Neutron activation analysis of trace elements in the Geulhemmerberg Cretaceous/Tertiary boundary section, SE Netherlands

Abstract

The Geulhemmerberg K/T boundary section was analysed for (trace) elements by instrumental neutron activation analysis (INAA). Twenty-seven elements were detected in almost all of the 22 samples. Another seven elements were above detection limit in only a few samples, and four elements were below the detection limit in all samples. Anomalous Ir levels have not been found in any sample. However, when Th-normalized, there is an indication for higher concentrations of Ir (and Cr) just below the K/T boundary, possibly due to downward diffusion. The distributions of most trace elements can be explained by the alternation of layers of clay and almost pure limestone in the section, and by the lithophile, chalcophile or siderophile character of the elements. Strontium, usually correlating positively with Ca and CaCO3, correlates negatively with Ca in the Geulhemmerberg section. The relatively high values of Sr in the clay-layers indicate that these layers were shielded from diagenesis. The La/Ce ratio is lower in the clay than in the limestone layers. This may reflect dysoxic conditions in seawater during the deposition of the clay layers. The La/Yb ratio is low in the uppermost Maastrichtian, and high in the basal Danian. An enrichment of Co and Fe at the Berg en Terblijt hardground can be explained by the presence of iron encrustations.