Nutrient-Gradient Controls On Devonian Reefs: Insight From The Ramp-Situated Alexandra Reef System (Frasnian), Northwest Territories, Canada
Bibliographic record
Abstract
Abstract Devonian reef systems are thought to represent the greatest phase of global reef development in the Phanerozoic. Despite this, ecological and environmental controls on the sedimentary nature of these vast systems have scarcely been investigated and remain enigmatic. The Late Devonian (Frasnian) Alexandra Reef System, exposed in the Northwest Territories of Canada, developed on a ramp that was situated on the western margin of Laurussia. The system consists of two reef complexes. The second reef complex developed basinwards of the first after sea level fell ~ 17 m. In contrast to stromatoporoid (± coral)-dominated reef facies in the first reef complex and the upper part of the second reef complex, reef facies in the lower part of the second reef complex are dominated by stromatoporoid-microbe associations. These include significant renalcid boundstone and stromatolite accumulations that are not found elsewhere in the reef system. It is concluded that the occurrence of the stromatoporoid-microbe reef facies indicates that a shift in the reef environment from oligotrophic to mesotrophic conditions took place. The mechanisms of nutrification were linked to the platform geometry, sea-level position, and oceanographic system, indicating that on carbonate ramps, systems tracts of falling sea level (forced regression) and sea-level lowstand may be particularly susceptible to nutrification. A nutrient-gradient model developed to explain different types of reef facies in the Alexandra Reef System indicates that trophic resources were an important control on the composition of Devonian reef-building communities, and that Devonian reefs and carbonate platforms were not highly susceptible to nutrient-invoked drowning.
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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 | 0.001 | 0.003 |
| Science and technology studies | 0.002 | 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".