北海道北部における後期更新世，広域風成塵起源粘土層の層序と分布

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タイトル別名
  • Stratigraphy and Distribution of the Late Pleistocene Clay Layers Derived from Long-range Transported Eolian Dust in Northern Hokkaido, Japan.
  • ホッカイドウ ホクブ ニ オケル コウキ コウシン セイ コウイキフウセイジン キゲン ネンドソウ ノ ソウ ジョ ト ブンプ

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The widespread eolian clay layer which covers the land surface of northern Hokkaido was investigated from the viewpoint of the long-term influence of eolian dust transported to this area during the Last Glacial age. The stratigraphy of the clay layer is composed of two formations, an upper (about 30cm thick) and a lower (about 130cm thick), which are separated by unconformity or intercalated dune sand. The estimated deposition periods of the two formations ranges from 10ka to 20ka and from 20ka to 110ka respectively on the basis of the age of the intercalated well-known tephras.<br>The mineral assemblage of the eolian clay layer is characterized by a combination of quartz, feldspar, illite, vermiculite, and smectite which is common to the mineral composition of widespread transported dust deposits in Japan and China. The analysis of the grain size of the clay minerals indicates that they are composed of two different size fraction peaks, mainly centered on a fine particle size of around 4μm and subcentered on a variety of particle sizes over 62.5μm. The high accumulation rate of stages of the long-range transported eolian dust with a value greater than 5g/cm2/kyr shows two main peaks ranging around MIS4 and MIS2 in northern Hokkaido. Our total investigation indicates that the wide-spread clay layer distributed in northern Hokkaido is strongly influenced by the deposition of long-range eolian dust during the Last Glacial age, whose accumulation rate is calculated as ranging from 14 mm/kyr to 30 mm/kyr.

収録刊行物

  • 第四紀研究

    第四紀研究 39 (3), 199-214, 2000

    日本第四紀学会

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