Stratigraphic restriction of stromatolites in a Middle and Upper Ordovician foreland-platform succession (Ottawa Embayment, eastern Ontario)
Bibliographic record
Abstract
Stromatolites are abundant and widely distributed within two narrow stratigraphic intervals in Middle (Darriwilian) and Upper (lower Turinian) Ordovician strata of the Laurentian foreland interior in the Ottawa Embayment, eastern Ontario. These lithostratigraphic markers coincide with rapid, tectonically driven flooding of the foreland interior and may identify an opportunistic microbial response to nutrient loading with shallow (peritidal, subtidal) marine reworking of terrestrial or nutrient-rich coastal systems. The remaining (Chatfieldian–Edenian) foreland-platform succession represents deeper-water deposition in response to elevated subsidence rates along the Laurentian margin. Stromatolites are absent in this higher-energy setting, but microbial calcite is preserved as coccoid-like microencrustations on skeletal debris. Stromatolites of Darriwilian age are dolomitic, occur in the Carillon Formation, and are part of a regional (200+ km) onlap of peritidal sediment during onset of Taconic orogenesis. Stratiform to large (2 m diameter) low-relief domal stromatolites contain rhythmic laminations of inclusion-rich and -poor dolomicrospar grouped by Fe-oxide-stained erosional surfaces. Domal forms also contain thrombolitic microstructure. Patterns of lamination and stable (C, O) isotopes suggest a balance between abiotic and microbial carbonate production, likely influenced by water depth and temperature. Stromatolites of Turinian age are calcitic and form a regional (80+ km) thin (<8 m) subtidal biostromal unit in the lowermost Pamelia Formation. Their occurrence defines an abrupt vertical transition from initial intrabasinal transgressive subtidal phosphatic siliciclastics and carbonates to an interbasinal stratigraphy of peritidal lime mudstone. Arrhythmic laminations of microbial peloid packstone, with possible eukaryote alga moulds, and locally evaporitic spongiostromate microstructure identify salinity and energy as primary depositional controls. The stromatolite–?eukaryotic association is similar to some modern subtidal microstructures and is part of the reef-community diversification in the Ordovician.
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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 | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 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".