四国南西部,松田川流域における九重第一テフラとの対比と低位段丘の年代  [in Japanese] Identification of the Kuju-Daiichi Tephra Layer, and the Age of the Late Pleistocene Fluvial Terrace along the Matsuda River in Southwestern Shikoku, Japan  [in Japanese]

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Abstract

本稿では四国南西部,松田川流域で見いだされた小川テフラ(新称)を記載し,本テフラと中部九州・九重火山から噴出した九重第一テフラとの対比を試みた.小川テフラは層厚20~40cm,中~細粒砂サイズの結晶質降下軽石層で,その鉱物組成は多量の普通角閃石と少量の斜方輝石・黒雲母・石英・磁鉄鉱からなる.小川テフラの層位は,鬼界アカホヤテフラ・姶良Tnテフラの下位に位置する.鉱物組成・重鉱物比・含有鉱物の屈折率の一致から,小川テフラは九重第一テフラに対比できる.また,広域テフラとの層位から推定した小川テフラの降下年代は,70~80kaに降下した九重第一テフラの年代と矛盾しない.<br>小川テフラとの層位関係をもとに,松田川中~下流に分布する低位段丘構成層が,70~80ka前後に堆積したと推定された.

We carried out the first identification of the Kuju-Daiichi tephra from central Kyushu in the lower reach of Matsuda River in southwest Shikoku. The tephra in the study area, named locally the Ogawa tephra, is 20 to 40cm thick, a fine- to medium-sand size pumice fall layer. The phenocrysts consist of hornblende, orthopyroxene, biotite, magnetite, and quartz. The age of the Ogawa tephra is estimated to be older than 50ka in Late Pleistocene based on its stratigraphic position among other widespread tephras of known ages. In terms of the similarities of mineral composition, refractive indices of hornblende and orthopyroxene, and age of both tephras, the Ogawa tephra is identified with the Kuju-Daiichi tephra that erupted 70 to 80ka.<br>The fill-top Late Pleistocene terrace developed extensively along the lower to middle reach of the Matsuda River. The Ogawa tephra is interbedded with the terrace deposit at Kamiari along the main stream of Matsuda River, suggesting that the terrace gravels were deposited around 70-80ka, when the regression occurred.

Journal

  • The Quaternary Research (Daiyonki-Kenkyu)

    The Quaternary Research (Daiyonki-Kenkyu) 41(3), 213-219, 2002-06-01

    Japan Association for Quaternary Research

References:  15

Cited by:  3

Codes

  • NII Article ID (NAID)
    10008632011
  • NII NACSIS-CAT ID (NCID)
    AN0034136X
  • Text Lang
    JPN
  • Article Type
    Journal Article
  • ISSN
    04182642
  • NDL Article ID
    6178710
  • NDL Source Classification
    ZM49(科学技術--地球科学--地質)
  • NDL Call No.
    Z15-67
  • Data Source
    CJP  CJPref  NDL  J-STAGE 
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