The palynofloras spanning the Cretaceous/Tertiary boundary in western Canada are affected by regional precipitation differences and paleolatitude. Sections containing the K/T boundary occur within three facies associations that are linked to precipitation: semiarid, intermediate, and humid. These facies differences are reflected in the palynoflora, the extremes being the near absence of triprojectate pollen from the late Maastrichtian semiarid facies and their greatest relative abundance in the humid coal facies. Imposed upon differences related to depositional environments are those reflecting latitudinal controls on the angiosperm palynoflora. Floral characteristics linked to latitude include the presence of endemic species as well as differences in relative abundances among more cosmopolitan species.

Notwithstanding these regional differences, five sequential palynoflora changes in uppermost Maastrichtian and lowermost Paleocene strata can be identified. As these changes both predate and postdate the K/T boundary, which is marked by a geochemical anomaly and a palynological extinction event, not all can be explained by a scenario in which the causal event is the impact of a single extraterrestrial body.