Benchmarking of the Isotope Diffusive Exchange Method Using Opalinus Clay and Queenston Shale Rocks Equilibrated with Synthetic Saline Solution
Notice bibliographique
Résumé
This study aims to test recent developments for advancing the isotope diffusive exchange technique in order to adapt it to high salinity porewaters and, in a more general way, to solutions with low water activities. This report documents work performed to: 1) investigate factors that might influence the results of the isotope diffusive exchange technique for saline solutions through solution-solution experiments; and 2) benchmark the adapted diffusive exchange method using rock samples previously equilibrated with synthetic solutions of known composition (chemical and isotopic). Two different rocks have been used to perform the benchmarking tests: 1) Queenston Shale from Ontario, Canada; and 2) Opalinus Clay from the Mont Terri Underground Research Laboratory (URL), Switzerland. Solution-solution diffusive-exchange experiments showed that perturbing factors include: 1) the water activity mismatch between the test and sample solutions; 2) the weight difference between the test and sample solutions; and 3) contrasting chemical compositions (NaCl versus CaCl2) between test and sample solutions. Benchmarking of the isotope diffusive exchange method using rock samples equilibrated with synthetic solutions has tested: 1) whether or not the isotopic composition obtained by the diffusive exchange method actually corresponds to the composition of the porewater; and 2) if there are additional perturbing factors, i.e., other than those identified in the solution-solution experiments. Equilibration of Opalinus Clay and Queenston Shale rocks (which are saturated with porewater at experiment initiation) with 0.3 and 5 molal NaCl, and 2.5 and 5 molal CaCl2 synthetic solutions has been performed successfully by immersing 2 to 4 cm diameter rock pieces into air-tight PVC containers for periods of 62 and 90 days, respectively. Equilibrium was apparently attained in about 1 day for Opalinus Clay rock samples, and 4 days for the Queenston Shale rock samples. The rock samples never disaggregated during these experiments, even at 0.3 molal NaCl solution concentrations. The density of the equilibrated rocks, in all cases, is lower than that of the intact porewater-saturated rock and increases with increasing salinity of the synthetic solution. This is probably because the confining pressure in the equilibration experiments is low compared to in-situ conditions. The rock density correlates with its water content, which is higher in low salinity solutions. Data obtained from Opalinus Clay and Queenston Shale rock experiments indicate that the diffusive exchange method gives reliable results of the isotope composition (δ18O and δ2H) of the porewater at all salinities when the chemistries of the porewater and test waters are similar. Results for δ18O values are shifted up by about 1‰ for contrasting chemistries (NaCl versus CaCl2), and insignificantly for δ2H. The diffusive exchange technique gives reliable results for rocks with water content as low as 0.5 wt%. For unknown reasons, the use of the diffusive exchange method for obtaining the water content of the rock gave good results at high salinities (≥2.5 molal), but overestimated values at low salinities (0.3 molal).
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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,001 | 0,002 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,001 | 0,000 |
| Science ouverte | 0,001 | 0,001 |
| Intégrité de la recherche | 0,001 | 0,001 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 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 source (Gemma direct ou Codex distillé), 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 ».