千葉県房総半島南端に分布する完新統沼層における鬼界-アカホヤテフラの降灰層準 : 生物攪拌作用の観点からのアプローチ  [in Japanese] Stratigraphic position for the Kikai-Akahoya tephra in the Holocene Numa Formation, southernmost part of the Boso Peninsula, Chiba, Japan : An approach from the viewpoint of biogenic sediment mixing process  [in Japanese]

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Abstract

千葉県房総半島南端地域に分布する完新統沼層において,露頭では視覚的に存在が全く確認できない鬼界-アカホヤテフラを研究対象とし,それ起源の火山ガラスの層位分布を明らかにするとともに,降灰層準を詳しく検討した.火山ガラスの形態的特徴と化学組成の結果は,鬼界-アカホヤテフラの火山ガラスが,津波堆積物T 3.1よりも上位の泥層中に存在することを示唆した.また,火山ガラスの存在する層準が物理営力の及ばない静穏な内湾の海底で堆積したこと,堆積場周辺の陸域面積が現在のそれよりもはるかに小さいことを重視し,海底に降灰・堆積した後の火山ガラスの挙動を支配するとともに,最終的な層位分布に最大の影響を及ぼした営力は生物攪拌であったと判断した.そして,生物攪拌による火山ガラスの拡散メカニズムを考慮し,鬼界-アカホヤテフラの降灰層準は津波堆積物T 3.1の約15 cm上位付近の層準に位置するものと推定した.<br>

Stratigraphic position of the Kikai-Akahoya (K-Ah) tephra in the Holocene Numa Formation distributed in the southernmost part of the Boso Peninsula, Chiba, Japan was mainly examined from the viewpoint of bioturbation. The K-Ah tephra in muddy sediments of the Numa is not recognizable as a visible geologic record due to complete dispersion of volcanic glasses induced by the intense biogenic sediment mixing after the deposition. A muddy sediment interval, which is cropped out along the Tomoe-gawa River, Tateyama City was selected for this study.<br> Petrographic and petrologic data on volcanic glasses in the muddy sediments show that the volcanic glasses of the K-Ah origin were found in mud interval above the Tsunami deposit T 3.1. Sedimentologic, paleontologic, and paleogeographic data indicate that biogenic sediment mixing process seems to represent the most important factor for controlling the diffusion mechanism and the final distribution pattern of volcanic glasses in the sediments. Stratigraphic distribution pattern of volcanic glasses of the K-Ah origin and mixing process strongly suggest that the initial stratigraphic position of the K-Ah in the Numa presents the restricted interval about 15 cm above the T 3.1 bed.<br>

Journal

  • The Journal of the Geological Society of Japan

    The Journal of the Geological Society of Japan 112(3), 210-221, 2006-03-15

    The Geological Society of Japan

References:  77

Cited by:  1

Codes

  • NII Article ID (NAID)
    110004705316
  • NII NACSIS-CAT ID (NCID)
    AN00141768
  • Text Lang
    JPN
  • Article Type
    Journal Article
  • ISSN
    00167630
  • NDL Article ID
    7903691
  • NDL Source Classification
    ZM49(科学技術--地球科学--地質)
  • NDL Call No.
    Z15-174
  • Data Source
    CJP  CJPref  NDL  NII-ELS  J-STAGE 
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