New Middle Cambrian (Drumian) U-Pb age of Cape Breton Island volcanism and Cambrian–lowest Ordovician stratigraphic reevaluation confirm the Bourinot belt (southern “Bras d’Or terrane”) is Avalonian
Bibliographic record
Abstract
The Avalonia microcontinent, now a 2,500 km-long terrane on the SE margin of the Acadian–Caledonian orogen, is defined by a terminal Ediacaran–Ordovician cover sequence (cs) unconformable on a basement collage of Proterozoic blocks that accumulated on the Avalonian transform fault (Atf). Strike-slip activity along the Atf controlled deposition of a siliciclastic-dominated marine cover sequence with minor igneous activity. Stratigraphic re-evaluation assigns the Mira belt in Cape Breton Island to the inner–marginal Avalonian platform transition area, and the northern Antigonish Highlands (i.e., Bourinot belt and southernmost Bras d’Or “terrane”) to the marginal platform. A new 500.55 ± 0.10 Ma date (CA-IDTIMS) from the tuff-dominated Gregwa Formation from the Bourinot belt is bracketed by re-evaluated trilobite faunas and is a radioisotopic control point on the middle Middle Cambrian and upper Drumian Stage. The Gregwa Formation, a volcanic edifice similar to two others on the Avalonian outer platform (i.e., Northern Antigonish Highlands, N.S.; Beaver Harbour, N.B.) likely overlies the Dugald Formation with a ca. 1 Ma hiatus as Avalonian depositional sequence 8. Gregwa volcanics, part of the ca. 1 Ma-duration, trans-Avalonian Manuels River–Nant-y-Big volcanic interval (new), are ca. 8 Ma younger than the late Early Cambrian Waites Lane–Eskasoni volcanic interval (new) in Maritime Canada. These two volcanic intervals emphasize Avalonian unity from the terminal Ediacaran. They are additional evidence that areas referred to the southern margin “Ganderia” (traditional Appalachian central mobile belt), as the Bourinot belt in Cape Breton, are Avalonian.
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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 | 0.002 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.014 | 0.001 |
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".