Evidence of an Impact Trigger for the Paleocene/Eocene Thermal Maximum and Carbon Isotope Excursion

Details Evidence of an Impact Trigger for the Paleocene/Eocene Thermal Maximum and Carbon Isotope Excursion Evidence of an Impact Trigger for the Paleocene/Eocene Thermal Maximum and Carbon Isotope Excursion

Dec 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmpp32a0509k&link_type=abstract

American Geophysical Union, Fall Meeting 2001, abstract #PP32A-0509

Physics

1512 Environmental Magnetism, 1630 Impact Phenomena, 3344 Paleoclimatology

Scientific paper

The Paleocene/Eocene (P/E) boundary is known to be associated with an extraordinarily rapid (probably less than 1 k.y.) and large (about -2.5 per mil) carbon isotope excursion (CIE) recorded in marine and terrestrial systems that coincided with a dramatic and equally rapid oxygen isotopic excursion interpreted as the Paleocene/Eocene (formerly latest Paleocene) Thermal Maximum (PETM). A widely accepted explanation for the rapid onset and magnitude of the CIE is the sudden dissociation of large amounts of 12C-enriched marine gas hydrates on a global scale. Such a large dissociation event could not have occurred spontaneously and requires either a thermal or mechanical trigger whose origin and efficacy remain uncertain. We postulate that the globally rapid simultaneous onsets of the CIE and PETM at about 55 Ma were induced by the impact of a large carbonaceous bolide (asteroid, or more likely, a comet). New evidence that an impact was involved is the discovery at three drill sites on the Atlantic Coastal Plain (Ancora, Bass River and Clayton in NJ) of abundant magnetic nanoparticles (MNP) in deposits that exactly coincide with the onset and nadir of the CIE as recorded in kaolinite-rich clays. The high concentration of MNP material is interpreted as derived from an impact plume condensate. The kaolinitic clay deposits are thus thought to represent the rapidly weathered product of impact ejecta dust. An iridium anomaly reported at the base of the CIE in Zumaya, Spain, and increased concentrations of extraterrestrial osmium and helium isotopes reported at around the P/E boundary level in a poorly dated North Pacific core, are interpreted as encouraging evidence for a P/E impact event. We suggest that the hypothesized bolide was of sufficient mass to deliver enough 12C-enriched carbon (-20 per mil and less) to initiate the CIE and the greenhouse warming at the PETM that coincide with a massive marine benthic extinction event and terrestrial mammalian turnover. If we are correct, then the P/E impact would be one of the few cases of a bolide encounter with a demonstrated biotic effect.

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