Rare earth element composition as evidence of the precursor material of Cretaceous–Tertiary boundary sediments at distal sections

Abstract

The Chicxulub impact event led to a worldwide deposition of impact materials originated from target rocks and the vaporized bolide. Relative contributions of both types of material to the K/T ejecta deposits vary with distance to the crater site. At distal sites (e.g., Agost and Caravaca in the SE of Spain) a major contribution of extraterrestrial material is indicated by different impact signatures, such as Os and Cr isotope composition, abundant microkrystites, platinum group elements and other siderophile elements that are typical of extraterrestrial components. Closer settings to the Chicxulub crater, for example the Blake Nose Plateau in the North American margin, display major continental crustal rock contributions in the ejecta layer. REE compositions provide additional evidence for terrestrial vs. extraterrestrial rock contributions. Previous research has not focused specifically on REE concentrations and corresponding C1- and NASC-normalized patterns. However, normalized REE patterns are already generating supplementary insights into the nature of the original material of the K/T boundary layer. Thus, Blake Nose ejecta C1-normalized patterns indicate a derivation from continental crustal target rocks. In more distal sections REE compositions point to a probable mafic precursor and confirm that extraterrestrial materials represent a major contribution the ejecta layer.