Is the Geodynamo Characterized by a Distinct Geomagnetic Secular Variation Regime During the Cretaceous Normal Superchron?
Bibliographic record
Abstract
Abstract The Earth's magnetic field stochastically reversed its polarity over geological time, yet enigmatically interrupted this process during the Cretaceous Normal Superchron (CNS; 84–121 Ma). Two scenarios have been proposed in terms of either gradual or abrupt changes to describe the transition of the geodynamo from the CNS to a period with frequent polarity reversals. To discriminate between these two scenarios, we sampled 136 volcanic flows emplaced 66–73 Ma in the eastern part of the Okhotsk‐Chukotka Volcanic Belt (NE Eurasia). The 1,700 collected paleomagnetic samples provide, after correction for serial correlation, a robust data set of 112 independent paleodirections characterizing the behavior of the geomagnetic field at a paleolatitude of N shortly after the end of the CNS. Compared to paleomagnetic data from Chukotka and Northern Canada emplaced at similarly high paleolatitude, the dispersion of the virtual geomagnetic poles, used as a proxy for paleosecular variation (PSV), is 19% (resp. 55%) higher at 66–73 Ma than at the end of CNS when transitional directions are discarded (resp. retained). In contrast, our value at 66–73 Ma is, whatever the filtering strategy, statistically indistinguishable from the value at 0–10 Ma derived from the Antarctica and Spitsbergen volcanics. From the viewpoint of PSV observed at high paleolatitude (70–80), our new results are consistent with an abrupt change between two geodynamo regimes. Nevertheless, once the geodynamo starts reversing its polarity, the vigor of PSV does not seem to correlate with the reversal rate.
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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 | 0.001 |
| 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 | 0.001 |
| 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".