Abstract
Plant macrofossil assemblages in the late Holocene that were obtained from the bottom of a dissected valley along the northern part of Tokyo Bay were described, and changes in the sedimentary environment of the plant macrofossil assemblages were discussed. The plant macrofossil assemblages were divided into local plant macrofossil zones I, II, and III. The plant macrofossil assemblages in the sandy layers of Zone I were deposited during the Middle J omon Age (from c. a. 4500 to 4000 y. B. P. ). The paleovegetation reconstructed from the fossil assemblages ranged throughout the upper reaches including the bottom and scarp of the dissected valley. Arboreal members in the fossil assemblage consisted of deciduous broad-leaf trees including Quercus serrata and Alnus japonica, but no evergreen broad-leaf trees. The plant macrofossil assemblages in Zone II were deposited after c. a. 4000 years BP. and were found in the herbaceous peat made from the emergent plants that flourished in the bottom of the dissected valley. Fossils of herbs, Alnus japonica, and Wisteria floribunda were autochthonous, but the other arboreal fossils were transported by birds from the slopes of the dissected valley. The assemblages in the gley soil of Zone III were characterized by the dominance of weeds that now occur in paddy fields. The rare occurrence of Cyclobalanopsis and Cryptomeria macrofossils including woods around the northern part of Tokyo Bay indicated that their distribution was restricted in the Jomon Age.
