U-PB AGES OF SHOCKED ZIRCON CRYSTALS FROM SITES IN SPAIN AND ITALY PROVIDE MORE EVIDENCE LINKING THE CHICXULUB IMPACT TO THE GLOBAL K-P BOUNDARY LAYER

The presence of shocked minerals and high levels of iridium in K-P boundary clays led to the consensus that this global layer was formed by a meteorite impact. The shocked minerals are considered to originate from basement rocks at the impact site and the iridium from a large asteroid. The ages of shocked zircon grains in Chicxulub impact breccia, and from K-P boundary sites in Haiti, the USA and Canada, demonstrate a genetic link between the Chicxulub impact crater and the K-P boundary, which is supported by the decrease in particle size with distance from Chicxulub. Here we present U-Pb ID-TIMS data of shock metamorphosed zircon grains from the K-P boundary at Caravacca, Spain, and Petriccio, Italy, which form a mixing line between a primary source age of 549 Ma and the approximate time of impact. The data are analytically identical to ages obtained previously for similarly shocked zircon grains from suevite breccia of the Chicxulub impact structure, and from K-P boundary sites in Haiti, the Western Interior USA, and southern Saskatchewan, Canada. As in previous studies, the new data show partial to near complete isotopic resetting in relation to the degree of intensity of the exhibited shock metamorphic effects. The zircon grains were obtained at paleodistances of ~8200 km at Caravacca, Spain, and ~9200 km at Petriccio, Italy, and are therefore the furthest K-P sites to be directly linked to the source crater by dating of individual zircon grains. The combined age data and correlated textural observations provide robust, unambiguous evidence of a Chicxulub source for the K-P boundary layer that is in conflict with the suggestion that the Chicxulub impact occurred ~300 Kyr prior to the K-P extinction event.