Late Pleistocene Climatic Changes in Central Japan
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概要
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The purpose of this work is to make clear the Late Pleistocene climatic changes in Central Japan. For this purpose the author tried to correlate nearshore sediments in the Nobi coastal plain with fluviatile sediments in the inland area by means of tephrochronology and rock magnetism. In the studied area, pumice and scoria beds erupted from Ontake Volcano are widely distributed being intercalated with peat beds and other sediments. These volcanic products were precisely examined with the features of field occurrence, mafic mineral composition and thermomagnetic property (J-T curve), and were classified into twelve pumice and two scoria beds. Then the stratigraphical relations among the Late Pleistocene sediments in Central Japan were made clear by these pumice and scoria beds, good marker beds (Fig. 4). Samples which have been stratigraphically confirmed were analysed palynologically and paleobotanically. Pollen diagram of each locality was classified into pollen zones based on characteristic and dominant taxa. The Late Pleistocene climatic changes in Central Japan were considered based on the vegetational feature of pollen zones. Plant remains were also very usefel in considering the vegetational features represented by the pollen zones. Lastly the Late Pleistocene time in Japan was subdivided into the following four periods based on climatic changes and carbon-14 dates. (1) Latest interglacial : R/W Interglacial (before than 65000 to 70000 yr B. P.) This period is characterized by the dominance of Cryptomeria and deciduous broad-leaved trees, including Fagus. The climate is estimated to have been warmer and wetter than that of the present. (2) Early Wurm Glacial (from 65000 to 55000 yr B. P.) Two interstadials are inferred by the dominance of Cryptomeria, Sciadopitys, Ulmus-Zelkova and Corylus during early half of this period. The later half of this period is characterized by the subarctic forest which is estimated to have been 5℃ to 6℃ lower than the present in average annual temperature. (3) Middle Wurm Glacial (from 55000 to 25000 yr B, P.) Cool climate prevailed throughout this period, intervening a remarkable warm climate which reached a maximum at about 37000 years ago. In the Nobi coastal plain, the Atusta Surface was formed by the transgression during the warm climate. (4) Late Wurm glacial (from 25000 to 10000 yr B. P.) This period is dominated by subarctic forest. Periglacial agency acted at the place higher than 1000 m above sea-level in the Kiso Valley during the early half of this period.
- 信州大学理学部の論文
- 1981-09-30
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