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TitleNewmarket Till aquitard: optimum grain packing with a pore-filling calcite-rich cement
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AuthorKjarsgaard, 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; by Russell, H A J; Ford, D; Priebe, E H; Holysh, S; Geological Survey of Canada, Open File 8363, 2018 p. 21, https://doi.org/10.4095/306539
Year2018
PublisherNatural Resources Canada
MeetingRegional-Scale Groundwater Geoscience in Southern Ontario: Open House; Guelph; CA; February 28 - March 1, 2018
Documentopen file
Lang.English
Mediaon-line; digital
RelatedThis publication is contained in 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, Geological Survey of Canada, Open File 8363
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; geophysics; geochemistry; groundwater; glacial deposits; tills; permeability; calcite; cementation; grain size distribution; sands; silts; clasts; boulders; vadose zones; seismic interpretations; seismic velocities; mineralogical analyses; electron microscope analyses; x-ray emission spectroscopy; x-ray diffraction analyses; drill core analyses; Newmarket Till; Dummer Moraine; aquitards; diamictons; pore-filling; Phanerozoic; Cenozoic; Quaternary
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Location
 
Natural Resources Canada Library - Ottawa (Earth Sciences)
 
ProgramAquifer Assessment & support to mapping, Groundwater Geoscience
Released2018 02 16
AbstractNewmarket 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).
GEOSCAN ID306539