Importance of Clay in Iron Transport and Sediment Reddening: Evidence from Reduction Features of the Abo Formation, New Mexico, U.S.A.
Bibliographic record
Abstract
Abstract Petrographic and geochemical data from reduction features in the Abo Formation (Permian) of central New Mexico provide insight into the source of iron for hematite precipitation in red beds. Reduction features in the Abo Formation include isolated reduction spots as well as zones of reduction associated with fractures and coarser-grained beds. The reduction features contain less iron and more copper than the host rock (mean values in ppm: host rock, Fe = 6456, Cu = 9; reduced Fe = 3730, Cu = 113). Hematite relics are present in reduced areas associated with fractures and reduced bedding but are absent in reduction spots. Hematite apparently never formed in the reduction spots because of localized reducing conditions present at the time of pervasive reddening. Reduced fractures and bedding most likely result from migration of reducing pore fluids flowing through more permeable areas, and postdate hematite precipitation. Iron-bearing sand and silt grains, which are typically regarded to be the principal source of iron for hematite precipitation in red beds, are uncommon (average < 1%) in the Abo Formation. Where present these grains are not significantly altered in either red host rock or in the white reduction features. Therefore, detrital iron-bearing clay-size material is the primary source of iron in the Abo Formation. Although compositionally variable, the clay-rich areas contain a mean of 8.4% FeO(total) in the host rock and a mean of 4.6% FeO(total) in reduction spots. Chemical and mineralogical data from clay-rich areas suggest that ferric oxyhydroxides associated with the clays are a more important iron source than iron from the clay crystal structure. Low whole-rock iron content of the Abo Formation relative to other red bed units is consistent with clay and associated ferric oxyhydroxides being the principal iron source. The Abo Formation may represent a clay-dominated end member in a continuum of red beds in which the iron needed for reddening is derived from clays and coarser iron bearing framework grains.
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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 | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| 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".