The nature of the KT impactor.: A 54Cr reappraisal

According to the variations observed in the various meteorite classes, Cr-54 represents an isotopic tool for planetary body discrimination. In the search for the nature of the Cretaceous-Tertiary (KT) impactor, Cr isotopic measurements were already performed at KT boundary. The current work is aimed to modernize Cr isotopic data with high-precision measurements to confirm a carbonaceous chondrite type infall, the contribution of which is also estimated. Isotopic signatures of two marine clays (Caravaca, Stevens Klint) exhibit an isotopic ratio which would represent a mixing of a carbonaceous chondrite of CM2 type with terrestrial material in a ratio 6% to 19%. A single impactor may account for both marine and continental Cr isotopic signatures. (c) 2005 Elsevier B.V. All rights reserved.