| Summary: | The Paleogene of the high paleo-Arctic provides valuable insights into the vegetation dynamics of one of the most climatically sensitive regions on Earth for past, present and future environmental change scenarios. At Sagwon Bluffs, (69°23’N, 148°43’W) Northern Alaska (Fig. 1), combined sedimentological and palynological data (Fig. 2) has identified six depositional sequences within the Prince Creek Formation, Sagwon Member. The base of each sequence is marked by fluvial channel or crevasse-splay sediments, followed by emergent floodplain facies and subsequent deposition of peat mires. These mires gave way to lake sediments with the continued rise in water table and in turn replaced by floodplain water bodies, which in the oldest and youngest sequence contained brackish water algae. Among the ninety-seven in situ palynomorph taxa recorded are the fungal spore Pesavis tagluensis, and the juglandaceous pollen Caryapollenites imparalis/inelegans indicating an age younger than Danian but older than Upper Paleocene. Taxa characteristic of the PETM are not recorded, suggesting that a Late Paleocene Selandian–Early Thanetian age (ca 61 Ma to 57 Ma; Gradstein et al. 2004) is appropriate. Paleogeographic reconstructions position the area at 85°N at that time (Smith et al. 1981; Ziegler et al. 1983). We have used Correspondence Analysis (Hill 1979) to derive ecological groups representing successional “communities” in the floodplain sediments (e.g. Fig. 3). In some sections this includes a lacustrine group containing Azolla and other freshwater aquatics. These reflect different substrate stabilities and drainage regimes on the Sagwon floodplain. Similar analysis of the seven coal beds shows some originated as lacustrine accumulations of drifted wood and were later subjected to gleysol formation. Autocthonous coals showed a succession from polypodiaceous fern dominance through mid seam Betulaceae, Myricaceae and Fagaceae rich assemblages, to Taxodiaceae-Nyssaceae dominance. This succession is disrupted in some coals by the ...
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