CGRG Bibliography of Canadian Geomorphology
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Author : England, J.H.; and Lajeunesse, P.
Date : 2004.
Title : Overview of the Innuitian Ice Sheet and new perspectives on episodic ice shelves on the NW Laurentide Ice Sheet.
Publication : 49th Annual Meeting of the Geological Association and the Mineralogical Association of Canada. May 12-14, 2004. Brock University, St. Catharines, Ontario.
Issue :
Page(s) :
Abstract
At least three till sheets deposited by the NW Laurentide Ice Sheet (LIS) are recognized on Dundas Peninsula, SE Melville Island. The oldest till sheet crosses the peninsula, extending northward to Liddon Gulf. The absolute age of Dundas Till is unknown, but earlier work suggests that it likely pre-dates the Late Wisconsinan. When Laurentide ice lay grounded across Dundas Peninsula, trunk glaciers wrapped around the Melville Island coastline extending westward into M’Clure Strait and northward into Byam Martin Channel where they eventually floated, forming ice shelves. The next (younger) till sheet, also of unknown absolute age, lies inside the Dundas Till limit, overlapping the south coast of the peninsula, (~20 km inland). The upper limit of this till sheet (Bolduc Till) is horizontal and together with its silty and occasionally fossiliferous matrix appears to represent the grounded, inland margin of a former ice shelf (originating from the LIS). A likley counterpart to the Bolduc Till occupies the mouth of Liddon Gulf to the west, also forming a coastal apron (Liddon Till). The youngest till sheet (Winter Harbour Till) on Dundas Peninsula is confined to within 5 km of its south coast, well inside the Bolduc Till limit. Its upper limit is also horizontal and is ascribed to the Viscount-Melville Sound Ice Shelf that covered ~60,000 km2, advancing >400 km to Melville Island after 10.4 ka BP and retreating ~9.6 ka BP. We report new fieldwork on these respective till sheets, and especially the effort to establish their absolute ages based on the associated former relative sea levels recorded along their margins. Approximately 50 shell samples are currently submitted for AMS radiocarbon dating. At several localities, a previously unreported marine limit overlies the Bolduc Till and regression from this shoreline to a slightly lower elevation entrapped sediment recording the arrival of Winter Harbour ice. Both the post-Bolduc marine limit, and sediments from the Winter Harbour relative sea level are widespread in the interior of Dundas Peninsula. These shorelines rise southwestward along the Dundas Peninsula coast towards Viscount Melville Sound, indicating the glacioisostatic dominance of the NW Laurentide Ice Sheet. New evidence suggests that the final retreat of ice responsible for Dundas Till contacted the same relative sea level into which the Liddon Ice Shelf floated. If so, the three nested till sheets on Dundas Peninsula are all of Late Wisconsinan age. New radiocarbon dates on ice-transported shells within Bolduc Till range from 25-28 ka BP, whereas two samples from the Dundas Till are 29 and 36 ka BP. Additional dates on both the arrival and departure of the Winter Harbour Till reinforce the previously reported chronology of 10.3 and 9.6 ka BP, respectively. This will be more rigorously tested by the pending AMS dates. The past history of episodic ice shelves (and the ice streams supplying them) is relevant to the mass flux of the former M’Clintock Ice Divide, to the sedimentary history of the adjacent Arctic Ocean Basin, and serve as analogues for modern ice shelves in Antarctica.
Bibliography of Canadian Geomorphology