Carbon Chemostratigraphy of the Paleoproterozoic Belcher, Nastapoka, and Richmond Gulf Groups
Bibliographic record
Abstract
The Paleoproterozoic Lomagundi δ13Ccarb excursion between 2.22 and 2.06 Ga corresponds to the most significant period of atmospheric oxygenation and is referred to as the “Great Oxidation Event” (GOE). Large δ13Ccarb excursions are often followed by periods of accelerated biological evolution, suggesting that rocks deposited immediately after 2.06 Ga might preserve changes in environmental chemistry and microbial communities after the GOE. The poorly studied rocks of the Belcher, Nastapoka, and Richmond Gulf Groups, along the northwestern margin of the Superior Craton, Canada, have been dated between 2.03 and 1.870 Ga (Chandler and Parrish, 1989; Hamilton et al., 2009), and thus represent ideal rocks to investigate the evolution of microbial communities and of the carbon cycle in a higher redox state. These Paleoproterozoic successions contain exceptionally well-preserved carbonates with abundant and diverse stromatolites. The Belcher Group preserves three successive transgressions of a drowning carbonate platform between two major volcanic episodes (Ricketts and Donaldson, 1989). Progressive transitions from green/gray to red argillites/mudstones and the development of beds of carbonate concretions indicate a progressive oxidation of fine-grained marine sedimentary rocks and organic matter near the end of the second and third megacycles (Tukarak and Costello-Laddie Fms.). Data from the McLeary and Kasegalik Fms. in the Belcher Group show uniform δ13Ccarb values around +0.1‰ and δ13Corg values between -26.1‰ and -22.1‰. Current work is focused on completing the carbon isotope chemostratigraphies to establish geochemical correlations between the entire Belcher Group and the correlative Richmond Gulf and Nastapoka Groups.
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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 | 0.003 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| 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".