CGRG Bibliography of Canadian Geomorphology
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Author : Barber, D.C.; Andrews, J.T.; and Farmer, G.L.
Date : 2001.
Title : NE Laurentide ice sheet-ocean interactions from 35 - 10 ka: Sr-Nd-Pb isotopic provenance of Northwest Atlantic Margin sediments
Publication : St. John's 2001. Geological Association of Canada - Mineralogical Association of Canada 2001 Joint Annual Meeting / l'Association géologique du Canada - l'Association minéralogique du Canada réunion annuelle conjointe. Memorial University, St. John's, Newfoundland, May 27-30 2001.
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Abstract
During the Late Foxe (=Wisconsin) glaciation, the marine margin of the northeastern Laurentide Ice Sheet advanced repeatedly onto the adjacent Labrador Sea shelf and discharged icebergs to the North Atlantic. Sediment provenance data and lithostratigraphy of marine cores elucidate the spatial and temporal patterns of these iceberg discharges, some of which are the well-known Heinrich (H) events. Source signatures are identified for multiple Laurentide ice flow paths based on TIC and TOC contents, trace element abundances, and Sr-Nd-Pb isotopes in glacial sediments from Hudson Bay, Hudson Strait, Cumberland Sound, and the Baffin Island and Labrador shelves. Provenance indicators were analyzed in five radiocarbon-dated cores from the NW North Atlantic to create time-series of ice margin proximity and sediment sources. In addition to the detrital carbonate (DC)-rich H-layers, cores from the SE Baffin Island slope also contain dark grey, DC-poor diamict layers that record ice stream advances from Cumberland Sound (north of Hudson Strait) onto the shelf during the Late Foxe. Ice discharges from Cumberland Sound occurred more frequently and at different times than those from Hudson Strait, implying a longer response time or different activating mechanism for the Hudson Strait ice stream. The Sr, Nd and Pb data indicate that subglacial processes transported isotopically distinct sediment along Hudson Strait from northern Hudson Bay to the Labrador Sea during H-events, with almost no change in isotopic composition along the 800 km transport path. The DC-rich H-layers of the NW Labrador Sea comprise nearly 100% western Hudson Strait-derived sediment. The fine-grained (<63 micron) siliciclastic fraction from this source has an average epsilon Nd value of -28.4, 87Sr/86Sr of 0.724, 207Pb/204Pb of 15.5, and 206Pb/204Pb of 18.3. Comparison of these data with published isotopic analyses of the same sediment fraction from North Atlantic H-layers (cf. Hemming et al., 1998, EPSL 164: 317-333) shows that Hudson Strait dominated the delivery of ice-rafted debris during H-2, 4 and 5. The relative proportion of sediment delivered to the Labrador Sea from Hudson Strait was reduced during intervals of hemipelagic sedimentation between major ice discharge events. The isotopic and trace-element compositions of the intervening hemipelagic deposits represent a binary mixture dominated by Canadian Shield-derived sediment (>80%) with the relative fraction of an East Greenland basaltic end-member varying inversely with overall Laurentide ice sheet extent (i.e., maximum Canadian Shield input at the LGM).
Bibliography of Canadian Geomorphology