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TitleMineralogical properties of Champlain Sea sediments and their effects on borehole geophysical logs, western Quebec
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LicencePlease note the adoption of the Open Government Licence - Canada supersedes any previous licences.
AuthorCrow, H LORCID logo; Enkin, R JORCID logo; Percival, J BORCID logo; Al-Mufti, O N
SourceGeological Survey of Canada, Open File 8763, 2021, 68 pages, https://doi.org/10.4095/327855 Open Access logo Open Access
Image
Year2021
PublisherNatural Resources Canada
Documentopen file
Lang.English
Mediaon-line; digital
RelatedThis publication is related to Geophysical, geotechnical, geochemical, and mineralogical data sets collected in Champlain Sea sediments in the Municipality of Pontiac, Québec
File formatpdf
ProvinceQuebec
NTS31F/08; 31F/09; 31G/05; 31G/12
AreaBreckenridge; Breckenridge Creek; Eardley Escarpment; Municipality of Pontiac
Lat/Long WENS -76.5000 -75.5000 45.7500 45.2500
Subjectssurficial geology/geomorphology; mineralogy; geophysics; engineering geology; Nature and Environment; Science and Technology; Health and Safety; postglacial deposits; marine sediments; marine clays; sensitive clays; silts; landslides; earthquakes; sediment properties; boreholes; geophysical logging; gamma ray logging; density logging; magnetic susceptibility; core samples; core analysis; mineralogical analyses; x-ray diffraction analyses; scanning electron microscope analyses; grain size analyses; depositional environment; Champlain Sea Sediments; Phanerozoic; Cenozoic; Quaternary
Illustrationslocation maps; geoscientific sketch maps; tables; geophysical logs; profiles; lithologic sections; spectra; photomicrographs; screen captures; plots
ProgramPublic Safety Geoscience Assessing Earthquake Geohazards
Released2021 01 21
AbstractThe Geological Survey of Canada is conducting geoscientific investigations in Breckenridge Creek Valley (Municipality of Pontiac, western Quebec) where ancient and modern landslides have occurred in the fine-grained, post-glacial sediments of the former Champlain Sea. Multidisciplinary studies aim to gain a better understanding of how these sediments respond to earthquake shaking, and what factors increase their susceptibility to retrogressive landslides. As part of these investigations, downhole geophysical logs collected in a 75-m borehole displayed relatively low and unvarying gamma-ray responses, downward increasing density and velocity trends, and variable magnetic susceptibility responses. Laboratory analyses of existing cores were undertaken to better understand these geophysical log responses, and relate them to depositional and post-depositional characteristics of the sediments.
The relatively low gamma log responses were found to result from the low quantities of potassiumbearing clay minerals. While clay-size grains made up 30 - 57% by volume of the samples tested, X-ray diffraction analyses revealed clay minerals made up only 20 - 45% by weight of the clay-size fraction.
Polished thin sections were prepared from three core samples at the top, middle, and bottom of the borehole. Scanning electron microscopy (SEM) imaged diverse grain orientations, sizes, and textures in each of these intervals, and evidence for compaction was observed in the middle sample where biotite grains were observed to be aligned around larger grains. A downhole trend of increasing bulk density and shear wave velocity is primarily accounted for by a relatively consistent grain density and a reduction in water content with depth as pore water was expelled by compaction under the weight of the overlying sediment column.
Concentration and grain size of magnetic minerals influence magnetic susceptibility and nuclear magnetic resonance (NMR) log responses, but little was known about these properties as the minerals are present at trace levels (<3%). Magnetic properties of iron oxides in clay- to silt-size grains were examined in seven core samples using a coercivity spectrometer and a thermomagnetic susceptibility meter in step-wise heating experiments. Results indicate that magnetite is present in varying concentrations and grain sizes in all samples tested, ranging from silt- and clay-size detrital particles down to nanoparticles. The presence of superparamagnetic nanoparticles identified in the three lower-most samples in the borehole coincided with an observed shortening of downhole NMR relaxation times.
This Open File Report summarizes the laboratory methods and datasets resulting from new analyses of sediment cores, and discusses the results in the context of the geophysical log responses. New insights on broader sedimentological and geochemical conditions in Champlain Sea sediments are also discussed.
Summary(Plain Language Summary, not published)
In 2010, the Geological Survey of Canada began conducting geoscientific investigations in Breckenridge Creek Valley (Municipality of Pontiac, western Quebec), where landslides, both ancient and modern, have been identified in clayey, post-glacial sediments. The purpose of the investigations was to gain a better understanding of how these sediments might respond to earthquake shaking, and what factors may increase susceptibility to retrogressive landslides. To support this research, a 75 m borehole was drilled in 2014 to collect downhole measurements of the physical and chemical properties of the sediments, and to recover cores for laboratory testing. Lab and field data were reported in Open File 7881. Since these results were released, new analyses of mineralogy and grain texture were carried out on the cores to further study the relationships between the downhole measurements and the depositional and post-depositional characteristics of the sediments. This open file documents the laboratory methods and the resulting datasets. The results contribute to ongoing research into the geological and hydrogeological conditions that influence sediment stability and landslide susceptibility in the area.
GEOSCAN ID327855

 
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