A Cenozoic-Style Scenario for the End-Ordovician Glaciation
Bibliographic record
Abstract
The end-Ordovician (Hirnantian) was an enigmatic interval in the Phanerozoic, known for massive glaciation potentially at elevated CO2 levels, biogeochemical cycle disruptions recorded as large isotope anomalies and a devastating extinction event. Such linkage of eustatic, biological and isotopic records to the climatically forced development of an ice sheet can only be contemplated within a framework of high-resolution sequence stratigraphy that integrates allo-, chemo- or biostratigraphic markers. We develop sequence stratigraphic correlations for two superbly exposed and exceptionally well-developed latest Ordovician successions, the Anti-Atlas of Morocco and Anticosti Island in Canada. Both offer sections, on a 100-km scale, from the basin edge to the axis of active sedimentary depocentres. Relative to the end-Ordovician ice-sheet centre (present-day north-central Africa), they provide a near-field (Anti-Atlas, siliciclastic platform) and a far-field (Anticosti Island, mixed carbonate and siliciclastic) stratigraphic records. These two successions, up to 300 and 100m thick, respectively, were deposited in basins with notable subsidence rates and significant (ca. 100 m) initial water depths, enabling the development of comprehensive archives of the latest Ordovician glaciation. This framework, driven by glacio-eustatic cycles tied to the evolution of polar continental-scale ice sheets over west Gondwana, enables the correlation of eustatic cycles at a level that is beyond the resolution capability of most absolute dating methods and of biozones, the latter typically of Myr duration. A proposed Cenozoic-style scenario including three main glacial cycles and higher-order phenomena necessitates the revision of the end-Ordovician, glaciation-related sequence of events.
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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 | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.006 | 0.001 |
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".