Geomorphological activity and stability of surfaces and soils formed in hyperarid alluvial deposits (Atacama Desert, Chile)
Bibliographic record
Abstract
Abstract. The hyperarid conditions of the central Atacama Desert, characterized by extremely low precipitation and high evaporation rates, create a unique environment where geomorphic stability is generally considered to be exceptionally high. Terrestrial cosmogenic nuclide-based surface exposure ages suggest that many surfaces underwent limited to no geomorphic changes since the Neogene or early Pleistocene. However, a number of recent studies reveal more recent landscape-scale geomorphic activity and link this to slightly wetter episodes during the Quaternary. In order to determine drivers of geomorphic activity, we performed a multi-proxy analysis of five profiles situated in alluvial deposits along a climatic transect from the coastal plain to the upper reaches of the Coastal Cordillera (~ 0–2000 m a.s.l.), combining single-grain feldspar luminescence dating with geochemistry, granulometry, and field observations. Alluvial deposits are prone to heterogeneous bleaching; therefore, we tested the bleachability of the feldspars and found a shallow effective bleaching depth (< 2 cm) and high near-surface bleachability. The five profiles studied could be grouped into geomorphological active and stable sites, based on our multi-method approach. Profiles located on geomorphologically active surfaces show evidence of recent sediment deposition and, in one case, vertical grain transport. In contrast, stable surfaces preserve reworking signals relating to bioturbation at the coast and desert pavement formation in the hyperarid Coastal Cordillera. While no clear chronological trend along the west–east climatic gradient could be found, two phases of widespread geomorphic surface activity – ~ 50 ka and during the last ~ 5 ka – coincide with regionally wetter intervals compiled from other studies. Our findings highlight the value of single-grain luminescence data for reconstructing local sediment dynamics and soil reworking in arid environments, and the need to account for both depositional and post-depositional processes in paleoenvironmental interpretations.
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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 | 0.002 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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".