| Abstrakt: |
A small basin on the Southwest (SW) margin of Melas Chasma in Valles Marineris, Mars, hosts a variety of previously identified sedimentary fans and layered strata hypothesized to have been formed by one or more paleolakes. This basin also contains light‐toned layered mounds that have distinct spectral absorption bands consistent with amorphous hydrated silica (e.g., opal). While the general morphology and mineralogy of these features and the basin itself have been previously characterized, the formation mechanism of the hydrated silica features and their temporal relationships with the proposed paleolake remain to be determined. We use Compact Reconnaissance Imaging Spectrometer for Mars visible through short‐wave infrared reflectance spectra (0.35–2.65 μm) and High Resolution Imaging Science Experiment digital terrain models and images to analyze the stratigraphic location and morphology of the opaline silica‐bearing features in the SW Melas basin. We find that the basin hosts fourteen high‐relief "mounds," eight low‐relief "patches," and two extended layers within the sedimentary strata that are light‐toned, fractured, and often exhibit hydrated silica‐like spectral signatures. We hypothesize that the mounds are spring deposits formed by sub‐aerial hydrothermal activity, while the patches and layers correspond to sub‐lacustrine hydrothermal activity. The varied elevations of the mounds and patches indicate at least one fluctuation of lake level in the basin during its history. The combination of contemporaneous hydrothermal and lacustrine activity to form silica‐cemented sedimentary deposits in a nutrient‐rich subaqueous environment would have been conducive to forming and preserving biosignatures in the SW Melas basin. Plain Language Summary: A small basin within Valles Marineris, the largest canyon system on Mars, is thought to have contained one or more lakes in its ancient past. This lake basin also contains signs of opal and other minerals that suggest the interaction of water with the rocks present in the basin. While the different features and minerals of the study site have been previously described, there are still many outstanding questions on how these features were formed and how they relate to the lake activity also seen in the basin. We use various orbital instruments on the Mars Reconnaissance Orbiter to answer these questions. We find that there are two different opal‐bearing features, which we separate into "mounds" and "patches," as well as some opal‐bearing sedimentary layers. The structure and mineralogy of these features indicate that hydrothermal activity was potentially contemporaneous with the ancient lakes, and that the variable features can be attributed to varying lake levels. The combination of lakes and hydrothermal activity may suggest that this basin had the right conditions for life to form and be preserved in this area. Key Points: Hydrated silica is present in a population of light‐toned mounds and patches consistent with subaerial and subaqueous hydrothermal springsNearby lake sediments are also silica/sulfate‐bearing, suggesting that the paleolake and hydrothermal activity were contemporaneousSubaqueous hydrothermal systems in Valles Marineris would have created a highly habitable environment with high biosignature preservation potential [ABSTRACT FROM AUTHOR] |
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