U-Pb volcanic zircon dates from New Brunswick constrain the Middle Cambrian Drumian Stage and trans-Avalonian green–black boundary
Bibliographic record
Abstract
Abstract The first precise, biostratigraphically bracketed U-Pb dates on the middle Middle Cambrian come from the Rte. 111 ash (new) in the lower Manuels River Formation of southern New Brunswick. Manuels River black mudstone (Avalonian depositional sequence [Ads] 8) unconformably overlies Fossil Brook Member greenish mudstone (Ads 7) of the Chamberlain’s Brook Formation, and the two units should not be combined into a ‘Forest Hills Formation’ (abandoned). This unconformity marks the trans-Avalonian (i.e., Rhode Island–Belgium) green–black boundary and onset of ca. 26 Ma of dysoxic/anoxic marine deposition. Trilobites and agnostids correlate the surprisingly endemic, upper Paradoxides abenacus Zone and Rte. 111 ash into the Hypagnostus parvifrons Zone (Drumian) in Avalonian Wales, Baltic upper ‘ Acidusus ’ atavus Zone and upper Mawddachites hicksii –lower Paradoxides davidis zones of Avalonian Newfoundland and Britain. The Manuels River Formation in SE Newfoundland and coeval Nant-y-big Formation in South Wales have not yielded ash dates. However, our U-Pb zircon analyses of the Rte. 111 ash in the lower Manuels River in southern New Brunswick yield statistically identical ages of 501.44 ± 0.10 and 501.45 ± 0.08 Ma. The Ads 7–8 unconformity is locally 6–10 m lower in New Brunswick and is somewhat older. Our ages for the Rte. 111 ash show the lower Drumian is significantly younger than previous estimates, is ca. 4.9 Ma younger than the Lower–Middle Cambrian boundary, and debunks claims of a continuous Lower–Middle Cambrian succession in Avalonian New Brunswick where a ca. 7 Ma hiatus is present.
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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 | 0.000 | 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 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.025 | 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 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".