New constraints on the PETM record in shallow-marine carbonates from the Adriatic Carbonate Platform, NE Italy

The Paleocene-Eocene Thermal Maximum (PETM; ~ 56 Ma) was an interval of extreme transient climate change, associated with global warming and a massive perturbation of the global carbon cycle (e.g., Zachos et al., 2003). This latter is testified by a sharp Negative Carbon Isotope Excursion (N-CIE) in the global marine and terrestrial d13C records, linked to the injection of large volumes of isotopically light carbon into the oceanatmosphere system. The source of such 13C-depleted carbon is still a matter of debate. The emplacement of the North Atlantic Igneous Province (NAIP) with the release of huge amounts of CO2 is suspected to be one of the factors that may have caused such a relevant change in the composition of the atmosphere/ ocean carbon reservoirs and the associated abrupt climate perturbation. Research is increasingly exploring mercury (Hg) anomalies as tracers of volcanism during the Paleocene-Eocene interval mostly in deep-water and subordinately in shallow-water settings (e.g., Tremblin et al., 2022 and references therein), arguing about their possible relationship to the NAIP emplacement and its impact on the PETM onset and duration. The aim of this contribution is to present an integrated study of sedimentology, stratigraphy (bio and chemo), and geochemistry of the deposits belonging to the Adriatic Carbonate Platform cropping out in the Classical Karst area of Friuli Region (NE Italy), encompassing the PETM event. In particular, here we show paired new carbon and oxygen isotope data combined with Hg concentrations and TOC analyses from two shallow-water marine carbonate sections across the Paleocene-Eocene boundary. This study is taking place in conjunction with a geological survey of the area in the framework of the realization of a new geological map of the area at the scale 1:50000 (CARG Project - Sheet 110 Trieste). The two investigated sections were deposited during the migration of the foreland basin related to the Dinaric orogeny and are today exposed in the Classical Karst area near Trieste (Italy) for about 50 and 300 meters, respectively, of Paleocene-Eocene platform carbonates evolving upward to hemipelagic marls and then to siliciclastic deposits. Vertical facies evolution of the carbonate platform indicates that an initial inner to midramp setting underwent a relative deepening and then was followed by multiple emersion episodes intercalated by proximal marine deposition (i.e., innermost to inner ramp environments). This latter was followed by a return to open marine facies which then persisted until the final drowning of the Adriatic platform that in our study area occurred in the late early Eocene. Our results show in both sections a negative excursion in the carbonisotope record that, associated with biostratigraphic data, can be correlated with the PETM N-CIE and is comparable to other coeval d13C records, both in shape and amplitude. These negative shifts are associated with anomalies in Hg concentration, strengthening the hypothesis that magmatism effectively occurred during this time interval, and its effects are also recorded in shallow-water deposits. These findings corroborate the hypothesis that vulcanism (the NAIP?) might have played a key role in climate change at the PETM.