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Nanometre-size diamonds in the Cretaceous/Tertiary boundary clay of Alberta

Naturevolume 352pages708709 (1991) | Download Citation

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Abstract

STARTING with the discovery of an iridium anomaly at the Cretaceous/Tertiary boundary in Italy1, the idea that a large asteroid or comet struck the Earth at the end of the Cretaceous period has gained wide acceptance2–4 although some workers suggest that massive volcanic eruptions can also explain the observations5. The abundance of small diamonds, 3–5 nm in size, in chondritic meteorites6,7 prompted us to search for such diamonds in the Cretaceous/Tertiary boundary clay of the Red Deer Valley of Alberta (the 'Knudsen's farm' locality). Dissolution and oxidation of this clay yielded 45 ng g−1 of a white fraction, consisting of more than 97% carbon, which was absent from rocks above and below the boundary layer. We present evidence that this material is indeed diamond, which strengthens further the case for an extraterrestrial impact. The diamond/indium ratio in the boundary clay may constrain the type of impactor; our estimate (1.22:1) is close to the value found in type C2 chondritic meteorites2.

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Affiliations

  1. Environment Canada, Ottawa, Ontario, Canada, K1A OH3

    • David Brez Carlisle
  2. Royal Tyrrell Museum of Palaeontology, Alberta Culture and Multiculturalism, PO Box 7500, Drumheller, Alberta, Canada, TOY OJO

    • Dennis R. Braman

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https://doi.org/10.1038/352708a0

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