三重県鈴鹿川流域の段丘構成層の層序・編年 -火山灰稀産地域での段丘編年の試み- Fluvial Terrace Deposits along the Suzuka River, Mie Prefecture, Central Japan : Chronology of Terraces Rarely Intercalted with Volcanic Ach

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西日本の四国・近畿・東海地方などの火山灰稀産地域の段丘では,火山灰層の発見は稀で,しかもそれを連続的に追跡することが困難である.そのため,火山灰に注目した層序・編年学的研究は露頭あるいは狭い地域に限定されたものとならざるを得ず,一般的な調査・研究法とはなっていない.このため,火山灰稀産地域における段丘の層序・編年は,火山灰多産地域に比べ精度が悪い.三重県鈴鹿川流域の段丘もまた,このような火山灰稀産地域に属している.そこで,筆者らは従来の地形・地質学的方法に加え,段丘構成層の上位に発達する細粒堆積物に注目して,この堆積物中に極微量に含まれる火山ガラスから火山灰降下の痕跡を見いだした.そして,これらから段丘の層序を検討し,編年を行った.本研究の結果,次のことが明らかとなった.(1)調査地域の段丘面(段丘構成層)は,高位のものから大谷池面(大谷池段丘層)・丸岡池面(丸岡池段丘層)・神戸面(神戸段丘層)・関面(関段丘層)・古廐面(古廐段丘層)に区分され,さらに神戸面および関面は,高位のものから神戸1面・神戸2面・神戸3面,関1面・関2面に細分できる.(2)各段丘構成層の上位にのる細粒堆積物の層相とそれらに含まれる火山ガラスの性質・含有量の特徴,関段丘層に挾まれる姶良Tn火山灰層(25~21ka),神戸段丘層中の海成粘土層などから,大谷池段丘層・丸岡池段丘層は最終間氷期以前に,神戸段丘層は最終間氷期に,関段丘層は最終氷期に,古廐段丘層は最終氷期以降にそれぞれ形成されたと考えられる.<br>今回行った段丘構成層の上位にのる細粒堆積物に極微量に含まれる火山ガラスを用いた層序・編年の試みは,今後,火山灰稀産地域でのより広域な段丘の対比・編年の可能性を示唆する.

In the distal areas from Quaternary volcanoes, like the Shikoku, Kinki and Tokai districts of western Japan, studies on terraces have not progressed due to lack of visible volcanic ash. Those studied were mainly approached from the geomorphological point of view, and therefore it is difficult to determine absolute ages and correlations between terraces. In the Suzuka river area, which is located in the west coast area of Ise Bay, there are no reports on terrace deposits with intercalated volcanic ash layers or on the absolute age of terraces.<br>In this study, we took a comprehensive approach, integrating aerial-photo interpretation, investigation on the geology and geomorphic features, and analysis of volcanic glasses which are included in finer deposits overlying the terrace gravels. (Finer deposits here means those mainly consist of eolian deposits and formed after terracing.) The following results were obtained.<br>1. The terraces of the Suzuka river area are classified into five, namely, Otani-ike terrace, Maruoka-ike terrace, Kambe terrace, Seki terrace, and Furu-umaya terrace in descending order of elevation. Kambe terrace is further subdivided into three terraces named Kambe 1, Kambe 2, and Kambe 3. Seki terrace is also subdivided, into Seki 1 and Seki 2.<br>2. Finer deposits overlying terrace gravels can be characterized by their color. At Otani-ike terrace and Maruoka-ike terrace, finer deposits are subdivided into reddish brown, yellowish brown, and dark brown units in ascending order. And at Kambe terrace, finer deposits are subdivided into yellowish brown and dark brown units in ascending order. At both Seki terrace and Furu-umaya terrace, all finer deposits show dark brown to black color.<br>3. At Otani-ike terrace and Maruoka-ike terrace, reddish brown units contain few volcanic glass. The yellowish brown units in Otani-ike terrace, Maruoka-ike terrace, and Kambe terrace include volcanic glasses that can be correlated with Aira-Tn volcanic ash (25-21ka). The blackish units in Otani-ike terrace, Maruoka-ike terrace, Kambe terrace, Seki terrace, and Furu-umaya terrace contain volcanic glasses which derived from Kikai-Akahoya volcanic ash (6.3ka).<br>4. In Seki terrace deposit, one tephra layer was identified with Aira-Tn volcanic ash. A previous study reported intercalation of marine clay in the Kambe terrace deposit. Together with the characteristics of volcanic glasses included in finer deposits, it is clear that Otani-ike and Maruoka-ike terrace deposits were formed before the Last Interglacial, Kambe terrace deposit during the Last Interglacial, Seki terrace deposit during the Last Glacial, and Furu-umaya terrace deposit after the Last Glacial.

収録刊行物

  • 第四紀研究  

    第四紀研究 36(4), 263-276, 1997-10-31 

    Japan Association for Quaternary Research

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各種コード

  • NII論文ID(NAID)
    10002509430
  • 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
    4332864
  • 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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