No geochemical evidence for an asteroidal impact at late Devonian mass extinction horizon

One way to test the proposed causal relationship between mass biotic extinction and asteroidal impact is to search for the geochemical signature of such an event at additional mass extinction horizons other than the Cretaceous-Tertiary (K-T) boundary. We report here the results of an extensive search for an indium (Ir) anomaly across the late Devonian Frasnian-Famennian (F-F) extinction horizon, ±367 Myr BP. Over a decade ago, McLaren ¹ proposed that this extinction was caused by an astrophysical catastrophe. We have examined three sedimentary sequences in New York State (the standard reference section for eastern North America) and one in Belgium (the type locality) which cross the F-F boundary. No Ir anomaly was found in any of the analysed stratigraphie sections. The highest values of Ir detected ranged from only 0.2% to 2% of those reported for the marine and terrestrial Ir analyses at the K-T boundary. Further, Devonian pyrite-rich sediments similar to those at the K-T boundary do not contain high Ir concentrations.