Vertical Variation of Rhenium, Cadmium, Silver and Platinum-group Elements within a Transitional Bed of Danish Cretaceous-Tertiary Boundary Layer.

Contents of Re, Cd, Ag and platinum-group elements in specimens from four sub-zones of a 3cm-thick bed of a K-T boundary layer from Stevns Klint in Denmark, were determined by stable isotope dilution using ICP mass spectrometer. The chondrite-normalized Re value linearly decreases in the upper zone. Also the content of Ag linearly diminishes upward. These relations lead us to a conclusion that, at the earliest stage of the formation of this bed, the marine site studied was hi ghlyreducing, and at the final stage of the bed formation, the sea recovered to the “normal” oxidation-reduction potential. That is, it is reasoned that the anomalously reducing condition at the site persisted for a relatively short period. Some discussions are given to effect of chemical valency state on distributional features and to fractionation in the dust fallout.