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LATE FOXE GLACIATION OF THE ASTON LOWLAND, BAFFIN ISLAND, NUNAVUT: SUPPORT FOR AN INTERMEDIATE ICE EXTENT IN THE EASTERN CANADIAN ARCTIC
COULTHARD, ROY D University of Alberta.
Davis, P. Thompson Bentley College.
Briner, Jason P INSTAAR, University of Colorado at Boulder.
Miller, Gifford H INSTAAR and Dept. of Geological Sciences, University of Colorado at Boulder.
The extent of glaciers and ice sheets during the last (late Foxe) glaciation of eastern Baffin Island has been debated for over 40 years. Ice was originally posited to have inundated the entire coastal region and terminated in the sea at the continental shelf break (cf. Flint, 1943). Research since the 1960’s largely discredited the “big” ice model based upon undisturbed sediments of pre-late Foxe age found adjacent to fiord troughs and the relatively advanced weathering of bedrock and glacial debris on surrounding landscapes (cf. Ives and Andrews, 1963; Løken, 1966; Boyer and Pheasant, 1974). In east-central Baffin Island, the Aston delta, a >25 km2, 80 m asl raised marine delta on the Aston Lowland with undisturbed sediments became the widely-cited type locality for this small late Foxe ice model, buoyed by in situ marine molluscs dated >54,000 yrs BP (Løken, 1966).
New air photograph and field mapping of the Aston Lowland confirmed the presence of two extensive raised marine features: an ~ 80 m asl marine limit shoreline sub-parallel to the modern coast that can be traced for ~ 30 km northward from the Aston delta; and a roughly 25 m asl shoreline that extends ~ 45 km parallel to, and seaward of the 80 m shoreline. Nine new radiocarbon ages confirm the pre-Last Glacial Maximum age (>54,700 yrs BP) of the Aston delta and the 80 m asl marine limit shoreline. A finite radiocarbon age of 36,490 yrs BP on ice-transported molluscs collected from the surface of the Aston delta, and post-depositional lateral meltwater channels crossing the delta and lowland indicate the area was inundated by minimally erosive cold-based ice during the late Foxe glaciation. These meltwater channels drain to the 25 m asl shoreline, which represents the early Holocene marine limit, and outline the retreat of three glaciers emanating from the local fiords that inundated the outer coast but were insufficiently thick to overwhelm the outermost summits and valleys. These uplands and valleys may have supported local snow and ice carapaces or alpine glaciers.
The chronology of initial ice retreat is provided by cosmogenic exposure ages of erratic boulders and basal radiocarbon ages on macrofossils from lake cores. Twenty-nine erratic boulder ages indicate ice retreated from the outer coast between about 13 and 15 ka (cal). Seven calibrated basal lake core radiocarbon ages from the Aston Lowland and Clyde Foreland to the north indicate the outer coast was ice-free before 12 ka (cal). Ice retreated to the fiord mouths before ~9.5 ka (cal; Andrews, 1990), and was at or inland of the fiord heads of Clyde Inlet and Inugsuin Fiord by ~8.6 ka (cal; Løken, 1965).
This study supports an extensive, but relatively thin Laurentide Ice Sheet cover of the Aston and adjacent lowlands during the late Foxe glaciation, terminating beyond the modern shoreline on the Baffin Shelf. Ice advanced some time after 36 ka BP, and retreated before 12 ka (cal). The preservation of older Quaternary sediment and landform assemblages indicates the most distal portion of the Laurentide Ice Sheet was composed of minimally erosive cold-based ice throughout the late Foxe and older glaciations. Erosive, warm-based ice was probably restricted to the centres of the major fiords during these glacial episodes. This suggests that much of the eastern Baffin Island landscape is ancient in origin and has not been substantially modified during the most recent glacial cycles. Late Quaternary glacial climate was probably too cold and dry to support large, warm-based ice sheets along the outer Baffin coast.
Andrews, J. T., 1990. Fiord to deep sea sediment transfers along the north-eastern Canadian continental margin: models and data. Géographie Physique et Quaternaire 44: 55-70
Boyer, S.J., Pheasant, D.R., 1974. Delimitation of weathering zones in the fiord area of eastern Baffin Island, Canada. Geological Society of America Bulletin 85: 805–810.
Flint, R. F., 1943. Growth of the North American ice sheet during the Wisconsin age. Geological Society of America Bulletin 54: 325-362
Ives J. D. and Andrews, J. T., 1963. Studies in the physical geography of north-central Baffin island, N.W.T. Geographical Bulletin 5: 5-48
Løken, O. H., 1965. Postglacial emergence at the south end of Inugsuin Fiord, Baffin Island, N.W.T. Geographical Bulletin 7: 243-258
Løken, O. H., 1966. Baffin Island refugia older than 54,000 years. Science 153: 1378-1380
Figure 1. Schematic reconstruction of the maximum extent of the Laurentide Ice Sheet on the Aston Lowland during the late Foxe glaciation. Areas that may have been ice free during the late Foxe maximum are indicated by question marks.
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