Siltstone: a key to cyclicity in mixed siliciclastic–carbonate successions: example from Upper Ordovician Kope Formation (Ohio, Indiana, Kentucky)
Bibliographic record
Abstract
The Upper Ordovician (mid-Katian) Kope Formation provides an example of how a detailed study of fine-grained siliciclastic sediment can provide sedimentological insights. The Kope Formation is an exemplar of mixed siliciclastic–carbonate cyclicity; however, most of the sedimentological research to date has focused on the fossiliferous limestone beds. Conversely, this paper provides a detailed investigation of siltstone within 42 metre-scale cycles from 26 locations spanning a large geographic area. The objective of the study is twofold: (i) to confirm the mineralogical nature of silt-sized sediment. Currently, silt-sized sediment is irregularly defined as being either carbonate or siliciclastic rich. This paper uses X-ray diffraction, thin-section, and elemental analyses to determine the mineralogy of the silt; (ii) to determine the stratigraphic distribution of siltstone beds. If a distinctive and reoccurring distribution of siltstone can be found, then it can provide additional information about environmental energy changes that led to cyclic fossiliferous limestone formation. This study finds that silt within the Kope Formation is siliciclastic and siltstone, therefore, records periodic minor pulses of coarser terrigenous sediment. Predominantly, metre-scale limestone–shale cycles show an increasing abundance of siltstone beds in the upper half of the shale interval, with a marked decrease just before the capping limestone. This finding supports the idea that limestone formation occurred during slowing sedimentation, perhaps at a time of maximum sea-level rise. Furthermore, decametre-scale fluctuations in siltstone abundance are similar in pattern to previously documented faunal variations, indicating that fauna assemblage might be more controlled by turbidity and not depth.
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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 | 0.001 |
| Science and technology studies | 0.001 | 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) | 0.002 | 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".