Abstract:
Processes responsible for the alternation of flora evolution stages are analyzed on the basis of the Late Cretaceous floras from northeastern Russia, among them two paleofloral successions from the Penzhina Bay (Turonian-Campanian) and the Rarytkin Range (middle Maastrichtian-Danian). Changes in the species diversity and ecosystem structures, as well as the extent of extinction and origin of taxons, mainly depend on the mode, trend, and sharpness of climatic changes at the stage boundaries and on the flora taxonomic composition. The flora renewal at each stage is significant (40-75% at the species level) and controlled by the intense evolution of flowering plants. However, there are many transient genera and species of conifers, which often become dominant or subdominant elements among various Late Cretaceous floras. Climatic conditions, especially humudification, affect the extent of geographic differentiation of floras as well.