Abstract
The magnetic fraction of some Cretaceous–Tertiary (K–T) boundary sediments sampled at two locations in Italy, contains a spheroidal component which has retained some relict mineral textures and, possibly, mineral chemistry from the K–T event. The spheroids contain small crystals (1–50 µm) of magnetite in a highly altered groundmass. These crystals are commonly skeletal, indicating formation by rapid growth from a high-temperature liquid. Variable concentrations of Ni, Mg and Al (differing by at least a factor of 5) in the magnetite may also reflect a relict chemistry. These spheroids contain higher concentrations of Ir and probably other siderophiles than the bulk sediment and may have been an important carrier for these elements at 65 Myr. This discovery supports evidence for a major accretionary event at the end of the Cretaceous.
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Smit, J., Kyte, F. Siderophile-rich magnetic spheroids from the Cretaceous–Tertiary Boundary in Umbria, Italy. Nature 310, 403–405 (1984). https://doi.org/10.1038/310403a0
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DOI: https://doi.org/10.1038/310403a0
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