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Geological Magazine; September 2009; v. 146; no. 5; p. 761-774; DOI: 10.1017/S0016756809006487
© 2009 Cambridge University Press (CUP)
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Right arrow Articles by URAMOTO, G.-I.
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Carbon isotope fluctuations of terrestrial organic matter for the Upper Cretaceous (Cenomanian–Santonian) in the Obira area of Hokkaido, Japan

GO-ICHIRO URAMOTO*, YOSHIHIRO ABE{dagger}, and HIROMICHI HIRANO{ddagger}

* Department of Earth Sciences, Graduate School of Science, Chiba University, Chiba 263-8522, Japan
{dagger} Marubeni Corporation, 1-4-2 Ote-machi, Chiyoda-ku, Tokyo 100-8088, Japan
{ddagger} Department of Earth Sciences, Faculty of Education and Integrated Arts and Sciences, Waseda University, Tokyo 169-8050, Japan

* Author for correspondence: uramoto_go-ichiro{at}graduate.chiba-u.jp

Stratigraphic fluctuations of carbon isotope values of terrestrial organic matter within the Upper Cretaceous (Cenomanian–Santonian) sequence in the Obira area of Hokkaido, Japan, record distinctive {delta}13C fluctuations for the Cenomanian–Turonian boundary, the Middle Turonian, the upper Turonian–lower Coniacian, and the Santonian. A biostratigraphic framework of the age-diagnostic taxa (ammonoids, bivalves and planktic foraminifers) indicates that these {delta}13C fluctuation events are comparable with those recorded in {delta}13C data of terrestrial organic matter in Japan and marine carbonates in Europe. These correlations reinforce the utility of these {delta}13C events in terms of global chemostratigraphy. In particular, the {delta}13C patterns within the overall positive interval of the Cenomanian–Turonian boundary event are highly conformable between marine and terrestrial records. The consistent nature of these different records of {delta}13C fluctuation patterns demonstrates that the terrestrial organic {delta}13C data mirror the global-scale {delta}13C patterns in the carbon reservoir of ocean–atmosphere–terrestrial biosphere during the Cenomanian–Turonian boundary event. In addition, global correlation of short-term marine and terrestrial organic {delta}13C fluctuations of the Upper Cretaceous sequence indicate that the magnitude of several terrestrial organic {delta}13C events appears more amplified than that of coeval marine carbonate {delta}13C events. This correlation is interpreted to mean that the effects of local CO2 emission into the atmosphere by release of terrestrial methane hydrate or biomass burning of terrestrial vegetation in the hinterland of the NE Asian region have been superimposed on the global {delta}13C trend and resulted in the terrestrial organic {delta}13C records of the Yezo Group.

Key Words: carbon isotope stratigraphy • Hokkaido • Japan • terrestrial organic matter • Upper Cretaceous






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