Fungal proliferation before and after the Cretaceous-Paleogene mass extinction in North America

Palynological evidence of post-catastrophe fungal proliferation after global calamities has been found for the Permian-Triassic and Cretaceous-Paleogene (K/Pg) extinction events. However, unlike the globally documented post-Permian fungal bloom, evidence of a post-Cretaceous event has previously been limited to a single site in New Zealand. Our analysis of a K/Pg boundary section from the Denver Basin in Colorado revealed a fungal proliferative spike occurring immediately after the Chicxulub impact. The discovery of a post-impact fungal bloom in North America corroborates the New Zealand finding and supports the interpretation that this was a global phenomenon. We also identified a prolonged interval of elevated fungal abundance in the Late Cretaceous, dating to approximately 30,000-10,000 years before the impact, temporally correlated to a period of climatic cooling at the site and intriguingly coincident with the Poladpur phase of the Deccan Traps. Taken together with reports of fungal expansion following prior global calamities, these findings indicate that fungi can often flourish in the aftermath of ecosystem-level collapse. Given the capacity of fungi to cause disease in both plants and animals, the occurrence of fungal proliferative events has major potential implications for the recovery of surviving species after global cataclysms. Significance StatementFungal proliferation evidenced by spikes in fungal abundance in geologic samples can signify major ecosystem disruptions. Such spikes are well documented globally for the Permian-Triassic extinction but for the Cretaceous-Paleogene extinction have been reported previously only in New Zealand. Here, we describe a North American fungal bloom that occurred immediately after the Chicxulub impact, as well as an earlier fungal spike in the Late Cretaceous that coincided with a cooling event hypothesized to have been driven by Deccan volcanism. Identification of this pre-impact fungal proliferative episode provides additional support for the uranium-lead-based model of Deccan eruptive rates, which places the high-volume Poladpur pulse tens of thousands of years before the bolide impact.