No iridium anomaly after the 1908 Tunguska impact: evidence from a Greenland ice core 

Meteoritics, Vol. 30, No. 6, p. 634-638, 1995 

K.L. Rasmussen
H.B. Clausen
Geofysisk Afdeling, Niels Bohr Instituttet for Astronomi, Fysik og Geofysik, Københavns Universitet
G.W. Kallemeyn

The authors have determined the abundances of Ir and other elements by neutron activation analyses on annual dust samples from an ice core from Site B in the Crete region in central Greenland covering the years 1905-1914. Iridium was detected in all samples, but the authors found no excess Ir above the background in the years following the Tunguska event.The lack of an Ir anomaly in the years after the Tunguska impact combined with the knowledge of the energy released during the impact and present knowledge about stratospheric transport implies either a very low Ir content of the impactor or an exceptionally high geocentric velocity of the impactor.