The paleoecology of high-latitude Eocene swamp forests from Axel Heiberg Island, Canadian High Arctic

Abstract

A record of high-latitude (79°55′N) Eocene polar vegetation is preserved on Axel Heiberg Island, Canadian High Arctic, in megafloras in an alternating sequence of swamp-coal, fluvio-lacustrine shale and channel-sand lithofacies of the upper coal member of the Buchanan Lake Formation. Some exposures of the swamp facies contain significant fossil forests represented by autochthonous assemblages of mummified in-situ tree stumps and forest-floor leaf-litter mats. Exposed trunks within a single coal layer represent multiple stands of trees killed and buried at the different times over 500–2000 yr. Stratigraphic examination of peat and coal megafossil floristics of the “level N” fossil forest at the centimetre-scale demonstrates small-scale changes in forest composition and swamp hydrology horizontally, and temporal variation vertically within this layer. A mosaic of taxodiaceous swamp ( Metasequoia dominant with or without Glyptostrobus), a mixed coniferous community, and Alnus/fern bog appears to have produced both the leaf mats and the in-situ stumps, with the taxodiaceous swamp the dominant peat-accumulating phase. Taxodiaceous layers are interpreted as areas of standing water which may have experienced seasonal water-level fluctuations. Alnus/fern (with or without other broadleaved angiosperms) communities reflect areas of slightly higher peat and hence locally lower water tables, but may also reflect successional processes. The areal extent and position of these different hydrologically-controlled plant communities appears to have changed throughout the interval of accumulation of the peat layer examined.