2026/04/19 by Inès Torres Auré, John Carter, Cathy Quantin-Nataf +3 · 1 voice
Engineering · Materials Science · #Soil and Unsaturated Flow #Geotechnical Engineering and Soil Mechanics #Clay minerals and soil interactions
paper · doi:10.1016/j.icarus.2026.117113
The Fe/Mg-phyllosilicate-bearing units at Oxia Planum and Mawrth Vallis, two key Noachian sites along the martian dichotomy, exhibit distinct compositions despite their proximity. Using novel spectral criteria developed in this study, we distinguish two clay types: Type-1 (Mg-rich smectites/Fe 2+ -bearing saponite/vermiculite) and Type-2 (Fe 3+ -rich nontronite). Hyperspectral (OMEGA/CRISM) and textural (HiRISE/CTX) analyses reveal a regionally extensive basal Type-1 unit continuous across both sites, overlain by a Type-2 unit limited to Mawrth Vallis and southeast of Oxia Planum (above main delta fan elevations). A cratered paleosurface, with a Type-1 spectral signature, marks their boundary, indicating a depositional hiatus. The Type-1 unit's lateral extent (>600 km) and elevation range (>1300 m) suggest a large-scale aqueous process, while the Type-2 unit's absence below Oxia Planum's delta fan implies either post-depositional erosion or environmental controls during deposition at Oxia Planum. Our results constrain early Mars' climate models, challenging localized deposition/alteration hypotheses and ocean scenarios. These findings reveal that Type-1 clays extend over a much broader area than previously assumed, indicating that the ExoMars Rosalind Franklin rover will not investigate a localized phenomenon but rather a process with significant regional–and potentially global–implications for the geological and climatic history of Mars.