Do hyperenriched black shales correspond with periods of elevated atmospheric O<sub>2</sub>?
Bibliographic record
Abstract
Hyperenriched black shales (HBS) contain anomalouslyhigh levels of organic carbon and a wide variety of traceelements, in particular Mo, Se, Zn, Ni, Cu, U, and V, and, insome cases, Cr, Co, Ag, Au, PGE, and REE. The source ofmetals has been controversial, but recent research (e.g. [1]),suggests that seawater could be the source for most redox-sensitiveelements.<p> </p>HBS occur at particular times during Earth history, forexample in the Early Cambrian to Early Ordovician (NiutitangFm., S. China; Arthur Creek Fm., N. Australia; Alum Shale,Sweden and Norway), Middle Devonian (Popovich Fm. W.USA; Canol Fm., NW Canada), Middle Carboniferous (Linton,Heath and Chattanooga Fms. USA; Lisburne Group Alaska;Mecca Quarry Shale of the Midcontinent USA), Middle toLate Permian (Kuperschiefer, N. Europe; Phosphoria Fm.,USA). Based on Se contents and Se/Co ratios in marine pyrite,periods of HBS deposition occur at peaks of atmosphere-oceanoxygenation [2]. This seems to be counter-intuitive as itsuggests that periods of global ocean anoxia suitable for HBSformation coincide with elevated atmospheric O<sub>2</sub>.<p> </p>We suggest the following scenario that may explain thisenigma. Cycles start with increased erosion related tocontinental uplift, which deliver a high nutrient flux of tracemetals to the oceans, promoting planktonic productivity andrelated oxygen release to the atmosphere. The downward fluxof organic matter produces widespread anoxia and draws downtrace metals, with ultimate deposition of organic-rich HBS inmarginal basins, epeiric seas, and on continental shelves.These coupled mechanisms produced nutrient-rich and anoxic-sulfidicdeep oceans with HBS peaks at 490-525 Ma,385-400 Ma, 310-335 Ma, 250-275 Ma, 205 Ma, 130 Ma, andthe present day.
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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) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 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".