Evolution of the Late Cretaceous Nanaimo Basin, British Columbia, Canada: Definitive provenance links to northern latitudes
Bibliographic record
Abstract
Abstract Accurate reconstruction of the Late Cretaceous paleogeography and tectonic evolution of the western North American Cordilleran margin is required to resolve the long-standing debate over proposed large-scale, orogen-parallel terrane translation. The Nanaimo Basin (British Columbia, Canada) contains a high-fidelity record of orogenic exhumation and basin subsidence in the southwestern Canadian Cordillera that constrains the tectonic evolution of the region. Integration of detrital zircon U-Pb geochronology, conglomerate clast U-Pb geochronology, detrital muscovite 40Ar/39Ar thermochronology, and Lu-Hf isotopic analysis of detrital zircon defines a multidisciplinary provenance signature that provides a definitive linkage with sediment source regions north of the Sierra Nevada arc system (western United States). Analysis of spatial and temporal provenance variations within Nanaimo Group strata documents a bimodal sediment supply with a local source derived from the adjacent magmatic arc in the southern Coast Mountains batholith and an extra-regional source from the Mesoproterozoic Belt Supergroup and the Late Cretaceous Atlanta lobe of the Idaho batholith. Particularly robust linkages include: (1) juvenile (εHf >+10) Late Cretaceous zircon derived from the southern Coast Mountains batholith; (2) a bimodal Proterozoic detrital zircon signature consistent with derivation from Belt Supergroup (1700–1720 Ma) and ca. 1380 Ma plutonic rocks intruding the Lemhi subbasin of central Idaho (northwestern United States); (3) quartzite clasts that are statistical matches for Mesoproterozoic and Cambrian strata in Montana and Idaho (northwestern United States) and southern British Columbia; and (4) syndepositional evolved (εHf >−10) Late Cretaceous zircon and muscovite derived from the Atlanta lobe of the Idaho batholith. These provenance constraints support a tectonic restoration of the Nanaimo Basin, the southern Coast Mountains batholith, and Wrangellia to a position outboard of the Idaho batholith in Late Cretaceous time, consistent with proposed minimal- fault- offset models (<~1000 km).
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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 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".