Stable isotope record of the Eifelian–Givetian boundary Kačák–<i>otomari</i> Event (Middle Devonian) from Hungry Hollow, Ontario, Canada
Bibliographic record
Abstract
The Kačák Event in the Middle Devonian (Eifelian–Givetian (E–G) boundary) is a period of apparent global anoxia coincident with widespread deposition of black shale in hemipelagic, pelagic, and some neritic facies. Conodont biostratigraphy in the North American Appalachian Basin has proven to be problematic in precisely demarcating the E–G boundary. In this study, we show that the E–G boundary may be defined more accurately through isotope stratigraphy (δ13C) in conjunction with a conodont faunal change across this boundary, identified as the Kačák– otomari Event. The Canadian Hamilton Group outcropping in Hungry Hollow, Ontario, is a 22 m sedimentary succession spanning the Middle Devonian. Conodont biostratigraphy for this section makes it difficult to define the E–G boundary, but the otomari Event can be detected. High-resolution isotopic analysis of bulk sedimentary carbonate and organic matter for this succession records a significant negative δ13C excursion (δ13Ccarb = up to 2‰; δ13Corg = ∼3.0‰) that is synchronous with total organic carbon (TOC) values up to 12.5%. We identify this negative δ13C excursion as a result of marine anoxia associated with the Kačák–otomari Event and suggest that the excursion is a global event driven by a source of isotopically light carbon, followed by a productivity event, similar to Mesozoic oceanic anoxic events. Such similarities between Devonian and Mesozoic oceanic anoxic events may become more evident with increased high-resolution isotopic and geochemical investigations of Devonian successions.
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.003 | 0.001 |
| Scholarly communication | 0.001 | 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".