SULFUR BEARING MINERALS IN SHOCK PROCESSES - THE NATURAL CASE: POPIGAI AND CHICXULUB

One of postulated effects of the Chicxulub event at the Cretaceous/Tertiary boundary is the impact-induced dissociation of anhydrite to form SOx and a solid residue. The predicted consequences of this process include a sudden increase of the aerosol content in the atmosphere yielding severe cooling, and acid rain causing severe chemical erosion of the continents. It is farther expected that large fractionation effects in sulfur may take place during impact-induced dissociation of CaSO4. Numerical modeling and shock experiments resulted in quite different estimates for the magnitude of SOx release. To tackle the problem in a different way, we commenced a study of sulfur contents and sulfur isotope compositions in target rocks, impactites (tagamites, impact melt breccias, suevites) and their fragment content. The sulfur isotope data will provide the basis for understanding impact-related chemical reactions that have contributed to the drastic environmental effects in the aftermath of the Chicxulub event. Sulfur concentration data may allow to estimate relative contributions of evaporites to the particular impactites. The samples investigated for this study are from the Popigai crater, Siberia, and from the Yucatan-6 well in the Chicxulub structure. Tagamites from Popigai contain 0.04 to 0.17 wt% sulfur, d34S (total sulfur) varies between +0.24 and +1.24 ‰ CDT. At Chicxulub, anhydrite clasts in the tagamites Y-6 N 19 have rather uniform d34S (sulfate) of +18.3 ‰ CDT (mean, n=7) which is indistinguishable to the value for Late Cretaceous seawater. The d34S obviously remained unchanged despite the fact that textural features indicate a severe annealing of the clasts in the impact melt. In contrast d34S for the yellow Haitian glass range from +1.5 to +13.2 ‰ (Chaussidon et al., 1996). The present evidence substantiates that only such distant ejecta lithologies, and probably secondary material inside the crater may display a severe fractionation of sulfur isotopes.