Detrital glass in a Bering Sea sediment core yields a ca. 160 ka Marine Isotope Stage 6 age for Old Crow tephra
Bibliographic record
Abstract
Abstract For decades, the Old Crow tephra has been a prominent stratigraphic marker for the onset of Marine Isotope Stage (MIS) 5e, the last interglaciation, in subarctic northwest North America. However, new zircon U-Pb dates for the tephra suggest that the tephra was deposited ca. 207 ka during MIS 7, with wide-ranging implications for chronologies of glaciation, paleoclimate, relict permafrost, and phylogeography. We analyzed ~1900 detrital glass shards from 28 samples collected at Integrated Ocean Drilling Program Site U1345 in the Bering Sea, which has a well-constrained age model from benthic foraminiferal δ18O. Except for one possibly contaminant shard dated at 165 ka, Old Crow tephra was absent from all samples spanning 220–160 ka. Old Crow tephra appeared abruptly at 157 ka, comprising >40% of detrital shards between 157 and 142 ka. This abrupt increase in the concentration of detrital Old Crow tephra, its absence in earlier intervals, and its presence at low concentrations in all samples between 134 and 15 ka collectively indicate that the tephra was deposited during the middle of MIS 6 with a likely age of 159 ± 8 ka. As a result, the late Quaternary chronostratigraphic framework for unglaciated northwest North America remains intact, and the timing of key events in the region (e.g., bison entry into North America; interglacial paleoclimate; permafrost history; the penultimate glaciation) does not require wholesale revision.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 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 | 0.001 |
| Insufficient payload (model declined to judge) | 0.023 | 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 teacher head, 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".