越後平野北部の沖積低地における汽水湖沼の成立過程とその変遷  [in Japanese] Formation and Environmental Changes of a Holocene Brackish Lake in the Northern Echigo Plain, Central Japan  [in Japanese]

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Abstract

越後平野北部における沖積層層序と堆積環境の変遷を解析し,縄文海進期に形成された汽水湖沼の成立過程とその変遷について検討した.その結果は以下のとおりである.(1)8,000年前以前には胎内川扇状地と加治川扇状地との間は低地であった.約8,000年前に海水準の上昇とともに,低地前面に砂州が発達し,低塩分の汽水湖沼が形成された.汽水湖沼の出口は加治川以南に求められる.(2)汽水湖沼は次第に塩分を減少していき,海水や淡水が交互に流入する時期を経て,約5,000年頃までに淡水湖化した.(3)淡水湖は約5,000年前以降に北部から埋積されたが,9世紀になって水域が拡大し,現在の塩津潟となった.

The upper Pleistocene and Holocene deposits in the northern Echigo Plain of central Japan are divided into lower, middle, and upper parts based on core data. The lower part was deposited from 40, 000 to 18, 000 yrs BP and consists of sand and gravel-supported conglomerate with alternating beds of sand and silt. The middle part (sedimentary unit I) was deposited from 10, 000 to 8, 000yrs BP and consists of sand and matrix-supported gravels. Facies analysis shows that the lower and middle parts comprise deposits of alluvial fan during the lowstand of sea level. The upper part (sedimentary units II and III) consists mostly of mud and sand that formed upward-coarsening sequences of lagoon-delta deposits. Detailed diatom analysis indicates that the history of the lagoon is divided into four stages. During the first stage (from 8, 000 to 5, 000yrs BP), a brackish lake environment with low salinity pervaded, due to flooding caused by a rapid rise in sea level of the Jomon transgression and the development of a sand dune. At the second stage (ca. 5, 000 yrs BP), the lagoon changed into a freshwater lake. During the third stage (from 5, 000 to 1, 000yrs BP), the lake accumulated a large amount of sandy sediments from the north to the south, and an eolian environment appeared. During the fourth stage (since 1, 000yrs BP), a freshwater area formed again, and has remained as the Shiotsugata Lagoon.

Journal

  • The Quaternary Research (Daiyonki-Kenkyu)

    The Quaternary Research (Daiyonki-Kenkyu) 41(3), 185-197, 2002-06-01

    Japan Association for Quaternary Research

References:  32

Cited by:  3

Codes

  • NII Article ID (NAID)
    10008631937
  • NII NACSIS-CAT ID (NCID)
    AN0034136X
  • Text Lang
    JPN
  • Article Type
    Journal Article
  • ISSN
    04182642
  • NDL Article ID
    6178661
  • 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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