The debate between the impact scenario and the hypothesis of the Deccan volcanism leading to Cretaceous/Tertiary (K/T) extinctions is far from settled. We add a new dimension to this debate by introducing an overlooked aspect of the Deccan volcanism, the emplacement and eruption of associated carbonatite-alkaline complexes, which are capable of rapidly injecting catastrophic amounts of CO2 and SO2 into the atmosphere. 40Ar-39Ar dating of one of the several coeval late-Deccan alkaline pulses has revealed that this alkaline volcanism took place at the K/T boundary. A conservative estimate shows that these activities can indeed emit a substantial amount of CO2 and SO2, comparable to that of an impact scenario, which could have enhanced the catastrophic effects of the ongoing basaltic eruptions. Other major Phanerozoic extinctions also show contemporaneity with the late carbonatite-alkaline pulses of associated flood basalt provinces, suggesting a causal relationship between such carbonatite-alkaline magmatisms and the mass extinctions. ¿ 1999 American Geophysical Union