On the causes of the end-Triassic mass extinction

The end-Triassic Mass Extinction (ETME) was one of the most severe biotic crises of the Phanerozoic. The ETME was marked by the extinction of conodonts and severe declines among ammonites, bivalves, brachiopods, and reef-building taxa. This catastrophe coincides with the emplacement of the Central Atlantic Magmatic Province (CAMP), suggesting a temporal and causal relationship. Additionally, globally distributed sedimentary mercury anomalies (Hg/TOC peaks and volcanogenic Δ199Hg signals) further link volcanogenic Hg emissions to the ETME. A cascade of environmental disturbances triggered by CAMP volcanism through magmatic outgassing and contact metamorphism likely played a driving role in causing the terrestrial and marine crises. Here, we review the extinction patterns of the ETME, CAMP-driven environmental and biogeochemical perturbations, and their synergistic causal relationships. Evidence indicates that the ETME occurred rapidly as a two-phased event within ∼100 kyr. On land, ecosystem stress and collapse was marked by deforestation, extensive wildfires and acid rain together with global warming. This last factor intensified continental weathering and increased terrestrial runoff that likely promoted eutrophication and water-column stratification, ultimately causing the widespread marine anoxia/euxinia that is implicated in the marine crisis. Furthermore, these drivers also acted in concert to disrupt biogeochemical cycles (e.g., carbon, nitrogen, and sulfur), inducing a scarcity of bioavailable nitrogen and a drawdown of seawater sulfate concentrations that further stressed environments and ecosystems.