Grain size of Cretaceous-Paleogene boundary sediments from Chicxulub to the open ocean: Implications for interpretation of the mass extinction event

The relationship between the Chicxulub impact event and the Cretaceous-Paleogene (K-Pg) boundary mass extinction has been repeatedly questioned. Specifically, Cretaceous planktonic foraminifera occurring in high-energy sediments in the Gulf of Mexico related to the impact have been used to argue that the impact preceded the mass extinction. Here we address this dispute by comparing grain size data from two Gulf of Mexico sections and a distal, pelagic sequence. Significantly larger grain sizes, combined with evidence for size sorting in the proximal sections, suggest that fossils in boundary deposits are redeposited and cannot be used to assign ages. Thus the grain size data support other evidence that indicates that high-energy deposits from around the Gulf of Mexico correlate stratigraphically with the Chicxulub impact and the K-Pg mass extinction.