Dating the Late Precambrian volcanicity of England and Wales
Bibliographic record
Abstract
Abstract: Ages for volcanism in the British Late Precambrian have been inferred from interpretations of SHRIMP zircon ages as follows: 559.3 ± 2.0 Ma for a tuff from the Beacon Hill Formation of the Charnian Supergroup; 566 ± 3 Ma for a tuff at Bardon Hill also in the Charnwood Forest area with abundant inherited grains at 590.5 ± 1.6; 566.6 ± 2.9 Ma and 555.9 ± 3.5 Ma for bentonite and tuff in the Stretton Group of the Longmyndian Supergroup; 604.7 ± 1.6 Ma for an ignimbrite of the Padarn Tuff Formation of the Arfon Group, and 572.5 ± 1.2 Ma for a tuff within the Fachwen Formation of the Arfon Group. These ages confirm that there were two major phases of volcanic activity in the English Midlands and Wales, one about 620–590 Ma and another about 575–550 Ma. This was followed in most of England and Wales by a major phase of tectonism before the Cambrian (Tommotian) transgression across the Midland Platform. Within the depocentre of the Welsh early Palaeozoic basin, however, sedimentation started within the second period of volcanism and may have continued without interruption well into the Cambrian Period. It is probable that the late phases of the Avalonian Orogeny lasted until after the beginning of the Cambrian. These new data show that the terranes of the Avalonian of England and Wales are comparable with those of eastern Canada and New England. The age estimate for the Charnia horizon is broadly similar to those obtained elsewhere in the world on rocks containing the earliest Ediacaran fauna and adds to the building of an extended time-scale for the global Ediacaran.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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 teacher head, 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".