Comment and Reply on ‘Keewatin Ice Sheet—Re-evaluation of the traditional concept of the Laurentide Ice Sheet’ and ‘Glacial erosion and ice sheet divides, northeastern Laurentide Ice Sheet, on the basis of the distribution of limestone erratics’

Geology ◽  
1980 ◽  
Vol 8 (10) ◽  
pp. 468 ◽  
Author(s):  
John T. Andrews ◽  
G. H. Miller
Keyword(s):  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Glacial Erosion ◽  
Traditional Concept

scholarly journals GIS analyses of ice-sheet erosional impacts on the exposed shield of Baffin Island, eastern Canadian Arctic

2015 ◽  
Vol 52 (11) ◽  
pp. 966-979 ◽  
Author(s):  
Karin Ebert
Keyword(s):  
Ice Sheet ◽  
Canadian Arctic ◽  
Laurentide Ice Sheet ◽  
Baffin Island ◽  
Glacial Erosion ◽  
Ice Sheet Erosion ◽  
The Impact ◽  
Exposure Ages ◽  
Eastern Canadian Arctic ◽  
Sheet Erosion

The erosional impacts of former ice sheets on the low-relief bedrock surfaces of Northern Hemisphere shields are not well understood. This paper assesses the variable impacts of glacial erosion on a portion of Baffin Island, eastern Canadian Arctic, between 68° and 72°N and 66° and 80°W. This tilted shield block was covered repeatedly by the Laurentide Ice Sheet during the late Cenozoic. The impact of ice-sheet erosion is examined with GIS analyses using two geomorphic parameters: lake density and terrain ruggedness. The resulting patterns generally conform to published data from other remote sensing studies, geological observations, cosmogenic exposure ages, and the distribution of the chemical index of alteration for tills. Lake density and terrain ruggedness are thereby demonstrated to be useful quantitative indicators of variable ice-sheet erosional impacts across Baffin Island. Ice-sheet erosion was most effective in the lower western parts of the lowlands, in a west–east-oriented band at around 350–400 m a.s.l., and in fjord-onset zones in the uplifted eastern region. Above the 350–400 m a.s.l. band and between the fjord-onset zones, ice-sheet erosion was not sufficient to create extensive ice-roughened or streamlined bedrock surfaces. The exception — where lake density and terrain ruggedness indicate that ice-sheet erosion had a scouring effect all across the study area — was in an area from Foxe Basin to Home Bay with elevations <400 m a.s.l. These morphological contrasts link to former ice-sheet basal thermal regimes during the Pleistocene. The zone of low glacial erosion surrounding the cold-based Barnes Ice Cap probably represents the ice cap’s greater extent during successive Pleistocene cold stages. Inter-fjord plateaus with few ice-sheet bedforms remained cold-based throughout multiple Pleistocene glaciations. In contrast, zones of high lake density and high terrain ruggedness are a result of the repeated development of fast-flowing, erosive ice in warm-based zones beneath the Laurentide Ice Sheet. These zones are linked to greater ice thickness over western lowland Baffin Island. However, adjacent lowland surfaces with similar elevations of non-eroded, weakly eroded, and ice-scoured shield bedrock indicate that—even in areas of high lake density and terrain ruggedness—the total depth of ice sheet erosion did not exceed 50 m.

Glacial Erosion by the Laurentide Ice Sheet

1978 ◽  
Vol 20 (83) ◽  
pp. 367-391 ◽  
Author(s):  
D. E. Sugden
Keyword(s):  
Thermal Regime ◽  
Basal Layer ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Lake Basin ◽  
List Type ◽  
Glacial Erosion ◽  
Ice Flow ◽  
Landscape Type ◽  
The North

