Emily H Hollingsworth, Robert B Sparkes, Jean M Self-Trail, Gavin L Foster, Gordon N Inglis

The Paleocene-Eocene Thermal Maximum (PETM) was a transient global warming event associated with rapid inputs of carbon into the ocean-atmosphere system. The oxidation of petrogenic organic carbon (OCpetro) may have acted as a positive feedback mechanism that helped prolong the PETM. However, there are few proxies that can estimate OCpetro oxidation in the geological past. Previous studies have applied Raman spectroscopy to reveal spatial variability in OCpetro oxidation within modern systems. Here, we use this approach to assess the extent of OCpetro oxidation during the PETM. Data from the mid-Atlantic Coastal Plain exhibits a shift from disordered to highly graphitised OCpetro following the onset of the PETM, which coincides with an increase in the input of thermally mature biomarkers. This suggests enhanced oxidation of OCpetro, indicating an additional source of CO2 within the PETM. Our work highlights the utility of Raman spectroscopy as a novel tool to constrain OCpetro oxidation during the PETM and other climatic events throughout Earth’s history.