重鉱物組成からみた中海・宍道湖湖底下の第四紀火山灰
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概要
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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.
- 日本第四紀学会の論文