A semi-quantitative ichnological approach to relative oxygen reconstruction: A case study over the Cenomanian-Turonian Oceanic Anoxic Event 2 in west-Central Alberta, Canada
Bibliographic record
Abstract
An exceptionally well-preserved organic-rich mudstone core from the Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE2) interval in the Canadian Western Interior Seaway offers an excellent opportunity for comprehensive ichnological analysis of paleo‑oxygen fluctuations. Vertical trends in burrow size and diversity (i.e., Size-Diversity Index - SDI) have previously served as a proxy for relative oxygenation in low-oxygen stratigraphic settings. We note two factors that greatly impact oxygenation interpretations of SDI: (1) high bioturbation intensities or reworking dominantly by small (meiofaunal) animals lead to a large underestimation of ichnofossil diversity; and (2) paleoenvironmental stressors other than lowered oxygen levels (e.g., fluctuating salinity, reduced food availability, and rapid sedimentation). A semi-quantitative relative oxygen equation is proposed to account for these complexities and better proxy bottom water oxygenation over the interval. The equation combines diversity counts, burrow sizes, and bioturbation intensity (all indicators of high oxygenation), scaled with total organic carbon measurements (the presence of which is interpreted as an indicator of low oxygenation, corroborated by carbon isotope measurements over the interval). Integrating ichnological data with total organic carbon measurements accounts for the diminution and low diversity that may stem from a multitude of physicochemical factors. The results suggest that the bottom water oxygen fluctuated continuously and only very rarely, if at all, reached persistent anoxia. The proposed equation offers a repeatable approach to integrate ichnological and TOC data, providing a better ichnological-oxygen proxy for organic-rich mudstones. • Common ichnological oxygen proxies (burrow size/diversity) have inherent problems. • Ichnology (size-diversity index + BI) divided by TOC yields a relative oxygen curve. • Oxygenation over the OAE2 was unstable, fluctuating between low-oxic and dysoxic. • Deoxygenation was most intense after the termination of OAE2.
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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 | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.005 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 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".