High-resolution terrestrial carbon isotope and planktic foraminiferal records of the Upper Cenomanian to the Lower Campanian in the Northwest Pacific

Abstract

Making Upper Cretaceous biostratigraphic correlations between the Northwest Pacific and Tethyan–Atlantic sections have been difficult because of rare frequencies of age-diagnostic macro- and microfossils in the sequences in the Northwest Pacific region. In order to correlate these sections precisely, an integrated planktic foraminiferal and bulk wood carbon-isotope stratigraphy from the upper Cenomanian to the lower Campanian succession (the middle–upper part of the Yezo Group) of Hokkaido, northern Japan is established with an average resolution of 50 k.y. The δ 13C curves from bulk wood of the Yezo Group and from bulk carbonate of English Chalk show remarkably similar patterns of isotopic fluctuation, allowing the correlation of 22 carbon isotopic events between these sections. This high-resolution correlation greatly improves the previous micro- and macrofossil biostratigraphic schemes in the Northwest Pacific region, and reveals that global events, such as the oxygen depletion at the OAE 2 horizon, the constant decrease in pCO 2 during the Late Cretaceous, and the eustatic sea-level falls in the late middle Turonian, Santonian/Campanian Boundary and early Campanian, are recorded in the Upper Cretaceous sequence of the Northwest Pacific.