Shock-induced devolatilization of calcium sulfate and implications for K-T extinctions

The devolatilization of calcium sulfate, which is present in the target rock of the Chicxulub, Mexico impact structure, and dispersal in the stratosphere of the resultant sulfuric acid aerosol have been suggested as a possible mechanism for the Cretaceous-Tertiary extinctions [1,2]. We measured the amount of SO₂ produced from two shock-induced devolatilization reactions of calcium sulfate up to 42 GPa in the laboratory: CaSO₄+SiO₂→CaSiO₃+SO₃↑CaSO₄→CaO+SO₂↑+ 1 2O₂↑. We found both to proceed to a much lower extent than calculated by equilibrium thermodynamic calculations. Reaction products are found to be ∼ 10^-2 times those calculated for equilibrium. Upon modeling the quantity of sulfur oxides degassed into the atmosphere from shock devolatilization of CaSO₄ in the Chicxulub lithographic section, the resulting 9 × 10¹⁶ to 6 × 10¹⁷ g (in sulfur mass) is lower by a factor of 10-100 than previous upper limit estimates, the related environmental stress arising from the resultant global cooling and fallout of acid rain is insufficient to explain the widespread K-T extinctions.