Utility and Limitations of Apatite Phenocryst Chemistry for Continent-Scale Correlation of Ordovician K-Bentonites
Bibliographic record
Abstract
Two prominent, Ordovician, altered volcanic layers, the Deicke and the Millbrig K-bentonites, crop out over a wide area of North America. These beds have been correlated over selected portions of North America but have not been successfully correlated throughout the entire Mississippi Valley, southern Appalachians, and New York–Ontario region. A dual approach that used trace element compositions and Sr isotopes in apatite phenocrysts was applied to Deicke and Millbrig candidates from this large region. Major (Ca, P, F) and minor (Mg, Mn, Cl, Fe, Sr, Si) concentrations within apatite phenocrysts were determined by electron microprobe analysis. Mg, Mn, and Cl proved to be the most diagnostic elements to distinguish apatite between the Deicke and Millbrig K-bentonites. These three elements have a restricted range in concentration within Deicke apatite whereas they vary significantly within Millbrig apatite and define three major clusters. Two of the Millbrig clusters appear to be mostly limited to the middle portions of the bentonite, whereas the third cluster appears to be largely restricted to apatite from the upper portion of the bentonite, based on analyses from a vertical profile within a thick bed from Hagan, Virginia. It is thus suggested that the Millbrig K-bentonite is composed of multiple eruptions or was derived from a chemically zoned magma chamber. Sr isotopic data are consistent with these scenarios (decreasing Sr/Sr with stratigraphic height) but are too variable within a single bed to be reliable discriminators of these two K-bentonites.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".