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The Palaeocene arctic supported a vegetation type quite distinct from the tundra and polar desert of today. Here we demonstrate, through the palynological record, the structure of this extinct vegetation and its dynamics over this period. The Late Palaeocene coal-bearing units of the Sagwon Bluffs on Alaska’s North Slope (present latitude 69 degrees N) are predominantly fine-grained, non-marine and rich in palynomorph-bearing sediments. From the analysed palynological assemblage we were able to demonstrate, using ’Detrended Correspondence Analysis’ (DCA) and ’Fuzzy c-Means Cluster Analysis’ (FCM), 1) a complex heterogeneous ecosystem, 2) its major successional states, and 3) its development over an extended period. The climax state of the floodplain was dominated by flood-tolerant, deciduous conifers such as Metasequoia. A more heterogeneous mid-successional assemblage is represented by angiosperm and gymnosperm co-dominance with an angiosperm dominance of Corylus, while early-successional ecological groups, dominated by ferns and bryophytes, are considered to represent riparian and post-disturbance niches. The structure of this vegetation does not remain static over the course of the stratigraphic interval represented. We observe a particularly dramatic ecological change for instance, following the deposition of a large conglomeratic unit. It is hypothesized that this corresponds to altered drainage and/or precipitation on the North Slope. The vegetation examined herein shows marked similarities to that of other palaeobotanical studies from various sites of similar age at high northern latitudes. It is hence considered to represent an extensive and long-lived circumpolar arctic biome. (C) 2011 Elsevier B.V. All rights reserved.