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TitreNewmarket Till aquitard: optimum grain packing with a pore-filling calcite-rich cement
TéléchargerTéléchargement (publication entière)
AuteurKjarsgaard, B A; Sharpe, D R; Knight, R D; Stepner, D; Russell, H A J
SourceRegional-scale groundwater geoscience in southern Ontario: an Ontario Geological Survey, Geological Survey of Canada, and Conservation Ontario geoscientists open house; par Russell, H A J; Ford, D; Priebe, E H; Holysh, S; Commission géologique du Canada, Dossier public 8363, 2018 p. 21, (Accès ouvert)
ÉditeurRessources naturelles Canada
RéunionRegional-Scale Groundwater Geoscience in Southern Ontario: Open House; Guelph; CA; février 28 - mars 1, 2018
Documentdossier public
Mediaen ligne; numérique
Référence reliéeCette publication est contenue dans Russell, H A J; Ford, D; Priebe, E H; Holysh, S; (2018). Regional-scale groundwater geoscience in southern Ontario: an Ontario Geological Survey, Geological Survey of Canada, and Conservation Ontario geoscientists open house, Commission géologique du Canada, Dossier public 8363
SNRC30M/13; 30M/14; 30M/15; 30M/16; 31C/04; 31D/01; 31D/02; 31D/03; 31D/04
Lat/Long OENS -80.0000 -77.7500 44.2500 43.7500
Sujetseau souterraine; dépôts glaciaires; tills; perméabilité; calcite; cimentation; repartition granulométrique; sables; silts; clastes; blocs; zones vadoses; interpretations sismiques; vitesse des ondes sismiques; analyses minéralogiques; analyses par microscope électronique; spectroscopie aux rayons x; analyses par diffraction des rayons x; analyses de carottes de sondage; Till de Newmarket ; Moraine de Dummer ; hydrogéologie; géologie des dépôts meubles/géomorphologie; minéralogie; sédimentologie; géophysique; géochimie; Phanérozoïque; Cénozoïque; Quaternaire
ProgrammeAquifer Assessment & support to mapping, Géoscience des eaux souterraines
Diffusé2018 02 16
Résumé(disponible en anglais seulement)
Newmarket Till is a stony, sandy (38%) silty (~47%) diamicton, which is of variable thickness (~1 - 69 m) and of widespread distribution in Southern Ontario. The Newmarket Till has unusually high densities
(2.2 - 2.4 g/cm3); elevated seismic velocities (Vp ~2600 m/s) determined by downhole geophysical studies are characteristic and the Till can be traced across the region as a seismostratigraphic marker. As the Till is highly indurated and has low permeability, it forms a regional aquitard that confines underlying aquifers, and is also a basal aquitard for overlying aquifers (e.g. Oak Ridges Moraine). Given the high sand content of this diamicton, the low permeability and indurated nature is surprising, and could be resultant from over-consolidation due to glacial loading, presence of a secondary cement, or both processes.
Recent observations from drill core and surficial sampling transects illustrate that Newmarket Till is not always cemented, but the observation of residual cement on pebbles indicates it was potentially formerly cemented. Our new studies indicate that the matrix of the Dummer moraine (adjacent to and south of the Shield - Paleozoic boundary and to the north of the Newmarket Till) is mineralogically and geochemically equivalent to Newmarket Till, and we thus suggest the Dummer Moraine is a very stone- to boulder-rich equivalent of the Newmarket Till. The matrix mineral assemblage of the Till (in decreasing abundance) is quartz, calcite, K-feldspar, plagioclase, dolomite, amphibole and clinopyroxene; these grains are comminuted and range in size from ~2000 ?m to ~2 ?m, leading to optimum packing, and potentially over-consolidation. The intra-grain matrix is exceptionally fine (<1 ?m, typically 0.25 - 0.50 ?m) and not resolvable by optical methods. Higher resolution SEM and FE-SEM backscattered electron and secondary electron images of the intra-grain matrix reveals a complex pore filling cement. The minerals comprising the secondary cement are a challenge to analyze due to their very fine grain size and composition. Semi-quantitative EDS analyses indicate a calcite (CaCO3) cement with minor phyllosilicates, as confirmed by XRD on the clay-silt and clay fractions. The calcite cements the silt- to sand-sized mineral grains and larger clasts, and result in the Newmarket Till being highly indurated and of low permeability. The timing and process of the initial cementation event is currently being evaluated; we also note that in the vadose zone the Till becomes uncemented (i.e. the original calcite cement dissolves out).