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TitleNewmarket Till aquitard: optimum grain packing with a pore-filling calcite-rich cement
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AuthorKjarsgaard, B A; Knight, R D; Russell, H A J; Sharpe, D R; Crow, H; Olson, L
SourceRegional-scale groundwater geoscience in southern Ontario: an Ontario Geological Survey, Geological Survey of Canada, and Conservation Ontario open house; by Russell, H A J; Ford, D; Priebe, E H; Geological Survey of Canada, Open File 8212, 2017 p. 22, https://doi.org/10.4095/299778
Year2017
PublisherNatural Resources Canada
MeetingOntario Geological Survey and Geological Survey of Canada groundwater geoscience open house; Guelph; CA; March 1-2, 2017
Documentopen file
Lang.English
Mediaon-line; digital
RelatedThis publication is contained in Russell, H A J; Ford, D; Priebe, E H; (2017). Regional-scale groundwater geoscience in southern Ontario: an Ontario Geological Survey, Geological Survey of Canada, and Conservation Ontario open house, Geological Survey of Canada, Open File 8212
File formatpdf
ProvinceOntario
NTS30M/13; 30M/14; 30M/15; 30M/16; 31C/04; 31D/01; 31D/02; 31D/03; 31D/04
AreaCentral Ontario; Newmarket; Aurora; Whitby; Toronto; Port Hope; Trenton
Lat/Long WENS -80.0000 -77.7500 44.2500 43.7500
Subjectshydrogeology; surficial geology/geomorphology; mineralogy; sedimentology; groundwater; glacial deposits; tills; permeability; calcite; cementation; grain size distribution; sands; silts; clasts; mineralogical analyses; electron microscope analyses; Holocene; Pleistocene; Newmarket Till; diamictons; aquitards; pore spaces; portlandite; Phanerozoic; Cenozoic; Quaternary
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Location
 
Natural Resources Canada Library - Ottawa (Earth Sciences)
 
ProgramAquifer Assessment & support to mapping, Groundwater Geoscience
ProgramAquifer Assessment & support to mapping, Groundwater Geoscience
Released2017 02 22
AbstractNewmarket Till is a stony, sandy (38%) silty (~47%) diamicton, which is of variable thickness (~1 - 69 m) and of widespread distribution (correlated with Catfish Creek Till) 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. Clasts larger than coarse gravel consist of granitoids and limestone, however clasts smaller than coarse gravel are dominated by limestone, with rare granitoids. The mineral assemblage (in decreasing abundance) is quartz, calcite, K-feldspar, plagioclase, dolomite, amphibole and clinopyroxene; these grains are comminuted and range in size from ~1000 micrometres to ~2 micrometres, leading to optimum packing. The intra-grain matrix is exceptionally fine (<1 micrometres, typically 0.25 - 0.50 micrometres) 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, with a very low percentage (<1%) of open pore space. The minerals comprising the secondary cement are a challenge to analyze due to their very fine grain size and composition. Preliminary semiquantitative EDS analyses suggest they consist of calcite (CaCO3) and portlandite (Ca[OH]2), with minor phyllosilicates, and possibly hydrated calcium-rich silicate minerals (CSH). The Ca-rich minerals cement the silt- to sand-sized mineral grains and larger clasts, and result in the Newmarket Till being highly indurated and of low permeability. The presence of calcite and portlandite in a glaciogenic sediment cement is quite unusual. Additional analytical work is being undertaken to fully characterize the mineralogy of these Late Wisconsin / Holocene cements.
GEOSCAN ID299778