Major and trace element concentrations, accumulation rates and carbonate content in ODP Hole 121-752B (Table 1)

Statistical analyses of sediment geochemical data from a Cretaceous/Tertiary (KT) boundary section at Broken Ridge indicate that the sediments here are composed of three major geochemical end-members: (1) a biogenic/dissolution residue component; (2) a volcanogenic component; and (3) a diagenetic/alteration product component. The KT boundary at Broken Ridge is overlain by a 6-m-thick ash-rich layer. Relative flux comparisons of the three geochemical end-members suggest, however, this layer is the result of a dramatic (11-fold) decrease in biological productivity immediately following the KT boundary event, while both the flux and composition of the volcanogenic component remain constant across the KT boundary. The volcanogenic component apparently is derived from a local source, and we find no evidence of a causal link between volcanic activity and the KT boundary event. The flux of the diagenetic component, which is enriched in Au, increases sharply at the KT boundary. All other elements associated with this component are present in significant amounts in the other two geochemical end-members. With the possible exception of Au, then, geochemical anomalies in the sediments just below the KT boundary appear to result from diagenetic alteration of biogenic and volcanogenic sediment precursors.