A palynological study of an extinct Arctic ecosystem from the Palaeocene of Northern Alaska

Here is presented a high resolution vegetation model and ecological analysis of an extinct floodplain ecosystem based on the palynology of deposits of the Sagwon Bluffs, northeast Alaska.  This fluvio – lacustrine succession of coal – bearing beds is of Late Palaeocene age and dominated by fine-grained sediment interspersed by coarse sandstones and conglomerates.  Deposition occurred at a latitude of ~ 85° N, but owing to the Palaeocene greenhouse climate, mean annual temperatures as high as 6 - 7°C allowed temperate plant ecosystems to exist.  The palynological dataset has been analysed here using ‘Correspondence Analysis’ (CA) and ‘Fuzzy c-Means Cluster analysis’ (FCM), allowing assessment of proposed ecological groups.  Geochemical analysis has been incorporated using ‘Canonical Correspondence Analysis’ (CCA), demonstrating affiliations of certain taxa to chemical signatures of associated sediments.  These techniques collectively reveal a gymnosperm – dominated floodplain forest with a substantial angiosperm, fern and bryophyte component analogous to modern wooded bogs and riparian swamp forests.  Principal taxa of late seral development include Metasequoia, Taxodium, Sequoia and Nyssa, representing the dominant component of such a forest.  Mid seral floras were characterised by coniferous gymnosperm and broad-leaved angiosperm co-dominance, incorporating Corylus, Alnus, Castanea, Ginkgo and a diversity of Pteridaceous, Polypodiaceous, Osmundaceous and Schizaceaen ferns.  Variably high abundances of Sphagnum-type bryophyte spores suggest extensive peat-forming mires.  The inconsistencies of the ecological structure displayed in the palynological assemblage suggest a dynamic floodplain, however, affected by a changing hydrological and climatic regime.  Climate cooling is considered to have affected the floras concurrent with an increasingly wet floodplain prior to a hypothesised period of mountain building to the south.