Evidence for Deposition of Chloride on Mars From Small‐Volume Surface Water Events Into the Late Hesperian‐Early Amazonian
Bibliographic record
Abstract
Abstract We determine the environmental setting and timing of enigmatic large‐scale chloride deposits on Mars, examining all available high‐resolution imagery globally, building digital elevation models, surveying targeted infrared images intersecting chloride deposits for accessory minerals (e.g., clay, carbonate, and sulfate), and performing crater counting for age‐dating when possible. We find that chloride deposits are commonly draped atop underlying topography, often associated with channels, sometimes perched above deep craters in local topographic lows, and span a wide range of elevations. Where measurable, chloride deposit thicknesses are typically <3 m. The deposits range in elevation over tens of meters, inconsistent with previous hypotheses of playa‐like environments, which are very flat. Chloride deposit elevations within larger basins are typically asymmetric with chloride deposits much higher on the inlet channel side, indicating that (a) surface water runoff was the most likely water source and (b) the basins were likely not filled completely with water in a deep lake setting but rather chlorides formed within a series of shallow ponds. Mass balance allows local sourcing from mobilization of cations and chlorine from dust/soil. Though prior global‐scale studies report chloride deposits superimposed on Noachian terrains, crater‐counting of local, stratigraphically‐associated datable surfaces shows chlorides superimposed on 3.4–2.3 Ga volcanic terrain. This indicates that surface waters forming chloride deposits continued through the Hesperian and into the Amazonian, making them among the latest‐formed, large‐scale deposits of water‐related minerals on Mars. Collectively, data suggest formation from meltwater from episodic ice/snow deposits continuing until 2.0–2.5 Ga.
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 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".