Chingandzha Paleoflora and Age of Cretaceous Volcanites of the Balygychan and Sugoy Interfluve and Adjoining Part of Okhotsk–Kolyma Watershed

Abstract

Most of the Okhotsk–Chukotka volcanogenic belt fossil floras differ significantly in systematic composition from the floras of coastal lowlands of the adjoining Anadyr–Koryak subregion dated by faunistic remains. That is the reason why its comparison is so difficult and, accordingly, why it is complicated to establish the age of volcanic formations. The only exception in this situation is a Chingandzha flora that is reliably compared with coastal floras and is dated to the Turonian–Coniacian. New data on the Chingandzha flora systematic composition make it possible to clarify its age. This flora shows the most similarity to a Kaivayam flora of the Anadyr–Koryak subregion; thus, it has to be dated to the Coniacian. The stratigraphic setting of the locations of the Chingandzha flora fossils makes it possible to date three lower strata of volcanites in the external zone of the Okhotsk-Chukotka volcanogenic belt to the Coniacian. During medium-scale geological mapping, younger formations were erroneously assigned to them in some cases. The Chingandzha flora could have preserved its coastal appearance and penetrated far into the continent along a lowland that probably originated in a linear zone of tectonic disturbances.