Organic geochemistry evidence for wildfire and elevated pO2 at the Frasnian–Famennian boundary

The Devonian experienced radiations of plants and animals, as well as a major mass extinction event during the Frasnian–Famennian (FF) interval. Proposed triggers have been linked to volcanism, extraterrestrial impact, sea-level fluctuations, and climate cooling, etc. However, the nature of the wildfires and its role in the biotic evolution have been rarely investigated for the FF interval. Here, we report organic geochemistry proxies (e.g., polycyclic aromatic hydrocarbons, PAHs) in three sections from New York (USA) to further investigate the wildfire activity and its potential link with the environmental and biotic perturbations around the FF interval. The studied intervals are dominated by three-ring PAHs which display an increasing abundance stratigraphically towards the FF boundary (FFB). An increase of 6-ring over 3-ring PAHs across the FFB is also observed for the studied sections, indicating elevated burning temperature. Additionally, slightly increased plant wax abundance and average chain length values and relatively constant Pr/Ph ratios are observed. Collectively, these results propose an increased burning frequency over the FF interval caused by elevated pO2 level, rather than a change in aridity. Terrestrial input only slightly increased across the FFB, and there is limited evidence for ocean anoxia. This correlates with the hypothesis that pCO2 drawdown and climate cooling could have been a driving mechanism of the FF biocrisis.