Significant changes in land vegetation and oceanic redox across the Cretaceous/Paleogene boundary

The impact of an extraterrestrial body 65.5 Ma caused the so-called Cretaceous/Paleogene (K/Pg) event that resulted in a mass extinction and rapid changes in the surface environment on Earth. Here we report changes in land vegetation and oceanic redox across the K/Pg boundary at Caravaca, southeastern Spain, using biomarkers. The results reveal that the basal 3-mm-thick layer of the K/Pg boundary clay is marked by a rapid increase in the concentration of terrestrial long-chain n-alkanes and dibenzofuran, indicating the destruction of land vegetation and an increase in the supply of terrestrial organic matter into the marine environment during the deposition of the K/Pg boundary clay. This layer also records a rapid increase in the concentration of dibenzothiophenes, which indicates a change in redox conditions from oxic to anoxic/euxinic conditions in the intermediate water over the seafloor. The low-oxygen conditions could have been caused by an increase in the influx of terrestrial organic matter into the ocean. A rapid increase in the concentration of retene and retene/cadalene occurred during the deposition of the upper part of the boundary clay 10 kyr after the mass extinction, indicating the recovery of conifers, which greatly decreased at the K/Pg boundary.