Upper Ordovician (Sandbian–Katian) carbonate outliers in the northern Ottawa–Bonnechere graben (central Canada): records of transgressions and sedimentation patterns in the Laurentian platform interior
Bibliographic record
Abstract
Small Ordovician sedimentary outliers, including Brent Crater, within the northern Ottawa–Bonnechere graben are remnants of a once expansive Upper Ordovician sedimentary cover extending across the southern Canadian Shield. Facies successions along with updated macrofossil and conodont biostratigraphy, and isotope (C, O, Sr) chemostratigraphy provide additional insights into the terrestrial-to-marine transformation, carbonate-platform development, and oceanographic communication across the southern Laurentian platform. Four of the outliers document Sandbian shoreline-to-nearshore deposition: near Deux Rivières, Manitou Islands, the upper part of the Brent Crater sedimentary fill, and at nearby Cedar Lake. Marine transgression initially reworked local fine-grained to boulder-rich regolith within high-energy shoreface siliciclastic environments that gave way to low- to high-energy inner carbonate-ramp setting. Continued transgression resulted in more offshore rhythmic and diverse lithofacies successions defining mixed heterozoan, photozoan, and microbial productivity and marine isotope (C, Sr) signatures, but δ13C excursions suggest periods of greater mixing of terrestrial and marine carbon reservoirs. Lower Katian strata are preserved near Lake Nipissing and characterize deepening from high-energy ooid-heterozoan skeletal shoals to deeper water mid-ramp siliciclastics and skeletal carbonates, host to a Cruziana ichnofacies. An upsection decline in δ13C values through this succession may identify deposition during the post-peak decline of the global Guttenberg δ13C excursion. This lithic succession fits well with contemporary expansion of heterozoan skeletal lithofacies across the Laurentian platform, yet the presence of ooids identifies prevailing warm waters within the platform interior during early stages of transgression.
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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 | 0.002 | 0.004 |
| Science and technology studies | 0.002 | 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".