Positive Eu anomaly development during diagenesis of the K/T boundary ejecta layer in the Agost section (SE Spain): implications for trace-element remobilization

K/T boundary geochemical anomalies have been used previously to support the impact event at the end of the Cretaceous. However, impact models and asse ssment of the extraterrestrial contribution to the boundary sediments shoul d also consider the diagenetic alteration of the impact signatures. Mineral ogical and geochemical studies centring on redox proxies reveal differences in trace-element concentrations at Agost and Caravaca (SE Spain), two of t he most complete K/T boundary sections. These differences probably derive f rom variations in the diagenetic evolution of the ejecta layer. Several red ox proxies, such as extensive pyrite formation, high authigenic uranium con centration and positive Eu anomalies, indicate very strong reducing conditi ons at Agost. Positive Eu anomalies are extremely unusual in sediments, and in this case are interpreted to indicate a highly reducing environment. In such conditions, certain trace elements such as Ir, may have been remobili zed, thereby masking the original signature of the impact.