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

Abstract

The U–Pbages of shockedzircon crystals from the Chicxulubimpact crater and Cretaceous-Paleogene (K-Pg) boundarysites 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–Pgboundary. Despite this, the inference that the K–Pgboundary layer formed as a direct consequence of the Chicxulubimpact has been repeatedly questioned. Here we present U–Pb (ID-TIMS) ages and textural evidence of shock metamorphosed zircongrains from the K–Pgboundary at Caravaca, Spain, and Petriccio, Italy, that establish a causal connection between the impact and formation of the K–Pgboundary layer. The shockedzircongrains 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–Pgboundarysites in North America. Caravaca and Petriccio were > 8000 km from Chicxulub at the time of impact, and are therefore the farthest K–Pgsites identified that can be linked to Chicxulub through the dating of individual shockedzircongrains. We conclude that the combined age data and textural observations provide unambiguous evidence that ejecta from the Chicxulubimpact formed the global K–Pgboundary layer. These data cannot be explained by the alternative scenario that the Chicxulubimpact occurred ~ 300 ka prior to the K–Pgboundary.