Calcareous nannofossil biostratigraphy of the late Albian : early Turonian time interval: implications for global correlations

Calcareous nannofossil biostratigraphy is proven to be a reliable tool for dating and correlating Cretaceous sequences at regional to global. However, assessment of nannofossil event reproducibility still demands detail investigations of different oceanic basins, paleolatitudes and settings. In this study we present the revision of nannofossil biostratigraphic events across the late Albian – early Turonian time interval. We investigated pelagic and hemipelagic sections located in different sedimentary basins in order to estimate reproducibility and variability of nannofossil bioevents in different paleoceanographic regimes and/or latitudes and to evaluate the applicability of the three major nannofossil zonations available for the mid Cretaceous. The studied sections are located in the Tethys Ocean, Vocontian Trough, Moroccan basin, Western Interior Seaway, and Pacific Ocean and were selected on the basis of availability of chemo-bio-stratigraphic data to constrain the age of nannofossil events relative to stages, C-isotope anomalies and Oceanic Anoxic Events (OAEs). Most of the observed taxa are unambiguously described in the literature, but some taxonomic revision has been applied to cases of potential misidentification and discrepant attribution. Each zonal and subzonal nannofossil event was evaluated for assessing the reproducibility, sinchroneity or diachroneity. Also, a few additional potential nannofossil events are discussed in comparison with zonal and subzonal markers. Nannofossil Biohorizons were also examined in the context of stage boundaries definition, namely the Albian/Cenomanian and the Cenomanian/Turonian boundary, to provide further information about the applicability of nannofossil events and the achievable resolution. Moreover, our investigation proved nannofossil events to be extremely useful to biostratigraphically constrain paleoceanographic events of the late Albian – early Turonian interval, namely the latest Albian OAE 1d, the mid Cenomanian MCE I and the latest Cenomanian OAE 2, which were successfully characterized in all the studied sequences.