Combustion of fossil organic matter at the Cretaceous-Paleogene (K-P) boundary

Abstract

Recognition of elevated concentrations of aciniform soot in Cretaceous-Paleogene (K-P) boundary sediments worldwide led to the hypothesis that global-scale forest wildfires could have been generated by the K-P boundary bolide impact and might have contributed directly to the extinction event. The wildfires are estimated to have injected 10¹³ t of CO₂ into the atmosphere, resulting in an interval of greenhouse warming. Yet minimal amounts of charred plant remains and abundant noncharred material occur in various K-P boundary locations across North America. This refutes the inference that wildfires occurred on a global scale, and requires an alternative explanation for the aciniform soot. Here we describe significant concentrations of carbon cenospheres in K-P boundary sediments from New Zealand, Denmark, and Canada. Carbon cenospheres are thought to derive solely from incomplete combustion of pulverized coal or fuel-oil droplets, which suggests that the impact may have combusted organic-rich target crust. The Chicxulub impact crater is located adjacent to the Cantarell oil reservoir, one of the most productive oil fields on Earth. This indicates that abundance of organic carbon in the Chicxulub target crust was likely to have been above global mean values. But even if we discount Chicxulub's organic-rich locality, the global mean crustal abundance for fossil organic matter is more than adequate to account for observed concentrations of both carbon cenospheres and aciniform soot, therefore making the global wildfire hypothesis unnecessary.