The flora of the Maastrichtian-Danian deposits of the Koryak Upland, Northeast Russia

Abstract

This investigation of the floristic succession within the Maastrichtian-Danian of the Koryak Upland in Northeast Russia is based on the study of six floral assemblages from the Rarytkin, Koryak, Kakanaut, Kholminsk and Vysokorechensk Formations. The floristic development is divided into two episodes: the Gornorechenian (middle Maastrichtian) and the Rarytkinian (late Maastrichtian-Danian). The ages of the floral assemblages were determined on the basis of correlation with ammonite and inoceramid zonation, since certain assemblages come from sections comprising alternating marine and nonmarine deposits. The most prominent floral change in the Koryak Upland took place at the boundary between the two episodes, which was somewhat earlier than the corresponding change in the middle latitudes of the Northern Hemisphere. Analysis of the taxonomic composition and leaf morphology indicates cooling and an increase in humidity during Rarytkinian time. The ecological and taxonomic patterns of the floristic development near the K/T boundary are discussed on the basis of the distribution and abundance of 86 species from 124 localities, occurring throughout the Maastrichtian-Danian deposits of the Rarytkin Formation in the Gornaya River Basin. This analysis leads to the conclusion that the floral change was the result of natural evolutionary processes and climatic change, rather than extraterrestrial events.