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Response of larger benthic foraminifera to Eocene Warming episodes in the Dinaric foreland basin

The study of Eocene deposits from the Dinaric foreland basin (Outer Dinarides, eastern Adriatic coast) documents a 300 m thick sequence of shallow-water carbonates originated on ramps that formed intermittently during the tectonic evolution of the basin. During the intense tectonic activity in this area, global sea-level changes, and warming events occurred (Early Eocene Climatic Optimum, EECO, Late Lutetian Thermal Maximum, LLTM and Middle Eocene Climatic Optimum, MECO). Up to 40% of all skeletal debris in these carbonates are larger benthic foraminifera (LBF). Ramp successions are rarely complete in terms of inner-, mid- and outer-ramp environments (availability of suitable benthic habitats for different LBF group) and very often stratigraphically incomplete. The LBF rich deposits document three distinctive groupings: i) the post - PETM phase (SBZ4 - SBZ10) ; ii) the EECO phase (from pre - to post - EECO phase, SBZ 10/11 - SBZ12/13) ; and iii) the late post - EECO phase including short-lived LLTM (SBZ13 - SBZ17). The studies of the dominant LBF (Drobne & Ćosović, 2009, 2010 ; Drobne et al., 2011 ; Pavlovec, 2012), showed no significant generic and species diversity across the foreland basin, from SBZ4 to SBZ17, but differences in species richness were found. The LBF assemblages included representatives of alveolinids, nummulitids, complex miliolids, conical agglutinated foraminifera, orthophragiminids, encrusting foraminifera and larger rotaliids. For this study, the diversity of the genera Alveolina, Assilina, Nummulites and conical foraminifera and complex miliolids was compared. The post-PETM stage showed similar species diversity of Alveolina, Nummulites, and Assilina (14-18-16) in contrast to the presence of three species of complex miliolids and seven species of conical foraminifera. The EECO stage favored representatives of Nummulites (32 species) over eighteen species of Alveolina, and five species of Assilina, while low species diversity showed conical foraminifera and complex miliolids (4 species per group). In the post - EECO and LLTM stages Nummulites species were the most abundant (39 species), Assilina less (16 species), while the other groups declined (3 species of Alveolina and six species of complex miliolids). From the Ypresian to the Bartonian, LBF maintained high species diversity, with differences in species richness most likely due to competition (e.g., alveolinids vs. complex miliolids), local shifts in the paleoenvironment and long-term evolution, rather than global atmospheric or oceanic conditions. The study was funded by the Croatian Science Foundation (HRZZ) through Project IP-2019-04-5775 (BREEMECO). Drobne K., Ćosović V., 2009, Palaeobiogeography of the Late Cretaceous to Paleogene larger Miliolids from topical to subtropical sea belts (Neotethys to Caribbean). Bull. Soc. Geol. Fr., 180/4, 317- 331. Drobne K., Ćosović V., 2010, Paleogene conical agglutinated walls foraminifera in the Tethyan realm. Abstract book, Forams2010, 78-79, Bonn. Drobne K., Ćosović V., Moro A., Bucković D., 2011, The role of the Paleogene Adriatic platform in the spatial distribution of alveolinids. Turkish Journal of Earth Sciences, 20/6, 721-751. Pavlovec R., 2012, The Nummulitins from the Outer Dinarids. Folia Biologica and Geologica, 53/3, 85- 109.

Larger benthic foraminifera, Eocene, Dinaric foreland basin, EECO, LLTM, MECO

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