New Occurrences of <i>Oldhamia</i> in Eastern Yukon, Canada: Stratigraphic Context and Implications for Cambrian Deep-Marine Biostratigraphy
Bibliographic record
Abstract
For over a century, the ichnogenus Oldhamia has been used as an index fossil for Cambrian deep-marine siliciclastic successions. New specimens from the Cambrian of Selwyn Basin, eastern Yukon, Canada, provide an opportunity to constrain the chronostratigraphic range of Oldhamia and test its potential for more detailed biozonation. The upper part of Narchilla Formation (Arrowhead Lake Member) yields O. antiqua, O. curvata, O. flabellata, and O. radiata. The overlying Gull Lake Formation yields a less diverse assemblage of O. antiqua, O. curvata, and O. flabellata. The upward disappearance of O. radiata is consistent with models that infer increasing complexity of Oldhamia ichnospecies through time but may also be a function of limited sampling. Regional stratigraphic correlations suggest Oldhamia appeared in Arrowhead Lake Member during Cambrian Stage 3. Archaeocyathans and trilobites from Gull Lake Formation confirm that Oldhamia was present during Cambrian Stages 3 to 4. A younger age limit on Oldhamia in Selwyn Basin is provided by syn-volcanic detrital zircons recovered from the base of the overlying Old Cabin Formation, which yield an age of 499.89 ± 0.14 Ma (earliest Guzhangian). Oldhamia appears to be a reliable index fossil for Cambrian Series 2 and Series 3 in Selwyn Basin.
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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 | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 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".