Oceanic anoxia during the permian-triassic transition and links to volcanism

One of the best-documented environmental perturbations at the Permian-Triassic transition is the development of extensive oceanic anoxia, a prime suspect in the mass extinction of marine organisms at the end-Permian (Wignall and Hallam, 1992). Ever since the eruption of the Siberian Traps flood basalt province was recognized as contemporaneous with the Permian-Triassic boundary (PTB; Renne et al., 1995), there has been ongoing research on how the Siberian Traps may have caused changes in ocean chemistry and, ultimately, mass extinction. Massive volcanism could affect ocean oxygen content through both greenhouse warming and reduced solubility of oxygen in seawater (Wignall and Twitchett, 1996) and continental weathering feedbacks on nutrient delivery, primary productivity and oxygen demand (Meyer et al., 2008). The development of new proxies for ocean redox chemistry over the last decade has enabled rapid increases in empirical constraints on Permian-Triassic ocean anoxia. Consequently, numerous proxy records have been produced since the last systematic review of the topic by Wignall and Twitchett (2002). Here, we review the constraints provided by each proxy (summarized in Table 18.1) and discuss insights from Earth system models and geological observations in evaluating the potential role for Siberian Traps volcanism in driving ocean anoxia. Lithological evidence for anoxia Bioturbation intensity and black shales Poorly bioturbated, fine-grained sediments are typical of dysaerobic to anoxic depositional settings (reviewed in Wignall, 1994).