Climate and tectonics along the southern margin of the Puna Plateau, NW Argentina: Origin of the late Cenozoic Punaschotter conglomerates
Bibliographic record
Abstract
Basins around the margin of the Puna Plateau in NW Argentina each record the onset over a few hundred thousand years of alluvial-fan facies sedimentation with the deposition of the Punaschotter conglomerates in the late Cenozoic, despite differing tectonic histories. Their striking similarity suggests that these conglomerates might have a common origin, such as the climatically driven coarsening and increase in sedimentation rate proposed to have occurred worldwide at 4–2 Ma. With this contribution, we present new U-Pb geochronology of intercalated ashes that bracket the onset of Punaschotter deposition along the margin of the Puna Plateau in the Fiambalá and El Cajon Basins. Combining this with existing data, we explore the relative roles of climate and tectonics in shaping sedimentation in this region. Our analysis reveals that Punaschotter deposition was diachronous and only occurred if both aridity and structural deformation were present. Development of orographic barriers and global climate change may have contributed to establishing regional aridity. In the eastern part of the study region (Santa Maria and Angastaco), onset of Punaschotter deposition tracks the establishment of aridity. In the already arid western basins (Fiambalá, Corral Quemado), a reactivation of structural deformation may have triggered the onset of Punaschotter deposition. Our study shows that initiation of coarse alluvial facies in this part of the Andes largely preceded the 4–2 Ma global climate change and emphasizes the coupled nature of local climate and tectonics in controlling sedimentation.
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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 | 0.001 |
| 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".