The first vertical high-resolution record of polycyclic aromatic hydrocarbons (PAHs) of pyrosynthetic origin and the corresponding δ13C profile of a terrestrial biomarker across the Cretaceous-Tertiary (K-T) boundary at Caravaca, Spain, reveals the following. In comparison with adjacent Cretaceous marlstones, the first thin horizon (0 to +0.5 cm; 0 = the K-T boundary) of the boundary-clay layer is (1) enriched as much as 112 to 154 fold in typical pyrosynthetic PAHs such as coronene, benzo(g,h,i)perylene, and benzo(e)pyrene and (2) shows an abrupt δ13C decrease of 1.4‰–1.8‰ in terrestrial higher plant-derived n-C29 alkane. The spike of pyrosynthetic PAHs associated with an abrupt decrease in δ13C value of a terrestrial biomarker is interpreted to reflect the prevalence of extensive fires with subsequent δ13C decrease in atmospheric CO2. It is estimated that the geologically instantaneous combustion of ∼18%–24% of the terrestrial above-ground biomass would be necessary to account for the measured negative isotopic shift at the K-T boundary, on the basis of carbon mass balance between terrestrial above-ground biomass and atmosphere.

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