Abstract: Burial dating of Klondike and Upper White Channel gravels confirms a Pliocene age for the earliest advance of the Cordilleran Ice Sheet
Bibliographic record
Abstract
The most extensive Cordilleran Ice Sheet (CIS) in northwestern Canada is also thought to be the earliest. Outwash gravel associated with this advance is magnetically normal, and predates the Mosquito Gulch tephra (ca. 1.4 Ma) in the Klondike area, suggesting either a Pleistocene (1.77–1.95 Ma; Olduvai) or Pliocene (2.58–3.58 Ma; Gauss) age. In the lower Klondike valley, this outwash (Klondike gravel) is interbedded with Upper White Channel (UWC) gravel, which is elsewhere associated with tephra beds dating to ca. 3 Ma on the basis of glass fission-track ages. Here, in situ-produced cosmogenic 26Al and 10Be, is used to test the age model for earliest CIS advancement by burial dating sediment at the top of the UWC, and at the base of the Klondike gravel at Australia Hill near Dawson City, Yukon Territory. Based on recent estimates for post-depositional deep muon production, a mean burial age of 2.8 ± 0.3 Ma is calculated for the Klondike gravel. This result assumes a depositional 26Al/10Be ratio equal to 6.75 (spallogenic production ratio). Depositional ratios can differ substantially from this value due to: (1) temporary burial of sediment during transport (sediment storage or ice cover); (2) deep-seated mass wasting of material whose production ratio is controlled by muons; and (3) long-term (>1 Ma) stability followed by rapid erosion of surfaces contributing sediment to the deposit. However, reconciling these results and the paleomagnetic record with a Pleistocene age requires unrealistic exposure and erosion scenarios for the catchments sourcing the UWC. Furthermore, the 26Al/10Be ratios measured in the UWC and Klondike gravels are identical, suggesting an insensitivity of their depositional ratios to the widely different sediment sources, glacial histories, and transport mechanisms responsible for the two deposits. These results confirm a Pliocene age for the earliest advance of the CIS, and imply that large ice volumes in the northern Cordillera predate extensive Laurentide glaciation.
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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 | 0.001 | 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) | 0.002 | 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".