Revision of Middle Cambrian trilobites and agnostids from Cape Breton Island, Nova Scotia, reveals a Guzhangian faunal interval in the Avalonian cover sequence
Bibliographic record
Abstract
The MacLean Brook Group of Cape Breton Island yields a Middle Cambrian trilobite and agnostid fauna that is unlike any other reported from Avalonia. A reassessment of this fauna based on new and archival collections shows that it includes Hypagnostus cf. H. brevifrons (Angelin) and Hypagnostus cf. H. confusus (Westergård), Holasaphus centropyge Matthew, Acrocephalaspis matthewi (Hutchinson), and species of Groenwallia Kobayashi and Bailiaspis Resser. It is assigned to an informal biostratigraphic unit, the H. centropyge Fauna. The composition of the H. centropyge Fauna points to a Guzhangian age, and closest similarities lie with the Erratojincella brachymetopa Zone of the Andrarum Limestone of Sweden (Baltica). This zone is correlative with the lower Lejopyge laevigata Zone of Sweden, which defines the base of the Guzhangian. Although the uppermost Guzhangian Agnostus pisiformis Zone is well documented in Avalonia, previous evidence for the basal part of the stage has been limited. Establishment of a Guzhangian age for the MacLean Brook Group in Cape Breton Island is consistent with the age of the group in Newfoundland and emphasizes the regional lithostratigraphic unity of the cover sequence of the Avalon terrane. It also provides an upper age constraint on the underlying Gregwa Formation volcanics. To completely bracket the Gregwa biostratigraphically, we also revise “ Erratojincella” bretonensis (Hutchinson) from the underlying Dugald Formation, which is consistent with an assignment to the Wuliuan Eccaparadoxides etemenicus Zone.
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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 | 0.001 |
| Science and technology studies | 0.001 | 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".