OVERVIEW OF END-PERMIAN EVENTS: IMPACTS AND MASS EXTINCTION

High-resolution geochronology at the Meishan, south China GSSP, detailed carbon isotope analyses and statistical analyses of fossil occurrences have established that the end-Permian mass extinction was rapid in the marine realm, probably occurring in > 200 k.y. Correlation to other marine sections using the negative carbon isotope excursion suggests that the extinction is equally rapid elsewhere in the world, although further statistical support for this claim is required. Carbon isotope records from the Karoo in South Africa and inter-fingering of marine and terrestrial Permo-Triassic (PT) rocks in Greenland suggest the extinction on land and sea was coincident, within the currently available temporal resolution. Further studies are required to evaluate the reliability of this view. The absence of evidence for continental glaciation, rapidity of extinction, rising sea level and at least sluggish oceanic circulation eliminate many proposed causes of extinction. Currently the most probable causes are the effects of the Siberian flood basalt volcanism or extra-terrestrial impact; in each case with the possible involvement of extensive marine anoxia. The extent of terrestrial extinction belies a significant role for marine anoxia. The possibility of impact has been rejuvenated with reports of fullerenes, the nature of boundary spherules and claims of an impact structure. Although much of the existing evidence is consistent with an impact, the claimed evidence for impact has yet to be independently replicated. The eruption of the Siberian flood basalts coincides, within error, with the extinction, but the causal link remains uncertain. The most plausible connections involve exsolved hydrogen sulfide producing acid rain, greenhouse effects from carbon dioxide (including from the underlying coal deposits), and possible methane release by oceanic heating. The available evidence may be insufficient to discriminate between these possibilities, emphasizing the need for collecting critical new data.