Cenozoic biostratigraphy of the Pogranichnyi Region, Eastern Sakhalin, Russia

Diatom assemblages from the Oligocene through late Miocene siliceous and terrigenous formations of the Pogranichnyi region of the East Sakhalin Basin are documented, with particular attention given to the recognition of diatom zones from the Oligocene and early Miocene in the Pilengskaya and Borskaya Formations. Improvements in the diatom biostratigraphic zonation scheme for the North Pacific have made it possible to recognize Oligocene rocks that may have previously been reported as unknown, or as lower Miocene deposits. This paper is the first to more fully describe the evidence for more widespread Oligocene and lower Miocene siliceous deposits in the northwestern Pacific than previously thought.