Bolide impact and long- and short term environmental change across the cretaceous-paleogene boundary

Abstract

The Cretaceous-Paleogene (K-Pg) boundary mass extinction, ~66 million years ago, was one of the most devastating events in the history of life, marking the end of the dinosaur era. This mass extinction event is now widely acknowledged to be related to the global environmental consequences of the impact of an asteroid with a diameter of ~10 km, at present day Chicxulub, Mexico. The impact at K-Pg boundary likely resulted in a sequence of regional and global catastrophes, including tsunami’s, a ‘fireball‐stage’ and a subsequent global impact winter, resulting from dust and sulphate aerosols that were ejected into the atmosphere, likely presenting a major driver of mass extinction because of the resulting global decimation of photosynthesis. To understand the true extent of the K-Pg boundary impact-related environmental perturbations, the effects of the impact need to be disentangled from these ongoing, long-term environmental changes. However, although decades of K-Pg boundary studies have brought important information, studies detailed and quantified enough to elucidate possible impact-provoked global environmental change mechanisms, or to test various proposed aftermath scenarios are still lacking, as the documentation both impact-related as well as long-term environmental K-Pg changes is still scarce. Therefore, the three main goals of this thesis are to (1) document short-term (centennial/millennial) regional and global climatic, oceanographic and biotic changes following the K-Pg boundary impact, (2) document the ecological succession and long-term biotic recovery following the K-Pg boundary catastrophe. (3) present these changes in a context of long-term background environmental change. Major extinctions amongst traditional proxy-carriers such as planktic foraminifera hamper accurate paleoenvironmental reconstructions across the K-Pg boundary. Therefore, focus should be on those groups which did not experience extinction, like benthic foraminifera and organic-cyst producing dinoflagellates (dinocysts). Although microfossil assemblages can reveal distinct trends in environmental parameters, quantification of such trends and values is not possible. Organic geochemical techniques can, however, provide valuable additional insights in biological and environmental changes across the K-Pg boundary and enable the quantification of these changes. The TEX86 index, an organic biomarker technique is based on the analysis of the distribution of archaeal tetraether membrane lipids in sediments has been successfully applied in deep time, notably when integrated with marine palynology. Therefore, the combinations of these techniques was applied in this thesis. In this thesis we are able to reconstruct the so-called impact winter, characterized by darkness and cooling, In addition, our results show that the extinctions resulted in decreased export of organic matter from the photic zone to the sea floor and more nutrients becoming available for the surviving phytoplankton groups, including dinoflagellates. The evolutionary recovery of phyto- and zooplankton communities took hundreds of thousands to a few million years, showing that the rapid and short-lived K-Pg boundary disaster had exceptionally long-lasting consequences. These climatic and biotic consequences of the K-Pg boundary impact occurred superimposed a long-term sea level regression and global cooling trend unrelated to the impact.