Studies on widespread tephras associated with Quaternary volcanism, sealevel fluctuations and climatic history in Japan

点击翻译按钮获取中文摘要

1 In this research project eleven major volcanic ashes of the Late Quaternary age are reported in and around Japan. All of them are characterized and identified by petographic and stratigraphical methods. They are of great significance in volcanology as well as Quaternary research. The widespread vitric fine-grained ashes which originated from gigantic caldera volcanoes are all interpreted as coignimbrite ash falls. This type of tephra should be the dominant class of widespread tephra.2 Chemical composition of volcanic glass shards analysed by EPMA proved to be a powerful tool in characterization and identification of submarine volcanic ashes around the Japanese islands.3 The ages of four marker tephras occurring in central Honshu are estimated by the <^(230)Th> / <^(238)U> method based on the <^(230)Th> - <^(238)U> radioactive disequilibrium observed in the mafic minerals of the tephras.4 Determinations of marker tephras in northern Japan and southern Kyushu are favorable for correlation and identification of marine terraces of the last interglacial age, resulting in revision of the chronological framework and recognition of the tectonic nature of these regions.5 Vertical changes in oxygen isotope values of the planktonic and benthic foraminiferal tests of the two tephrochronologically dated cores from the northwestern Pacific are reported, resulting in establishment of the standard sequence of deepsea sediment chronology around Japan.