Redox conditions of the Late Cretaceous Western Interior Seaway recorded by rare earth elements of Bearpaw molluscan fossils
Bibliographic record
Abstract
Understanding the causes of the low-biodiversity faunas in the Western Interior Seaway (WIS), overwhelmingly dominated by ammonite and bivalve molluscs, will help us to understand paleoenvironmental conditions in the WIS. In this study, we examined rare earth elements (REEs) in well-preserved molluscs from the Bearpaw Formation to reconstruct WIS redox conditions. Both nektonic and benthic molluscs share similar REE patterns with enrichment in light REEs. There is only a slight Ce depletion in both types of molluscs, indicating no significant fractionation of Ce from the other REEs. A lack of significant Ce anomalies in molluscs points to oxygen-deficient (probably dysoxic) conditions in the middle to bottom part of the water column where the molluscs lived. Given the general lack of significant Ce anomalies also in molluscs from older formations, oxygen deficiency was likely prevalent in the Late Cretaceous in the WIS. A warmer climate in the Cretaceous is probably a driver of such conditions, as predicted by ocean models. Long-term oxygen deficiency and stratification, inferred from the heterogeneity in δ 18 O and δ 13 C values of molluscs, may also imply weak circulation, reducing the exchange of surface water and subsurface water, and the transport of oxygen into the WIS. The oxygen deficiency and weak circulation of the seaway is also expressed in the general characteristics of faunas and possibly Bearpaw sedimentary rocks. Oxygen deficiency rather than the brackish water conditions may have been largely responsible, therefore, for the low diversity of the WIS fauna.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.005 | 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 teacher head, 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".