Delayed calcareous nannoplankton boom-bust successions in the earliest Paleocene Chicxulub (Mexico) impact crater

The Cretaceous-Paleogene (K-Pg; 66 Ma) mass extinction was caused by a bolide impact on the Yucatán platform near modern Chicxulub, Mexico. Calcareous nannoplankton, a dominant group of primary producers, were almost eradicated at this time. Post-impact nannoplankton assemblages from Northern Hemisphere sites were characterized by a short-lived series of high-dominance, low-diversity acmes ("boom-bust" successions), which likely represent an unstable post-impact environment. Although these boom-bust successions are a global signal, the mechanisms that controlled the taxonomic switchovers between acmes are currently unknown. Here, we present detailed analyses of calcareous nannoplankton and planktic foraminiferal assemblages in a new K-Pg section from the peak ring of the Chicxulub crater. We show that although nannoplankton assemblages resemble the typical series of acmes at Tethyan sites, the termination of the "disaster" acme in the crater is delayed by at least 500 k.y. The coincidence between shifts in the dominant planktic foraminiferal trophic group and switchovers in nannoplankton boom-bust taxa suggests that this series of acmes may represent a gradual trend toward oligotrophy driven by the global restoration of biological pump efficiency. Thus, the global diachroneity of boom-bust successions likely reflects the differential pacing of biological pump restoration between oceanic basins and settings.