Mineralogical properties of Champlain Sea sediments and their effects on borehole geophysical logs, western Quebec
Notice bibliographique
Résumé
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.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,001 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».