Evaluating redox conditions during the Cambrian SPICE event, western Newfoundland, Canada
Bibliographic record
Abstract
The Steptoean Positive Isotopic Carbon Excursion, or SPICE event, was a global +3-6‰ shift in d13C values during the later Cambrian (ca. 500Ma). The excursion has been broadly correlated with the Sauk II-III subsequence boundary in North America and several trilobite mass extinctions globally, yet the mechanism(s) for these events and the excursion itself are unconfirmed. The recent discovery of mercury enrichments accompanying the SPICE in Scotland has prompted reconsiderations about the global nature of the SPICE excursion and the use of mercury as a large igneous province (LIP) volcanism indicator. Sedimentary mercury enrichments have frequently been interpreted as a LIP indicator, yet modern studies have shown that mercury can be rereleased from sediments during anoxic intervals. To further investigate these new hypotheses, we analyzed mercury enrichments as well as a suite of other geochemical and mineralogical information in an outcrop of the SPICE located along the south-facing shore of the Port au Port Peninsula, western Newfoundland. These mixed carbonate and siliciclastic strata record small mercury enrichments coupled with high glauconite abundance after, but not during, the SPICE peak. Since glauconite is a mineral sensitive to local redox oscillations, we interpret the period just after the SPICE peak to have had frequent oxic/anoxic switches. The pattern of mercury enrichments found in Scotland, however, suggests redox oscillations constrained to the SPICE peak. These differences highlight how local processes can affect the manifestation of a global event in different environments. Both studies support the use of sedimentary mercury as a new proxy for tracking local redox oscillations.
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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 | 0.002 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 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".