Pulse of intense oxidative weathering during the latest Paleoproterozoic
Bibliographic record
Abstract
Abstract The mid-Proterozoic (ca. 1.8–0.8 Ga) is broadly characterized by low atmospheric oxygen and pervasive oceanic anoxia punctuated by pulses of oxygenation. However, the causes underpinning these transient events remain elusive. Here, we report on 1.64 billion-year-old black shales and dolostone from the Chuanlinggou Formation in the North China Craton that represent sediment deposited during the break-up of the supercontinent Columbia. The rocks are characterized by high initial 187Os/188Os values, comparable to modern seawater values, alongside positive isotopic compositions of copper similar to those found in shales deposited during the Great Oxidation Event between 2.5 and 2.2 billion years ago. Additionally, we note high Th/U ratios and Chemical Index of Alteration values. Collectively, our data suggest a positive feedback initiated by continental fragmentation, with increased oxidative weathering on land, greater nutrient supply to the oceans, enhanced primary production of marine cyanobacteria, and ultimately, higher rates of oxygen production, perpetuating the feedback loop.
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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 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".