Collapse of tropical rainforest ecosystems caused by high-temperature wildfires during the end-Permian mass extinction

The end-Permian mass extinction (EPME) caused significant changes in the marine and terrestrial realms because of global environmental deterioration caused by intensive volcanic activities. Polycyclic aromatic hydrocarbons (PAHs) in sediments are powerful proxies indicating the frequency and intensity of wildfires during the Permian-Triassic (P-T) transition, providing critical information on floral turnovers and paleoclimatic conditions associated with P-T deforestation. In this study, we investigated high-resolution PAHs in a non-marine P-T transitional sequence from the HK-1 drill core at the Lengqinggou section of Southwest China. The consistency of the PAH distribution patterns as well as the positive correlation between the PAH contents in the whole sequence indicates that they are derived from the same source or process. Similarly, multiple PAH ratios (e.g., fluoranthene/(fluoranthene + pyrene)) changed dramatically with generally higher values in the Lopingian, indicating that the PAHs were more likely derived from a pyrogenic source (i.e., high-temperature wildfire events) compared to those in the Lower Triassic. The enrichment of PAHs at the HK-1 drill core in the terrestrial EPME interval indicates that the paleotropical rainforest ecosystem provided sufficient fuel for large-scale high-temperature wildfire combustion events. Furthermore, the extremely low PAH contents in the Lower Triassic indicated a fuel shortage after the mass deforestation, the highly diversified rainforest assemblage disappeared and was replaced with herbaceous, hinterland-like vegetation. The high coronene/phenanthrene ratio and coronene index indicated that although vegetation was scarce, high-temperature burning events were still common in the Lower Triassic, this evidence further supports the vegetation changeover during the P-T transition. These results indicate that intensified high-temperature wildfire combustion events in the paleotropical rainforest in Southwest China occurred because of global warming and aridity caused by intensive volcanic activities during the P-T transition.