Hydrothermal dolomite in the Timiskaming outlier, central Canadian Shield: Proxy for Late Ordovician tectonic activity
Bibliographic record
Abstract
The Timiskaming Paleozoic outlier on the central Canadian Shield preserves a thin distal portion of the once extensive Taconic deep-water shale succession that extended across eastern Laurentia. Within this succession, a thin (5 cm) lithic and phosphatic sandstone occurs a few meters above the top of the buried shallow-water carbonate platform, and contains abundant (40-60%) euhedral dolomite, rare fluorite, pyrite-cemented shale microbreccia, and crystal mosaics of subhedral dolomite with pyritic veinlets. The dolomite formed local cement, and precipitated very near the sediment-water interface as illustrated by a relatively uncompacted sandstone framework and a 3-dimensional fabric of clay particles trapped by dolomite growth. The majority of dolomite has planar crystal faces, with ferroan (4.1 ± 0.3 mol% FeCO~3~) crystal cores and non-ferroan (0.9 ± 0.2 mol% FeCO~3~) rims. Fluid inclusions, too small (\<2 μm) for reliable microthermic analysis, are mostly liquid, which, in keeping with interpreted near-surface diagenesis, as well as temperature-controlled dolomite-crystal roughening models, may indicate that formation temperatures were no more than ∼60 to 80°C. δ^13^C~PDB~ values (∼1.2 ‰) are similar to a Late Ordovician seawater composition, but δ^18^O~PDB~ values (−4.8 to −5.2 ‰) are too negative compared to the expected values for contemporary deep-marine dolomite. Combining the regional paleoceanographic framework with diagenetic constraints and revised models for Late Ordovician seawater temperature and δ^18^O compositions, the dolomite is interpreted to be a proxy for a low-temperature (at least ∼50°C) hydrothermal anomaly near the sediment-water interface. Fragments of shale microbreccia, pyrite veinlets, and subhedral dolomite, along with the region9s structural history, allow speculation that this event coincided with local reactivation of a Precambrian fault, part of an ancestral fault system now manifest regionally by an extension of the Ottawa-Bonnechère Graben. Late Ordovician craton-interior tectonism, in a region previously considered tectonically stable at this time, is defined by local response of inherited Precambrian structure driven by, but distal to, Taconic orogenesis.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.003 | 0.004 |
| Science and technology studies | 0.003 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".