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TitleDeformation 'boundary front' movements in subglacial tills - a microsedimentological perspective from till sequences near Pine Point, NWT, Canada
AuthorMenzies, J; Paulen, R CORCID logo; Rice, J MORCID logo; McClenaghan, M BORCID logo; Oviatt, N M; Dhillon, N
SourceThe Depositional Record vol. 5, issue 2, 2019 p. 230-246, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20170389
Mediapaper; on-line; digital
File formatpdf; html
ProvinceNorthwest Territories
NTS85A; 85B; 85G; 85H
AreaPine Point Mining District; Pine Point
Lat/Long WENS-116.0000 -112.0000 62.0000 60.0000
Subjectssurficial geology/geomorphology; sedimentology; Nature and Environment; Science and Technology; glacial deposits; tills; stress analyses; deformation; shear stress; till samples; lithofacies; depositional environment; glaciation; ice sheets; ice flow; modelling; grain size distribution; clays; Western Canada Sedimentary Basin; Canadian Shield; Laurentide Ice Sheet; Phanerozoic; Cenozoic; Quaternary
Illustrationslocation maps; photographs; ternary diagrams; tables; rose diagrams; stereonets; photomicrographs; lithologic logs; 3-D models
ProgramGEM2: Geo-mapping for Energy and Minerals Mackenzie Corridor, Southern Mackenzie Surficial Mapping
Released2019 05 18
AbstractInvestigations of glacial sediment exposures in a former open pit in the Pine Point Mining District, Northwest Territories, reveal evidence of changes in stress magnitude as exhibited by the movement of deformation 'fronts' within subglacial tills, as evident through micromorphological analysis. Indications of deformation, driven by stress fluctuations, were observed throughout a set of vertical subglacial till samples associated with the Laurentide Ice Sheet (LIS). These tills exhibit multiple sub-lithofacies variations in concert with marked changes in microshear orientation, which can be directly related to changing stress levels within a subglacial deforming bed. The evidence of changes in till stress conditions is typical of subglacial tills occurring beneath an active temperate ice mass within a soft deforming bed. As differing 'layers' of till that form a mosaic-like pattern, become immobilized and 'detached' subjacent to the deforming bed sediments, a signature of this action is recorded within the tills as sequences of specific microstructures. These microstructures are part of a spectrum of micro-forms that develop as consequence of changes in stress, porewater content, and clay content within the 'fault-gouge' - like environment formed beneath an active temperate ice sheet. A model is developed that uses data from Pit O-28 demonstrating where deformation 'boundary front' evidence in the form of deformation bands has developed as basal driven stress levels have penetrated active deforming sediments. The evidence from Pine Point indicates that till acts as an excellent palaeo-strain record of past active glacial processes, subglacial basal thermal conditions and sediment mobility.
Summary(Plain Language Summary, not published)
This journal paper is a summary of the research conducted by Mr. Rice for his GEM1 supported MSc thesis conducted at the Pine Point mine site, and is value added science and knowledge added to three published data sets which include: GSC Current Research Paper 2013-5, GSC OF 7526 and Rice's MSc thesis. This journal paper discusses the nature of the thick sequence of glacial sediments that were deposited on the southern edge of Great Slave Lake, NWT, using novel techniques of micromorphological analysis (i.e., examination of thin sections created from the till units). This type of research helps us understand the glacial dynamics of till formation and deposition, in context of application of mineral dispersal and drift exploration in glaciated terrain.

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