A desert responds to Pleistocene climate change: Saline lacustrine sediments, Death Valley, California, USA
Bibliographic record
Abstract
A core taken in 1993 from the modern saltpan at Badwater Basin in Death Valley, California, USA recovered about 185 m of saline lacustrine sediments. The sediments reflect climate fluctuations during the last 200 ka, encompassing two major glacial-interglacial cycles. This paper describes sediments in the lower half of the core, dated from about 200 to 100 ka. Perennial saline lake black muds and associated evaporite sediments, deposited between about 186 and 120 ka, encompass over half of the lower core. They are bracketed by saline mudflat and saltpan/ephemeral saline lake facies. Halite dominates evaporite mineralogy in the lower core; primary growth textures and syndepositional alteration fabrics provide qualitative indicators of brine depth and stratification and subaerial exposure events. Paleotemperatures from fluid inclusions in halite and pseudomorphs of hydrohalite suggest a climate 10 to 15°C cooler than present, with winter lows below 0°C. The Amargosa River may have begun to drain into Death Valley sometime during the early phase of the perennial lake. Sierra Nevada runoff via a series of over flowing basins probably reached Death Valley briefly just before the end of the perennial lake phase. The perennial lake interval, which reflects increased precipitation regionally, began at the beginning of global glacial stage 6 and persisted through it into the early stage 5 interglacial. The appearance or growth of perennial lakes during glacial periods has been noted in other interior-drained valleys in the US Great Basin, opposite to the response of many global desert-latitude areas, which become drier during glacial periods.
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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 | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 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) | 0.001 | 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".