<sup>40</sup>Ar/<sup>39</sup>Ar and Pb-Pb study of individual hornblende and feldspar grains from southeastern Baffin Island glacial sediments: implications for the provenance of the Heinrich layers
Bibliographic record
Abstract
Lead isotope analysis of individual feldspar grains and 40Ar/39Ar analysis of individual hornblende grains from three samples taken from Baffin Island ice-proximal till deposits are consistent with a provenance recording a two-stage geologic history including formation of continental crust in the Late Archean and partial isotopic resetting and (or) reequilibration during major Paleoproterozoic regional metamorphism and magmatism. Significantly, although the populations are small, and the two-stage Archean-Paleoproterozoic history of their sources are similar, the Pb isotope compositions of samples from Baffin Island do not match the results from Heinrich layer H2 in core HU87-033-009 from northeast of the Hudson Strait in the Labrador Sea. Specifically, in H2 samples from HU87-033-009, the 207Pb/204Pb is high for a given value of 206Pb/204Pb. Additionally, the range in 206Pb/204Pb is greater in HU87-033-009 samples, and there are two distinct trajectories of 208Pb/204Pb. The steeper of the 208Pb/204Pb versus 206Pb/204Pb trends is not seen in the studied Baffin Island glacial sediment samples. Samples of feldspar grains from Heinrich layers H1, H2, H4, and H5 from core V28-82 in the eastern North Atlantic have a 207Pb/204Pb versus 206Pb/204Pb relation similar to that of Baffin Island till samples, but there is also a high 208Pb/204Pb that we have not captured in this suite of glacial sediment samples. Our results highlight the strength of a combined radiogenic isotope approach to characterizing the geological history of sediment sources and provide a first step in assessing the variability in isotope character in this region of dynamic glacial events during the late Quaternary Period.
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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 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| 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".