ABSTRACT: The geomorphic footprint of a Late Wisconsinan Ice stream in northeast Newfoundland.

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Abstract

A recent conceptual model of late Wisconsinan glaciation of Atlantic Canada proposed that an ice stream in Notre Dame Bay drained a large part of northeastern Newfoundland through Notre Dame Channel to the continental shelf edge. Recent progress on ice flow mapping in the Exploits Valley region of northeast Newfoundland has revealed that topographically-controlled ice streaming was active during the last deglaciation. This region is dominated by bedrock-controlled topography, with granitic intrusions forming local topographic highs and lowlands underlain by siliclastic sediments. Ice flow history was interpreted based on landform mapping from 1:50 000 aerial photograph and SRTM digital elevation data, as well as a striation database maintained by the Geological Survey of Newfoundland and Labrador. Mapped features, including drumlins, megaflutes, crag-and-tail hills, and ribbed moraine, were integrated into flow sets using a glaciological inversion model. Several criteria were used for the interpretation of ice streaming: convergence of subglacial, flow-parallel landforms; distribution of subglacial, flow-perpendicular landforms; and patterns of highly attenuated bedforms. A total of 4 ice flow events were identified on the basis of cross-cutting of flow-parallel features and striations. The earliest ice flow was an east to southeastward flow, followed by a regional north-northeastward flow, which is interpreted to have overridden major topographic highs. A third flow is interpreted to represent deglacial ice streaming. A final localized eastward ice flow has been identified in the striation record only and likely represents a re-advance from a remnant ice cap to the west of Grand Falls. Flow parallel features within the interpreted ice stream flow set display a convergent pattern of landforms. The ice-stream footprint has a width of 55 km at its head narrowing to 25 km in the trunk, with a total length of 75 km. Landforms in the footprint are typically longer than those in adjacent areas (mean = 1730 m vs. 1490 m). Landforms typically increase in length in a downstream direction with a mean length of 1610 m in the onset zone and 1840 m (maximum of 5060 m) in the trunk. Additionally, elongation ratios increase in a down¬stream direction with a mean of 3.6:1 in the onset zone and 5.7:1 in the trunk with a maximum of 18:1 along a central line. Ribbed moraine are most common at the head of the flow, although there are minor occurrences throughout. Where they co-occur, ribbed moraine overprint flow-parallel features. These observations are interpreted to represent the geomorphic footprint of a topographically-controlled ice stream that continued offshore through a deep marine trough.

Bibliography of Canadian Geomorphology