Cenomanian, Turonian, and, probably, in the early Coniacian.