青森県八戸市, 天狗岱のテフラ-土壌累積層の植物珪酸体群集に記録された氷期-間氷期サイクル The Glacial-Interglacial Cycle Recorded in Phytolith Assemblage of Tengutai Tephra-Soil Section near Hachinohe, Northeastern Japan

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八戸市天狗岱に位置するテフラ-土壌累積層について,最終間氷期以降の土壌層の植物珪酸体分析を行った.その植物珪酸体群集は,氷期-間氷期サイクルに対応する変動を示し,植物珪酸体分析がテフラ-土壌累積層に記録された環境変動を解読する有効な方法になることが確かめられた.最終氷期の土壌層は,イチゴツナギ亜科起源,針葉樹起源の珪酸体が優勢な寒冷な気候を示す珪酸体群集で特徴づけられた.また,最終間氷期の土壌層では,酸素同位体比ステージ(δ<sup>18</sup>O stage)5a,5b,5eに対応する珪酸体群集の明瞭な変動がとらえられた.ステージ5aの土壌層の珪酸体群集は,ササ属起源と広葉樹起源の珪酸体が優勢で,前後の時代より温暖な気候を指示した.ステージ5bの土壌層では,イチゴツナギ亜科起源と針葉樹起源の珪酸体の頻度が相対的に高く,最終間氷期内の一つの寒冷期を示した.さらに,ステージ5eの土壌層の珪酸体群集は,メダケ属起源の珪酸体が優勢であり,完新世より温暖な気候が推定された.

Phytolith analysis of soils interstratified with tephras in Tengutai section near Hachinohe, northeastern Japan, revealed a record of climate fluctuations since the Last Interglacial. The Holocene soils have phytolith assemblages in which Panicoid dominates over Festucoid, suggesting a warm climate period. In addition, they are characterized by dominant non-Bambusoideae phytoliths, suggesting the existence of a grassland composed of non-Bambusoideae taxa. Such a grassland was thought to be the result of human impact through deforestation. The Last Glacial soils have phytolith assemblages which are characterized by dominant Pooideae, suggesting a cold climate period. In soils between Hachinohe Pumice (HP) and Biscuit-1 Pumice (BP-1), corresponding to δ<sup>18</sup>O stage 2, coniferous phytoliths generally occurred with relatively high frequency, indicating that boreal coniferous forest spread throughout this region. Soils between Biscuit-1 Pumice and Kibidango Pumice (KbP), corresponding to δ<sup>18</sup>O stage 3 to 4, were characterized by relatively high frequency of Bambusoideae phytoliths. The Last Interglacial soils generally have phytolith assemblages characterized by dominant Bambusoideae phytoliths. In the lowest layers of the soils over Madara Pumice (MP), which correlates to δ<sup>18</sup>O stage 5e, Bambusoideae phytoliths from <i>Pleioblastus</i> were dominant. This assemblage indicates a warmer climate condition than the present because <i>Pleioblastus</i> is a dominant taxon in warmer climate zones than the study region. In the uppermost layers of the soils, which correlate to δ<sup>18</sup>O stage 5a, Bambusoideae phytoliths from <i>Sasa</i> were dominant, indicating a warm to cool climate condition similar to the present. The lower part of these soils, which are interbedded with Okoshi Pumice (OP), had a relatively higher frequency of a broadleaved deciduous tree phytolith such as elliptical multifaceted phytolith from <i>Magnolia</i>, suggesting the existence of a broadleaved deciduous forest. The soils interbedded with Aosuji Pumice (AP), which correlate to δ<sup>18</sup>O stage 5b, had assemblages characterized by relatively higher frequency of Pooideae phytoliths, suggesting a cold period in the Last Interglacial. The soils which correlate to δ<sup>18</sup>O stage 5d, probably with an assemblage characterized by a relatively higher frequency of Pooideae phytolith, are yet to be recognized.

収録刊行物

  • 第四紀研究  

    第四紀研究 38(5), 353-364, 1999-10-01 

    Japan Association for Quaternary Research

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各種コード

  • NII論文ID(NAID)
    10004720971
  • NII書誌ID(NCID)
    AN0034136X
  • 本文言語コード
    JPN
  • 資料種別
    ART
  • ISSN
    04182642
  • NDL 記事登録ID
    4860824
  • NDL 雑誌分類
    ZM49(科学技術--地球科学--地質)
  • NDL 請求記号
    Z15-67
  • データ提供元
    CJP書誌  CJP引用  NDL  J-STAGE 
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