High-diversity larger foraminiferal assemblages calibrated with calcareous nannoplankton biozones in the aftermath of EECO (Collio, Friuli-Venezia Giulia, northeastern Italy)

Abstract

The Eocene of Collio (easternmost Friuli-Venezia Giulia, northeastern Italy) contains rich larger foraminiferal assemblages mainly dominated by nummulitids of genera Nummulites and Assilina. Herein, we document, by typological and biometric approaches, upper Ypresian to lower Lutetian taxa, dated by an integrated biostratigraphy combining the Shallow Benthic Zones (SBZ) with the nannofossil biozones. A total of seven species of Alveolina, 12 species of Assilina and 33 of Nummulites are described (in Appendix A), some of them left in open nomenclature. The larger foraminiferal assemblages indicate that all the collected samples are assignable to SBZ12 and SBZ13 and their high diversity suggests high resilience of these shallow-water taxa after the Early Eocene Climate Optimum warming event. The occurrence of the calcareous nannofossil Blackites inflatus together with Alveolina violae Nummulites friulanus, N. campesinus, N. quasilaevigatus, Assilina maior maior and A. cuvillieri, typical SBZ12 markers, suggests that SBZ12 extends at least to the basal Lutetian, thus the SBZ12/13 boundary occurs in the lowermost Lutetian instead of at the Ypresian/Lutetian transition.