ABSTRACT: Variations in sedimentary environments and macrofossil assemblages during postglacial emergence of a High Arctic coastline.

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This paper examines the spatial and temporal variations in sedimentary environments and associated macrofossil assemblages during postglacial emergence of coastal valleys on easternmost Axel Heiberg Island, Canadian High Arctic. The area experienced both regional glaciation by ice flowing northward from Eureka Sound and local glaciation associated with the expansion of upland ice masses. The timing of regional glaciation has not been determined; however, there is abundant evidence for more extensive local ice during the last glaciation. Holocene marine limit varies between 130 and 135 m above sea level and is marked by deltas, beaches and washing limits in till. Six sedimentary facies are recognized on the basis of their lithology and associated macrofossil assemblages: Facies 1 - gravelly till containing reworked marine shells (Hiatella arctica, Mya truncata); Facies 2 - glaciofluvial gravel and sand with reworked marine shells (33,400 +/- 790 yr BP); Facies 3 - deltaic gravel and sand with organics (12,400 +/- 150 yr BP); Facies 4 - proximal glaciomarine laminated mud containing Hiatella arctica and Mya truncata (7890 +/- 80 yr BP); Facies 5 distal glaciomarine massive mud containing Astarte borealis (5400 +/-70 yr BP); Facies 6 - peat (4800 - 5600 yr BP). Facies 1 occurs pervasively as a till veneer on the landscape. Coarse-grained glaciofluvial sediments (Facies 2 and 3) are found in the upper reaches of valleys and record fluvial incision of the landscape accompanying glacio-isostatic rebound and marine regression. Fine-grained marine sediments (Facies 4 and 5) record glaciomarine sedimentation in shallow nearshore environments. Facies 4 sediments are preserved as benches along valley sides, whereas Facies 5 sediments mantle the landscape in the lower reaches of valleys. Radiocarbon dating of macrofossils (see above) facilitates the reconstruction of temporal variations in the nature of sedimentation in the study area. In the early Holocene, meltwater derived from upland ice caps flowed across proglacial sandar supplying sediments to construct deltas and beach ridges. A paraglacial sedimentation regime, characterized by high rates of meltwater and sediment supply, contributed to delta and beach progradation during the initial phase of marine regression. Shoreline progradation is recorded by coarsening upward sequences of glaciofluvial gravels and sands overlying marine mud with shallow marine faunas. Laminated muds were deposited contemporaneously in fiord-head environments. Mid-Holocene marine sedimentation was characterized by deposition of massive marine mud in nearshore environments. On land, massive ground ice bodies developed beneath emerged fine-grained marine sediments. Paludification of the landscape is recorded by peat accumulation in valley bottoms.

Bibliography of Canadian Geomorphology