AbstractThe aim of the paper is to analyse landscapes of glacial erosion associated with the Laurentide ice sheet at its maximum and to relate them lo the three main variables affecting glacial erosion, namely former basal thermal regime of the ice sheet, the topography of the bed, and the geology of the bed. The key to the analysis is the comparison of the distribution of landscape types with the simulated pattern of the basal thermal regime of the former ice sheet.Landscapes of areal scouring are found to be associated with zones of basal melting and occur beneath much of the former ice-sheet centre and in those places where the topography favoured converging ice flow. The landscape type may also have formed beneath cold-based ice when it was carrying debris inherited from an up-stream zone of regelation. Areas with little or no sign of glacial erosion occur primarily in the north in the Queen Elizabeth Islands but they also occur on uplands associated with diverging ice flow; they coincide with areas calculated to have been covered by cold-based ice devoid of debris. Landscapes of selective linear erosion are common on uplands near the eastern periphery of the ice sheet. In these situations, pre-existing valleys channelled ice flow and created a situation where there was warm-based ice over the valleys and cold-based protective ice over the intervening plateaux. Variations in the permeability of the bedrock base have modified the landscape pattern, mainly in those areas where there was a change from one basal thermal regime to another. In general, permeable rocks tend to have experienced less erosion than impermeable rocks.Using lake-basin density as an indication of the intensity of glacial erosion, a zone of maximum erosion is identified and this forms a ring between the centre of the former ice sheet and its periphery. This ring coincides with a zone where melt water from the ice-sheet centre is calculated to have frozen on to the bottom of the ice sheet. This regelation incorporated basal debris into the ice, forming a basal layer 20-50 m thick and afforded an efficient means of debris evacuation.A conceptual model is developed and hangs round the following postulates: (1)Landscapes of glacial erosion are related primarily to the basal thermal regime of the ice sheet.(2)Landscapes of glacial erosion are equilibrium forms related to maximum glacial conditions. This implies that at some stage in the Pleistocene the Laurentide ice sheet was in a stable maximum condition for a long period of time.(3)Mechanisms allowing evacuation of debris rather than those of abrasion or fracture may be the most important in influencing the amount of erosion achieved by an ice sheet.(4)Cold-based ice may accomplish erosion if it contains debris.

Keewatin Ice Sheet—Re-evaluation of the traditional concept of the Laurentide Ice Sheet

Geology ◽  
1979 ◽  
Vol 7 (11) ◽  
pp. 537 ◽  
Author(s):  
W. W. Shilts ◽  
C. M. Cunningham ◽  
C. A. Kaszycki
Keyword(s):  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Traditional Concept

Glacial dispersal of rock debris in central Gaspésie, Quebec, Canada

1993 ◽  
Vol 30 (8) ◽  
pp. 1697-1707 ◽  
Author(s):  
Rémi Charbonneau ◽  
Peter P. David
Keyword(s):  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Glacial History ◽  
Dispersal Pattern ◽  
Glacial Erosion ◽  
Ice Flow ◽  
Granite Pluton ◽  
Alpine Glacier ◽  
History Of ◽  
Late Wisconsinan

The lithological content of tills in central Gaspésie is evaluated by pebble counting of 231 samples collected in excavation pits and containing 200 pebbles each. The results are used here to establish the pattern of debris dispersal and to infer the glacial history of the area. The dispersal pattern is characterized by well-defined southeasterly (160–170°) and northeasterly (40–60°) trending trains. Half-distance values of glacial transport along the trains range from 5 to 9 km for both directions, suggesting ice flow events of considerable magnitude. The volume of material in the trains represents 1–6 m of glacial erosion of the bedrock. Glacial cirques and short U-shaped valleys, about 100–200 m deep, are incised into the McGerrigle Mountains granite pluton as well as the adjacent metabasalt. The corresponding trains are aligned with these erosional features, indicating that their clast content was derived from those features during an early Alpine Glacier Phase. The southeasterly trending dispersal trains are associated with an invasion of central Gaspésie by the Laurentide Ice Sheet during the Early Wisconsinan, whereas the northeasterly trending trains are associated with a local centre of outflow over Gaspésie during the Late Wisconsinan.

