MINERALOGICAL CHANGES IN A PREDOMINANTLY FLUVIOLACUSTRINE SUCCESSION AT GALE CRATER, MARS
Geochemical and mineralogical variability in the Murray formation point toward changes in depositional and diagenetic environments and sediment sources over time. The base of the Murray formation, represented by the Pahrump Hills and Marias Pass localities, was deposited in a lacustrine environment and displays incredible mineralogical and geochemical variability over ~15 m of section. CheMin data show a change from samples with abundant pyroxene, phyllosilicate, and hematite with minor jarosite at the base of the Pahrump Hills to a sample in Marias Pass that lacks these minerals and instead is dominated by feldspar and amorphous and crystalline SiO2 with minor magnetite and Ca-sulfate. This variability may represent a change in the sediment source region, in addition to a change in depositional and/or diagenetic environment. The most recent CheMin measurements of the Murray formation show remarkable consistency in mineralogy over ~50 m of section. These samples contain abundant phyllosilicate, hematite, Ca-sulfate, and feldspar, with minor pyroxene. The observation of significant Ca-sulfate is consistent with geomorphological and geochemical evidence for desiccation of the lake environment in this interval. Furthermore, the abundance of hematite suggests the fluids at the time of deposition and/or diagenesis were oxidizing.