The Diatom Dark Ages: Identification of mid-Cretaceous Arctic Platform diatoms from the basal transgression of the Kanguk Formation, Devon Island, Nunavut, Canada
Bibliographic record
Abstract
The lower part of the mid-Cretaceous Kanguk Formation (Lower Turonian interval) contains an important paleontological record crucial to the characterization of a poorly known interval of fossil marine diatoms history. Kanguk Formation mudstones are exposed in a ~200 m-thick section on Devon Island, Nunavut, Canadian High Arctic. Diatoms at this location are well-preserved due to shallow burial on this Arctic Platform site. The rock sequence was protected from glacial erosion that removed much of the Cretaceous record by being down-faulted in a linear graben. Study of these well-preserved fossil diatoms allows for a documentation of the assemblage, identification of potentially important biostratigraphic events, and an opportunity to assess paleoenvironmental changes that may have influenced their growth and sedimentation. This study identified 45 fossil marine diatom species and varieties, representing 22 genera, and some taxa that are treated informally. The lower ~60 meters of the Kanguk mudstone sequence on Devon Island is barren of diatoms, indicating that environmental conditions suitable for diatom growth were not coincident with the initial transgression, but developed later, or that marine connections that allowed migration of diatoms into the Arctic occurred after the marine transgression. Planktonic and benthic species are present in similar abundance suggesting a shallow water environment. The lower interval of the Kanguk Formation reported herein spans a ~3 m.y. time interval (~90.5 to ~93.5 Ma, Early Turonian) as indicated by carbon isotope chemostratigraphic correlations and silicoflagellate biostratigraphy, which allow correlation to other Kanguk Formation sections that are dated with bentonite ages. The presence of diatoms Gladius antiquus, Costopyxis antiqua, and Bascillicostephanus sp. 1 support these ages. Several events are identified as potentially important new biostratigraphic datum levels, which help divide the Gladius antiquus Zone and increase biostratigraphic resolution. In ascending order these are: the first appearances (FA) of Thalassiosira wittiana and Lepidodiscus elegans, the last appearance (LA) of Azpeitiopsis morenoensis, and the FA of Stellarima steinyi. Future studies from other sections will be required to establish their use in biostratigraphy. Documentation of these diatom assemblages represents an initial phase in characterizing the early history of diatoms during the mid-Cretaceous. It will anchor future work higher in this stratigraphic section. Advisor: David M. Harwood
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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 | 0.000 |
| 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 | 0.000 |
| 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".