Origin of the Odd-twins anomaly: magnetic effect of a unique stratigraphic marker in the Appalachian foreland basin, Gulf of St. Lawrence
Bibliographic record
Abstract
The "Odd-twins magnetic anomaly" is a pair of linear asymmetric positive anomalies located in the Gulf of St. Lawrence, over the post-Taconian, pre-Acadian foreland basin fill related to the development of the Appalachians. A marine magnetic survey allowed the anomaly to be traced close to the coast of Newfoundland, and an on-land survey identified both peaks within the area of outcrop of the Late Ordovician Long Point Group. Sandstones of high susceptibility sampled from sparse outcrops close to the locations of the anomaly peaks contain up to 0.58% magnetite. Models involving dipping sheets of sandstone having similar and slightly higher susceptibility can explain both the onshore and offshore anomaly. The magnetite is of detrital origin and represents a paleoplacer heavy mineral concentration formed in a marginal marine environment. The anomaly provides a unique tie point between the known onshore stratigraphy and the succession in the foreland basin, known only from industry seismic profiles. This tie point indicates that nearly half of the recorded subsidence of the post-Taconian foreland basin took place in the Late Ordovician, suggesting that a major event within the Appalachian orogen loaded the Laurentian margin at this time. A subsequent hiatus, representing the Early Silurian, may record thermal uplift associated with the Salinian orogeny. Renewed Late Silurian to Devonian loading and sedimentation resulted from the Acadian orogeny.
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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".