Middle Pleistocene Pollen Assemblages and their Implications for the Yabu Formation, Boso Peninsula, Central Japan.

Palynological results from the lower part of the Sakata section (35°20′42″N, 139°53′02″E; 20m a. s. l.), belonging to the Yabu Formation (Marine Isotope Stages 9-8) of the Pleistocene Shimosa Group, show good agreements with sedimentological facies changes. A muddy lagoonal unit provides well-diversified pollen assemblages with abundant conifers and consistently high pollen concentrations. By contrast, a sandy shoreface unit provides possibly exotic assemblages with low pollen concentrations and poor floral diversity. The dominant taxon in the lagoonal unit is Picea (spruce) associated with Abies, Pinus, Tsuga, Betula, Fagus, Cupressaceae, etc. The corresponding abundance of Alnus and herbs (mainly Artemisia) indicates the vicinity of the coast. Therefore, the coniferous assemblages do not consist of exotic pollen transported over long distances, but indicate the spread of boreal conifer forest in the Boso Peninsula during cold stages near the end of Stage 9 or Stage 8. This is equivalent to Picea-dominated subarctic to cool-temperate conifer forest reconstructed for the Stage 4 glacial in the Sagami region, Kanagawa Prefecture.