INCREASED WILDFIRES CAUSED BY MARINE ORGANIC CARBON BURIAL DURING THE LATE DEVONIAN FRASNIAN–FAMENNIAN MASS EXTINCTION

The Frasnian–Famennian (F–F) boundary is characterized by worldwide depositions of organic-rich strata and a series of marine anoxia events that are thought to result in one of the biggest five mass extinction events of the Phanerozoic. Due to the enhanced burial of organic matter, there is a coeval positive carbon isotope (δ¹³C) excursion around the F–F boundary, raising questions about carbon cycle feedbacks during the F–F mass extinction. In this study, we test the hypothesis that enhanced burial organic carbon during the F–F mass extinction led to the rise of wildfire occurrences. Here, we reconstructed paleo-wildfire changes across the F–F boundary via analyzing fossil charcoal (inertinites) and pyrogenic polycyclic aromatic hydrocarbons (PAHs) from an Upper Devonian Chattanooga Shale in the southern Appalachian Basin. Here, we found the abundances of inertinites and pyrogenic PAHs were consistently low before the F–F transition. A slight increase of wildfire occurrences was observed during the F–F transition, followed by a sustained enhancement through the entire Famennian interval. Furthermore, we constructed a forward box model for the global carbon cycle to quantify the amount of organic carbon burial required to drive the observed δ¹³C excursion. The modeling results show an enhancement of organic carbon burial rate after the onset of the F–F transition and peaking during its termination. The comparison of the carbon burial rate and wildfire proxies indicates that widespread organic carbon burial during the F–F transition caused elevated atmospheric oxygen levels and increased occurrences of wildfires. In addition, chemical index alteration index and plant biomarkers suggest a change in climate during the F–F transition and a drying climate through the Famennian interval, implying that the enhanced organic carbon burial probably resulted in the climate change and amplified the wildfire occurrences.