PLIOCENE-QUATERNARY BIOSTRATIGRAPHY AND PLANKTONIC FORAMINIFERA EVOLUTION IN THE NORTH PACIFIC

Abstract

In analysis of the stratigraphic distribution of planktonic foraminifers in the Pliocene–Lower Quaternary sediments of the North Pacific, and research of the space-time distribution dynamics of 60 species at four levels corresponding to the foraminiferal zones N 19, N 20, N 21, and N 22 revealed, significant evolutionary changes at that time were revealed. Twenty-five species became extinct and ten species appeared. Since the early Pliocene, the foraminifer diversity decreased from 53 to 34 species. Three groups of species were revealed: (1) short-lived species; (2) species who reduced and extended distribution areas and abundances, and (3) species whose distribution patterns remained relatively stable. It was shown that the reduction of distribution areas proceeded from the periphery toward the center (i.e., toward the areas with the highest abundances) and, in contrast, distribution areas of the newly appearing and evolving species expanded from their center toward the periphery