Unravelling the Cretaceous-Paleogene (KT) Turnover, Evidence from Flora, Fauna and Geology

Abstract

The global devastation of ecosystems as a consequence of a meteorite impact 65 million years ago is clearly detectable in palaeontological and geological records all over the globe. Here we compare and contrast the consequences of the impact expressed in the vegetation, vertebrate fossil record and geological signatures left by the devastation, including information from new proximal KT boundary exposures and new palynological data. The geological evidence of the Chicxulub impact crater shows that the target rock was composed by higher percentages of anhydrite (sulfur source) than carbonates. Atmospheric radiative transfer models suggest that the vaporized target rock rapidly converted into sulfuric acid H2SO4 aerosols where it was injected in the stratosphere by the force of the impact and globally distributed. It took at least 10 years for the H2SO4 to dissipate, making the Earth’s atmosphere opaque to sunlight, leading to a reduction of solar transmission to 10–20% of normal for that period. Southern Hemisphere terrestrial Cretaceous-Paleogene boundary sediments in New Zealand reveal that a diverse Late Cretaceous vegetation was abruptly followed by a short interval dominated by fungi, before the pioneer vegetation of ferns re-conquered the soil. The fern dominated interval, so called fern spike is also evident from Northern Hemisphere Cretaceous-Paleogene boundary sections. The massive depletion in sporepollen diversity is interpreted to reflect devastation of photosynthetic plant communities, a scenario that agrees well with the atmospheric radiative transfer models. The pattern of vertebrate extinctions revealed by the fossil record accords with the temporary, global devastation of photosynthetic plant communities. Vegetation depletion at high latitudes may also explain the extinction of polar dinosaurs, which apparently were able to withstand relatively cool temperatures and periods of low light intensity: the main reason for their disappearance appears to have been lack of food rather than darkness and cooling.