Finding of probable Tunguska Cosmic Body material: isotopic anomalies of carbon and hydrogen in peat

Method of a search for traces of Tunguska Cosmic Body (TCB) material using layer-by-layer analysis of the isotopic composition of light elements in pe at has been offered. Four peat columns sampled at the explosion epicentre i ndicated significant carbon and hydrogen isotopic effects in its 'near cata strophic' layers. The shifts, opposite in direction, for carbon (Delta(13)C reaches +4.3 parts per thousand) and hydrogen (Delta D reaches -22 parts p er thousand) cannot be attributed to any known terrestrial reasons (fall-ou t of terrestrial dust and fire soot; emission from the Earth of oil-gas str eams; climate changes, humification of peat, and so on). Moreover, the isot opic effects are clearly associated with the area and with the time of the 1908 event. They are absent in the uppermost and the lowest peat layers and also in the control peat columns sampled at the remote places. Since calcu lated delta(13)C value for an admixture of carbon (+51-64 parts per thousan d) is very high, these effects may not be explained by contamination of pea t with material similar to ordinary chondrites or achondrites, too. Such he avy carbon occurs in the most primitive CI and CM types of carbonaceous cho ndrites. However, C/Ir ratio in a cosmic admixture is 10,000 times as many as in CI chondrites that points to cometary nature of the TCB. The isotopic effects are in agreement with the increase of the Ir content observed in p eat, but, at the same time, small content of Ir points to the low content o f dust in the Tunguska comet that sharply differs it from Halley's comet. ( C) 1999 Elsevier Science Ltd. All rights reserved.