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Deformation of the Batestown till of the Lake Michigan lobe, Laurentide ice sheet

Journal of Glaciology

By:
,
DOI: 10.3189/002214309788608877

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Abstract

Deep, pervasive shear deformation of the bed to high strains (>100) may have been primarily responsible for flow and sediment transport of the Lake Michigan lobe of the Laurentide ice sheet. To test this hypothesis, we sampled at 0.2 m increments a basal till from one advance of the lobe (Batestown till) along vertical profiles and measured fabrics due to both anisotropy of magnetic susceptibility and sand-grain preferred orientation. Unlike past fabric studies, interpretations were guided by results of laboratory experiments in which this till was deformed in simple shear to high strains. Fabric strengths indicate that more than half of the till sampled has a <5% probability of having been sheared to moderate strains (7-30). Secular changes in fabric azimuth over the thickness of the till, probably due to changing ice-flow direction as the lobe receded, indicate that the bed accreted with time and that the depth of deformation of the bed did not exceed a few decimeters. Orientations of principal magnetic susceptibilities show that the state of strain was commonly complex, deviating from bed-parallel simple shear. Deformation is inferred to have been focused in shallow, temporally variable patches during till deposition from ice.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Deformation of the Batestown till of the Lake Michigan lobe, Laurentide ice sheet
Series title:
Journal of Glaciology
DOI:
10.3189/002214309788608877
Volume
55
Issue:
189
Year Published:
2009
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Journal of Glaciology
First page:
131
Last page:
146
Number of Pages:
16