Evidence for Adsorption of Chlorine Species on Iron (III) (Hydr)oxides in the Sheepbed Mudstone, Gale Crater, Mars
Bibliographic record
Abstract
Abstract Ancient aquatic environments in Yellowknife Bay, Gale crater, Mars, could create favorable conditions for adsorption of chlorine compounds (perchlorate and chloride) on Fe (III) (hydr)oxides present in the Sheepbed mudstone, such as akaganeite and ferrihydrite. In this work, 5.2 mM ClO 4 − and 1.7 to 12 mM Cl − were adsorbed onto ferrihydrite and 5.2 mM ClO 4 − was adsorbed onto akaganeite at ultraacidic (pH 2–2.5), acidic (pH 3.8–4.5), and near‐neutral (pH 6.2–7.7) pH. Samples were characterized by evolved gas analysis and compared to the data collected for the Cumberland sample from the Sheepbed mudstone. Evolved gas analysis showed that ferrihydrite with 0.5–1 wt.% ClO 4 − adsorbed under ultraacidic and acidic conditions had a well‐resolved O 2 peak at 306 °C due to the thermal decomposition of adsorbed ClO 4 − . All akaganeite samples with 0.5 wt.% adsorbed ClO 4 − had a weak peak at 312 °C tentatively assigned to decomposing perchlorate. Evolved gas analysis demonstrated that 0.5–2 wt.% Cl − adsorbed on ferrihydrite at ultraacidic and acidic pH was the main contributor to HCl evolved at >470 °C. Comparison with martian observations indicated that the temperature of the O 2 peak originating from ClO 4 − adsorbed on ferrihydrite matched well with the thermal evolution of O 2 from the Cumberland. Evolved HCl originating from Cl − adsorbed on ferrihydrite was within the temperature range of the high‐temperature HCl release from Cumberland (~770 °C). These observations suggest that ferrihydrite containing adsorbed ClO 4 − and Cl − could exist in the mudstone. Experimental results are consistent with adsorption at acidic pH < 4 environments through postdepositional water‐rock interactions of ferrihydrite with acid‐sulfate groundwater containing dissolved chloride and perchlorate.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 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 | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 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 teacher head, 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".