北海道幌延地域における深部地球化学環境の長期変遷シナリオの構築 Scenario Development of Long-term Evolution for Deep Hvdrochemical Conditions in Horonobe Area, Hokkaido, Japan

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著者

    • 岩月 輝希 IWATSUKI Teruki
    • 日本原子力研究開発機構幌延深地層研究センター Horonobe Underground Research Center, Japan Atomic Energy Agency
    • 石井 英一 ISHII Eiichi
    • 日本原子力研究開発機構幌延深地層研究センター Horonobe Underground Research Center, Japan Atomic Energy Agency
    • 新里 忠史 NIIZATO Tadafumi
    • 日本原子力研究開発機構幌延深地層研究センター Horonobe Underground Research Center, Japan Atomic Energy Agency

抄録

 A methodology to estimate long-term hydrochemical evolution of deep underground is indispensable for the safe geological isolation of high-level radioactive waste (HLW). This study demonstrates the methodology by illustrating scenarios of past geological events, processes, and their interrelationships with present-day hydrochemical conditions. Besides, we infer long-term variations of groundwater chemistry at Horonobe, Hokkaido, Japan.<br> The region is underlain mainly by Neogene to Quaternary marine sedimentary rocks, (the Wakkanai Formation (Fm) and the overlying Koetoi Fm: siliceous and diatomaceous mudstones). During various events in the geological past, such as deposition, compaction, uplift, and denudation, and the more recent Neotectonic activities in this area, highly permeable hydrogeological structures formed at depths not over than 400m below ground level in the Wakkanai Fm. The hydrogeological system can be subdivided into three hydrogeological sub-systems: (1) overlying, relatively low permeability Koetoi Fm., (2) highly permeable, upper Wakkanai Fm at depths less than 400m and (3) relatively low permeability Wakkanai Fm, at depths greater than 400m. The present-day hydrochemical conditions in each sub-system have been influenced by hydrogeological properties and hydraulic conditions over a long period. In subsystems 1 and 2, recharging with meteoric water flushed connate seawater during uplifting and denudation during the last 1Ma. In contrast, fossil seawater with one-third to one-half the salinity of present-day seawater has been preserved in subsystem 3.<br> The relatively low permeability sequence in sub-system 3 was formed by the compaction of diatomaceous mudstone during subsidence prior to 1.0Ma. After that, changes of climatic conditions and geographical features would not have influenced groundwater flow. The groundwater chemistry evolved from seawater during long-term geochemical diagenesis in a relatively closed system. The long-term variations of salinity probably range from that of seawater to that of present-day groundwater. The occurrence of secondary minerals shows that the buffer reactions of carbonate and sulphide minerals have preserved the near neutral pH and reducing condition since initial diagenesis immediately after deposition of the rock formation.

収録刊行物

  • 地學雜誌

    地學雜誌 118(4), 700-716, 2009-08-25

    公益社団法人 東京地学協会

参考文献:  66件中 1-66件 を表示

被引用文献:  4件中 1-4件 を表示

各種コード

  • NII論文ID(NAID)
    10030366159
  • NII書誌ID(NCID)
    AN00322536
  • 本文言語コード
    JPN
  • 資料種別
    ART
  • ISSN
    0022135X
  • NDL 記事登録ID
    10415096
  • NDL 雑誌分類
    ZM41(科学技術--地球科学)
  • NDL 請求記号
    Z15-169
  • データ提供元
    CJP書誌  CJP引用  NDL  J-STAGE 
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