Investigating the glacial history of the northern sector of the Cordilleran Ice Sheet with cosmogenic 10Be concentrations in quartz
Bibliographic record
Abstract
Exposure durations of glacial landforms in widely separated areas of central Yukon Territory affected by the northern sector of the Cordilleran Ice Sheet (CIS) and alpine glaciers have been determined using cosmogenic 10Be in quartz. The aim of our research is to test previous reconstructions of glacial history and to begin to address the paucity of chronological control for the lateral and vertical extent of the northern CIS. Chronological evidence for CIS expansion predating the Last Glacial Maximum comes from minimum surface exposure durations of c 100 ka for two bedrock samples within the Reid glacial limit, indicating a possible marine Oxygen Isotope Stage (OIS) 6 age for this event, and from minimum exposure durations of about 40 ka for boulders on moraines constructed by alpine glaciers on a nunatak within the McConnell glacial limit (OIS 2), indicating a possible OIS 4 age. High elevation minimum surface exposure durations within the McConnell limit indicate that some areas formerly mapped as nunataks were covered by cold-based ice prior to 30 ka. Montane glaciation in the Mackenzie Mountains, outside the McConnell glacial limit, was contemporaneous with nearby CIS advance at 17 ka, with CIS retreat by 15 ka. Deglaciation of the Tintina Trench, a major ice discharge route, was completed by 12 ka. At this time ice in an adjacent discharge route to the south was still entering higher-elevation valleys in the Pelly Mountains. A Lateglacial readvance may have peaked at ca 10 ka in the Ogilvie Mountains. Considerable variation in ages from individual landforms, and possible complex histories, require additional cosmogenic nuclide measurements to confirm interpretations.
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 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) | 0.001 | 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".