SOMETHING IS MISCORRELATED IN THE STATE OF DENMARK: THE LATE ORDOVICIAN MILLBRIG AND KINNEKULLE K-BENTONITES

The Kinnekulle “Big Bed” and Millbrig K-bentonites have been considered correlative and thus comprising one of the largest eruptions of the Phanerozoic. However, geochemical data from previous work on biotite phenocrysts suggest that both beds may be different. Whether these two K-bentonites correlate is important for understanding the paleogeographic reconstructions of Laurentia and Baltica, trans-oceanic biostratigraphic correlations of graptolites and conodonts, and the potentially global occurrence of the Guttenburg carbon istotope excursion. We have previously shown that correlated K-bentonites in North America have persistent apatite trace element concentrations despite environment of deposition and post-depositional tectonism. These findings are also consistent with apatite chemistry from modern eruptions. Trace element analyses of apatite phenocrysts were thus measured to provide possible discrimination for the Kinnekulle and Millbrig K-bentonites. On the basis of F, Mg, Cl, Mn, Fe, Ce, and Y concentrations in apatite, the Kinnekulle and Millbrig K-bentonites must be viewed as representing two different eruptions. Vertical sub-sampling of several layers from each bed indicate that both beds are composed of multiple eruptions that do not coincide with one another. These results suggest that the Millbrig and Kinnekulle cannot both be derived from a single ultra-plinian eruption as proposed in recent literature.