Late Cenozoic Stratigraphy and Paleoenvironmental Change of the Coastal Area along the Sea of Japan

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Late Cenozoic stratigraphy was examined in eight provinces along the borderland of the sea of Japan, namely northwest Hokkaido, southwest Hokkaido, Aomori, Akita-Yamagata, Niigata, Shinshu, Hokuriku and San-in provinces. Lithostratigraphic classification inclusive of biostratigraphy, tephrastratigaraphy and chronostratigraphy, was established in each province and Heagene carrelatiorl from Hokkaida to San-in were completed.According to it, more than five sheets of Neogene paleogeographical maps of each province wore drawn at intervals of about half million to a million year. Moreover, in accordance with them six sheets of Neagene paleageographical map in the borderland of the sea of Japan were drawn.Neagene marine environment in the palea-sea of Japan was studied from the viewpoint of fossil (diatom, foraminifera, radiolaria, molluscs), sedimentary and tectonic faces. Some of important results and problems are cited as follows.The study an turbidits faces of sedimentary basin during mid … More dle Middle Miocene in northeast Japan was advanced. Some models an sedimentation of coarse materials and formation of submarine fan were proposed. Focus change of siliceous sediments, its sedimentary environment and the sedimentary ratio were discussed. Organic matters (kerogen) in mudstone is available for reconstruction of sedimentary environment. Geographical and stratigraphical distributions of fossils, such as foraminifera, malluscs and marine vertebrate assemblages were examined and their changes were discussed.From the results, important marine events in the east marginal area of the sea of Japan are mentioned. During early Middle Miocene time, commencement of large transgression under tropical environment, nothing of tropical fauna and flora; During Middle Miocene commencement of upheaval of island arc, appearance of temperate assemblage, expansion and deeping of the sea of Japan, formation of deep sea environment like the recent sea of Japan; during Late Miocene time, appearance of land area, in cardillera of northeast Japan and marginal sea, establishment of temperate Pacific realm: During Mid-Pliocene time, occurrence of serious crtistal movement and southing of cool-temperate marine organisms. The relationship between the change of paleoenvironment and assemblages was made clear. Less