秋田県男鹿半島における上部更新統層序の再検討 Stratigraphic Re-examination of the Upper Pleistocene in the Oga Peninsula, Akita Prefecture, Northeast Japan

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秋田県男鹿半島の安田海岸では,海成更新統が連続露出し,上部更新統層序は安田層とその上位に不整合関係で重なる潟西層に区分されていた.しかし,火山灰層序学,含有動植物化石群集組成にもとづく検討により,安田層は安田海岸から約5km東方の模式地域における潟西層の一部で,同層の沖浜堆積相であることが判明し,安田砂部層と再定義した.安田海岸では,安田砂部層以上が潟西層を構成し,下位の鮪川層を不整合関係で覆う.ここでの潟西層には,模式地域の潟西層の離水層準より上位で,酸素同位体比ステージ5aに対比される可能性がある海成層が含まれる.また,模式地域における潟西層の最下部の部層は,洞爺火山灰との層位関係ならびに含有動植物化石群集の特徴から,安田海岸における鮪川層最上部に対比される可能性がある.それゆえ,男鹿半島において上部更新統層序を確立するためには,潟西層の下限と上限の確定に関連した上記の課題を解明する必要がある.

Middle and Upper Pleistocene deposits successively crop out at a sea cliff near Anden at the northern coast of the Oga Peninsula, Akita Prefecture, Northeast Japan. The deposits have been historically classified into the Shibikawa, Anden, and Katanishi formations in ascending order. The type localities of the Shibikawa and Anden formations are located in this sea cliff, and that of the Katanishi formation is placed in the Katanishi area, in the easternmost part of the Peninsula. The aim of this report is to stratigraphically re-examine these formations.<br>The Katanishi formation is subdivided into the following four members: the Tarusawa Sand, Kakumazaki Mud, Matsukizawa Sand and Gravel, and Honnai Sand. The Kakumazaki Mud member conformably overlies the Tarusawa Sand member, the lowermost of the formation, and interfingers with the Matsukizawa Sand and Gravel member. The Honnai Sand member lies upon the Matsukizawa Sand and Gravel member with conformity.<br>Recently, volcanic ash intercalated both in the Anden formation and in the Kakumazaki Mud member was identified as Toya ash, which erupted from the Toya Caldera, Hokkaido, and which is one of the prominent marker tephras in Japan. Consequently the Anden formation is regarded as a part of the Katanishi type formation tephrostratigraphically. Furthermore, faunal, floral, and lithological evidence shows that the Anden formation consists of offshore deposits correlatable with the Kakumazaki Mud and Matsukizawa Sand and Gravel members of the Katanishi type formation. Thus, the Anden formation is here called the Anden Sand member of the Katanishi formation.<br>The lower boundary of the Katanishi formation coincides with the basal unconformity of the Anden facies at Anden, where submarine sedimentation continues over the emergence horizon in the type area of the formation. The Tarusawa Sand member yields pollen and cold water molluscan fossils. The pollen assemblage of the member is characterized by dominance of coniferous tree pollen, which resembles that of the uppermost Shibikawa formation. These facts indicate that the definition of the upper and lower boundaries of the Katanishi formation is still questionable.

収録刊行物

  • 第四紀研究  

    第四紀研究 38(1), 29-39, 1999-02-01 

    Japan Association for Quaternary Research

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各種コード

  • NII論文ID(NAID)
    10002510954
  • 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
    4644697
  • 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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