EVIDENCE FOR A COMET IMPACT TRIGGER FOR THE PALEOCENE/EOCENE THERMAL MAXIMUM AND CARBON ISOTOPE EXCURSION

We suggest that the rapid onset of the carbon isotope excursion (CIE) at the Paleocene/Eocene boundary (~55 Ma) may have resulted from the accretion of ~900 Gt of 12C-enriched carbon from the impact of a volatile-rich comet, an event that would also trigger greenhouse warming leading to the Paleocene/Eocene thermal maximum (1, 2). New evidence of an impact is the unusual abundance of magnetic nanoparticles in kaolinite-rich shelf sediments from the Atlantic Coastal Plain that coincide with the onset and nadir of the CIE. TEM observations suggest that the magnetic nanoparticles are not of biogenic origin but, by analogy with the reported detection of iron-rich nanophase material at the Cretaceous/Tertiary boundary (3, 4), can be interpreted as derived from an impact plume condensate. Rapid continental weathering, erosion and redeposition on the marine shelf of an impact dust blanket could account for the enigmatic kaolinitic sediments at the CIE. Published reports (5, 6) of a significant albeit small iridium anomaly at or close to the Paleocene/Eocene boundary provide supportive evidence for an impact, especially if it was a volatile-rich comet with a much lower relative concentration of rock-forming elements than associated with carbonaceous chondrites (7). We suggest that rapid major carbon isotope perturbations in the geologic record should be considered as potential indicators of comet impact events, which provide a viable and more direct alternative to dissociation of methane clathrate as a source of 12C-enriched carbon.

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