PALEOGENE FOREST COMMUNITIES AND CLIMATES OF WESTERN AND ARCTIC CANADA

Paleogene megafloras are known from all of the western provinces of Canada, and from the Arctic Archipelago. The Paleocene is well represented by floras from Alberta and Saskatchewan, with minor floras known from Manitoba. Floras from British Columbia principally span the Early to Middle Eocene. Floras in the Arctic, however, span the Paleocene to Middle Eocene. These fossil floras reflect extensive forests composed of deciduous angiosperms and both evergreen and deciduous gymnosperms, extending over 30° of latitude. Interpretation of mid- and high-latitude floristic change over the early Paleogene is complicated by uneven sampling. Nonetheless, taxonomic composition of Arctic Archipelago paleovegetation over the Paleocene to Middle Eocene showed step-wise replacement, with a significant number of microtherm-mesotherm taxa first appearing in the megafloral record in the Middle Eocene, somewhat later than their appearance at middle latitudes in elevated sites of the Early Eocene of British Columbia. A moderate number of taxa in the Arctic ranged through the early Paleogene, or were restricted to the Paleocene. Diversity in the Arctic was lowest in Paleocene floras, but differences may be confounded by uneven sampling. The polar deciduous forest of the Early to Middle Eocene was diverse, reflecting globally equable and warm climates. Quantitative NLR analysis indicated upper microthermal to lower mesothermal climates for most floras, although a cooler phase was reconstructed for part of the Early Eocene. Paleocene and Eocene leaf assemblages from high and middle latitudes in north-western, southern, and north-eastern Canada were shown to have foliar physiognomic signatures indicative of deciduous forests, based on leaf Length/Width and size. Deciduousness in Paleogene high latitude forests (the polar deciduous forest) is climatically anomalous and considered an adaptation to the polar light regime, although an influence from seasonal temperature variation seems superimposed in some regions. The polar deciduous forest represents a globally extinct biome.