Primary producer dominated environments of the Ediacaran-Cambrian transition: palaeontological insights from the Mackenzie Mountains, Canada
Bibliographic record
Abstract
The early evolution of macroscopic life, including the Cambrian ‘explosion’ of animals, took place over more than 100 million years against the backdrop of dynamic environmental changes like unstable redox conditions and nutrient supply. The terminal Ediacaran to early Cambrian transition is marked by the appearance of macroscopic biomineralizers, but also a seeming decline in diversity, in contrast to rich communities of macroscopic Ediacara-type biota preserved in older units worldwide. Our understanding of this biotic change as well as its environmental divers suffers from stratigraphic incompleteness, as continuous mid and upper Ediacaran, and Cambrian strata are rarely exposed in a continuous sequence in the same area, or represent different depositional settings.The Mackenzie Mountains in the Northwest Territories, Canada are a home to a nearly continuous sedimentary succession from the Cryogenian to the Cambrian and as such, provide a great target to analyse biotic and environmental changes through time. We have investigated the interval of carbonates and siliciclastics through the Blueflower, Risky, Ingta, Backbone, and Vampire formations and present integrated palaeontological and geochemical data to produce a high resolution biostratigraphic and chemostratigraphic profile for the Ediacaran-Cambrian boundary interval.The Ediacaran-Cambrian boundary occurs in the Ingta Formation, marked by sporadic trace fossils Treptichnus and Harlaniella. Simple surficial traces Planolites occur throughout the formation. Also common are well-preserved bacterial filamentous organic-walled microfossils in mudrocks, but the boundary interval lacks complex acritarchs or cuticular animal remains. Macroscopic carbonaceous fossil problematica were also recovered. Complex trace fossils occur in the overlying Backbone Ranges Formation and become more common in the Vampire Formation, but are absent from the lowermost Cambrian strata in the Mackenzie Mountains. The primary producer dominated environment and the absence of organically preserved animal remains in a setting conducive to organic preservation imply a true decline in diversity through the boundary interval – possibly a result of either phylogeny or ecology.
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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 | 0.003 | 0.006 |
| Science and technology studies | 0.004 | 0.001 |
| Scholarly communication | 0.002 | 0.000 |
| Open science | 0.001 | 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".