Diatom species were classified as environmental indicators based on the species groups of benthic diatoms presented by KOSUGI (1987) and on planktonic diatoms from Tokyo Bay and Uraga Channel. All data on diatom ecology were obtained from living cells discriminated by the staining method (KOSUGI, 1985). The species groups identified by KOSUGI (1987) were classified on the basis of similarities in adaptation to both salinity and substratum factors, so it can be said that they were classified from the biological viewpoint. In order to obtain indicators applicable to reconstruct paleoenvironments, it is necessary to clarify the relationship between the species groups and real environments. From this point of view, the environments specified by the salinity and substratum of each species group was examined. The diatom environmental indicators were classified as follows; A: Indicators of an outerbay B: Indicators of an innerbay C1: Indicators of an aquatic plant vegetation in saline water C2: Indicators of an aquatic plant vegetation in brackish water D1: Indicators of a sand flat in saline water D2: Indicators of a sand flat in brackish water E1: Indicators of a mud flat in saline water E2: Indicators of a mud flat in brackish water F: Benthic diatoms in fresh water G: Planktonic diatoms in fresh water H: Indicators of a river mouth As an example of application to paleoenvironmental reconstruction, the Holocene fossil datom assemblages from the lower reach of the Murata River, Chiba prefecture, were analyzed using diatom environmental indicators. As a result, most fossil diatoms could be classified on the basis of each environmental indicator. And their vertical changes in fossil assemblages could be related to successive changes of paleoenvironments in the Murata River region. It is an important part of this application that the paleoecological analysis using those indicators has the ability to reconstruct environments and their changes clearly. The main reason is that the indicators have been classified based on the data from living diatoms only, and that the relationships between them and both salinity and substratum as environmental factors have been clarified by the gradient analyses.
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.