Evidence for a very high carbon/iridium ratio in the Tunguska impactor

We have measured excess Ir and depletion of C-14, two independent indicator s of cosmic material, in peat cores from the central Tunguska impact site. Both Ir and 14C show pronounced anomalies in the same stratigraphical depth interval. We have estimated an integral deposition of nonradioactive cosmo genic C of 6.8 +/- 1.0 mg C cm(-2), and an integrated Ir deposition of 5.9 +/- 1.2 pg Ir cm(-2). The very high C/Ir ratio and a deduced delta(13)C val ue of +55 +/- 10 parts per thousand relative to V Pee Dee Belemnite (VPDB) of the impactor material found in this study points towards a cometary type impactor, rather than a chondritic or achondritic asteroidal type impactor .