Depositional controls on Palaeoproterozoic iron formation accumulation, Gogebic Range, Lake Superior region, USA
Bibliographic record
Abstract
Abstract Shallowing‐upward, decametre‐scale, Palaeoproterozoic iron formation cycles in northern Wisconsin record the combined effects of tectonism and changing oceanographic conditions on a storm‐dominated shelf. Cycles consist of a lower unit of laminated, Fe‐ and Si‐rich chemical mudstone that is transitional into an upper unit dominated by trough cross‐stratified chert grainstone. Grainstone lenses become progressively thicker upwards in cycles with the largest at cycle tops, where they are sharply overlain by a unit of slumped chemical mudstone. The cycles developed through progradation when offshore‐directed storm currents transported chert sand intraclasts that were formed in nearshore settings into middle and distal shelf environments. Abrupt subsidence events, probably resulting from normal faulting associated with extensional tectonism, repeatedly terminated chert grainstone accumulation and may also have generated the slumped units at cycle boundaries. The episodic storm currents are also interpreted to have transported biologically oxygenated waters from the shallow‐water, inner shelf into otherwise anoxic bottom waters of the strongly stratified distal shelf. The consequence of such transport and mixing was rapid deposition of chemical mud, mainly as precipitated Fe‐oxide. In many cases, the resultant decrease in Fe2+ in the water column, together with pelagic inorganic precipitation of SiO2 and rainout of terrigenous clays, resulted in submillimetre‐ to millimetre‐thick, chemically graded laminae. The concomitant decreasing Fe2+/Mn2+ ratio also led to increasing Mn‐compound precipitation and enrichment in the upper portions of some chemically graded layers.
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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 | 0.000 | 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) | 0.001 | 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".