Geochemical characteristics of glacial Lake Agassiz sediments and new ages for the Moorhead Phase at Fargo, North Dakota, USA
Bibliographic record
Abstract
The cause and age of the Moorhead low-water Phase of glacial Lake Agassiz remains uncertain. New geochemical (X-ray fluorescence (XRF) and elemental analysis) and chronological (optically stimulated luminescence (OSL)) data are used to test for evaporative enrichment within lacustrine sediment from Rabbit Lake, a small basin just above the highest Lake Agassiz strandline, and from two Lake Agassiz sediment cores at Fargo, North Dakota. Increases in quartz and gypsum interpreted to be of aeolian origin suggest increased aridity at Rabbit Lake sometime after 13 540–13 750 cal years BP. From the Fargo cores, lacustrine sediment of the Brenna and Sherack formations did not show convincing evidence for evaporative enrichment. However, this result is complicated by an erosional contact at the top of the Brenna Formation. A thin middle sand unit between the Brenna and Sherack formation clays is stratigraphically equivalent to the Poplar River Formation, West Fargo Member, but its properties differ from the fluvial sand of the West Fargo Member. Four OSL ages from the organic-poor, middle sand unit at Fargo range between 12.8 ± 0.2 and 13.5 ± 0.2 ka (with ±1.6 ka uncertainty) and suggest lake level fell at Fargo at, or before, 13.1 ± 0.2 ka, the average of the OSL ages. With different sedimentological properties, and a difference of ∼1750 years between the new OSL ages and previously published ages on the West Fargo Member sand, additional work is required to determine whether the middle sand unit is a new member of the Poplar River Formation, recording an earlier and different depositional environment than the West Fargo Member. From a plot of available ages for the Moorhead Phase, the regression remains poorly constrained in time.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.002 | 0.001 |
| Science and technology studies | 0.001 | 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".