| Title | Newmarket Till aquitard: optimum grain packing with a pore-filling calcite-rich cement |
| Download | Download (whole publication) |
| |
| Licence | Please note the adoption of the Open Government Licence - Canada
supersedes any previous licences. |
| Author | 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; 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  Open
Access |
| Year | 2018 |
| Publisher | Natural Resources Canada |
| Meeting | Regional-Scale Groundwater Geoscience in Southern Ontario: Open House; Guelph; CA; February 28 - March 1, 2018 |
| Document | open file |
| Lang. | English |
| Media | on-line; digital |
| Related | This publication is contained in Regional-scale groundwater
geoscience in southern Ontario: an Ontario Geological Survey, Geological Survey of Canada, and Conservation Ontario geoscientists open house |
| File format | pdf |
| Province | Ontario |
| NTS | 30M/13; 30M/14; 30M/15; 30M/16; 31C/04; 31D/01; 31D/02; 31D/03; 31D/04 |
| Area | Central Ontario; Newmarket; Aurora; Whitby; Toronto; Port Hope; Trenton |
| Lat/Long WENS | -80.0000 -77.7500 44.2500 43.7500 |
| Subjects | hydrogeology; 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; Phanerozoic; Cenozoic; Quaternary |
| Program | Groundwater Geoscience Aquifer Assessment & support to mapping |
| Released | 2018 02 16 |
| Abstract | 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). |
| Summary | (Plain Language Summary, not published)
Proceedings for a workshop in Guelph Ontario as part of the program S&T exchange. Abstracts have been contributed by Ontario Geological Survey, Ministry
of Environment and Climate Change, Conservation Authorities, Universities, private sector, and Unites States Geological Survey. |
| GEOSCAN ID | 306539 |
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