Euxinic versus ferruginous anoxia before and during the Toarcian Oceanic Anoxic Event
Bibliographic record
Abstract
Abstract Mesozoic oceanic anoxic events are recognized as widespread deposits of marine organic-rich mudrocks temporally associated with mass extinctions and large igneous province emplacement. The Toarcian Oceanic Anoxic Event (T-OAE) is one example during which expanded ocean anoxia is hypothesised in response to environmental perturbations associated with emplacement of the Karoo–Ferrar igneous province. However, the global extent of total seafloor anoxia and the relative extent of ferruginous (anoxic and Fe2+-rich) versus euxinic (anoxic and H2S-rich) conditions during the T-OAE and other Mesozoic OAEs are poorly constrained. Here we present new estimates of the global anoxic and euxinic seafloor area before and during the T-OAE based on rhenium and molybdenum enrichments in organic-rich mudrocks of the Fernie Formation (British Columbia, Canada). Trace metal concentrations and ratios, together with high organic carbon contents, indicate that this previously unstudied locality was minimally restricted from global ocean circulation, experienced deep-water nutrient upwelling, and had O2-deficient bottom waters. Pronounced rhenium and molybdenum enrichments in mudrocks deposited from locally anoxic and euxinic waters, respectively, point to large global oceanic reservoirs of these metals. Mass balance models suggest that the T-OAE likely comprised a modest expansion of up to ~7% anoxic seafloor dominated by euxinia. Hence, anoxic seafloor was likely confined to epicontinental seaways, semi-restricted basins, and continental margin oxygen minimum zones during the T-OAE.
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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 | 0.000 | 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".