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Basal gravel and sand mantling the bedrock floors of buried valleys throughout the Canadian Interior Plains, and conformably overlying proglacial lacustrine sediment, comprise the Empress Group. While previously conceptualized as stratigraphically equivalent deposits of preglacial rivers prior to the first and most extensive continental and montane glaciations, subsequent stratigraphic studies indicated that buried valley basal gravel must have been deposited between, or during, progressively more extensive continental glaciations and could not be stratigraphically equivalent throughout the buried valley network. However, in the general absence of formation-rank stratigraphic description of basal gravel units that might better inform the geologic history of the deposits, most workers simply consider Empress Group sediments time-transgressive. In this paper, we examine basal gravel at provincial and regional scales to understand its genesis and geologic history. At the provincial scale, we map basal gravel in three dimensions using a novel machine learning approach. At the regional scale, we formally define basal gravel formations at either end of the largest buried valley system in Alberta, which informs its glacial history and physiographic development and shows the importance of formation-rank stratigraphic description. Our results indicate that the buried valley network across Alberta is palimpsest in genesis and basal gravel units within it are chronostratigraphically intercalated between tills. We advocate that the Empress Group definition be extended across Alberta with modifications to improve its clarity and utility, and formally define the Old Fort, Unchaga, Ipiatik, and Winefred formations as part of the Empress Group. [ABSTRACT FROM AUTHOR]

The Paskapoo Formation of southern Alberta supports more groundwater wells than any other aquifer system in the Canadian Prairies. Located in a region of rapid population growth and straddling watersheds where no new surface water licenses are available, this aquifer system is under increasing pressure to provide water supply. The Paskapoo Formation represents a foreland deposit of a siltstone- and mudstone-dominated fluvial system. The system is highly heterogeneous with broad ranges in physical properties that impact groundwater production. High-porosity coarse-grained channel sandstone can provide productive wells, whereas thin and fractured sands and siltstones are low producers. The basal Haynes Member and western portion of the Paskpaoo Formation have higher sandstone volumes than other portions of the system. Fracture density shows a strong inverse relationship to bed thickness, such that fracture flow becomes more important for thinner sandstone beds. There is no regional-scale flow system associated with the Paskapoo Formation; rather it is dominated by local-scale recharge processes. The geochemistry of Paskapoo Formation groundwater is largely controlled by the variable composition of immediately overlying glacial deposits. La Formation de Paskapoo du sud de l’Alberta supporte plus de puits d’eau souterraine que tout autre système aquifère des Prairies canadiennes. Situé dans une région à forte croissance démographique et chevauchant des bassins versants pour lesquels aucun nouveau permis d’eau de surface n’est disponible, ce système aquifère est de plus en plus sollicité pour des approvisionnements en eau. La Formation de Paskapoo représente un dépôt d’avant-pays d’un système fluvial composé surtout de siltstones et de mudstones. Le système est hautement hétérogène et ses propriétés physiques couvrent une vaste plage de propriétés physiques qui ont un impact sur la production d’eau souterraine. Le grès de chenal, à porosité élevée et à grain grossier, peut alimenter des puits productifs alors que les siltstones et les sables fracturés minces produisent peu. Le membre Haynes à la base et la partie ouest de la Formation de Paskapoo ont des volumes de grès supérieurs aux autres parties du système. La densité des fractures présente une relation inverse à l’épaisseur des lits, telle que pour les lits de grès minces, l’écoulement dans les fractures devient plus important. Il n’y a aucun système à l’échelle régionale associé à la Formation de Paskapoo, il est plutôt dominé par des processus de recharge à l’échelle régionale. La géochimie de l’eau souterraine de la Formation de Paskapoo est principalement contrôlée par la composition variable des dépôts glaciaires qui reposent sur la formation. [ABSTRACT FROM AUTHOR]