NO IRIDIUM ANOMALY AFTER THE 1908 TUNGUSKA IMPACT - EVIDENCE FROM A GREENLAND ICE CORE

We have determined the abundances of Ir and other elements by neutron activation analysis on annual dust samples from an ice core from Site B in the Crete region in central Greenland covering the years 1905-191 4. Iridium was detected in all samples, but we found no excess Ir abov e the background in the years following the Tunguska event. The lack o f an Ir anomaly in the years after the Tunguska impact combined with t he knowledge of the energy released during the impact and our present knowledge about stratospheric transport implies either a very low Ir c ontent of the impactor or an exceptionally high geocentric velocity fo r the impactor.