On the Postglacial Sea Level Changes in Japan

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Recently, S. Yamanouchi and T. Sato, archaeologists, have proposed an entirely new chronology of the Neolithic age of Japan. In Japan the Neolithic age divided into two times, namely the Jomon and the Yayoi. It has been estimated that the beginning of the Jomon time was older than 9000 years by C14-dating. However, Yamanouchi and Sato have concluded that the beginning of the Jomon time was not so old, but was dated in B.C. 3000's based on a typology of implements. While C14-dating is generally a useful method for the investigations of paleogeographical problems during the Holocene, it is difficult to say that all the results of this dating referred to the former Neolithic absolute chronology of Japan are reasonable, because Japan is in one of the areas observed the low concentration of C14 in the air or the sea water in the world.Now, the author re-investigated the data concerning to the movements of the sea level during the Holocene in northern Japan, which have been published in the Journal of the Faculty of Science, University of Tokyo (Sec. II, Vol. XII, Pt. 3) in 1961. Further, adding some available data to the newly achieved results, the author discussed the problems of Postglacial sea level changes in Japan. According to the former hypothesis, the sea level reached the maximum height during the early Jomon time, and afterwards the regression occurred. However, this hypothesis is not acceptable. The shell bed of a midden in the Tokyo Lowland clarifies that the transgression still continued during the late Jomon time. This cannot be only a local phenomenon.According to the curve of the sea level changes estimated by the author, the highest stage of the sea level was probably dated between B.P.4000 and B.P. 2000 in Japan, and its height was about 5m. The inmost shore-line stage along Japan coasts in the Holocene does not always correspond with the highest level stage. The Postglacial transgression occurred and the rapid rise of the sea level took place. Sea invaded into valleys formed during a sea level falling period. When a sea level came near the maximum, the velocity of rising of the sea level gradually decreased. In large drawned valleys accumulation is active. In such a valley no matter what a transgression continued, actually the progress of the shore line, namely the apparent regression occurred. However, in small valleys or in areas without rivers men could see transgression. consequently, in some places the age of the inmost shore-line stage corresponds with one of the highest level stage, but in many places both ages do not agree to each other. In such a case the former was always older than the latter. The age of the stage of Kurohama, the early Jomon time, has been dated to B.P.5100 by C14-method. If it is correct, the sea level would not have reached the maximum. yet. If the stage of the maximum sea level corresponded with the Kurohama stage, C14-dating would not be correct. In the latter case, the beginnig of the early Jomon time may be at least 1000 years later than the formerly estimated one.Judging from the above-mentioned discussion, it is clear that the former Neolithic absolute chronology of Japan is necessary to be re-investigated.
日本第四紀学会の論文

著者

阪口豊
東京大学理学部地理学教室

On the Postglacial Sea Level Changes in Japan

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