Abstract
This paper discusses relative sea-level (RSL) changes from 6,300BC to 2,000BC for the coast of Ito City, on the northeastern Izu Peninsula, central Japan. RSL along this coast was evaluated by synthesizing a depositional curve suggesting the former sea floor height and paleo-water depth obtained from drilling cores. The depositional curve was reconstructed for two cores, IT-1 (30m deep) and IT-2 (10m deep), using a total of 37AMS 14C ages. Paleo-water depth was estimated from the analyses of sedimentary facies and fossil ostracode and molluscan assemblages in cores IT-1 and IT-2. Existing core logging data (a total of 23 cores) and 14C ages obtained in Ito City helped the analyses of sedimentary facies. A total of six water depth control points were obtained from these data. The reconstructed RSL curve suggests that the paleo-mean sea level rose from 〜−16m ca. 6,300BC to 〜−13m ca. 5,900BC and reached the maximum of +3〜4m ca. 4,800BC. The paleo-mean sea level positions were +1.5m around 4,600BC, +1m around 2,900BC, and 〜0 (zero) m around 2,000BC. Estimated RSL rise value between 6,300BC and 4,800BC was 10m or more, larger than that for the areas without large vertical crustal movement. This discrepancy may reflect local subsidence in the Ito area.
