Direct dating of a laminated speleothem coating a karst wall in southeastern Gaspé Peninsula, Quebec, Canada: Carboniferous, not Silurian
Bibliographic record
Abstract
In the Gaspé Peninsula, karsts associated with subaerial exposure are interpreted to have developed either during the Silurian or the Carboniferous. Determining the timing of karst formation is valuable for economic reasons (including petroleum system characterization) and for the understanding of basin/climate evolution. In this study, a laminated calcite speleothem coating a karst wall in the McInnis cement plant quarry is studied in detail through petrographic observations, stable and clumped isotope analysis, and geochronology. The speleothem is made of laminae of different colours that are geochemically and isotopically distinct. White and red laminae have δ18O and δ13C values comparable to contemporaneous (within uncertainty) phreatic calcrete hardpans described in southern Gaspé Peninsula and northern New Brunswick, suggesting that both the speleothem and calcrete precipitated from primarily fresh groundwaters that interacted with soils. Changes in laminae colour most likely reflect different kinetics of precipitation and amounts of impurities. LA-ICP-MS in situ dating of calcite from white laminae gives a date of 331.8 ± 9.1 Ma, which is the first direct evidence that the cavity formed during the Visean (Carboniferous). From a regional point of view, subaerial exposure and karst formation during the Visean could have resulted from a glacially induced sea-level lowstand and/or from an uplift episode associated with magmatic underplating/plume-related magmatism in the offshore part of the Maritimes Basin.
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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".