Impact of the Middle Eocene Climatic Optimum (MECO) on Foraminiferal and Calcareous Nannofossil Assemblages in the Neo-Tethyan Baskil Section (Eastern Turkey): Paleoenvironmental and Paleoclimatic Reconstructions

The Middle Eocene Climatic Optimum (MECO; ~40 Ma), which interrupted for ~500-600 kyrthe long-term cooling trend culminating at the Eocene/Oligocene boundary, still requires a comprehensive understanding of the biotic resilience. Here we present a high-resolution integratedforaminiferal and calcareous nannofossil study across the MECO from the expanded and continuousTethyan Baskil section (eastern Turkey) that offers a complete magneto-biostratigraphic and geochemical framework. The five MECO phases identified reveal a transition from oligotrophic (pre-MECO)to eu-mesotrophic conditions, possibly related to accelerated hydrological cycle, during the initial MECO and MECO delta13C negative excursion phases. The MECO WARMING PEAK phase, marking thehighest carbonate dissolution interval, records the most striking biotic changes, such as peak in warmand eutrophic nannofossils, virtual disappearance of the oligotrophic planktic foraminiferal largeAcarinina and Morozovelloides, and peak in eutrophic deep dwellers Subbotina. Benthic foraminiferasuggest in this phase an improvement in the quality of organic matter to the seafloor. The post-MECOphase shows only a partial recovery of the pre-event conditions. Large Acarinina and Morozovelloidesdid not recover their abundance, possibly due to cooler conditions in this phase. Our reconstructionreveals how paleoenvironment and marine biota from the studied Neo-Tethyan setting reacted to theMECO perturbations.