U–Pb ages of shocked zircon grains link distal K–Pg boundary sites in Spain and Italy with the Chicxulub impact

The U–Pb ages of shocked zircon crystals from the Chicxulub impact crater and Cretaceous-Paleogene (K-Pg) boundary sites in Haiti, the USA, and Canada, and the pattern of decreasing particle size with paleodistance from the crater, have been used as evidence of a genetic link between Chicxulub and the K–Pg boundary. Despite this, the inference that the K–Pg boundary layer formed as a direct consequence of the Chicxulub impact has been repeatedly questioned. Here we present U–Pb (ID-TIMS) ages and textural evidence of shock metamorphosed zircon grains from the K–Pg boundary at Caravaca, Spain, and Petriccio, Italy, that establish a causal connection between the impact and formation of the K–Pg boundary layer. The shocked zircon grains give data that produce a characteristic age pattern, which indicates a primary source age of 549.5 ± 5.7 Ma and a secondary event at the approximate time of impact at 66 Ma. The intensity of the shock features is proportional to the degree of isotopic resetting, and all textural features and ages are analytically identical to those of previously analyzed zircon from Chicxulub and K–Pg boundary sites in North America. Caravaca and Petriccio were > 8000 km from Chicxulub at the time of impact, and are therefore the farthest K–Pg sites identified that can be linked to Chicxulub through the dating of individual shocked zircon grains. We conclude that the combined age data and textural observations provide unambiguous evidence that ejecta from the Chicxulub impact formed the global K–Pg boundary layer. These data cannot be explained by the alternative scenario that the Chicxulub impact occurred ~ 300 ka prior to the K–Pg boundary.