Chicxulub Crater, Yucatan: Tektites, impact glasses, and the geochemistry of target rocks and breccias

A comparison of breccias and basement rocks from four drill holes near the Chicxulub impact structure, Yucatan (a possible Cretaceous-Tertiary [K-T] boundary crater), with black and yellow impact glasses from the Haitian K-T boundary layer shows that mixtures of andesite-like rocks with carbonates and evaporites from Chicxulub are compositionally different from the yellow glasses. At the time of impact, the Chicxulub area was covered by evaporitic and carbonate deposits several kilometres thick. Because impact glasses are generally produced by shock melting of surface rocks, a link between the Haitian glasses and Chicxulub is difficult to understand. The δ³⁴S isotopic signature of Chicxulub breccias and evaporites is incompatible with that of a continental K-T boundary. We suggest that the pre-impact target stratigraphy at Chicxulub as well as the interpretation of the carbonate-evaporite rocks as breccias should be revised.