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

In analysis of the stratigraphic distribution of planktonic foraminife rs in the Pliocene-Lower Quaternary sediments of the North Pacific, an d research of the space-time distribution dynamics of 60 species at fo ur levels corresponding to the foraminiferal zones N 19, N 20, N 21, a nd N 22 revealed, significant evolutionary changes at that time were r evealed. 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 a bundances, and (3) species whose distribution patterns remained relati vely stable. It was shown that the reduction of distribution areas pro ceeded from the periphery toward the center (i.e., toward the areas wi th the highest abundances) and, in contrast, distribution areas of the newly appearing and evolving species expanded from their center towar d the periphery.