Plant fossil assemblage of the Last Glacial age in the northern part of Niigata Prefecture, Central Japan.

Abstract

A Late Pleistocene peat bed, the Chugenmachi peat bed, yielding abundant plant fossils, was found in the northern part of Niigata Prefecture, Central Japan. The bed unconformably overlies the Middle Pleistocene and Pliocene and is three meters thick. The 14C age of wood from the peat bed is 23, 000±350y.B.P.. The age of the peat bed indicates the later Last Glacial Age. Most palnt remains in the bed were transported from the surrounding area, as indicated by the location of the bed in a small valley and the well-preserved condition of the remains.The plant fossil assemblage consists of 7 families, 13 genera and 14 species. The result of pollen analysis indicates a consistent floral composition. The species are mainly of submontane evergreen conifers such as Picea jezoensis var. hondoensis, Pinus koraiensis and Tsuga diversifolia. They are not presently found in the fossil locality. The composition of the fossil assemblage indicates the cold climate of the Glacial Age. In addition to cold elements, the flora consist of cool-temperate conifers, such as Cryptomeria japonica and Thuja Standishii, and also of a few temperate broad-leaved trees, such as Fagus crenata, Corylus heterophylla and Styrax japonica. They indicate that the mild climatic floral elements survived at that time especially in areas bordering the Sea of Japan. Moreover, the fossil assemblage includes a few evergreen conifers which are not found in high snowfall areas, such as Abies homolepis, Picea jezoensis var. hondoensis, Tsuga diversifolia. The index species of the cool-temperate zone of the Pacific coast, such as Abies homolepis, are also commonly found.These facts are an interesting contribution to the study of paleo-climatology and the paleovegetation of the Last Glacial age of the Sea of Japan coast.