According to many micropaleontologists, worldwide correlation of Tertiary successions in tropical and subtropical areas can be based on planktonic foraminiferal zones (chronozones). The taxonomic assemblages of such zones correspond to evolution stages of foraminifers. Current studies show that many of these zones can be traced in Japan and, to a certain extent, on Sakhalin, in Kamchatka, and in North America. For the first time, the stratigraphic scales of the North Pacific area can be related rather confidently to the general world scale. The following have helped make worldwide correlations more reliable: studies of nannoplankton and mammals (hipparions and Desmostyliidae in particular) and use of isotopic-age dating, paleomagnetism, and paleoclimatology.

Unfortunately, the planktonic fauna is very sparse in the Tertiary rocks of the North Pacific region. Therefore, the establishment of regional scales there must be based mainly on benthonic faunas. A change of systematic composition of some mollusk genera (Yoldia, Acila, and genera of the families Arcidae and Pectenidae) and the general number of species and newly-appearing species in certain stages of their development are reflections of their evolution stages. These stages can be used to subdivide the sections into several zones and to correlate them. Distinguishing such zones independent of the facies composition of the rocks and correlation of the zones with the planktonic zones are the bases for applying the international scale in the Boreal Pacific area. Seven such zone have been proposed for the Neogene of the USSR on the basis of Yoldia and other fossil groups; many of the zones have analogues in adjacent areas.

Establishment of the faunal succession relative to evolution is of great importance because the composition of each faunal assemblage in any particular section is related to stratigraphic facies; underestimating this factor has resulted in significant mistakes in correlation.

To make the provincial schemes more exact, it may be necessary to use data on other faunal groups, floral successions, paleoclimatology, etc. In order to work out regional stratigraphic scales, the establishment of evolution stages of ancient basins--including changes of fauna and lithology during each of these stages--and also the study of faunal assemblages of like and unlike facies of contemporaneous and successive levels are of great importance.

Local subdivisions (suites, members, beds) that are related to facies peculiarities of the sequences should be based on this framework of zones that was established according to evolution stages of the faunas. Paleoecologic and paleogeographic methods also are important in these studies.