神戸沖海底コアから推定した完新世の大阪湾の海況変動 Temporal variation of Holocene Osaka Bay conditions estimated from a core in off-Kobe

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神戸沖の大阪湾底で掘られたコアの完新統の部分について, 堆積相解析を行い, 高密度の^<14>C年代値と相対的海水準変動から, 次のような完新世の大阪湾の海況変動を復元した.11000年前に海面高度は約-50 mにあった.海進に伴い後退する三角州はエスチュアリーとなった.海面高度が約-30 mに上昇した9700年前に, 明石海峡での潮流が発生した.海面高度が約-12 mになると, 淀川河口が河内湾に退き, 備讃瀬戸が繋がり, 現在のような瀬戸内海が成立した.この時から約3000年前まで, 大阪湾全体が強い潮流の影響下にあった.5300年前〜5000年前が大阪湾では最も海面が高い時期であった.1700年前頃に, 河内湾が埋め立てられ, 淀川三角州が大阪湾にまで前進し, 1000年前には神戸沖にまでその影響がおよぶようになった.

Temporal variation of Holocene Osaka Bay environment was inferred from facies analysis and many highly dense ^<14>C age determination of a core collected from the bay floor off-Kobe. The results indiate the following detailed variation of depositional environments and conditions of Osaka Bay in Holocene time.The depositional environments inferred from the core succession are as follows : The lower muds (8.5 m thick) are estuary and inner bay deposits and deposited rapidly (8 mm/yr) during rapid rising stage of sea-level ; the middle sand and mud (8 m thick) are tidal delta deposits showing rapid deposition (about 7 mm/yr) ; the upper sand and mud (9 m thick) are bay-floor deposits of slow deposition (0.9 to 1.8 mm/yr)during a marine flood and highstand in sea-level ; and the uppermost clay (4 m thick) is bottomset deposits of the modern Yodo River and shows increasing depositional rates (2.0 to 3.7 mm/yr).The following bay environments also are given from the core analysis : the sea-level at 11000 B.P., was -51 m below the modern sea-level in Osaka basin ; in 9700 B.P., -31 m in sea-level high, the Akashi Strait was formed ; in 8000 B.P., the sea-level of -12 m high, the Setouchi Inland Sea (Setonaikai) was formed when the seas were linked together at the Bisan-Seto ; during 5300 to 5000 B.P., the maximum highstand of sea level in the Osaka basin was +1 to 2 m in elevation ; during 8000 to 3000 B.P., coarser deposits were distributed in all Osaka Bay with slow deposition by strong tidal-currents in the Akashi Strait ; restarting of inflow of much flood clay from the Yodo River into Osaka Bay in about 1700 B.P. and spread the distribution until off-Kobe in 1000 B.P.

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  • 地質學雜誌

    地質學雜誌 106(7), 482-488, 2000-07-15

    日本地質学会

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各種コード

  • NII論文ID(NAID)
    110003013127
  • NII書誌ID(NCID)
    AN00141768
  • 本文言語コード
    JPN
  • 資料種別
    ART
  • ISSN
    00167630
  • NDL 記事登録ID
    5445710
  • NDL 雑誌分類
    ZM49(科学技術--地球科学--地質)
  • NDL 請求記号
    Z15-174
  • データ提供元
    CJP書誌  CJP引用  NDL  NII-ELS  J-STAGE 
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