Provenance of the Proterozoic Thelon Basin, Nunavut, Canada, from detrital zircon geochronology and detrital quartz oxygen isotopes
Bibliographic record
Abstract
The Paleoproterozoic Thelon Basin in Nunavat, Canada, is one of several large quartz-dominated sedimentary basins devel-oped on Paleoproterozoic and Archean rocks of the Canadian Shield. Coarse-grained quartz to sub-feldspathic sandstones and conglomerates of the Thelon Formation comprise the basin fill. Detrital zircons from the Thelon Formation have LAM-ICP-MS 207Pb–206Pb ages ranging from 3.94 to 1.78 Ga, but most are Neoarchean (2.70–2.50 Ga). The δ18O values of quartz range from 7.7 to 13.9‰, and are typically 10–12‰. Ages, U/Zr ratios, and oxygen isotopic compositions of detrital quartz are consistent with a predominantly Neoarchean metasedimentary source, such as surrounds the eastern Thelon Basin and comprises the bulk of basement rocks within the Rae domain. The three stratigraphic sequences of the Thelon Formation have δ18O ranges for detrital quartz and zircon ages that further constrain the source areas and support previous sequence-stratigraphic interpretations. The lower sequence contains reworked siltstone and sandstone clasts and 2.50–1.85 Ga zircons indicating a contribution from Paleoproterozoic terranes. Detrital quartz δ18O values range from 9.8 to 13.9‰, indicating a metamorphic source also, which is consistent with a proximal source for the lower sequence. The middle sequence contains zircons exhibiting the widest range of ages (3.94–1.78 Ga). A>3.4 Ga Paleoarchean zircon population, cannot be correlated to the immediately surrounding basement and therefore indicates a distal source, possibly in the order of 1000–2000 km away. The upper sequence contains relatively few zircons due to extensive
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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 | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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".