Early Neoproterozoic scale microfossils in the Lower Tindir Group of Alaska and the Yukon Territory
Bibliographic record
Abstract
The Tindir Group is a <4-km-thick Neoproterozoic succession exposed in the Tatonduk inlier of east-central Alaska and the western Yukon Territory.The Tindir Group is informally divided into the Lower Tindir Group, which consists of <2 km of mixed carbonate and clastic rocks, and the overlying Upper Tindir Group, which contains two Cryogenian glacial deposits and an additional Ediacaran succession of mixed carbonate and clastic strata.Unique mineralized scale microfossils have been recovered from sections previously correlated with the Upper Tindir Group, and interpreted variously as Cryogenian to early Cambrian in age.Our remapping of the area indicates that these sections are stratigraphically below an early Cryogenian glacial diamictite, unit 2 of the Upper Tindir Group, and are actually part of the Lower Tindir Group.Carbon and strontium isotope correlations further suggest that the fossiliferous Lower Tindir Group is correlative with early Neoproterozoic strata of the northwestern Canadian Cordillera.This new age model is consistent with the accompanying microfossil assemblage and indicates that the diverse microfossils in the Lower Tindir Group can be added to the early Neoproterozoic record of eukaryotic evolution.87 Sr/ 86 Sr values, Kaufman et al. ( 1992) suggested that the fossil-bearing portion of the Upper Tindir Group was deposited during the Cryogenian and is correlative with the Twitya Group in the Mackenzie Mountains.Since then, the age assignment of these microfossils has remained ambiguous; consequently, these unique forms have not been fully integrated into the framework of early eukaryotic diversifi cation. STRATIGRAPHYThe Tindir Group is exposed in the Tatonduk inlier, a wedge of the relatively unmetamorphosed Laurentian margin, which straddles the Alaska-Yukon border (Fig. DR1 in the GSA Data Repository 1 ).Herein we follow Payne and Allison's (1981) original, and commonly used (e.g., Young, 1982;Rainbird et al., 1996), separation of the Lower and Upper Tindir Groups, which is a useful distinction for regional correlation schemes as it roughly corresponds to the boundary between the Mackenzie Mountains and Windermere Supergroups of the Canadian Cordillera.
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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 | 0.000 | 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".