Emma Rae Rogers

and 4 more

A small basin on the southwest 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 has been previously characterized, the formation mechanism of the hydrated silica features and their temporal relationships with the proposed paleolake remains to be determined. We use Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) visible through short-wave infrared reflectance spectra (0.35-2.65 µm) and High Resolution Imaging Science Experiment(HiRISE) digital terrain models and images to analyze the stratigraphic location and morphology of the opaline silica-bearing features in the Southwest 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 activitiy, while the patches and layers correspond to sub-lacustrine hydrothermal activity. The varied stratigraphic 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 lacustrine deposits in a nutrient-rich subaqueous environment would have been conducive to forming and preserving signs of biological activity in the Southwest Melas basin.