Glacial Erosion by the Laurentide Ice Sheet

1978 ◽  
Vol 20 (83) ◽  
pp. 367-391 ◽  
Author(s):  
D. E. Sugden
Keyword(s):  
Thermal Regime ◽  
Basal Layer ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Lake Basin ◽  
List Type ◽  
Glacial Erosion ◽  
Ice Flow ◽  
Landscape Type ◽  
The North

Abstract The aim of the paper is to analyse landscapes of glacial erosion associated with the Laurentide ice sheet at its maximum and to relate them lo the three main variables affecting glacial erosion, namely former basal thermal regime of the ice sheet, the topography of the bed, and the geology of the bed. The key to the analysis is the comparison of the distribution of landscape types with the simulated pattern of the basal thermal regime of the former ice sheet. Landscapes of area scouring are found to be associated with zones of basal melting and occur beneath much of the former ice-sheet centre and in those places where the topography favoured converging ice flow. The landscape type may also have formed beneath cold-based ice when it was carrying debris inherited from an up-stream zone of regelation. Areas with little or no sign of glacial erosion occur primarily in the north in the Queen Elizabeth Islands but they also occur on uplands associated with diverging ice flow; they coincide with areas calculated to have been covered by cold-based ice devoid of debris. Landscapes of selective linear erosion are common on uplands near the eastern periphery of the ice sheet. In these situations, pre-existing valleys channelled ice flow and created a situation where there was warm-based ice over the valleys and cold-based protective ice over the intervening plateaux. Variations in the permeability of the bedrock base have modified the landscape pattern, mainly in those areas where there was a change from one basal thermal regime to another. In general, permeable rocks tend to have experienced less erosion than impermeable rocks. Using lake-basin density as an indication of the intensity of glacial erosion, a zone of maximum erosion is identified and this forms a ring between the centre of the former ice sheet and its periphery. This ring coincides with a zone where melt water from the ice-sheet centre is calculated to have frozen on to the bottom of the ice sheet. This regelation incorporated basal debris into the ice, forming a basal layer 20-50 m thick and afforded an efficient means of debris evacuation. A conceptual model is developed and hangs round the following postulates: (1) Landscapes of glacial erosion are related primarily to the basal thermal regime of the ice sheet. (2) Landscapes of glacial erosion are equilibrium forms related to maximum glacial conditions. This implies that at some stage in the Pleistocene the Laurentide ice sheet was in a stable maximum condition for a long period of time. (3) Mechanisms allowing evacuation of debris rather than those of abrasion or fracture may be the most important in influencing the amount of erosion achieved by an ice sheet. (4) Cold-based ice may accomplish erosion if it contains debris.

Displacement of Salt by the Laurentide Ice Sheet

1992 ◽  
Vol 38 (3) ◽  
pp. 305-315 ◽  
Author(s):  
William A. White
Keyword(s):  
New York ◽  
North America ◽  
Ice Sheet ◽  
Canadian Shield ◽  
Laurentide Ice Sheet ◽  
Glacial Erosion ◽  
Saginaw Bay ◽  
Central New York ◽  
Lower Peninsula ◽  
Salt Deposits

AbstractIn central New York, deformation of salt of the Salina Formation by the Laurentide Ice Sheet is shown by a thinning of the salt stratum in and near the outcrop zone where it was overridden by the ice sheet and by a thickening down-dip near the glacial limit. Less definitive suggestions of deformation by glacial overriding of the Salina outcrop zone in northeastern Ohio are seen in salt-cored anticlines in the vicinity of the glacial limit. In the lower peninsula of Michigan, isopachs of salt curve around Saginaw Bay, which suggests that the salt was displaced southwestward, away from the bay, by pressure of the Saginaw lobe of the ice sheet. All but one of the major Paleozoic salt deposits of North America lie in a zone that girdles two-thirds of the Canadian Shield from where glacial erosion removed all but occasional outliers of Phanerozoic strata.

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