THE PERMO-TRIASSIC MASS EXTINCTION: SEARCHING FOR THE CULPRIT (Invited Presentation)

The temporal link between the Permo-Triassic mass extinction and the eruption of the Siberian Traps flood basalts has been known for over 30 years but the causal link has been the subject of debate ever since. Initial ideas focused on a volcanic winter scenario in which sulphate aerosol-driven cooling triggered a short-lived but intense glaciation and eustatic regression. This idea has been resurrected in recent years but latest atmospheric modelling experiments show that the effects of increasing SO₂ fluxes are self-limiting and unlikely to have serious consequences. Most current extinction models focus on the role of carbon dioxide release from volcanism. The postulated effects are familiar to us today: global warming, ocean acidification and anoxia, whilst siltation and hypercapnia have been added to the Permo-Triassic mix. The evidence for the many of these environmental factors in Permo-Triassic sediments is substantial. In particular, marine anoxia was widespread, intense, and manifest from the ocean floor to very shallow waters. Understanding the relative importance of these related factors is of relevance to today’s oceans because acidification is postulated to be a severe threat now and within the next few decades whilst widespread ocean anoxia is unlikely to occur for several millennia. However, detecting acidification is inherently difficult because there are no reliable proxies and it leaves no direct sedimentary evidence. Searching for selective extinction of non-buffered taxa does not produce unique solutions because such taxa are also common in warm shallow-water settings that experienced other stressful conditions such as temperature extremes.