著者

栗原 憲一 川辺 文久

出版者

日本古生物学会

雑誌

化石 (ISSN:00229202)

巻号頁・発行日

vol.74, pp.36-47, 2003-09-20 (Released:2017-10-03)

参考文献数

47

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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).