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Buried valleys and till in the Canadian Prairies: geology, hydrogeology, and origin

We review over 100 years of literature on Prairie buried valleys and till to provide a platform for future research and policy development. Buried-valley aquifers in the Prairies commonly yield abundant groundwater. They have distinct geologies and distinct stratigraphic settings, which
impart them with distinct hydrogeological properties and give clues as to how they formed and filled. Prairie buried-valley aquifers are commonly encased in low-permeability strata: Cretaceous shale tends to underlie them and thick (10-300 m) low-permeability Quaternary till tends to overlie them.
This reduces recharge, in rare cases nearly completely, while protecting groundwater resources from contamination and drought. It also tends to lead to highly mineralized groundwater chemistries. The stratigraphic positions of Prairie buried valleys also speak to their origin: those that subtend
('hang') from the bedrock unconformity were likely eroded by preglacial fluvial systems during late Tertiary uplift of the Rocky Mountains, whereas those that subtend from surfaces within the till package are likely glaciofluvial valleys eroded in proglacial spillway or tunnel-valley settings.
Another key trait of Prairie buried valleys is that their fills tend to be heterogeneous and architecturally complex. Sand, gravel, mud, and diamicton are common; any one can dominate the fill at a given location. This heterogeneity, in conjunction with irregularity common to buried-valley bedrock
floors, commonly causes aquifer compartmentalization and makes prediction of aquifer potential difficult prior to drilling. It also suggests that most Prairie buried valleys filled over time, and possibly over multiple glaciations, in multiple deposition environments.

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