Sedimentary Environments and the Height of Relative Sea Level during the Late Holocene at Kasumi-Awara Archaelogical Site in the Toyooka Basin, Hyogo Prefecture, Japan

Abstract

We obtained sediment samples from the Kasumi-Awara archaeological site in the Toyooka Basin, Hyogo Prefecture, Japan. In order to clarify changes in sedimentary environments at this site, we analysed the diatom assemblages and carried out sulfur analysis of sediments. These were then used along with two radiocarbon dates to determine the Holocene marine limit (HML), which provides a sea-level index point approximating the height of the high water level. Although no diatoms are found in the clay sediments containing abundant shell remains between -1.68m and +0.04m altitude, sedimentary sulfur content more than 0.3% in most samples generally indicates marine influence at these horizons. Sedimentary sulfur is abundant and brackish-water diatoms are contained ≪ 10 valves per miligram of dry sediment) in clay and sand sediments between +0.04m and +0.48m, indicating marine influence in sedimentary environments. Freshwater diatoms dominate and sulfur content is less than 0.3% in the peaty clay sediments between +0.48m and +0.85m, indicating freshwater depositional conditions. Thus the height of HML is regarded to be +0.48m altitude .From the altitud eof the HML and the inferred paleo-tida lrange at this site ,the height of paleo-mean sea level at about 2150 calBP is estimated to be +0.26m altitude