Introduction

One of the most exciting aspects of episodic mantle plume activity is the consequences it may have had in Earth history and especially the effects on near-surface Earth systems (Kerr 1998; Condie et al., 2000; 2001). For instance, the extensive volcanism associated with a superplume event should pump significant amounts methane (CH4) into the ocean–atmosphere system, where it is rapidly oxidized to carbon dioxide (CO2). Because CO2 is an important greenhouse gas, a superplume event should lead to rapid global warming followed by cooling as weathering draws down the CO2 level. Because new ocean ridges form during supercontinent breakup, the supercontinent cycle may also have important consequences for near-surface Earth systems (Worsley et al. 1986; Veevers 1990). Increased CO2 levels in the atmosphere should also affect the carbon cycle – perhaps enhancing photosynthesis and the burial rate of carbon. This should be reflected in the sedimentary record by black shales, hydrocarbons, and coal. Increased hydrothermal fluxes on the seafloor may also increase nutrient supplies to oceanic life. The increase in volume of oceanic plateaus as well as elevation of the oceanic lithosphere by superplumes should raise sea level, producing widespread shallow marine environments available for expansion of marine life and for carbonate platform and reef formation. Superplume events may also contribute to mass extinctions. As documented for the Deccan traps 65 Ma and the Siberian traps 250 Ma, even single superplumes may contribute to mass extinctions (Hallam 1987; Renne et al. 1995).