Late Cenozoic paleoenvironments in the Sea of Okhotsk area

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In order to reconstruct the late Cenozoic paleoenvironmental history in the Sea of Okhotsk area, such two sections in Sakhalin as the Makarov and Schmidt Peninsula investigated from paleontological and geological point of views. On the basis of detailed columnar sections (1 : 1000 scale), samples for bio-and chrono-stratigraphical analysis collected more than 500 localities in Makarov region in 1995 and in Schmidt Peninsula in 1996. Paleontological studies such as Diatom, benthic Foraminifera, Mollusca, Pollen, Dinoflagellate have done as coupled with sedimentological studies (facies's analysis, heavy minerals and geochemical analysis). As the result, the Oligocene to Pliocene lithostratigraphy and biostratigraphy of the studied areas were established. A big chronological gape was first recognized between the Chefov and Verkhne Due Formation in Makarov region on the basis of the Dinoflagellate and Pollen biostratigraphy. The Ar-Ar dating, 22-23 Ma of the basaltic rocks from the Chefov Formation may indicated the initial rifting stage of the Sea of Okhotsk. The beds corresponding to the first mid-Neogene climatical optimum were recognized in the Verkhne Due Formation in Makarov region and Pili Formation in the Shmidt Peninsula based on benthic fossils and pollens. The Denticulopsis hyalina Zone was recognized both from the Maruyama (Makarov region) and Pili (Schmidt Peninsula) Formations, respectively. Molluscs occurred from the Machigar Formation in Schmidt Peninsula were comparable with those of the Oligocene Asagai Fauna of Japan. Consequently, the Cenozoic paleoenvironmental history of the Sea of Okhotsk area was well understood in reference to that of the Japanese Islands and Northern Pacific.