Palynological age constraints on the Cadomin and Dalhousie formations in SW Alberta

The Cretaceous Cadomin Formation is the basal unit of the Blairmore Group in the southern Rocky Mountains and Foothills of Alberta and British Columbia. The Cadomin is predominantly a conglomerate and is overlain by sandstone of the Dalhousie Formation. The Pocaterra Creek Member is a conglomerate, mudstone, and caliche-bearing subunit of the Cadomin Formation, having a restricted westerly distribution. The ages of the Cadomin and Dalhousie formations have not been well constrained previously because the units are generally too coarse-grained for optimum palynomorph recovery. The strata have previously been considered to be of Barremian-Aptian age, except for the Pocaterra Creek Member which is of Berriasian age. For this study, twenty-two palynology samples from the Crowsnest Pass area were examined, spanning strata from the Mist Mountain Formation to the Dalhousie Formation. Age interpretations are possible for nine samples. Palynological assemblages from a conglomeratic outcrop at Bellevue are of Late Jurassic-earliest Cretaceous age. These assemblages argue for inclusion of a conglomeratic bed in the Mist Mountain Formation east of the Fernie area. Palynological assemblages from the Cadomin and Dalhousie formations fall into three main groups. One assemblage group has neither angiosperm nor Appendicisporites pollen, and may be of Berriasian-Valanginian age. Another group lacks angiosperm pollen but is characterized by the presence of Appendicisporites and Klukisporites, and is probably of Hauterivian to early Barremian age. A third group has the angiosperm pollen Clavatipollenites and Retimonocolpites, but no Appendicisporites and rare Klukisporites, and is probably of late Barremian to ?early Aptian age. These ages suggest that deposition of the Cadomin Formation in the study area occurred over a long period of time during the Neocomian, beginning with the Berriasian Pocaterra Creek Member. This thin stratigraphic unit accumulated over a long time period as northerly-flowing rivers migrated laterally across the 50 km E-W extent of the braid plain, thereby producing many local diastems of varying duration.