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 f our sub-zones of a 3 cm-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 decreas es in the upper zone. Also the content of Ag linearly diminishes upwar d. These relations lead us to a conclusion that, at the earliest stage of the formation of this bed, the marine site studied was highly redu cing, and at the final stage of the bed formation, the sea recovered t o the ''normal'' oxidation-reduction potential. That is, it is reasone d that the anomalously reducing condition at the site persisted for a relatively short period. Some discussions are given to effect of chemi cal valency state on distributional features and to fractionation in t he dust fallout.