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  • 1 Academia Sinica Institute of High Energy Physics P.O. Box 2732 100 080 Beijing (PR China)
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The geological samples: Cretaceous-Tertiary (K-T) boundary clays, meteorites, volcanic lava, and ultrabasic rock were separated into carbonate, metal, sulfide, oxide, silicate and acid-resistant residue by a selective chemical dissolution procedure developed in our laboratory. Some conclusions were drawn by analyzing the chemical speciation of anomalous iridum in the above samples and especially by studying the characteristics of mineral components in those residue phases. (1) It is impossible that the anomalous Ir was caused by geochemical enrichment; (2) The iridium enrichment in the K-T boundaries did not necessarily associate with kerogen; (3) The volcanic activity has participated in the extinction event at the end of Cretaceous; (4) Extraterrestrial impact was the trigger of K-T event. Then, we proposed a mixed model by which the extant anomalous Ir in K-T boundary clays was interpreted as a combined effect of extraterrestrial impact, volcano eruption and post-depositional redistribution.