Revisiting the age of the Fish Canyon sanidine dating standard
Bibliographic record
Abstract
In 2008, Kuiper and others published an astronomically calibrated age of 28.201 ± 0.046 Ma for the Fish Canyon sanidine (FCs), the most widely used standard in Ar/Ar dating. This age was incorporated in GTS2012 and GTS2020, but has been challenged by later studies that used various approaches, leading again to a ∼ 1.5 % age scattering. This uncertainty hampers the construction of a uniform and coherent time scale that is key to modern high-resolution, multi-disciplinary studies in Earth history. To solve this ongoing uncertainty, we present 1) a visual and statistical re-examination of the astronomical tuning on which the FCs age of 28.201 Ma is based and 2) new single crystal U/Pb ID-TIMS zircon ages of the astronomically calibrated Faneromeni A1 ash bed and the Fish Canyon Tuff (FCT). Our results corroborate the initial tuning and invalidate astronomical and U/Pb based FCs age calibrations, which are much younger or older. The preferred astronomical calibration seems to converge to a slightly younger age of 28.171–28.176 Ma. This is in good agreement with our new Bayesian zircon eruption age of 28.171 + 0.039/− 0.044 Ma for the FCT and the recently published Bayesian calibration of the 40 K decay scheme with a coupled FCs age of 28.183 ± 0.070 Ma. Importantly, the astronomical and U/Pb-based calibrations now yield similar ages, implying mutual agreement between the three main dating methods to construct our time scale. However, by contrast, the Cretaceous/Paleogene (K/Pg) boundary, which represents a critical triple point for the intercalibration, now produces divergent ages. In summary, much progress has been made in solving the critical issue of the age of the FCs dating standard. For the moment, we either recommend the continued use of the astronomically calibrated age of 28.201 ± 0.046 Ma or, preferentially, a slightly younger age of 28.171–28.176 Ma. We further endorse investigation in a community-based effort where new data and improved methodologies may lead to further insight into fundamental properties and potentially a definitive age not only for the FCs dating standard, but importantly also for the K/Pg boundary.
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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 | 0.002 | 0.004 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 0.001 |
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".