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RESEARCH |
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Jerome Lesemann (2012)
Abstract This thesis explores subglacial processes, glacier dynamics, and deglacial processes and patterns associated with the Cordilleran Ice Sheet (CIS) in Okanagan Valley and the neighbouring Thompson Plateau in southern British Columbia. Reconstructions of subglacial processes in an area of streamlined bedforms (drumlins) on Thompson Plateau reveal that sediments within drumlins and in intervening areas record evidence of lodgement, deformation, poreflow, conduit flow, debris flows, and suspension settling of fines within a network of subglacial cavities. These subglacial cavities developed within a regional bedrock basin, and these sediments demonstrate that substrate deformation is not a dominant and pervasive process recorded within the drumlins. Based on i) drumlin morphology and pattern, including the presence of stoss-side crescentic troughs and en echelon arrangement, ii) drumlin composition consisting of sediment and bedrock, it is argued that drumlins on Thompson Plateau have an erosional origin. Further, regional spatial associations between drumlins and tunnel valleys (including some in bedrock) on Thompson Plateau and in Okanagan Valley, and arguments relying on the conservation of eroded sediments suggest that erosion by subglacial meltwater underburst(s) best explains the range of observations. Underbursts may have been associated with development and drainage of a subglacial ‘catch lake’ in Okanagan Valley. High geothermal heat flux in Okanagan Valley could have favoured subglacial lake development. Subglacial volcanic eruptions may have acted as triggers for lake drainage. Lastly, deglaciation of the CIS led to development of a proglacial lake in Okanagan Valley (glacial Lake Penticton - gLP). Sediment delivery to gLP occurred via tributary valleys and possibly from an ice tongue along the valley axis. Regional delta correlations record a highstand of gLP at 500-525 m asl followed by a single drainage event which eroded a portion of the lacustrine valley fill to produce distinctive remnant valley-side benches (‘White Silt’ terraces) of lacustrine sediments. No evidence of glacioisostatic tilting could be discerned within the gLP basin, this absence is tentatively ascribed to lithospheric conditions favouring rapid crustal rebound, and to thin ice with uniform thickness in the gLP basin.
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