Late Cenozoic paleoenvironments in the Sea of Okhotsk area

为了重建鄂霍次克海地区晚新生代的古环境史，从古生物学和地质学的角度对库页岛马卡罗夫半岛和施密特半岛两个剖面进行了考察。1995年在马卡罗夫地区和1996年在施密特半岛分别采集了500多个地点的生物和年代地层分析样本，以详细的柱状剖面（1:10 00比例尺）为基础。古生物学研究，如硅藻、底栖有孔虫、软体动物、花粉、鞭毛藻等，与沉积学研究（相分析、重矿物和地球化学分析）相结合。建立了研究区渐新世—上新世岩石地层学和生物地层学。根据鞭毛藻和花粉生物地层学，首次发现马卡罗夫地区Chefov组与Verkhne Due组之间存在较大的年代学差距。切夫夫组玄武岩的Ar-Ar测年（22 ~ 23 Ma）可能反映了鄂霍次克海的初始裂陷阶段。根据底栖生物化石和花粉，在Makarov地区的Verkhne Due组和Shmidt半岛的Pili组中发现了第一个中新近纪气候最适层。在Maruyama组（Makarov地区）和Pili组（Schmidt半岛）分别发现了Denticulopsis hyalina带。施密特半岛Machigar组的软体动物与日本渐新世浅井动物群的软体动物具有可比性。因此，参照日本列岛和北太平洋的古环境史，可以很好地了解鄂霍次克海地区新生代的古环境史。

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.