A HIGH RESOLUTION ANALYSIS OF FAUNAL AND ENVIRONMENTAL CHANGE IN A SHALLOW –WATER BENTHIC COMMUNITY DURING THE PALEOCENE-EOCENE THERMAL MAXIMUM (SLOVENIA)

The Paleocene-Eocene Thermal Maximum event (56.3 Ma) was a period of massive carbon release into the earth system, which corresponds to major environmental upheaval. Within 10,000 years, global temperatures increased approximately 5°C, and there were shifts in ocean chemistry including ocean acidification and anoxia. Ecologically, there was an extinction of deep-sea benthic foraminifera, major originations and radiations in planktic foraminifera, a turnover of shallow-living larger benthic foraminifera, and a metazoan reef crisis. Much work has been done documenting the PETM in the deep marine realm; however, significant questions remain about the environmental impact and ecological response in shallow waters.

This detailed, quantitative paleoecological investigation of two mid-latitude sites on the Adriatic Carbonate Platform (Kras region, Slovenia) provides a long-term record of shallow marine faunal and environmental change from the Late Paleocene through the Early Eocene. These sites record a major carbon-isotope excursion at the Paleocene-Eocene transition indicating a carbon cycle perturbation similar in magnitude to excursions observed globally. To measure biotic change, fossils were identified in thin section and hand sample, and quantified using equal area counting. Biofacies were identified using cluster analysis and principal coordinates analysis, and ecologic metrics (e.g. abundance, diversity) were calculated. Major faunal transitions are noted in these sites from the Paleocene through early Eocene. In the late Paleocene, an encrusting foraminifera-microbial mound containing scleractinian corals developed in a mid-ramp setting, then transitioned to a large benthic foraminifera-dominated ecosystem prior to the Paleocene-Eocene boundary. Foraminiferal assemblages and abundances are substantially different from the Paleocene to the Eocene, and large benthic foraminifera undergo a step-wise turnover during the early Eocene. Environmental consequences of the Paleocene-Eocene carbon excursion (e.g. nutrient enrichment, anoxia) are further explored with trace element and carbonate phase analysis (X-Ray Fluoresence and X-Ray Diffraction). This study gives a high resolution, quantitative perspective on faunal turnover during a time of extreme climate change.