Geochemical study of the Cenomanian-Turonian boundary oceanic anoxic event in the northwestern Pacific Forearc Basin - an example from the Cretaceous Yezo Supergroup, Hokkaido, Japan

Cretaceous sediments of the Yezo Forearc basin in the eastern margin of the Eurasian plate record the Cenomanian-Turonian Oceanic anoxic event. The stratigraphic level of the event is biostratigraphically correlated with the uppermost Cenomanian. The preservation of laminae is not always complete, suggesting the condition may have not been strictly anoxic. In this study, samples were obtained every 1 m of the section across the Cenomanian-Turonian boundary for a range of 49 m and analysed for major, minor and REE in order to reconstruct the redox conditions and assess the plume activity as the ultimate cause of the event. The results suggest reducing conditions prevailed from outer shelf to upper shelf slope, but the effects of the plume activity are not directly detected.