第四紀研究
Online ISSN : 1881-8129
Print ISSN : 0418-2642
ISSN-L : 0418-2642
11 巻 , 2 号
選択された号の論文の2件中1~2を表示しています
  • 正岡 栄治
    1972 年 11 巻 2 号 p. 61-69
    発行日: 1972/08/30
    公開日: 2009/08/21
    ジャーナル フリー
    The sequence of heavy-mineral association of tephras in the subsurface Holocene and upper Pleistocene deposits of the Lakes Naka-umi and Shinji-ko was clarified, and its stratigraphic correlation with those of the terrestrial volcanic ejects from Mts. Sanbe and Daisen is discussed.
    The sequence is represented by six horizons of tephra, namely N1 in the middle-upper part of Holocene Naka-umi formation, Du of the Daisen upper pyroclastics, Yg2 in the upper part of upper Pleistocene Yasugi formation, Yg1 in the middle-lower part of the Yasugi, and Ym2 and Ym1 which are kept in the upper and middle part of upper Pleistocene Yumigahama formation respectively, in descending order.
    Through the whole horizons, hornblende, hypersthene and Fe-minerals are the representatives of heavy-minerals, and they are associated with a small amount of augite, oxy-hornblende, zircon and so on.
    The quantity of mica and total heavy-minerals differs clearly in each horizon, and they play an important role in discrimination of tephras.
    The heavy-mineral composition of the certain terrestrial tephras from the Mts. Daisen and Sanbe are very similar to and correlated with some horizons of subsurface tephras in the lakes.
  • 野上 道男
    1972 年 11 巻 2 号 p. 71-80
    発行日: 1972/08/30
    公開日: 2009/08/21
    ジャーナル フリー
    It is the purpose of this paper to infer the atomospheric circulation pattern in the Andes Mountains during the last glacial period, Wisconsin, from the former snow line, on the basis of relationship of the present snow line to the present circulation pattern. The former snow line was reconstructed from the altitude of lowest cirque bottoms. Data were obtained from my own field observations, map interpretations and literatures of some authors. Hights of snow line are shown as distribution map in Fig. 1 and as generalized meridional section in Fig. 2.
    The curve of present snow line (PSL) takes a maximum value in the center of the subtropical high pressure belt. No difference is apparent in the position of the maximum point between PSL and Wisconsin snow line (WSL). PSL drops abruptly from the maximum point to lat. 40°S, and gently from there to the south pole. This break point in the snow line gradient coincides with the northern limit of the rainy zone where we have much precipitation by westerlies throughout the year. It did not move either. And WSL appears to be somewhat in parallel with PSL for the most part of the Andes Mountains.
    From the facts described above, it can be concluded that the atomospheric circulation pattern during the Wisconsin glacial period was much the same as the present pattern, and that the Wisconsin snow line depression in the Andean sector was not caused by increasing of precipitation, which would be resulted from climatic zone shift, but mostly by cooling of atomosphere. It. may be considered that the distinctive shift of climatic zones in the Northern Hemisphere was a secondary phenomena caused by enormous expansion of continental ice sheets in the glacial period.
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