2025/09/15 by Lucas N. Weaver, Thomas Tobin, Courtney J. Sprain +5
Earth and Planetary Sciences · #Paleontology and Stratigraphy of Fossils #Geology and Paleoclimatology Research #Geological formations and processes
paper · pdf · doi:10.1038/s43247-025-02673-8
Continental Cretaceous-Paleogene boundary sections are best known from North America, where they invariably exhibit a marked shift in sedimentary facies at or very near the boundary level. Uppermost Cretaceous strata typically reflect water-logged soils and unstable meandering-river deposits, whereas lowermost Paleogene strata typically reflect coal swamps and broad, stable meander-belt deposits. Causal links between facies shifts at the Cretaceous-Paleogene boundary and the end-Cretaceous mass extinction have been largely dismissed. Here, we present five new Cretaceous-Paleogene boundary sections identified via iridium anomalies in the Bighorn and Williston basins and assess the sedimentological changes that occur at North American Cretaceous-Paleogene boundaries. We hypothesize that the geographically widespread Cretaceous–Paleogene facies shifts were driven by the extinction of dinosaur megafauna. Large-bodied dinosaurs likely promoted open vegetation structure, prompting fluvial avulsion and clastic sediment input to distal floodplains. After the end-Cretaceous mass extinction, dense forests could establish, stabilizing meander belts and starving the floodplain of clastic sediment, favoring the accumulation of organic-rich strata. More empirical data are needed, but facies change in continental Cretaceous-Paleogene boundary sections suggests dinosaurs were ecosystem engineers that promoted habitat openness in the Late Cretaceous, and their extinction likely led to a dramatic reorganization of ecosystem structure in the earliest Paleogene. Dinosaurs promoted open habitats in the Late Cretaceous, and their extinction could have led to a radical reorganization of the landscape and ecosystem structure at the beginning of the Paleogene, according to sedimentology, biostratigraphy, and geochemistry data from western North America.