Glacial Dynamics and Stratigraphy in the Southern Great Slave Lake Region, Northwest Territories
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AbstractA detailed stratigraphic study was undertaken on a thick (>20 m) glacial diamicton at a former open pit (M-52) in the north-central part of the Pine Point mining district, adjacent to the southern shore of Great Slave Lake. This research augments the established regional Quaternary stratigraphy and investigates the mechanics of till deposition/emplacement throughout a continuous till sequence to understand better the glacial dynamics for the western margin of the Laurentide Ice Sheet. The exposures at pit M-52 sit directly on bedrock, and two visibly distinct tills are exposed, a grey till exposed at the base of the section and brown till in the upper portion. When a complete vertical section was cleared and examined, the contact between the two tills was indiscernible and suspected to be gradational over several metres. The gradational contact is likely a product of extensive glacial inheritance and mixing as glacial dynamics shifted during till accretion. The study at pit M-52 was correlated with studies conducted at pits K-62 and O-28. While at M-52, the contact was gradational, the studies at K-62 and O-28 had layered stratigraphy indicating that different depositional environments existed near each other, as described in the subglacial till mosaic model. Micromorphological examination of 25 till samples from pit M-52 show that tills were deposited in a soft subglacial deforming bed. The tills have evidence of multiple generations of deformation beginning with pervasive and transitioning into localized shear strain. Clast fabrics were measured in the section and revealed that the grey till close to the bedrock surface reflects SW ice flow, the upper two clast fabrics display evidence of NW ice flow.
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