Dating dirty speleothems using paleomagnetism
Bibliographic record
Abstract
Abstract The U-series dating of young and dirty speleothems is challenging due to difficulties in assessing the isotopic composition of contaminating detrital fractions and the low- abundance of the in situ-generated 230Th. Here we propose a new dating approach based on the comparison of magnetic directions recorded by speleothems with reference curves from global paleomagnetic reconstructions. The studied stalagmite was collected in the Soprador do Carvalho cave, in the Central Region of Portugal. The radiometric age model, built using four U-series ages and three 14C, suggests relatively steady carbonate precipitation from ~ 5760 BCE until ~ 1920 CE. Forty-five, 6 mm-thick, subsamples were submitted to alternating field and thermal demagnetization, providing well-defined, primary magnetic directions. An archaeomagnetic age model of the stalagmite was obtained by fitting its paleomagnetic record with the reference paleosecular variation curves obtained by previous paleo-reconstruction models, applying statistical bootstrapping analysis to define their best fit. The resulting archaeomagnetic age models fit closely with the radiometric age model but provide a significantly higher time resolution. We reach the same conclusion when applying this approach to another stalagmite from the Algarve region of Portugal. Archaeomagnetic age models thus appear a promising alternative to date dirty speleothems.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 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".