Calcareous nannofossil biostratigraphy and biochronology across the Eocene-Oligocene transition: the record at IODP Site U1509 (Tasman Sea) and a global overview

The abundance, wide distribution, and high evolutionary rates of calcareous nannofossils provide a powerful and reliable tool for correlating and dating marine sedimentary records, especially during the Cenozoic. Their assemblage turnover has been documented extensively across the Eocene-Oligocene transition (EOT), but without a parallel framework toward detailed biostratigraphy. We present highly resolved semi-quantitative calcareous nannofossil data from a continuous Eocene-Oligocene transition record recovered during International Ocean Discovery Program (IODP) Site U1509 (Expedition 371), presently located at 34.4° S latitude in the New Caledonia Trough (Tasman Sea). We present an improved age model for sedimentation at this site based on integrated bio-magnetostratigraphy. Our high resolution biostratigraphic data provide an independent age calibration for biohorizons, both established and additional, which we compare to previous biochronological estimates from low-middle and high latitudes. This allows for a critical evaluation of the accuracy, reliability, synchroneity or diachroneity of each biohorizon across different oceanographic domains. Finally, we infer that Site U1509 belonged to the subtropical low-middle latitude domain during the late Eocene to early Oligocene, with a paleolatitude of ~45°S. This result has important implications for paleoceanographic reconstructions.