Responses of calcareous nannofossil assemblages, mineralogy and geochemistry to the environmental perturbations across the Paleocene/Eocene boundary in the Venetian Pre-Alps

Calcareous nannofossil, mineralogical and geochemical data are presented from the expanded Paleocene–Lower Eocene Forada section in the Venetian Pre-Alps. The short-lived Paleocene Eocene Thermal Maximum (PETM) is characterized by profound and temporally constrained changes among calcareous nannoplankton assemblages, triggered by global modifications of the ocean– atmosphere system. The Calcareous Nannofossil Excursion Taxa (CNET) represent transient adaptations to changes in the chemical (nutrients, CO2, pH) and temperature structure of surface waters typifying the PETM. Oligotrophic taxa, such as Sphenolithus, Zygrhablithus, Octolithus and Fasciculithus, exbihit a sharp decrease in abundance, whereas reworked forms show a sharp increase. These changes reflect a response to the modified environmental conditions, characterized by sharp increase in nutrient availability. This increase likely resulted from a huge terrigenous input, suggesting that the siliciclastic pump was intensified by enhanced weathering and runoff. The high correlations between mineralogical/geochemical data and calcareous nannofossil fluctuations is consistent with this scenario. Highly-resolved age estimations are established for several calcareous nannofossil biohorizons based on cyclostratigraphy.