EXTREME PALEOTEMPERATURE CHANGE ACROSS THE LATE PERMIAN EXTINCTION EVENT: NEW DATA FROM NORTHERN ITALY

One of the key ‘facts’ that has constrained models of the latest Permian mass extinction event for some two decades is the supposed coincident temperature rise of 5-6°C. The original paleotemperature estimate was derived from oxygen isotope analyses of carbonate samples spanning the Permian/Triassic boundary in the Gartnerkofel-1 core of Southern Austria. The analyses were, however, performed on severely recrystallized bulk samples. As oxygen isotopes are particularly sensitive to alteration during burial and diagenesis, the 5-6°C paleotemperature estimate is long overdue for critical reassessment. In this study, we analyzed articulate brachiopods from the upper Bellerophon Formation and lowest Werfen Formation (i.e. spanning the extinction horizon) from localities in northern Italy. Bulk rock samples from the same sections were also analyzed to provide a comparative dataset. We used a combination of thin section analyses, cathodoluminescence and trace element geochemistry to evaluate the preservation state of each brachiopod sample. Fossil brachiopod shells faithfully record the geochemical signature of the seawater inhabited by the living animal, but only if they are well preserved. Paleotemperature estimates were derived from isotopic analyses of those specimens that passed all the screening tests. Results show that if δ¹⁸O_seawater values were constant through the study interval, temperatures in the shallow, tropical seas of the study area rose by 6–10°C through the extinction event. Assuming a δ¹⁸O_seawater value of 0‰, for example, absolute temperatures rose from approximately 28°C directly before the event to 35–38°C immediately afterwards. This temperature rise was short-lived, however, and temperatures subsequently fell back to 25-26°C within the basal Werfen Formation (Tesero Member). Our brachiopod-derived paleotemperature estimates show that temperature rise across the latest Permian extinction was of greater magnitude than previously thought, and was of very short duration. Some samples were excluded due to high Fe concentrations. Although we have yet to fully evaluate these data, these shells may be recording a primary, rather than diagenetic, Fe signature. If so, then the oxygen isotope data from these high-Fe shells imply an even greater temperature increase through the event.