関東平野東端の太平洋岸に分布する銚子層群・那珂湊層群・大洗層の地質学的位置づけ(<特集>関東平野下に伏在する東西日本の境界-地表および地下地質からのアプローチ-) Geologic setting of the Choshi and Nakaminato Groups and Oarai Formation exposed along the Pacific coast in the eastern end of the Kanto Plain(<Special Issue>Geotectonic boundary between Northeast and Southwest Japan concealed beneath the Kanto Plain-integrated approach of surface and subsurface geology-)

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著者

    • 安藤 寿男 Ando Hisao
    • 茨城大学理学部地球生命環境科学科 Department of Environmental Sciences, Faculty of Science, Ibaraki University

抄録

関東平野東端には下部白亜系銚子層群, 最上部白亜系那珂湊層群, 古第三系大洗層が孤立して分布し, 東北日本, 西南日本の地帯構造を考える上で重要な情報をもたらす.3つの地層群の研究の現状をまとめた上で, それらの地質学的意義を考察した.東北日本の蝦夷堆積盆の北上および常磐亜堆積盆における上部アプチアン以上の白亜系〜古第三系には, 時代・層序・堆積相の上で3地層群に比較可能な地層は見られない.銚子層群は層序分布から関東山地北部の西南日本外帯秩父帯の山中白亜系の東方延長と見なされる.那珂湊層群は西南日本内帯南縁の和泉層群との共通性が高い.大洗層は礫の放射年代, 植物化石などから白亜系ではなく古第三系の可能性が高い.那珂湊層群と大洗層は棚倉構造線の南方延長の破砕帯に含まれた古期岩類の断層隆起地塊をなしており, 西南日本の要素と見なされる.大洗層は, 関東山地北部の寄居層および神農原層とに対比できる可能性がある.

The Lower Cretaceous Choshi Group, Upper Cretaceous Nakaminato Group and Paleogene Oarai Formation show isolated distribution in the eastern end of the Kanto Plain along the Pacific coast, central Japan. The current status of their geological studies and significance are reviewed, because they are important for reconstructing the tectonic relation between Northeast Japan and Southwest Japan. On the basis of age, stratigraphy and depositional facies, there are no correlative strata with the above in the Cretaceous-Paleocene Yezo forearc basin sediments of Northeast Japan. Despite the difference in facies, the Barremian to Upper Aptian Choshi Group seems to be an eastern extension correlative with the Sanchu Group of the Chichibu Belt in the northern Kanto Mountains, Southwest Japan. The Upper Campanian to Lower Maastrichtian Nakaminato Group has some characteristics common to the Izumi Group along the southern part of the Inner Zone of Southwest Japan. It forms a fault-bounded basement-uplifting block associated with the Oarai Formation and Miocene sediments within the southern extension of the Tanakura Tectonic Zone. The Oarai Formation is thought to be Paleogene in age based on isotopic age of gravel, plant fossils and geologic setting. It may be correlative with the Yorii and Kanohara Formations in the northern Kanto Mountains, judging from lithofacies and tectonic setting.

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参考文献:  95件

被引用文献:  3件

各種コード

  • NII論文ID(NAID)
    110004027155
  • NII書誌ID(NCID)
    AN00141768
  • 本文言語コード
    JPN
  • 資料種別
    ART
  • ISSN
    00167630
  • NDL 記事登録ID
    7823372
  • NDL 雑誌分類
    ZM49(科学技術--地球科学--地質)
  • NDL 請求記号
    Z15-174
  • データ提供元
    CJP書誌  CJP引用  NDL  NII-ELS  J-STAGE 
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