LGM DISPERSAL TRAINS OF THE WESTERN INNUITIAN ICE SHEET
COULTHARD, ROY . Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada, now at INSTAAR.
England, John . Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada.
Atkinson, Nigel . Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada.
The distribution of glacially transported erratics in the westernmost Canadian Arctic Archipelago was mapped on western Axel Heiberg and Meighen islands, Nunavut. On Axel Heiberg Island, boulders up to eight metres in length were observed above marine limit. The provenance of sandstone boulders is attributed to the Isachsen Formation that outcrops at the mountain front to the east. The association of these boulders with till and radiocarbon-dated deglacial (Holocene) marine sediment suggests that they were deposited during the Last Glacial Maximum (LGM). Isachsen Fm. boulders traced westward from the interior mountains of Axel Heiberg Island suggest a vigorous westward glacier flow during the LGM.
Forty km to the west of Axel Heiberg Island, on the continental shelf, Meighen Island is capped by unconsolidated sand of the Neogene Beaufort Formation (Thorsteinsson, 1961). Faceted and striated boulders, interpreted to be till, overlie the Beaufort Fm. across the island. The till was composed of sandstone, diabase, quartzite and pink and red granites, all foreign to Meighen Island. Granite erratics were ubiquitous on the southwestern two-thirds of the island, but were absent on the northeastern third where diabase erratics were dominant. Granite erratics have not been observed on southern or western Axel Heiberg Island, nor on the small, basaltic Fay Islands within Sverdrup Channel, between Axel Heiberg and Meighen islands. The absence of granite on northeastern Meighen Island and the Fay Islands suggests that most of a trunk glacier in Sverdrup Channel was fed directly from Axel Heiberg Island ice which displaced regional granite-bearing ice farther to the west. Hand sample analysis of Meighen Island granite erratics suggests they are compositionally similar to Shield bedrock on southeast Ellesmere Island (Frisch, 1988), as well as to granite erratics on the sedimentary terrain of southern Ellesmere Island, (O Cofaigh et al., 2000) and granite erratics from Amund Ringnes Island (Atkinson, 2001). Consequently, a common Ellesmere Island provenance is suggested for granite erratics extending northwestward to Meighen Island.
This study provides further support for the Innuitian Ice Sheet (IIS) model of Blake (1970). We support the conclusion of Atkinson (2001) that a northwestward-flowing trunk glacier (or ice stream), fed by convergent Ellesmere Island and Axel Heiberg Island ice, occupied Massey Sound (west of Axel Heiberg Island) during the LGM. Northwestward-flowing ice from the axis of the IIS in the central Arctic (Dyke 1999) also crossed Cornwall Island (Lamoureux and England 2000), contributing additional ice to Massey Sound that collectively advanced across Meighen Island and adjacent channels to the continental shelf. This conclusion raises the possibility that clastic sediment may have been delivered to the Arctic Ocean Basin from the former margin of the IIS in Heinrich-like events.
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Frisch, T., 1988. Reconnaissance geology of the Precambrian Shield of Ellesmere, Devon and Coburg Islands, Canadian Arctic Archipelago. Geological Survey of Canada Memoir 409. 102pp.
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O Cofaigh, C., England, J. and Zreda, M., 2000. Late Wisconsinan glaciation of southern Eureka Sound: evidence for extensive Innuitian ice in the Canadian High Arctic during the Last Glacial Maximum. Quaternary Science Reviews, 19: 1319-1341
Thorsteinsson, R. 1961. The history and geology of Meighen Island, Arctic Archipelago. Geological Survey of Canada Bulletin 75. 20pp.
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