CARBON ISOTOPIC EVIDENCE FOR BIOMASS BURNING AT THE K-T BOUNDARY

A new interpretation of existing carbon isotopic data combined with re sults from a biogeochemical model suggests that burning of terrestrial biomass occurred on a global scale at the Cretaceous-Tertiary (K-T) b oundary. Carbon isotopic ratios from planktonic and benthic microfossi ls across the K-T boundary reveal not only a breakdown in the normal s urface-water to deep-water gradient of C-13/C-12, but also a reversal at the boundary. This reversal cannot be explained by the cessation of primary production alone. We propose that combustion of terrestrial b iomass with subsequent transfer of isotopically light carbon to surfac e waters is the most likely cause of this anomaly-A biogeochemical mod el is used to quantify the extent of burning at the boundary: combusti on of roughly 25% of the above-ground biomass at the end of the Cretac eous is necessary to account for the observed isotopic signal.