HR: 0830h
AN: PP41B-0837    [PDF]
TI: Correlation, Fauna And Sedimentary Environments Of The Mid-Cretaceous Oceanic Anoxic Event Horizons In North-west Pacific Margin.
AU: * Takashima, R
EM: takashima_rei4@hotmail.com
AF: Kyushu University, 4-2-1 Ropponmatsu, Chuo-ku, Fukuoka, 810-8560 Japan
AU: Nishi, H
EM: hnishi@rc.kyushu-u.ac.jp
AF: Kyushu University, 4-2-1 Ropponmatsu, Chuo-ku, Fukuoka, 810-8560 Japan
AU: Kawabe, F
EM: fkawabe@aoni.waseda.jp
AF: Institute of Natural History, 3-14-24 Takada, Toshima-ku, Tokyo, 171-0033 Japan
AU: Moriya, K
EM: moriya@scs.kyushu-u.ac.jp
AF: Kyushu University, 4-2-1 Ropponmatsu, Chuo-ku, Fukuoka, 810-8560 Japan
AU: Wani, R
EM: wani@kahaku.go.jp
AF: National Science Museum, 3-23-1, Hyakunincho, Shinjuku-ku, Tokyo, 169-0073 Japan
AU: Okada, H
EM: oka@ep.sci.hokudai.ac.jp
AF: Hokkaido University, N10W8, Kita-ku, Sapporo, 060-0810 Japan
AB: The Cretaceous Yezo Group exposed in northern Japan consists mainly of mudstone and turbiditic sandstone deposited in the continental slope to shelf off the eastern margin of Asian continent. The 10000-m-thick sequence provides a synthesis concerning paleontological, sedimentological and paleoenvironmental histories during early Aptian to Maastrihitian in the mid-latitude North-west Pacific margin. Based on an integration of bio- and chemo-stratigraphic results of the Yezo Group using macrofoaails (ammonoids and inoceramids), microfossils (planktic foraminifers and calcareous nannofossils) and carbon isotope of wood fragments, we can recognize five chemo-stratigraphic events corresponding to the Oceanic Anoxic Events (OAE 1a, 1c, 1d, MCE, 2) that are accompanied with prominent negative or positive $\delta^{13}$C$_{wood}$ excursion. No black shales or marine-organic rich sediments were consequently detected at these horizons in the Yezo Group because voluminous siliciclastic influx from the Asian Continent diluted organic matter content in the sediments. The characteristics of faunal turnover and chemo-stratigraphic changes during the OAEs are summarized as follows. \\The OAE 1a horizon of the Yezo Group is recognized by the presence of a pair of negative-and-positive $\delta^{13}$C$_{wood}$ excursions during the Early Aptian. Mudstone at the horizon is characterized by finely lamination with rare or barren benthic macro- and microfaunas. The OAE 1b may be missing by a significant hiatus between late Aptian and early Albian. The OAE 1c represents a distinct negative $\delta^{13}$C$_{wood}$ excursion of 1 $\permil$ with an explosion of radiolarians and moderate bioturbations during the {\it Biticinella brggiensis} Zone. Calcareous foraminifers disappear at the horizon. The rocks at the OAE 1d level consists of weakly laminated pyrite-rich mudstones with a broad positive excursion of $\delta^{13}$C$_{wood}$. Planktic and calcareous benthic foraminifers are lacking, while radiolarians are abundant at the horizon as well as the OAE 1c. A 1.2 $\permil$ positive excursion of $\delta^{13}$C$_{wood}$ within the {\it Rotalipora cushmani} Zone can be correlated with the horizon of the mid Cenomanian Event (MCE). Step-wise extinction of calcareous benthic foraminifers and a noted decrease in radiolarian abundance begin above the horizon. The OAE 2 horizon is marked by laminated pyrite-rich mudstone with a prominent $\delta^{13}$C$_{wood}$ positive excursion of 2.5 $\permil$. Investigation of benthic foraminiferal assemblages demonstrates that the two lowest oxygen conditions developed during 0.15 m.y. before the C/T boundary and 1.5 m.y. after. Significant radiolarian explosion also occur just above the boundary.\\These characteristics of major faunal turnover and paleoenvironmental changes at the OAE horizons of the Yezo Group are very similar to those of the Tethyan and Atlantic regions.
DE: 1055 Organic geochemistry
DE: 3022 Marine sediments--processes and transport
DE: 3030 Micropaleontology
DE: 4267 Paleoceanography
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting