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TitleA hydrostratigraphic framework for the Paleozoic bedrock of Southern Ontario
AuthorCarter, T R; Fortner, L D; Russel, H A JORCID logo; Skuce, M F; Longstaffe, F J; Sun, S
SourceGeoscience Canada vol. 48, issue 1, 2021 p. 23-58, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20200731
PublisherGeological Association of Canada
Mediapaper; on-line; digital
File formatpdf; html
Lat/Long WENS -83.1667 -76.0000 45.5000 41.0000
SubjectsScience and Technology; groundwater; hydrochemistry; aquifer; bedrock; hydrostratigraphy; Paleozoic
Illustrationsdiagrams; location maps; stratigraphic charts; photographs; tables
ProgramGroundwater Geoscience
Released2021 03 31
AbstractGroundwater systems in the intermediate to deep subsurface of southern Ontario, and their past and current interaction with shallow potable groundwater and surface water, are poorly understood, despite their value for a number of societal uses. A regional hydrostratigraphic framework is a necessary precursor for improving our understanding and enabling development of a 3-D hydrostratigraphic model to visualize these groundwater systems. This study is a compilation and integration of published and unpublished geologic, hydrogeologic, hydrochemical and isotopic data collected over the past 10 years to develop that framework. Aquifers in the bedrock are thin and regionally extensive, separated by thick aquitards, within a well-defined lithostratigraphic framework and a well-developed hydrochemical depth zonation comprising: a shallow fresh water regime, an intermediate brackish to saline sulphur water regime, and a deep brine regime of ancient, evaporated seawater. Occurrence and movement of groundwater in shallow bedrock is principally controlled by modern (Quaternary) karstic dissolution of subcropping carbonate and evaporite rocks, and in the intermediate to deep subsurface by paleokarst horizons developed during the Paleozoic. Flow directions are down-gradient from topographic highs in the shallow regime and down the regional dip of bedrock formations in the intermediate regime, with recharge at subcrop edges by modern meteoric water and by glacial meltwater in the geologic past, and local discharge in topographic lows, quarries and up unplugged boreholes. Hydraulic gradient is up-dip in the deep brine regime, at least for the Guelph Aquifer and the Cambrian Aquifer, with no isotopic or hydrochemical evidence of infiltration of meteoric water and no discharge to the surface. Bedrock is covered by a thin veneer of surficial sediments that comprise an aquifer/aquitard system of considerable local variability and complexity. Fourteen bedrock hydrostratigraphic units are proposed, and one unit comprising all the surficial sediments. Assignment of lithostratigraphic units as hydrostratigraphic units is based principally on hydrogeologic characteristics of Paleozoic bedrock formations in the intermediate to deep groundwater regimes, below the influence of modern meteoric water. Carbonate and evaporite rocks which form aquitards in the subsurface may form aquifers at or near the surface, due to karstic dissolution by acidic meteoric water, necessitating compromises in assignment of hydrostratigraphic units.
Summary(Plain Language Summary, not published)
Description of different zones of nonsaline to saline water in southern Ontario and a hydrostratigraphic framework of the bedrock geology.

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