Continental-scale wildfires during end-Triassic greenhouse warming

Two-hundred-million years ago, the emission of an estimated 100,000 Gt of CO2 during pulsed eruptions in the Central Atlantic Magmatic Province had dire consequences for the biosphere driving the end-Triassic mass-extinction (ETME). Palynological assemblages obtained from drill cores in Germany, Luxemburg, Denmark and the UK that span the extinction event exhibit a remarkable darkening of pollen and spores that is at odds with simple thermal maturation. Here, we investigate this latest Triassic “Dark Zone”, using the Palynomorph Darkening Index (PDI) obtained from trilete fern spores and Classopollis pollen. Coinciding with a collapse of forest communities and the spread of a fern-dominated pioneer vegetation, PDI reaches peak darkness in the Germanic Triletes Beds and equivalent strata elsewhere. Comparison of PDI records from fossil pollen and spores to the results of controlled heating experiments of modern Lycopodium spores indicates that latest Triassic darkening of palynomorphs was caused by surface fires carried in fern savannahs. Frequent wildfires were widespread in Europe during the ETME based on elevated levels of micro-charcoal and pyrolytic polycyclic aromatic hydrocarbons (PAHs) during the “Dark Zone”. Continental-scale wildfires during the end-Triassic mass-extinction suggests intense climate change-induced heat stress on vegetation contributed to the collapse of terrestrial ecosystems.