Dynamic Environmental Change at the Cusp of the Great Oxidation Event: The Gowganda-Lorrain Formation Transition, Cobalt Basin, Ontario and Quebec
Bibliographic record
Abstract
The Huronian Supergroup, an early Paleoproterozoic (ca. 2.45-2.22 Ga) sedimentary succession preserved in Ontario and Quebec, catalogues evidence for the Great Oxidation Event (i.e., the initial rise of oxygen in the atmosphere) through the preservation of redox sensitive minerals in terrestrial deposits: (1) detrital pyrite and uraninite in older strata (evidence of an anoxic atmosphere), and (2) Earth’s earliest red, hematitic, sandstone in younger strata (indicative of a shift to an oxidizing atmosphere). This dissertation comprises three studies from the Cobalt Basin, a northern sub-basin of the greater Huron basin. The first two studies develop depositional models of the northern and easternmost portions of the Cobalt Basin providing details on the glacial to post-glacial paleoenvironments that preserve Earth’s earliest red sandstones. Stratigraphic measurements and correlations reveal that strata are preserved within paleovalleys, interpreted to have developed from glacial excavation as evidenced by basal subglacial deposits. Above these subglacial deposits, strata show a single progradational succession, which captures a transition from glaciomarine to warm and humid fluvial braidplain environments. At the flanks of the paleovalleys, alluvial and/or colluvial deposits occur indicating that terrestrial sedimentation was triggered by enhanced weathering in an unvegetated warm and humid setting due to topographic variations. The successions occur at proximal limits of a passive margin and indicate that progradation was influenced by relative sea-level fall linked to glacio-isostatic uplift. The third study investigates the petrogenesis of reddened sandstone of the aforementioned braidplain deposits. Petrography reveals single-grain rims of pigmentary hematite dust on detrital quartz that are encased by quartz overgrowth cement. This encapsulates evidence that reddening is a syn-sedimentary or early diagenetic feature, formed from widespread oxidizing meteoric waters in a terrestrial setting under an oxygenated atmosphere, prior to burial and lithification of the fluvial deposits. Reddening likely happened close to 2.31 Ga, providing an approximate age for the initiation of oxidative weathering in a terrestrial setting, triggering key feedbacks in nutrient cycling that possibly thrusted Earth’s atmosphere into a stable oxidizing state.
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.003 | 0.001 |
| Scholarly communication | 0.002 | 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".