Stratigraphy of Marine Paleogene and Neogene of Northeast Asia (Chukotka, Kamchatka, Sakhalin): GEOLOGIC NOTES

Abstract

Marine Paleogene and Neogene sequences of the Soviet Far East are present along a 3,500-km arc of the western North Pacific margin extending from the Kuril Islands and Sakhalin northeastward to Chukotka. Initial correlations based on lithostratigraphy were largely unsuccessful and were replaced by chronostratigraphic subdivisions for each of the three major regions of Tertiary deposition: the Koryak upland, Kamchatka Peninsula, and Sakhalin Island. Regiostages (provincial stages) and horizons for these regions are based primarily on mollusks aided by foraminifers, diatoms, and spores and pollens. Planktonic foraminifers are locally abundant in the Paleogene but are rare and not diagnostic in the Neogene. Initial age assignments of northeast Asian sequences were made with eference to the stratigraphic sequences of northern Japan and the west coast of North America. Far-reaching revision and recalibration of existing chronostratigraphic schemes in 1974 caused a major hiatus in age assignment of stratigraphic units. Many of the units were determined to be significantly older than originally believed. The age of these northeast Asian Tertiary deposits, particularly the late Paleogene and Neogene, continues to be determined largely through correlation with stratal sequences of Japan and western North America.