北海道中頓別地域における上部白亜系 : 暁新統函淵層群の岩相層序と大型化石層序 Upper Cretaceous to Paleocene Hakobuchi Group, Nakatonbetsu area, northern Hokkaido : lithostratigraphy and megafossil biostratigraphy

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中頓別地域の蝦夷超層群上部は上部蝦夷層群寿層, 函淵層群上駒層・平太郎沢層・奥宇津内層・宇津内川層に区分できる.他地域に比べ細粒の沖合相が卓越し, 非海成層は見られないが, 下部外浜のストーム成浅海成砂岩も少なからず含まれる.上駒層下部以下は下部カンパニアンのSphenoceramus schmidti帯, 上駒層上部はInoceramus shikotanensis帯で下部マストリヒシアン, 上駒層最上部から平太郎沢層下部はSphenoceramus hetonaianus帯で下部マストリヒシアンの上部に位置づけられる.平太郎沢層中上部はイノセラムスが消滅し, アンモナイト数種とTenuipteria awajiensisで特徴づけられ, マストリヒシアン上部に達している.マストリヒシアン最上部は奥宇津内層基底のシーケンス境界によって侵食され確認できない.堆積相変化と宇津内川層からの暁新世微化石記録から, 両層間にマストリヒシアン最上部〜ダニアンが欠如しており, K/T境界は存在しない可能性が高い.

The uppermost part of the Yezo Supergroup in the Nakatonbetsu area, northern Hokkaido witnesses to the lithostratigraphy and magafossil biostratigraphy from the lower Campanian to Paleocene. It is subdivided into the Kotobuki Formation of the Upper Yezo Group (offshore siltstone), the Kamikoma (siltstone intercalated with fine sandstone layers), Hcitarozawa (sandy siltstone), Oku-utsunai (fine sandstone) and Utsunaigawa (sandy siltstone) Formations of the Hakobuchi Group in ascending order. The Hakobuchi Group is dominated by offshore sandy siltstone, in contrast with the Ashibetsu, Oyubari and Hobetsu areas in central Hokkaido representing the westerly marginal shallow-marine sandy facies of the Yezo forearc basin along the Northwestern Pacific rim. The shallowest facies is represented by HCS sandstone of the lower parts of the Heitarozawa and Oku-utsunai Formations formed on storm-dominated lower shoreface. In terms of newly collected ammonites and inoceramids, we can establish three inoceramid zones with the geologic age as follows ; Kotobuki and lower part of Kamikoma Formations : Sphenoceramus schmidti Zone (lower Campanian), upper Kamikoma Formation : Inoceramus shikotanensis Zone (lowest Maastrichtian), uppermost Kamikoma to lower Heitarozawa Formations : Sphenoceramus hetonaianus Zone (upper part of lower Maastrichtian), upper Heitarozawa Formation : an unnamed ammonite zone above the inoceramid extinction horizon (upper Maastrichtian). A sharp erosional surface between the Heitarozawa and Oku-utsunai Formations in thought to be an unconformable sequence boundary. The surface itself was represented by ravinement surface and covered by transgressive lags containing Glycymeris shell beds of shallow-marine storm origin. The Oku-utsunai and Utsunaigawa Formations show a transgressive facies succession, consisting of the lag deposits, HCS sandstone, bioturbated silty sandstone and sandy siltstone. This facies succession and the previous micropaleontological control suggest that the strata of the uppermost Maastrichtian to Danian including the K/T boundary seem to have been eroded away.

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  • 地質學雜誌

    地質學雜誌 107(2), 142-164, 2001-02-15

    日本地質学会

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各種コード

  • NII論文ID(NAID)
    110003013172
  • 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
    5681536
  • 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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