Mineralogical properties of Champlain Sea sediments and their effects on borehole geophysical logs, western Quebec
Bibliographic record
Abstract
The 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.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".