Siltstones, shales, and coals from sections of the Bonnet Plume Formation at the confluence of the Peel and Wind Rivers were analyzed for plant microfossils. Assemblages recovered indicate the presence of 3 pollen-biostratigraphic zones belonging to 3 distinct time intervals. The oldest (zone 1) containing such species as Appendicisporites trichacanthus trichacanthus, A. matesovae, A. erdtmannii, Foveosporites sp., Cicatricosisporites perforatus, and Retitricolpites vulgaris, is considered to be mid-late Albian. In general, it is correlative to parts of the Mannville Group of Alberta, the Potomac of the Atlantic seaboard, and Albian assemblages from Siberia. The middle assemblage (zone 2) is Maastrichtian, containing such diagnostic palynomorphs as Aquilapollenites, Mancicorpus, Cranwellia, and Wodehousea. The third zone is considered to be Paleocene, with such characteristic species as Betulaceoipollenites infrequens, Fraxinoipollenites variabilis, Myricipites dubius, Extratriporopollenites sp., Paraalnipollenites confusus, and Pistillipollenites mcgregorii. The stratigraphic, time, and spatial relationships of the 3 zone-units are illustrated and discussed, and a general reconstruction of the paleoecology is attempted. Probable relationships to strata in other regions of North America and eastern Asia are also considered.

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