Flame out! End-Triassic mass extinction polycyclic aromatic hydrocarbons reflect more than just fire

Abstract

Global warming induced-wildfires of the 21st century reveal the catastrophic effects that widespread biomass burning has on flora and fauna. During mass extinction events, similar wildfire episodes are considered to play an important role in driving perturbations in terrestrial ecosystems. To better evaluate the record of biomass burning and potential carbon cycle feedbacks at the end-Triassic mass extinction (∼202 Ma; ETE), we investigated the relative abundances of a range of polycyclic aromatic hydrocarbons (PAHs) and the δ13C values of regular isoprenoids and n-alkanes at key sections in the SW UK. These data reveal little evidence for intensive wildfire activity during the extinction event, in contrast to what has been reported elsewhere in European, Chinese, and Greenland ETE sections. Herein, PAHs instead reflect greater contributions from an episode of soil erosion that we attribute to Large Igneous Province (LIP)-driven acid rain, and possible distal sources of smoke, suggestive of fire elsewhere in the UK/European basins. This terrestrial ecosystem perturbation is coincident with those in the marine realm, indicating ecosystem perturbations occurred across multiple habitats throughout the latest Rhaetian in the SW UK. Additionally, this geochemical approach reveals that the precursor carbon isotope excursion (CIE) routinely used in chemostratigraphic correlations is unrelated to LIP activity, but instead results from the increased input of terrestrially derived 13C-depleted plant material. Furthermore, we find the initial CIE (commonly used to mark the extinction level, but which is now known to precede the ETE) is also unrelated to biomass burning. Collectively, these data reveal that processes other than combustion of terrestrial material are important for the terrestrial phase of the ETE in the SW UK. Similar investigations are required on other ETE sections, both those in close proximity to the LIP driving the extinction and those further afield, to more clearly determine the negative effect(s) of LIPs and their geographic extent in the terrestrial realm.