Molluscan faunal changes across the Cenomanian/Turonian boundary : A comparison between the Oyubari area, Hokkaido, Japan and the Western Interior, USA

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  • Kurihara Kenichi
    Division of Geology, Graduate School of Science and Engineering, Waseda University:(Present address)Mikasa City Museum
  • Kawabe Fumihisa
    Institute of Natural History

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Other Title
  • セノマニアン/チューロニアン期境界前後の軟体動物相 : 北海道大夕張地域と米国西部内陸地域の比較(<特集>白亜紀海洋無酸素事変の解明)
  • セノマニアン/チューロニアン期境界前後の軟体動物相:北海道大夕張地域と米国西部内陸地域の比較
  • セノマニアン チューロニアンキ キョウカイ ゼンゴ ノ ナンタイドウブツソウ ホッカイドウ オオユウバリ チイキ ト ベイコク セイブ ナイリク チイキ ノ ヒカク

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Abstract

This paper documents extinction-recovery patterns of ammonoids and inoceramids across the Cenomanian/Turonian boundary (CTB) including the Oceanic Anoxic Event 2 (OAE2) in the Hakkin-zawa River section, Oyubari area, Hokkaido, Japan, and the Pueblo section, Western Interior, USA. The timing of extinction and recovery in these molluscan faunas occurred synchronously in both areas, based on micro-and macrofossil biostratigraphy and carbon-isotope chemostratigraphy. In the Hakkin-zawa, an ammonoid diversity decreased 0.5 to 0.9 m.y. prior to the CTB (extinction interval), reached a minimum just after the CTB (survival interval), and recovered 0.2 to 0.5 m.y. after the CTB (recovery interval). Inoceramids became increasingly dominant during the extinction and survival intervals, and the genus Inoceramus was replaced by the genus Mytiloides in the latter part of the survival interval. In the Western Interior, the extinction interval spanned 0.42 m.y. before the CTB, and the recovery of faunas took place after 0.15 m.y. from the CTB. In the Western Interior, nekto-benthic ammonoids of acanthoceratids disappeared earlier than planktonic heteromorph ammonoids such as Sciponoceras and Allocrioceras in the extinction interval. By contrast, the nektobenthic desmoceratids also appeared in the later part of the extinction interval in Hokkaido. This inconsistency presumably resulted from different expansion processes for oxygen-depleted water in an open ocean setting (Hokkaido) and a restricted seaway (Western Interior).

Journal

  • Fossils

    Fossils 74 (0), 36-47, 2003

    Palaeontological Society of Japan

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