2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 7
Presentation Time: 3:00 PM

Smoke without Fire - Geochemical Evidence for Combustion of Hydrocarbons at Chicxulub

BELCHER, Claire M.1, FINCH, Paul2, COLLINSON, Margaret E.3 and SCOTT, Andrew C.3, (1)School of Biology and Environmental Science, University College Dublin, Belfield, Dublin, Dublin 4, Ireland, (2)School of Biological Sciences, Royal Holloway University of London, Egham, TW20 0EX, United Kingdom, (3)Department of Earth Sciences, Royal Holloway University of London, Egham, TW20 0EX, United Kingdom, claire.belcher@ucd.ie

Models have proposed that the Cretaceous-Paleogene (K-P) impact event was associated with extensive wildfires. An abundance of soot and polycyclic aromatic hydrocarbons (PAHs) in marine K-P rocks have been considered to support for the wildfire hypothesis. However, non-marine K-P rocks, from across North America, contain limited amounts of charcoal and abundant non-charred plant remains, indicating that wildfires did not play a role in end Cretaceous events. PAHs and soot can be formed from a variety of sources, including combustion of vegetation and hydrocarbons whereby modern pyrolitic PAH signatures are traceable to their source. Here we present the results of a study of PAHs from 6 non-marine K-P sections from North America and reveal that the K-P boundary rocks yield pyrolitic PAH abundances that are typically lower than that of the background record. This pattern is similar across all 6 sites that stretch 1183km in distance and follow a similar trend to charcoal distribution, further confirming that extensive wildfires are unlikely to have played a role in the K-P events. A comparison of the signature of the PAHs with those from the combustion of coal, lignite, oil, diesel, gymnosperms and angiosperms indicates that the K-P PAHs show evidence of being sourced from hydrocarbon combustion. The global distribution of PAHs need not invoke global wildfires and in fact provides compelling evidence that a significant volume of hydrocarbons or organic fossil carbon were combusted during the K-P impact event. The K-P charcoal and PAH record requires that extinction and recovery mechanisms be reassessed in order to include mechanisms that do not involve high amounts of thermal radiation.