ORIGIN OF CHALCOPHILE TRACE ELEMENTS IN THE CRETACEOUS-PALEOGENE BOUNDARY CLAYS FROM STEVNS KLINT IN DENMARK

Chalcophile elements are enriched in the Cretaceous-Paleogene (K-Pg) boundary clays as well as siderophile elements. Chondritic abundance patterns of siderophile elements in the K-Pg boundary clays suggested that the siderophile elements enriched in the K-Pg boundary clays are attributed to the incorporation of meteorite condensates. On the other hand, it cannot be assumed that the chalcophile elements in the K-Pg boundary clays were supplied by meteorite condensates, because the ratios of chalcophile and siderophile elements in the K-Pg boundary clays, such as Zn/Ir, As/Ir, and Sb/Ir, are one to two orders of magnitude higher than those in chondrites. In this study, to elucidate the processes that could have contributed to the enrichment of chalcophile elements in the K-Pg boundary clays, we analyzed the chemical compositions of major and trace elements in the K-Pg boundary clays from Stevns Klint in Denmark.

The concentrations of major and trace elements in the K-Pg boundary clays varied among the collected samples even from neighboring outcrops. Cross plots of the concentrations of these elements suggested the mixing of three materials with different chemical compositions. The first component was enriched in chalcophile elements and iron. The second component was depleted in chalcophile elements and iron and enriched in calcium. The third component was enriched particularly in copper, silver, and lead. The first and third components contained iridium that was obviously supplied at the K-Pg meteorite impact. These two components were likely supplied by phenomena associated with the meteorite impact at the K-Pg boundary, such as the impact heating of the target rocks and intense acid rain.