| Titre | Newmarket Till aquitard: optimum grain packing with a pore-filling calcite-rich cement |
| Télécharger | Téléchargement (publication entière) |
| |
| Licence | Veuillez noter que la Licence du gouvernement
ouvert - Canada remplace toutes les licences antérieures. |
| Auteur | Kjarsgaard, B A ;
Sharpe, D R; Knight, R D; Stepner, D; Russell, H A J |
| Source | Regional-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, https://doi.org/10.4095/306539  Accès ouvert |
| Année | 2018 |
| Éditeur | Ressources naturelles Canada |
| Réunion | Regional-Scale Groundwater Geoscience in Southern Ontario: Open House; Guelph; CA; février 28 - mars 1, 2018 |
| Document | dossier public |
| Lang. | anglais |
| DOI | https://doi.org/10.4095/306539 |
| Media | en ligne; numérique |
| Référence reliée | Cette publication est contenue dans Regional-scale groundwater geoscience in southern Ontario: an Ontario Geological Survey, Geological Survey of Canada, and Conservation Ontario geoscientists open house |
| Formats | pdf |
| Province | Ontario |
| SNRC | 30M/13; 30M/14; 30M/15; 30M/16; 31C/04; 31D/01; 31D/02; 31D/03; 31D/04 |
| Région | Central Ontario; Newmarket; Aurora; Whitby; Toronto; Port Hope; Trenton |
| Lat/Long OENS | -80.0000 -77.7500 44.2500 43.7500 |
| Sujets | eau 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 |
| Programme | Géoscience des eaux souterraines , Aquifer Assessment & support to mapping |
| Diffusé | 2018 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). |
| Sommaire | (Résumé en langage clair et simple, non publié)
Compte rendu d'un atelier à Guelph, en Ontario, dans le cadre du programme Échange de ST. Des résumés ont été fournis par la Commission
géologique de l'Ontario, le ministère de l'Environnement et du Changement climatique, les Conservatin Authorities, les universités, le secteur privé, et Unites States Geological Survey. |
| GEOSCAN ID | 306539 |
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