Large igneous provinces and mass extinctions

• Published in: Earth-science reviews 2001-03, Vol.53 (1), p.1-33
• Main Author: Wignall, P.B.
• Format: Article
• Language: English
• Subjects: Extinction; flood basalts; Floods; Geological time; Global warming; marine anoxia; mass extinctions; runaway greenhouse; Volcanoes
• ISSN: 0012-8252; 1872-6828
• DOI: 10.1016/S0012-8252(00)00037-4

Comparing the timing of mass extinctions with the formation age of large igneous provinces reveals a close correspondence in five cases, but previous claims that all such provinces coincide with extinction events are unduly optimistic. The best correlation occurs for four consecutive mid-Phanerozoic examples, namely the end-Guadalupian extinction/Emeishan flood basalts, the end-Permian extinction/Siberian Traps, the end-Triassic extinction/central Atlantic volcanism and the early Toarcian extinction/Karoo Traps. Curiously, the onset of eruptions slightly post-dates the main phase of extinctions in these examples. Of the seven post-Karoo provinces, only the Deccan Traps coincide with a mass extinction, but in this case, the nature of the biotic crisis is best reconciled with the effects of a major bolide impact. Intraoceanic volcanism may also be implicated in a relatively minor end-Cenomanian extinction crisis, although once again the main phase of volcanism occurs after the crisis. The link between large igneous province formation and extinctions remains enigmatic; volume of extrusives and extinction intensity are unrelated and neither is there any apparent relationship with the rapidity of province formation. Violence of eruptions (proportions of pyroclastics) also appears unimportant. Six out of 11 provinces coincide with episodes of global warming and marine anoxia/dysoxia, a relationship that suggests that volcanic CO 2 emissions may have an important effect on global climate. Conversely, there is little, if any, geological evidence for cooling associated with continental flood basalt eruptions suggesting little long-term impact of SO 2 emissions. Large carbon isotope excursions are associated with some extinction events and intervals of flood basalt eruption but these are too great to be accounted for by the release of volcanic CO 2 alone. Thus, voluminous volcanism may in some circumstances trigger calamitous global environmental changes (runaway greenhouses), perhaps by causing the dissociation of gas hydrates. The variable efficiency of global carbon sinks during volcanic episodes may be an important control on environmental effects and may explain why the eruption of some vast igneous provinces, such as the Paraná–Etendeka Traps, have little perceptible climatic impact.