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Fireball passes and nothing burns—The role of thermal radiation in the Cretaceous-Tertiary event: Evidence from the charcoal record of North America

¹ Department of Geology, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK
² Geological Survey of Canada, 3303 33rd Street NW, Calgary, Alberta T2L 2A7, Canada
³ Department of Geology and Geophysics, University of Calgary, Alberta T2N 1N4, Canada
⁴ Department of Geology, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK

High soot contents have been reported in Cretaceous-Tertiary (K-T) sedimentary rocks, leading to the suggestion that the amount of thermal power delivered from the Chicxulub impact was sufficient to have ignited wildfires. Soot cannot be used to indicate fire location, however, as soot from one large fire could spread globally. Sources other than biomass burning could also yield soot. Charcoal in nonmarine sedimentary rocks (here quantified in situ in polished blocks) provides a unique tool to record the distribution of wildfires and therefore assess the extent of any thermal radiation associated with the impact at Chicxulub. The K-T and lowermost Tertiary sedimentary rocks of six nonma rine sequences (Colorado to Saskatchewan) contain no charcoal or below-background levels of charcoal and a significant quantity of noncharred organic materials, revealing that there was no distinctive wildfire across the North American continent related to the K-T event. This finding indicates that the K-T impact cannot have delivered a peak irradiance of >95 kW·m^–2 of thermal power to the atmosphere and <19 kW·m^–2 to the ground. Therefore, the thermal power delivered from the impact to North America did not have the destructive potential previously predicted. High amounts of thermal radiation were not responsible for the environmental perturbations or extinctions associated with the K-T event.

Key Words: Cretaceous-Tertiary boundary • charcoal • fire • impacts • thermal radiation • asteroid

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