A palynological study was carried out using a 25.3m long sediment core taken from the Okute basin, Mizunami city, central Japan. The sediments of this core had accumulated for a period exceeding 300, 000 years. Based on the pollen analysis results, the sediments were divided into 15 pollen assemblage zones -Zone I to XV- in an ascending order.
Zone I, III and V are pollen blank zones. Fagus crenata forests were interspersed with Cryptomeria japonica in Zone II. In Zone IV, forests were predominantly composed of Pinus subgen. Haploxylon with Betula. Cryptomeria japonica was dominant in Zone VI. In Zone VII and IX, forests were composed of cool-temperate deciduous broad-leaved trees such as Fagus crenata and Quercus subgen. Lepidobalanus. Forests of Zone VIII were predominantly composed of Cryptomeria japonica with Sciadopitys verticillata and Pinus subgen. Haploxylon. Cool-temperate pinaceous forests were maintainedin Zone X and XIII. In Zone XI and XIV, cool-temperate mixed forests were composed mainly of Quercus subgen. Lepidobalanus, Fagus crenata and pinaceous trees. Zone XII was a temperate coniferous forest stage of Sciadopitys verticillata and Cryptomeria japonica. In Zone XV, cool-temperate deciduous broad-leaved trees were dominant. Warm temperate species such as Quercus subgen. Cyclobalanopsis were recognized in Zone VIIa, XI and XVb.
These changes show a repetition of five warm and four cool stages. Each stage corresponds to marine isotope stage (MIS) 9-1, as follows: Zone II=MIS 9, Zone IV-VI=MIS 8, Zone VII-IX=MIS 7, Zone X=MIS 6, Zone XI-XII=MIS 5, Zone XIII=MIS 4, Zone XIVa=MIS 3, Zone XIVb=MIS 2 and Zone XV=MIS 1.
From the pollen frequencies of Quercus subgen. Cyclobalanopsis and Fagus crenata, the temperature of MIS 5 was suggested to be higher than those of MIS 7 and 9. The temperature of MIS 9 was not considerably high.

View full abstract