Evidence for partially chloritized smectite in Gale crater, Mars
Bibliographic record
Abstract
Abstract Characterizing the structure and composition of clay minerals on the surface of Mars is important for reconstructing past aqueous processes and environments. Data from the CheMin X-ray diffraction (XRD) instrument on the Mars Science Laboratory Curiosity rover demonstrate a ubiquitous presence of collapsed smectite (basal spacing of 10 Å) in ~3.6-billion-year-old lacustrine mudstone in Gale crater, except for expanded smectite (basal spacing of 13.5 Å) at the base of the stratigraphic section in a location called Yellowknife Bay. Hypotheses to explain expanded smectite include partial chloritization by Mg(OH)2 or solvation-shell H2O molecules associated with interlayer Mg2+. The objective of this work is to test these hypotheses by measuring partially chloritized and Mg-saturated smectite using laboratory instruments that are analogous to those on Mars rovers and orbiters. This work presents Mars-analog XRD, evolved gas analysis (EGA), and visible/shortwave-infrared (VSWIR) data from three smectite standards that were Mg-saturated and partially and fully chloritized with Mg(OH)2. Laboratory data are compared with XRD and EGA data collected from Yellowknife Bay by the Curiosity rover to examine whether the expanded smectite can be explained by partial chloritization and what this implies about the diagenetic history of Gale crater. Spectral signatures of partial chloritization by hydroxy-Mg are investigated that may allow the identification of partially chloritized smectite in Martian VSWIR reflectance spectra collected from orbit or in situ by the SuperCam instrument suite on the Mars 2020 Perseverance rover. Laboratory XRD and EGA data of partially chloritized saponite are consistent with data collected from Curiosity. The presence of partially chloritized (with Mg(OH)2) saponite in Gale crater suggests brief interactions between diagenetic alkaline Mg2+-bearing fluids and some of the mudstone exposed at Yellowknife Bay, but not in other parts of the stratigraphic section. The location of Yellowknife Bay at the base of the stratigraphic section may explain the presence of alkaline Mg2+-bearing fluids here but not in other areas of Gale crater investigated by Curiosity. Early diagenetic fluids may have had a sufficiently long residence time in a closed system to equilibrate with basaltic minerals, creating an elevated pH, whereas diagenetic environments higher in the section may have been in an open system, therefore preventing fluid pH from becoming alkaline.
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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 | 0.001 | 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".