The effect of grain texture on the occurrence of microstructural properties in subglacial till
In this paper, we examine whether till grain size affects the range and occurrence of micromorphological features associated with subglacial shear. Our till samples were collected from two glaciers in Iceland, and varied in texture from a coarse, sandy clast-rich till (Fjallsjokull) to a fine-graine...
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2004
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ftucl:oai:eprints.ucl.ac.uk.OAI2:36356 2023-05-15T16:21:48+02:00 The effect of grain texture on the occurrence of microstructural properties in subglacial till Hart, JK Khatwa, A Sammonds, P 2004-12 http://discovery.ucl.ac.uk/36356/ unknown PERGAMON-ELSEVIER SCIENCE LTD QUATERNARY SCI REV , 23 (23-24) 2501 - 2512. (2004) GLACIER BED ICE STREAM MICROSCOPIC EVIDENCE PARADIGM SHIFT DEFORMATION DEBRIS SIZE CLASSIFICATION SEDIMENTATION PARTICLE Article 2004 ftucl 2017-02-09T23:10:52Z In this paper, we examine whether till grain size affects the range and occurrence of micromorphological features associated with subglacial shear. Our till samples were collected from two glaciers in Iceland, and varied in texture from a coarse, sandy clast-rich till (Fjallsjokull) to a fine-grained silty-sandy till (Vestari-Hagafellsjokull). We found a wide range of deformational microstructures that included skelsepic plasmic fabric, intraclasts of pre-existing eroded bedrock (basalt) and weathered clay and 'mini-shear zones' between clasts. We classified our micromorphological data into three classes; rotational, intermediate and linear. In addition to these observations, we performed extensive microfabric analysis at different scales on all of our samples. We found that the coarse-grained till contained a greater number and variety of microstructures than the fine-grained till. In addition, the fine-grained till showed a distinct lack of rotational structures that we attribute to the lack of significantly sized clasts in the matrix. We argue that the varied texture of the coarse-grained till provides a greater degree of perturbation within the shearing layer and so more distinct microstructures form. In a more fine-grained till, shearing is more homogeneous since there are less perturbations in the matrix and this leads to a more singular kind of microstructure. Our observations suggest that subglacial shear occurs within a multi-layered patchwork of different grain sizes, competence and pore water pressures. It is these factors that are so crucial in determining the occurrence and type of microstructural evidence we see in subglacial tills. (C) 2004 Elsevier Ltd. All rights reserved. Article in Journal/Newspaper glacier Iceland University College London: UCL Discovery |
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University College London: UCL Discovery |
op_collection_id |
ftucl |
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topic |
GLACIER BED ICE STREAM MICROSCOPIC EVIDENCE PARADIGM SHIFT DEFORMATION DEBRIS SIZE CLASSIFICATION SEDIMENTATION PARTICLE |
spellingShingle |
GLACIER BED ICE STREAM MICROSCOPIC EVIDENCE PARADIGM SHIFT DEFORMATION DEBRIS SIZE CLASSIFICATION SEDIMENTATION PARTICLE Hart, JK Khatwa, A Sammonds, P The effect of grain texture on the occurrence of microstructural properties in subglacial till |
topic_facet |
GLACIER BED ICE STREAM MICROSCOPIC EVIDENCE PARADIGM SHIFT DEFORMATION DEBRIS SIZE CLASSIFICATION SEDIMENTATION PARTICLE |
description |
In this paper, we examine whether till grain size affects the range and occurrence of micromorphological features associated with subglacial shear. Our till samples were collected from two glaciers in Iceland, and varied in texture from a coarse, sandy clast-rich till (Fjallsjokull) to a fine-grained silty-sandy till (Vestari-Hagafellsjokull). We found a wide range of deformational microstructures that included skelsepic plasmic fabric, intraclasts of pre-existing eroded bedrock (basalt) and weathered clay and 'mini-shear zones' between clasts. We classified our micromorphological data into three classes; rotational, intermediate and linear. In addition to these observations, we performed extensive microfabric analysis at different scales on all of our samples. We found that the coarse-grained till contained a greater number and variety of microstructures than the fine-grained till. In addition, the fine-grained till showed a distinct lack of rotational structures that we attribute to the lack of significantly sized clasts in the matrix. We argue that the varied texture of the coarse-grained till provides a greater degree of perturbation within the shearing layer and so more distinct microstructures form. In a more fine-grained till, shearing is more homogeneous since there are less perturbations in the matrix and this leads to a more singular kind of microstructure. Our observations suggest that subglacial shear occurs within a multi-layered patchwork of different grain sizes, competence and pore water pressures. It is these factors that are so crucial in determining the occurrence and type of microstructural evidence we see in subglacial tills. (C) 2004 Elsevier Ltd. All rights reserved. |
format |
Article in Journal/Newspaper |
author |
Hart, JK Khatwa, A Sammonds, P |
author_facet |
Hart, JK Khatwa, A Sammonds, P |
author_sort |
Hart, JK |
title |
The effect of grain texture on the occurrence of microstructural properties in subglacial till |
title_short |
The effect of grain texture on the occurrence of microstructural properties in subglacial till |
title_full |
The effect of grain texture on the occurrence of microstructural properties in subglacial till |
title_fullStr |
The effect of grain texture on the occurrence of microstructural properties in subglacial till |
title_full_unstemmed |
The effect of grain texture on the occurrence of microstructural properties in subglacial till |
title_sort |
effect of grain texture on the occurrence of microstructural properties in subglacial till |
publisher |
PERGAMON-ELSEVIER SCIENCE LTD |
publishDate |
2004 |
url |
http://discovery.ucl.ac.uk/36356/ |
genre |
glacier Iceland |
genre_facet |
glacier Iceland |
op_source |
QUATERNARY SCI REV , 23 (23-24) 2501 - 2512. (2004) |
_version_ |
1766009791039143936 |