Paleomagnetism and rock magnetism of East and West Clearwater Lake impact structures
Bibliographic record
Abstract
The East and West Cleawater Lake impact structures (Wiyâshâkimî Lake, Québec), ∼26 and 32 km in diameter, respectively, have been proposed to represent an impact doublet. We investigated their paleomagnetism to contribute to this debate. The paleomagnetic directions of the impact melt rocks and impact melt-bearing breccias from the West Clearwater structure are compatible with the radiometric age of 280–290 Ma previously determined for this structure and indicate that the impact occurred during a reverse polarity interval of the geomagnetic field. A similar remagnetization direction is found in the basement within 10 km of the structure center, whereas basement farther away from the center has escaped remagnetization by the impact. Samples for the East Clearwater structure come from two holes drilled in 1963 and 1964. Unfortunately, the drill hole through the melt rocks is tilted by 30° from the vertical with an unknown azimuth. The paleomagnetic inclination of these melt rocks cannot be constrained to better than between −28° and +32°. This is, however, distinct from the inclination of the melt rocks of the West Clearwater Lake impact structure (−27.8° ± 3.7°), suggesting that the two structures do not represent an impact doublet, in agreement with recent radiometric dating. The basement rocks and the melt rocks within 10 km of the center of the West Clearwater Lake impact structure show a magnetic signature of titanohematite that crystallized during postimpact hydrothermal activity under oxidizing conditions. This is not observed in the basement or the melt rocks from the East Clearwater Lake impact structure.
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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 | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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".