Abstract
The hypothesis that the Late Devonian (Frasnian-Famennian) mass extinction was triggered by an asteroidal impact has received renewed attention with the discovery of a Late Devonian Ir anomaly in Australia. In Europe, the mass-extinction event corresponds stratigraphically to the geographically widespread Kellwasser black-shale and bituminous limestone units, and the biological crisis itself has been alternatively designated the “Kellwasser Event.” We report here the results of an extensive geochemical analysis of the Kellwasser stratigraphic interval in a section with exceptional conodont zonal control in the Federal Republic of Germany. No Ir anomaly was found, neither at the biological crisis horizon recognized in Europe nor at the conodont horizon that corresponds to the Ir anomaly zone reported in Australia. No shock-metamorphosed quartz, sanidine spherules, or siderophile-rich magnetic spherules were found, which might have been indicative of a cometary impact. Oxygen-isotope ratios show little variation across the mass-extinction horizon, though carbon-isotope data suggest a sudden increase in phytoplankton activity. We further note that the Australian Ir anomaly (1) is most likely not associated with a large-body impact because no equivalent Ir signature occurs in Europe and (2) is stratigraphically above the European biological crisis horizon, thus postdating the Kellwasser mass-extinction event.
