Hydrochronology of a proposed deep geological repository for low- and intermediate-level nuclear waste in southern Ontario from U–Pb dating of secondary minerals: response to Alleghanian events
Bibliographic record
Abstract
U–Pb ages have been measured on secondary dolomite and silica cements in Cambrian sandstone at the base of an 840 m thick sub-horizontally bedded sedimentary sequence beneath the Bruce nuclear site in southern Ontario to document the history of fluid movement. Results show an average U–Pb age of 320 ± 10 Ma. The initial common Pb end member is slightly, but distinctly, enriched in 206Pb compared with that in older and younger calcite cements elsewhere within the sedimentary section. Combined with previous hydro-geochemical and fluid inclusion studies of the same rocks, the age is interpreted to record episodic migration of a saturated hydrothermal brine. Previously dated calcite cement in sub-horizontal fractures about 500 m higher in the stratigraphic section near the base of the Silurian sequence records similar U–Pb ages of 318 ± 10 Ma by laser ablation inductively coupled plasma mass spectrometry and 313 ± 1 Ma by isotope dilution thermal ionization mass spectrometry. We suggest that the subhorizontal fractures were generated by slumping that resulted from dissolution of underlying evaporite deposits. These ages overlap with the peak of plutonism in the Alleghanian mountains, which were being uplifted contemporaneously 500 km to the southeast. The results suggest the transport of hydrothermal brine from areas of crustal melting through the deep Cambrian sandstone aquifer, while at higher crustal levels meteoric water was also driven over equally large distances by hydraulic gradients from the Alleghanian mountains.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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 source (direct Gemma or distilled Codex), 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".