Provenance constraints on the Late Triassic ejecta layer from Churchwood Quarry, <scp>SW</scp> England: An impactite suite from Manicouagan
Bibliographic record
Abstract
Abstract In situ LA‐ICP‐MS/MS U‐Pb and Rb‐Sr geochronology combined with geochemical analysis and electron microscopy have been performed on ejecta components sampled from the Mid‐to‐Late Triassic Mercia Mudstone Group at Churchwood Quarry, SW England. The layer comprises altered impact spherules, melt‐rich and fragment‐rich accreted grain clusters (AGCs), along with shocked mineral phases. Late Triassic ages are obtained: a U‐Pb age of 219 ± 72 Ma from variably shock‐metamorphosed apatite and a Rb‐Sr age of 213 ± 31 Ma from melt‐rich AGCs. A post‐depositional U‐Pb age of 200 ± 7.5 Ma obtained from the carbonate host matrix correlates with an early Jurassic dolomitization event associated with regional marine transgression. Several links to the Manicouagan impact structure, Canada, are identified that complement previous provenance studies: (1) rare earth element compositions of impact spherules and melt‐rich AGCs match those of the Manicouagan impact melt sheet; (2) the preservation of Archean and Paleo‐ to Neoproterozoic target rock U‐Pb ages in zircon and apatite match those recorded within Manicouagan basement lithologies; and (3) impact spherules and melt‐rich AGCs record initial 87Sr/86Sr compositions that overlap with those of the Manicouagan impact melt sheet and the target rocks involved in their generation.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.002 | 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) | 0.001 | 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".