The Eocene–Oligocene Transition in the Paratethys: boreal water ingression and its paleoceanographic implications

The Eocene–Oligocene Transition (EOT) represents a pivotal period in Earth’s climatic history, marked by the onset of Antarctic glaciation and global cooling. While deep-sea records have extensively documented this transition, its impacts on marginal and epicontinental seas remain less understood. This study investigates the impacts of the EOT in the Karaburun composite section, located in the Eastern Paratethys. Using a multidisciplinary approach that integrates biostratigraphy, geochemistry, geochronology, and sequence stratigraphy, a robust chronostratigraphic framework for the latest Eocene to early Oligocene was established. The stable isotopic shifts observed in benthic and planktic foraminifera 18O and 13C records at Karaburun align with global patterns but also reveal regional effects, such as freshwater influx and basin restriction, specific to the semi-restricted Paratethys. The abrupt negative 18O shift across the Eocene–Oligocene Boundary (EOB) in the Paratethys reflects boreal water ingressions driven by the onset of anti-estuarine circulation between the Nordic Seas and the Atlantic and the closure of the Arctic–Atlantic gateway, which redirected cold, low-salinity boreal waters through interconnected basins towards the Paratethys. These findings highlight the interplay between global climate drivers and regional hydrological dynamics, providing critical insights into the evolution of marginal marine environments during the EOT. Our results underscore the significance of the Paratethys as a unique archive for studying the onset of global icehouse climate conditions and regional responses.