| Title | What pore water chemistry in Champlain Sea muds reveals about hydrogeology, marine salinity, and sensitivity to landslides |
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| Author | Hinton, M ; Alpay,
S; Crow, H |
| Source | GAC-MAC-IAH 2019: where geosciences converge/AGC-AMC-AIH 2019 : où les géosciences convergent; GAC-MAC-IAH Joint Meeting, Abstract volume vol. 42, 2019 p. 109-110  Open Access |
| Links | Online - En ligne (complete volume, volume
complet, PDF, 6.08 MB)
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| Image |  |
| Year | 2019 |
| Alt Series | Natural Resources Canada, Contribution Series 20180422 |
| Publisher | Geological Association of Canada |
| Meeting | GAC-MAC-IAH 2019 / AGC-AMC-AIH 2019; Québec, QC; CA; May 12-15, 2019 |
| Document | serial |
| Lang. | English |
| Media | on-line; digital |
| File format | pdf (Adobe® Reader®) |
| Province | Quebec |
| NTS | 31F/08; 31F/09; 31G/05; 31G/12 |
| Area | Breckenridge |
| Lat/Long WENS | -76.5000 -75.5000 45.7500 45.2500 |
| Subjects | surficial geology/geomorphology; geochemistry; hydrogeology; geophysics; engineering geology; Nature and Environment; Science and Technology; Health and Safety; marine sediments; muds; sensitive clays;
pore water samples; water geochemistry; salinity; landslides; groundwater regimes; groundwater flow; geophysical logging; modelling; geochemical dispersion; sea water geochemistry; chlorine geochemistry; bromine geochemistry; sodium geochemistry;
isotopic studies; oxygen isotopes; Champlain Sea Sediments; Leda Clay; St. Lawrence Lowlands; Phanerozoic; Cenozoic; Quaternary |
| Program | Public Safety Geoscience Assessing Earthquake Geohazards |
| Released | 2019 05 01 |
| Abstract | Champlain Sea muds, also known locally as Leda Clays, form a regionally extensive aquitard in the St. Lawrence Lowlands and the Ottawa Valley. Investigations of pore water chemistry, borehole
geophysics, and geotechnical sensitivity (ratio of undisturbed to remoulded compressive strength) within a thick sequence of Champlain Sea muds provide insights into groundwater flow across the aquitard, original salinity, and development of
landslide susceptibility. Typically, the assumption is that diffusion alone controls solute transport through Champlain Sea muds. However, this study uses 1D groundwater modelling to demonstrate that both advection (Darcy flux of approx. 4 mm/a) and
diffusion contribute to solute transport at a site located in thicker (~ 75 m) Champlain Sea mud deposits at Breckenridge, QC, northwest of Ottawa. Previous hydrogeological studies estimate Champlain Sea salinity to be approximately 33 % of
contemporaneous ocean salinity. However, in this study, where the sequence of Champlain Sea muds is thicker, the peak measured ionic concentrations in pore water represent at least 60 % of relic seawater salinity. Geophysical logs of bulk apparent
conductivity corroborate this finding. Additionally, transport modelling constrains the Champlain Sea concentration of seawater constituent ions (e.g. [Cl-]), and hence, the original salinity. Although the concentrations of seawater ions (Cl-, Br-,
Na+) allow estimation of the seawater fraction, when combined with isotopic signatures (e.g. 18O), these multiple tracers form the basis to estimate relative proportions of seawater, meteoric fresh water, and fresh glacial melt water of the Champlain
Sea episode. Champlain Sea salinity, along with the combined effects of advection, diffusion, and thickness of the muds, controls the current pore water chemistry, which in turn, influences sensitivity development of Leda Clays and susceptibility to
landslides. |
| Summary | (Plain Language Summary, not published)
Pore water was extracted from 75 m thick muds (Leda clays) deposited in the former Champlain Sea at a site near Breckenridge, Quebec. Results of chemical
analyses show that the pore water contains at least 60% ocean water. Models of groundwater and chemical transport provide an estimate of groundwater flow (4 mm/year) and diffusion of saline water in the muds. The original and current salinity of pore
water influences the sensitivity of Leda clay to landslides. |
| GEOSCAN ID | 313770 |
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