Detrital zircons from the Nanaimo basin, Vancouver Island, British Columbia: An independent test of Late Cretaceous to Cenozoic northward translation
Bibliographic record
Abstract
Abstract The development of the Cordilleran orogen of western North American is disputed despite a century of study. Paleomagnetic observations require large‐scale dextral displacements of crustal fragments along the western margin of North America, from low latitudes to moderate latitudes during the Cretaceous‐Paleogene. A lack of corroborating geological evidence for large‐scale (>1500 km) displacements has prevented the widespread integration of paleomagnetic data into most contemporary tectonic models for the margin. Here we use detrital zircons from the Nanaimo basin, southwestern British Columbia, Canada as an independent test of its Late Cretaceous paleogeographic position. We compare 4310 detrital zircon U/Pb dates from 16 samples to potential source areas in western North America to test hypothesized northern and southern Late Cretaceous paleogeographic positions. Our detrital zircon data suggest that sediment in the Nanaimo basin derives from either a geographically restricted portion of the Belt‐Purcell basin or the Mojave‐Sonoran region of southwestern North America. A paleogeographic position for the basin adjacent to the Mojave‐Sonoran region is preferred as it is consistent with the paleomagnetic results, but further geological, isotopic, or geophysical data are required to rule out a Belt‐Purcell source.
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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 | 0.003 |
| Science and technology studies | 0.002 | 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) | 0.002 | 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".