Holocene environmental history in and around the paleo-Nagareyama Bay, central Kanto Plain

Abstract

The continuing history of paleoenvironments in the Holocene was investigated in a small valley, the Sakagawa lowland (Paleo-Nagareyama Bay), situated in Nagareyama City, north of Tokyo. In this area, the seawater of the Jomon transgression invaded the valley, which had been deeply dissected during the last glaciation. 14C dating, tephra identification, grain component analysis, diatom analysis, and pollen analysis showed that the sediments recorded some important evidence of paleogeographic changes, especially in sea-level and vegetation. As a result of the comparison in vertical changes among some fossil assemblages, the ages 6500, 5300, 4500, and 3500 BP were recognized as common and important boundaries in Holocene environmental history. Moreover, such ages correspond to the turning points in the relative sea-level change curve which was drawn based on 65 14C dates obtained in the central Kanto Plain. -from English summary