The early Middle Devonian Choteč Event in northern Spain: a brief anoxic pulse driven by enhanced weathering and eutrophication
Bibliographic record
Abstract
The (Basal) Choteč Event, first recognised in the 1980s in Czechia, is a globally widespread anoxic pulse associated with transgression and eutrophication just above the Emsian-Eifelian (Early-Middle Devonian) boundary (cycle 1c of the Johnson et al. [1985] Devonian eustatic sea-level curve). Despite being one of several anoxia-driven faunal turnovers during the Devonian, the Choteč Event remains poorly understood. The global reach, intensity, and duration of anoxia is not constrained and nor is it clear whether eutrophication had its “roots” in contemporary floral developments on land (as suggested for younger Devonian anoxic events).We present a geochemical (carbon isotopes; trace metals as proxies for redox and productivity; and major elements for the Chemical Index of Alteration [CIA] as a weathering proxy) and palynological study of the Cabonera section (León, Spain). This succession is part of an extensive Devonian sequence developed around isolated islands in the Armorican Terrane Assemblage that was located between the supercontinents Laurussia and Gondwana. Here, limestones of the Emsian-Eifelian Santa Lucia Formation are abruptly overlain by siltstones and shales belonging to the Eifelian Huergas Formation. This conodont- and brachiopod-constrained manifestation of the Choteč Event sees the onset of a gradual 4‰ negative δ13Ccarb excursion (CIE) consistent with records in other regions. The lower part of the Huergas Formation (Cabornera Bed) records a brief interval of anoxia (low Th/U, elevated V/Al and U/Al) at the same level that sees the onset of the negative CIE. This appears to have been accompanied by, or was perhaps driven by, greatly enhanced primary productivity, with enrichment factors (EFs) of Ba, and particularly Ni, Zn and P, all >>1. This brief burst of productivity and anoxia soon ended, with EFs falling
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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 | 0.000 | 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) | 0.001 | 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".