Palynological evidence for dating Jurassic-Cretaceous boundary sediments in the Bureya basin, Russian Far East

Palynological complexes from the coaliferous Talyndzhan and Dublikan formations of the Bureya sedimentary basin are analyzed. The palynological assemblage from the upper part of the Talyndzhan Formation is characterized by dominant gymnosperms largely close to Pinaceae and Ginkgocycadophytus. The content of ferns is insignificant against the background of their relatively high taxonomic diversity. The assemblage is marked by the last occurrence of Staplinisporites pocockii, Camptotriletes cerebriformis, C. nitida, and Cingulatisporites sanguinolentus spores typical of the Late Jurassic palynofloras. The palynological assemblage from the Dublikan Formation is dominated by Pteridophyts representing mainly by Cyathidites and Duplexisporites. In addition to the conifer, the role of Classopollis increased among the gymnosperms in this assemblage. It also includes the first-appearing Stereisporites bujargiensis, Neoraistrickia rotundiformis, Contignisporites dorsostriatus, Duplexisporites pseudotuberculatus, D. rotundatus, Appendicisporites tricostatus, and Concavissimisporites asper. These sporomorphs are characteristic of the Berriasian palynofloras. Thus, the Jurassic-Cretaceous boundary is most likely located between the Talyndzhan and Dublikan formations.