Paper No. 178-2
Presentation Time: 1:45 PM-2:05 PM
KENT, Dennis V.1, CRAMER, Benjamin S.2, LANCI, Luca2, WANG, Daming3, WRIGHT, James D.4, and VAN DER VOO, Rob5, (1) Geological Sciences, Rutgers University and Lamont-Doherty Earth Observatory, Piscataway, NJ 08854,, (2) Geological Sciences, Rutgers University, Piscataway, NJ 08854, (3) Geological Sciences, University of Michigan, Ann Arbor, MI 48109, (4) Dept. of Geological Sci, Rutgers Univ, 610 Taylor Rd, Piscataway, NJ 08854-8066, (5) Geological Sciences, Univ of Michigan, Ann Arbor, MI 48109

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.

References: 1. J. P. Kennett, L. D. Stott, Nature 353, 225-229 (1991). 2. P. L. Koch, J. Zachos, P. D. Gingerich, Nature 358, 319-322 (1992). 3. H. C. Verma et al., Lunar and Planetary Science 32, 1270.pdf (2001). 4. T. J. Wdowiak et al., Meteoritics & Planetary Science 36, 123-133 (2001). 5. B. Schmitz et al., Palaeogeography, Palaeoclimatology, Palaeoecology 133, 49-68 (1997). 6. T. Dolenec, J. Pavsic, S. Lojen, Terra Nova 12, 199-204 (2001). 7. E. Jessberger, K., J. Kissel, in Comets in the Post-Halley Era R. L. Newburn, e. al., Eds. (Kluwer Academic Publishers, Amsterdam, 1991), vol. 2, pp. 1075-1092.

2002 Denver Annual Meeting (October 27-30, 2002)
Session No. 178
Impact Stratigraphy
Colorado Convention Center: A102/104/106
1:30 PM-5:30 PM, Tuesday, October 29, 2002

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