The impact of the Cretaceous/Tertiary bolide on evaporite terrane and generation of major sulfuric acid aerosol

Impact glasses from the K/T boundary in Haiti include high-Ca glasses with up to 1 wt.% SO3, formed by the fusion of anhydrite- or gypsum-rich evaporite sediments in the presence of high-silica melts, derived from melting of continental crust. Experimental studies have duplicated these two melts by fusion of gypsum and andesite, and suggest a formation temperature of 1300°C. Geochemical evidence from the glasses is consistent with their derivation from the 180 km diameter Chicxulub impact crater on the Yucatan peninsula (Mexico), situated in a thick late Cretaceous evaporite succession. This large-diameter crater is most likely the result of a cometary impact, on the basis of bolide scaling from the Ir anomaly in K/T boundary sediments. The sulfur degassing associated with formation of the high-Ca glass alone could have formed a 2 × 1016 g H2SO4 stratospheric aerosol. However, the total sulfur degassing from the evaporite-rich sediments in the Chicxulub impact site may have led to formation of 3.8 × 1018 to 1.3 × 1019 g sulfate aerosol, and global atmospheric mass loading from the sulfate aerosol alone is estimated to beof the order of 1-2.6 g cm-2. Combined with the great optical depth estimates of Pollack et al. [1] and Covey et al. [2] resulting from an impact dust cloud, the sulfate aerosol may have contributed not only to a rapid decline in global surface temperatures to near-freezing in about one week, but also prolonged the cooling for several years because of the time-dependent conversion of SO2 to H2SO4 aerosol in the atmosphere. The contribution of sulfur to acid rain following the K/T boundary event may have equalled the proposed rainout of nitric acid. © 1992