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Sanidine spherules at the Cretaceous–Tertiary boundary indicate a large impact event


The hypothesis that a catastrophic impact of an extraterrestrial body caused the terminal Cretaceous mass extinctions of dinosaurs, planktonic foraminfera and other species is now accepted as respectable following the discovery of a worldwide iridium enrichment in the Cretaceous–Tertiary (K–T) boundary clay1–5. In the basal lamina of the K–T boundary clay of Caravaca (Spain)7 numerous spherules were discovered composed of finely crystallized, almost pure K-feldspar in the structural state of high sanidine. It is concluded here that these spherules solidified from a melt and were probably derived from the impacting body. This poses problems as high K-values are not reported from bulk analyses of meteorites6. The K-feldspar phenocrysts reported in some iron meteorites23 suggest the body may have been a metal–sulphide–silicate planetesimal. A cometary body is suggested as an alternative.

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Smit, J., Klaver, G. Sanidine spherules at the Cretaceous–Tertiary boundary indicate a large impact event. Nature 292, 47–49 (1981).

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