제4기 후기 동해 한국대지에서 얻어진 주상시료에 대한 연대학

Abstract

The East Sea (Sea of Japan) is connected with the neighboring seas through the four straits characterized by shallow water depth, causing the distinct environmental variation contrasted between interglacial and glacial conditions. During the glacial period, the topographic restriction by eustatic sea-level lowering results in a lake-type oceanographic setting where the dark laminated mud (DLM) layer formed and the negative shift of planktonic foraminiferal 18O values occurred. These paleoceanographic features widely obtained as the inter-basinal scale also indicate the usefulness of chronological criteria. The great thickness of the late Quaternary sediments in the Ulleung Basin, characterized by dominant mass-flow deposits and lack of hemipelagic deposition, limits the temporal span of paleoceanographic reconstruction. A 11-m long piston-core sediments collected from the topographic-high Korea Plateau (about 1400 m deep) have been analyzed through a variety of approaches for the reconstruction of late Quaternary chronology. Normal 14C age dates, identification of tephra layer, oxygen isotope stratigraphy, and the correlation of DLM were applied to obtain the precise chronostratigraphy. Four distinct DLM layers were well preserved to show the consistent geochemical characteristics. Two 14C age dates and AT tephra layer signify the clear identification of first DLM during the last glacial period. In addition, the other DLM layers reflect the same condition for the formation, corresponding to the glacial stages. The planktonic foraminiferal 18O values also confirm the negative excursion during the stage 6. Thus, these core sediments are likely preserve more-than 250-ky paleoclimatic history in the East Sea (Sea of Japan).