KEYNOTE: REBOUNDING PLANT DIVERSITY WITHIN A DYNAMIC PALEOGENE WORLD: EXAMPLES FROM NORTHWESTERN, NORTH AMERICA

Mid to high latitude Paleogene palynofloras reflect selective survivorship at the Cretaceous/Tertiary boundary, phylogenetic changes, climatic shifts, tectonic events and intercontinental migrations. Angiosperms with morphologically simple and probably anemophilous pollen (e.g. Juglanaceous) most commonly survived into the Paleocene and then diversified during the Paleogene. Fewer taxa from probable zoophilous angiosperm lineages crossed the Cretaceous/Tertiary boundary and into the Paleocene, and then most often only in restricted ecological niches. Examples of this are the triprojectate (Aquilapollenites s.l.) and oculate (Wodehouseia) lineages, both prominent and diverse in most uppermost Cretaceous lithofacies but less so in the Paleogene. Paleogene survivors of the morphologically exotic Cretaceous triprojectate and allied pollen-types tend to be subdued and rarely innovative in morphology (e.g. Aquilapollenites spinulosus, and Cranwellia subtilis). In contrast, the Early Paleocene oculate taxa, Wodehouseia fimbriata, represents an acme in a Cretaceous trend towards a larger size and wider flange. The stratigraphic range of triprojectate pollen extends into the Oligocene and oculate pollen into the Arctic Eocene. Contemporaneous with (or a driver of) phylogenetic change were physical events affecting environmental conditions. Orogenic uplift enhanced rain shadow effects in the Western Interior Basin. Plate movements opened and closed migration routes as exemplified by the influx of Normapolles pollen into the eastern Arctic during the Early/Late Paleocene (Bache Peninsula, eastern Ellesmere Island and Somerset Island). Highest plant diversities generally correspond to times of relative warmth (Early/Late Paleocene, Early to early Middle Eocene, and Late Eocene) and this in itself provides useful biostratigraphic information. Late Early and Middle Eocene Arctic plant communities are taken to represent warm temperate and humid conditions. New evidence of oak-dominated pollen spectre, in which ferns are rare, from Middle Eocene sediments preserved as kimberlite crater fill deposits in the Slave Craton, Northwest Territories suggests a drier, scrubland habitat developed in the northern continental interior during the Early Eocene (Cenozoic) Thermal Maximum.