NSFGEO-NERC: Developing A New Lower Cretaceous Time Scale: Foundation For The Next Generation Of Paleoceanographic And Biogeochemical Studies

During unusually warm greenhouse conditions of the Aptian to Cenomanian, several major perturbations
in the global carbon cycle are reflected by black shale deposits and/or carbon isotope excursions (OAEs).
To fully understand the ocean-climate dynamics of this greenhouse world, and the mechanistic drivers
that propel ocean anoxia and deterioration of ecosystems, new radioisotopic dating, in parallel with a
more geographically dispersed array of high-quality Cretaceous sedimentary records are essential. The
Yezo Group (YG), Japan comprises Aptian to Maastrichtian sediment deposited in a high latitude Pacific
Ocean-facing fore arc basin. Unlike other well-studied Lower Cretaceous sequences, e.g., the Vocontian
Basin, France (VB), the YG contains rhyolitic tuffs amenable to precise U-Pb and 40Ar/39Ar dating. We
propose to obtain new radioisotopic dates from the YG in concert with new osmium (Os) and carbon (C)
isotope chemostratigraphy. This new chronology and chemostratigraphy can be exported and correlated to
records from Tethys, including the VB for which we aim to generate new Os and C isotope
chemostratigraphy and an astrochronologic age model focused on the critical onset interval of OAE1a.
Our proposed research to update and improve the Lower Cretaceous time scale by integrating French and
Japanese strata is designed to rectify critical time scale inaccuracies, and employ refined time scales and
new proxy data to address fundamental questions concerning lithosphere-hydrosphere-biosphere
interactions associated with major Cretaceous C-cycle perturbations such as OAEs.