Multiple diachronous “Black Seas” mimic global ocean anoxia during the latest Devonian
Bibliographic record
Abstract
Abstract The Devonian-Carboniferous boundary (DCB) Hangenberg extinction in Europe (ca. 359 Ma) and interval of black shale deposition has been considered a global anoxic event, the cause of which remains debated. However, the lack of a prominent global carbon isotope excursion and the duration of anoxia (3–4 m.y. at least) is inconsistent with other global anoxic events (e.g., Mesozoic ocean anoxic events) throughout the Phanerozoic. We examined geochemical and biostratigraphic data along with radiometric dating from purported Hangenberg event sections across the DCB in western Canada and demonstrate that the onset of anoxic pulses in Laurentian seas started before 363 Ma, diachronous with those in Baltica (Europe). Thus, DCB black shales do not record a single global anoxic event. We suggest instead that black shales near the DCB record multiple, but diachronous, Black Sea–like basins around the globe, promoted by the Late Devonian tectonic configuration. This drove a gradual biotic crisis in the form of regional punctuated benthic faunal extinction events.
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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 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| 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".