Comparison between the Helen Iron Formation (Algoma-type) and the Sokoman Iron Formation (Superior-type)
Bibliographic record
Abstract
The Sokoman Iron Formation with an age of 1.88 Ga in the Labrador Trough and the Archean Helen Iron Formation in Wawa, Ontario (2.75 Ga) are examples of shallow and deep water iron formations respectively, which are of a low metamorphic grade. The two iron formations vary greatly in their mineralogy and geochemistry. The deep water Helen Iron Formation is dominated by siderite and quartz and provides an example of a direct precipitate from seawater which had a strong but distal hydrothermal component as indicated by the lack of Cu, Pb and Zn enrichment. It has a thickness of 100m. The first 20 meters are dominated by input of detrital material of both basaltic and felsic sources before deepening of the basin led to purely chemical sedimentation. Iron in the Helen Iron Formation occurs predominantly as Fe2+, indicating that oxygen played no role in the deposition of this iron formation. Negative carbon isotope excursions close to organic rich horizons in the Helen Iron Formation are the result of dissimilatory iron reduction. In contrast, the mineralogy of the Sokoman Iron Formation is dominated by magnetite, hematite and quartz and has a thickness of 180m. The depositional environment was variable and ranged from a fairly deep, reducing basin to shallow, oxidizing water. The original mineralogy probably consisted of a silica-iron hydroxide gel which was precipitated due to oxidation of Fe2+to Fe3+. The source of the Fe2+ was probably a distal hydrothermal input. Anoxic deep water allowed the transport of Fe2+over long distances to the site of iron formation deposition. When this deep, anoxic water mass came into contact with shallow water, which was enriched in oxygen due to the photosynthetic activity of cyanobacteria, a silica-iron hydroxide gel precipitated. Dewatering of this gel during burial caused the strong diagenetic overprint preserved in the section in which the original mineralogy is obscured. The high degree of diagenesis also explains the present low organic matter content of the Sokoman Iron Formation as well as the presence of Fe2+ minerals, since organic matter may have reacted as an electron acceptor reducing Fe3+ to Fe2+.
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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 | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".