THE CARBON ISOTOPE RECORD OF PERMIAN TO JURASSIC LIP-RELATED EXTINCTION EVENTS

Mass extinctions are commonly associated with perturbations in the global carbon cycles, registered in the stratigraphic record as carbon isotope anomalies. These anomalies are interpreted as proxies of global environmental change and offer clues to causes of the biotic crises. Much stable isotopic data has been obtained recently across major mass extinction horizons at the Permian-Triassic and Triassic-Jurassic boundary, and at a secondary extinction event in the Toarcian (Early Jurassic). These extinctions are synchronous with emplacement of continental flood basalts of the Siberian traps, the Central Atlantic Magmatic Province, and the Karroo-Ferrar province, respectively. Prominent negative carbon isotope anomalies up to -6‰ are a common feature to all three events. The published isotope curves show complex patterns of gradual shifts, single or multiple spikes of short duration, and abrupt or gradual rebound. Previous model results suggested that volcanic CO₂ emission alone couldn't sufficiently explain the observed shifts in δ¹³C. Alternative and/or supplementary explanations invoke oceanic overturn, depressed primary productivity, and release of methane through dissociation of gas-hydrates. A major concern in the interpretation of preserved isotopic signals is the effect of diagenetic overprint. Distinguishing the primary isotopic ratio from altered values remains a challenge. In this review I present a new compilation of available isotopic data and statistical approaches to assess their reliability. Results of the comparative study help identify similarities and differences among the three events. The increasingly global dataset suggests that volcanism of large igneous provinces triggered a cascade of global environmental, chemical and biotic changes.