Multiple Mineral Horizons at Mawrth Vallis , Mars , Represent Changing Environmental Conditions

Mineralogical evidence for multiple aqueous alteration settings at Mawrth Vallis, Mars, indicates changes in the geochemical environment. A thick layered horizon of Fe/Mg-smectite is covered by a unit containing Al-phyllosilicates, opal and allophane. Smaller outcrops of sulfates are observed in many locations and spectral “doublet” features of several small outcrops between the phyllosilicate units are likely due to mixtures of sulfates and phyllosilicates and may represent evaporite or hydrothermal settings.