Was the K/Pg boundary Classopollis ‘spike’ a singular event? A review of global palynological records suggests otherwise, with potentially broad implications

Abstract

The Cretaceous/Paleogene (K/Pg) boundary Classopollis pollen “spike” in Patagonia, Argentina, is viewed as a singular event with no coeval analog anywhere else in the world. Review of global palynological records, however, reveals that similar K/Pg boundary Classopollis spikes involving monotaxial C. classoides (Pflug) Pocock and Jansonius assemblages have previously been reported from the Colorado Basin, Argentina, as well as the Tarim Basin, China, suggesting that this was a global phenomenon. The presence of this morphotaxon in the Danian strata of western North America has previously been interpreted as evidence of reworking from older, pre-Turonian (i.e., Triassic through Early Cretaceous) sediments during the Laramide orogeny. This hypothesis appears supported by the results of contemporary detrital zircon studies coupled with the physical degradation of pollen. However, the interpretation that all Danian examples of this pollen, particularly those from coal deposits, have been reworked from much older sediments is questioned on the basis of this review. Within this context, assorted hypotheses regarding the enigmatic coup de grâce of Classopollis-producing Cheirolepidiaceae are also considered, particularly the hypotheses that the ecologic distribution of Cheirolepidiaceae retracted to include xeric, upland habitats (e.g., the Rocky Mountains) or brackish-water, physiologically dry habitats (e.g., the margin of the Cannonball Sea) during the Late Cretaceous and Danian.