福島県駒止湿原の形成過程と古環境の変遷

摘要

福島県の鞠止湿原水無谷地から得られたボーリングコアの~(14)C年代測定とテフラ分析，花粉分rn析の結果から，約4万年前以降の湿原の形成過程および古環境の変遷について考察した．この湿rn原は，スギ属，コナラ亜属，ブナ属を伴う亜寒帯性針葉樹林が分布する寒冷気候のもとで，約4万rn年前から泥炭の形成を開始した．その後，最終氷期極相期には一部の泥炭を残して削剥され，約rn1.85万年前には再び泥炭の堆積が開始された．湿原周辺では，約1.85～1.64万年前には冷涼気rn候のもとでカバノキ属と亜寒帯性針葉樹の混交林となった．約1.64～1.56万年前には温暖化にrnより冷温帯性落葉広葉樹林となったが，約1.56～1.43万年前には再びカバノキ属の森林となっrnた．この寒冷化は，北大西洋地域におけるYounger Dryas期のそれに対応する．約1.24万年前rn以降には，温暖気候のもとでブナ属やコナラ亜属を主とする冷温帯性落葉広葉樹林となり，約rn1,300年前以降にはスギ林が拡大した．%Depositional process and vegetation history from ca. 40 ka to the present were reconstructed by means of tephra, facies, and pollen analyses and radiocarbon measurement for six drilling cores in Mizunashi-yachi, Komado Mire (a.s.l. ca. 1,100 m), Fukushima Prefecture, Northeast Japan. In ca. 40 ka, the boreal coniferous forest accompanied by Cryptomeria, Quercus, and Fagus was distributed in this area, where peat was deposited and mire was formed. The peat was partly eroded during the Last Glacial Maximum period, and subsequently it began to deposit again at ca. 18.5 ka. Between ca. 18.5 ka and ca. 16.4 ka the forest dominated by Betula admixed with boreal conifers was distributed in the surroundings. Cool temperate deciduous broad-leaved forest dominated by Quercus and Fagus expanded under the microtherm climate between ca. 16.4 ka and ca. 15.6 ka, but Betula forest expanded again between ca. 15.6 ka and ca. 14.3 ka. The time period during which Betula forest expanded corresponds to the Younger Dryas cooling event in the North Atlantic region. After that, Betula forest reduced gradually and was replaced by cool temperate deciduous broad-leaved forest composed mainly of Fagus and Quercus. Since ca. 1.3 ka, Cryptomeria japonica forest has expanded.