北海道能取湖付近の上部中新統呼人層の放散虫・珪藻化石層序  [in Japanese] Radiolarian and diatom biostratigraphy of the Upper Miocene Yobito Formation near Lake Notoro, Hokkaido, Japan  [in Japanese]

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Abstract

<p>能取湖北部に分布する呼人層から抽出した放散虫化石と珪藻化石に基づいて,湖口の東西(西ルートと東ルート)の対比を行った.両化石データを総合すると,西ルートと東ルートの呼人層の年代は,それぞれ11.4~6.5Maと7.0~3.5Maと見積もられた.これは,西ルートの珪藻質堆積物の上部の大部分は層序的に東ルートの硬質泥岩相(能取層)に相当すること,また,西ルートの珪藻質堆積物の下部は能取岬の網走層の火山岩類に相当することを示している.このうち呼人層と能取層の同時異相関係は,シリカの相転移を伴う続成過程の地域差を反映していると考えられる.また,珪藻データは,呼人層中部の砂岩層の層準に不整合が存在することを示している.不整合層準よりも上位の地層から放散虫および珪藻の誘導化石と硬質泥岩礫が産出することを考慮すると,10Ma頃を境に後背地が侵食域へ転じたことが推定される.</p>

<p>Radiolarian and diatom fossils recovered from diatomaceous sediments of the Yobito Formation in the northern region of Lake Notoro, eastern Hokkaido, enable the correlation of two stratigraphic sections, the West and East sections. Integrated radiolarian and diatom data suggest ages of 11.4-6.5 and 7.0-3.5 Ma for the West and East sections, respectively. This finding indicates that the diatomaceous sequence of the West Section is stratigraphically equivalent to the siliceous hard mudstone facies (Notoro Formation) and pyroclastic rocks (Abashiri Formation) that underlie the Yobito Formation of the East Section. This facies correlation between the Yobito and Notoro Formations probably reflects regional differences in the diagenetic history associated with silica phase transformations. Diatom data also reveal an unconformity within a sandstone layer in the diatomaceous sequence of the Yobito Formation of the West Section. This unconformity is represented by the absence of Neogene North Pacific Diatom zones (NPD) 5D and 6A. The occurrence in the interval above the unconformity of reworked radiolarian and diatom specimens of older (Miocene) age and gravel clasts of indurated mudstone suggest that the hinterland became exposed to an erosive environment at ~10 Ma.</p>

Journal

  • The Journal of the Geological Society of Japan

    The Journal of the Geological Society of Japan 124(7), 517-532, 2018

    The Geological Society of Japan

Codes

  • NII Article ID (NAID)
    130007436857
  • NII NACSIS-CAT ID (NCID)
    AN00141768
  • Text Lang
    JPN
  • ISSN
    0016-7630
  • NDL Article ID
    029191736
  • NDL Call No.
    Z15-174
  • Data Source
    NDL  J-STAGE 
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