Stratigraphic Significance of Ooidal Ironstones from the Cretaceous Western Interior Seaway: The Peace River Formation, Alberta, Canada, and the Castlegate Sandstone, Utah, U.S.A.
Bibliographic record
Abstract
Abstract Ooidal ironstones form prominent units, and an appreciation of their sedimentological and stratigraphic significance is important for the interpretation of sedimentary successions. Ooidal ironstones from the Albian Paddy Member of the Peace River Formation, Alberta, Canada, and the Campanian Castlegate Sandstone of the Mesaverde Group in Colorado have been analyzed. The ooidal ironstones are associated with a major sequence boundary and subsequent transgressive surface. Both are interpreted to have been deposited under conditions of low net sediment accumulation in well-oxygenated bottom-water conditions, with episodic storm events reworking the sediments. The Paddy Member ironstone is interpreted to have been deposited in an estuarine environment, and the Castlegate ironstone is interpreted to have been deposited in a shallow-marine environment. Both ironstones are dominated by berthierine ooids and grain-rimming and pore-filling siderite, with later ferroan dolomite and calcite in the Castlegate ooidal ironstone. Petrographic, geochemical, and isotopic evidence, coupled with thermodynamic considerations, indicates that the ooidal ironstone mineralogy formed during suboxic diagenesis. The conditions required for suboxic diagenesis were extensive sediment reworking and slow net sediment accumulation rates. We propose that these conditions arose as a result of marine transgression during the initial relative sea-level rise following the development of a sequence boundary. Ooidal ironstone formation ceased once sedimentation rates increased and transgression deepened water depths considerably. These results illustrate the association between ooidal ironstones and major stratal surfaces in sedimentary successions, and highlights the complexity that early diagenesis at such surfaces can take.
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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 | 0.001 | 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) | 0.001 | 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 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".