日本海と象 (日本海沿岸の更新世の古地理と古環境特集号)

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This is a summary of the presidential address to the public at the 19th annual meeting of the Japanese Association for Quaternary Research, held at Tottori August 18-20, 1989. The address had two parts: one was an introduction to the concept of "Quaternary" and the significance of Quaternary research, and the other was an elucidation of the discussion at the symposium on "Paleogeography and Paleoenvironments around the coastal areas of the Japan Sea", exemplified by elephant fossils from the sea-bottom of the southern Japan Sea. The pioneers of Quaternary research in Japan, the German geologists E. NAUMANN and D. BRAUNS, were very interested in the elephant fossils of Japan and published papers on them in 1881 and 1883, respectively. Since that time, the study of elephant fossils and Quaternary research in Japan have been closely related.Since about 20 years ago, several elephant tusks and molars have been dredged by dragnet fisheries off the San'in district and also off the Noto peninsula in the southern Japan Sea. They were obtained from depths of 120m to 400m, on either the continental shelf or on the drowned bank of the sea-bottom. Formerly, those materials were considered to verify the presence of a landbridge in the past around the area of the Tsushima strait between Korea and Kyushu, but now this idea has come to be rejected. The results of analysis for the boring cores drilled at several places on the bottom of Japan Sea afford much information about paleoenvironmental changes during the Late Pleistocene. For example, an inflow of the Tsushima warm current to the Japan Sea, which is one of the remarkable tributaries of the Kuroshio, was reduced or arrested at that time by mixing with fresh water from the Hwang Ho River running through North China. This created a stagnant condition in the bottom water of the Japan Sea, and much influenced the biotic community there. Again, the inflow of the Tsushima warm current to the Japan Sea was regenerated beginning about 6, 500 y. B. P.The elephant fossils on the sea-bottom consist of tusks and molars of Naumann's elephant Palaeoloxodon naumanni and a molar tooth of woolly mammoth Mammuthus primigenius. The radiocarbon dating carried out for these and others found on land showed that the former was older than 30, 000 y. B. P. and the latter was younger, around 20, 000 y. B. P. It is known that during the maximal cold phase in the Last Glacial, woolly mammoths came down from Siberia southward to Hokkaido, but did not cross over the Tsugaru strait to Honshu. Therefore, it is reasonable to assume that the remains of woolly mammoths would be transported by drifting from the Hwang Ho area to that off San'in and then sink to the bottom of the Japan Sea. However, the idea is still a matter of imagination, more investigation for the environmental changes during the Quaternary in Japan needs to be done.
日本第四紀学会の論文

日本海と象 (日本海沿岸の更新世の古地理と古環境特集号)

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