TESTING FOR CAUSAL RELATIONSHIPS BETWEEN LARGE PYROCLASTIC VOLCANIC-ERUPTIONS AND MASS EXTINCTIONS

The Permo/Triassic mass extinction, the most extensive of all Phanerozoic extinctions [Erwin, 1990], has been correlated with both massive pyroclastic eruptions [Yang and Yin, 1987; Yin et al., 1989; Jinwen, 1989] and flood basalts [Rampino and Strothers, 1988]. More tentatively, the end-Cretaceous mass extinction has also been linked with massive volcanic events [Officer et al., 1987; Rampino and Strothers, 19881. However, the nature of the connection between volcanism and either mass extinction remains uncertain. Rather than study volcanic events at known extinction horizons, another approach is to identify extremely large (> 1000 km3) pyroclastic eruptions with well-constrained age determinations, and evaluate the fossil record for evidence of significant regional or global extinctions. We selected the largest, best constrained pyroclastic events known, (Toba Tuff, Huckleberry Ridge Tuff, Tuff of Blacktail and the Elkhorn Mountain volcanics); neither global marine diversity nor global or regional terrestrial vertebrate diversity exhibit any biological effect from these extremely massive pyroclastic eruptions. We conclude that massive pyroclastic eruptions are unlikely to have been an effective cause of mass extinctions. Mass extinction events involve a substantial loss of biologic diversity and may have substantial long-term evolutionary effects. Five major Phanerozoic events have been identified, and a number of smaller events may qualify as well [Sepkoski, 1990]. Loss of habitable area during marine regressions, extra-terrestrial impact, volcanic eruption, climatic change, marine anoxia, paleomagnetic reversal and salinity fluctuation are among the more prominent causes mooted to explain one or more of these events. Yet since many physical event may correlate with an individual mass extinction, it is frequently difficult to discriminate between various hypotheses proposed for a single mass extinction.