Detrital zircon geochronology of the Fredericton Trough, New Brunswick, Canada: Constraints on the Silurian Closure of remnant Iapetus Ocean
Bibliographic record
Abstract
The Fredericton Trough in the Appalachians of southwestern New Brunswick is filled by the Silurian Kingsclear Group, consisting mainly of turbidites, deposited during convergence of Laurentia with components of the peri-Gondwanan domain Ganderia. Its tectonic setting has been interpreted as a successor basin, trench, foredeep or foreland basin. We present new detrital zircon U-Pb data from four formations of the Kingsclear Group, collected north and south of the Fredericton Fault, which bisects the trough. South of the Fredericton Fault, detrital zircon ages from an early Silurian (Llandovery) unit show a late Neoproterozoic peak, typical of peri-Gondwanan provenance. Detrital zircons from a younger Silurian unit (Wenlock - Ludlow, intruded by the Pocomoonshine pluton, 422.7 ± 3 Ma) display a distinctive asymmetric peak at ∼1.0 Ga with a tail of older Proterozoic zircons, suggesting Laurentian provenance. North of the Fredericton Fault, a Llandovery sample also shows a signature consistent with Laurentian sources. In a mid-Silurian (Wenlock) unit zircon peaks indicate mixed Laurentian and peri-Gondwanan sources, consistent with exhumation of the Miramichi terrane to the north. The absence of Laurentian material in Llandovery strata south of the fault, contrasted with a strong Laurentian signature in rocks to the north, suggests that a remnant of the Iapetus Ocean, in which turbidites of the Kingsclear Group were deposited, persisted until at least the mid-Silurian. The timing of its closure is constrained by the arrival of Laurentian detritus south of the Fredericton Fault before 422.7 ± 3 Ma, and probably by the mid-Wenlock.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.002 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".