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Microstructures and microshears as proxy for strain in subglacial diamicts; implications for basal till formation

Nicolaj K. Larsen, Jan A. Piotrowski and Frits Christiansen
Microstructures and microshears as proxy for strain in subglacial diamicts; implications for basal till formation
Geology (Boulder) (October 2006) 34 (10): 889-892

Abstract

Ring-shear experiments were used to study subglacial sediment deformation and the development of S-matrix microstructures and microshears to constrain glacially induced deformation in diamicts. The experiments approximated subglacial conditions, and the diamict was sheared and sampled incrementally to strains of 0, 7, 18, 33, 57, and 107. At strains between 7 and 18, a steady association of S-matrix microstructures developed, which did not evolve further despite continued shearing. The I (sub L) -index, a measure of microshear-orientation strength parallel to the shearing direction correlates log-linearly with strain, which indicates its potential use as strain proxy. The ring-shear data were compared with the characteristics of Quaternary basal tills from Denmark, Poland, and Svalbard. Based on I (sub L) -index values, we conclude that these tills only experienced strain of approximately 10 (super 1) , which is orders of magnitude lower than expected for deformation tills. This suggests that pervasive subglacial deformation and sediment advection in the mobile layer at the ice-bed interface may be less significant than previously assumed.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 34
Serial Issue: 10
Title: Microstructures and microshears as proxy for strain in subglacial diamicts; implications for basal till formation
Affiliation: University of Aarhus, Department of Earth Sciences, Aarhus, Denmark
Pages: 889-892
Published: 200610
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 29
Accession Number: 2006-083973
Categories: Quaternary geologySedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus.
N54°15'00" - N58°00'00", E08°00'00" - E13°00'00"
N49°00'00" - N54°45'00", E14°15'00" - E24°15'00"
N74°25'00" - N81°00'00", E10°03'00" - E30°00'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 200647
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