The planktonic foraminiferal Contusotruncana plummerae Zone and additional bioevents improving the Santonian-Campanian biozonation

The new mid Campanian Contusotruncana plummerae Zone, recently defined as the stratigraphic interval between the lowest occurrence of the nominate species and the lowest occurrence of Radotruncana calcarata (Petrizzo et al., 2011) is here discussed. This zone replaces the Globotruncana ventricosa Zone, which cannot be reliably applied, because of the uncertain identification and diachronous appearance across latitudes of its nominate marker species. This study is based on the detailed biostratigraphic analyses of the Santonian–Campanian time interval recovered at the following deep-sea drilling sites (a) Shatsky Rise (ODP Leg 198, Hole 1210B), (b) Exmouth Plateau (ODP Leg 122, Hole 762C), (c) Caribbean Sea (DSDP Leg 15, Site 146), and of four boreholes drilled by the Tanzania Drilling Project (TDP) in southeastern Tanzania (TDP23, TDP28, TDP32 and TDP35). Results have been compared to the sequence of planktonic foraminiferal bioevents falling in the coeval stratigraphic interval at the Bottaccione section, that represents the standard for the Tethyan Realm. A high-resolution biostratigraphy of this section was provided by Premoli Silva and Sliter (1995), but their study was based on thin section analysis only. In this study, planktonic foraminiferal bioevents have been revised thanks to the recent availability of washed residues that allow more reliable species identification. Validity of identified bioevents have been integrated with calcareous nannofossil and magnetostratigraphic data when available in literature and their reliability for correlations at regional and global scale has been tested through depth vs. depth plots. Age-depth curves have been tentatively created for the Bottaccione section and for the Exmouth Plateau to obtain a reliable estimate of the relative timing of species first and last occurrence data. This study also provides evidence that the lowest occurrence of Globotruncanita atlantica and other secondary planktonic foraminiferal bioevents are very promising to further improve the Santonian–Campanian biostratigraphic resolution across mid and low latitudes.