<scp>RioM</scp> ‐1: A New Calcite Reference Material for U‐Pb <scp>LA</scp> ‐ <scp>ICP</scp> ‐ <scp>MS</scp> Geochronology
Bibliographic record
Abstract
Determining absolute ages of carbonate diagenesis, faulting, fossil formation, speleothem growth, carbonate‐hosted hydrocarbon deposits, vein mineralisation and hydrothermal alteration has become increasingly accessible through LA‐ICP‐MS U‐Pb dating of calcite, complementing traditional isotope dilution methods still applicable to certain materials (e.g., speleothems via micro‐drilling). However, well‐calibrated reference materials for LA‐ICP‐MS calcite geochronology remain scarce. Here, we characterise the Rio Maior calcite, designated ‘RioM‐1’, as a potential reference material for U‐Pb dating by LA‐ICP‐MS. Fragments (0.1 to 1 cm 3 ) from a single scalenohedral crystal were analysed by ID‐TIMS (U‐Pb), LA‐ICP‐MS (U‐Pb and 87 Sr/ 86 Sr), and SIMS (O isotopes). RioM‐1 displays high U mass fraction and low, though variable, proportions of common Pb. Combined ID‐TIMS analyses from two independent laboratories yielded a Tera‐Wasserburg lower intercept date of 63.93 ± 0.11 Ma (2 s , MSWD = 1.3, n = 16). LA‐ICP‐MS U‐Pb data from three independent laboratories are concordant with the TIMS age, producing a pooled date of 64.10 ± 0.12/1.2 Ma (2 s , MSWD = 7.7, n = 708) and an initial 207 Pb/ 206 Pb ratio of 0.85 ± 0.01. Other calcite reference materials, when normalised to RioM‐1, yielded dates within uncertainty of their published values. SIMS measurements returned a mean 18 O/ 16 O of 0.002044450 ± 181 (1 s ) and δ 18 O SMOW of 19.57 ± 0.92‰ (1 s ), while LA‐ICP‐MS strontium isotope measurement yielded a mean 87 Sr/ 86 Sr of 0.708177 ± 9 (2 s ).
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.004 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 0.002 |
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".