A High-Resolution Palynological Analysis, Axel Heiberg Island, Canadian High Arctic (original) (raw)
A high-resolution sampling protocol was used to study the microflora from a two-meter thick siltstone unit located between two prominent coals representing Metasequoia-dominated swamp forests from the middle Eocene (ca. 45 million years old) Buchanan Lake Formation at Napartulik, Axel Heiberg Island, Nunavut, Canada. This detailed analysis facilitated the reconstruction of the local vegetation history and provided possible explanations for the changes seen in the local shifting vegetation patterns. These changes are likely due to two phenomena: environmental disturbances, such as flooding and/or climate change and floral succession. Members of the Pinaceae dominated the local flora at times when the area was relatively dry, whereas Metasequoia Miki was predominant when local environmental conditions were more mesic. The pollen data provide evidence of successional processes and suggest that the local vegetation responded to climatic and environmental changes. More importantly, the pollen data indicate that the local floodplain vegetation was part of a larger, dynamic floral mosaic within a regional polar broad-leaved deciduous forest community and that periods of prolonged environmental stasis were generally limited to the swamp forest communities. Two major fern spikes were identified in the sequence and large-scale flooding was identified as being the likely disturbance factor responsible for landscape level reorganization.
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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 M' fossil forest at the centimetre-scale demonstrates small-scale changes in forest composition and swamp hydrology horizontally, and temporal variation verticallyw ithin this layer. A mosaic of taxodiaceous swamp (Metesequoia 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.
A record of polar Eocene forests is preserved as in situ tree-stump fields and leaf-litter mats in Buchanan Lake Formation sediments on Axel Heiberg Island, in the Canadian Arctic Archipelago. Stratigraphic examination at the centimetre to metre scale of peat-coal lithology and macrofossil floristics in two levels of these fossil forests reflects small-scale changes in forest composition and swamp hydrology horizontally and temporal variation vertically. Root system structure and tree base stratigraphy suggest that exposed tree stumps may not include only coeval individuals of a single forest stand, but rather also individuals representing different phases of the forest through one cycle of the hydrological development of this Eocene polar forest community. Earlier calculations of stand density and biomass, based upon the assumption that all stumps represent coeval trees, may therefore be greatly overestimated. A mosaic of Alnus - fern bog, mixed coniferous community, and taxodiaceous (Metasequoia-Glyptostrobus) swamp appears to have produced both the leaf mats and the in situ stumps, with the taxodiaceous swamp the dominant peat-accumulating phase.
Palaeontologia Electronica, 2021
A new correlation scheme primarily concerning macroand meso-floral remains of bryophytes and vascular plants from 26 Neogene sites and over 50 florules in Alaska and northern Canada is presented. Flora are valuable for correlating Arctic Neogene sites, especially where absolute dating methods are not possible. These taxa clearly differentiate Neogene from Quaternary deposits in the North American Arctic. Recent age estimates provided using terrestrial cosmogenic nuclide (TCN) dating provide tiepoints for these correlations and tend to confirm earlier dates achieved by relative and correlative methods. Our knowledge of North American Arctic/Subarctic palaeofloras and faunas is sufficiently detailed to allow inter-regional comparisons. This paper contains the first attempt to compare and contrast Neogene and early Pleistocene macroand meso-floras from the entire circum-Arctic region. The subfossil and fossil floras are valuable for understanding the evolution of the boreal realm, from...
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