Chitinozoan biostratigraphy of the Rheidol Gorge Section, Central Wales, UK: a GSSP replacement candidate for the Rhuddanian–Aeronian boundary
Bibliographic record
Abstract
Abstract As part of an international effort to evaluate potential replacement sections for the current Aeronian GSSP, the stratigraphy of the Rheidol Gorge section (central Wales, UK) is being restudied. A total of 28 samples from the Rhuddanian–Aeronian boundary interval at Rheidol Gorge were studied for chitinozoans. This famous Welsh Basin section, its stratigraphy rooted in the work of O.T. Jones and M. Sudbury, comprises a series of laminated black shales with abundant graptolites, alternating with grey mudstone intervals, deposited in anoxic to dysoxic/oxic seafloor conditions, respectively. The exposed section of c. 20 m spans the middle part of the upper Rhuddanian Pernerograptus revolutus Biozone through the lower Aeronian Neodiplograptus magnus Biozone of the lower to mid‐Llandovery Series (Cwmere and Derwenlas formations). Our chitinozoan analysis yielded an assemblage of over 2300 specimens distributed approximately uniformly throughout the entire succession. A total of 16 different taxa are identified, of which 12 remain in open nomenclature, reflecting the poor to moderately intact preservation of the specimens. Based on the presence of key species such as Spinachitina maennili and Conochitina iklaensis, the Rheidol Gorge section is referred to the Spinachitina maennili Biozone. This observation is in perfect alignment with the typical signature of other Rhuddanian–Aeronian boundary successions in the Welsh Basin and in other parts of the world.
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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 | 0.000 | 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) | 0.002 | 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".