title: Phyllosilicate diversity and past aqueous activity revealed at Mawrth Vallis, Mars.
abstract: Observations by the Mars Reconnaissance Orbiter/Compact Reconnaissance Imaging Spectrometer for Mars in the Mawrth Vallis region show several phyllosilicate species, indicating a wide range of past aqueous activity. Iron/magnesium (Fe/Mg)-smectite is observed in light-toned outcrops that probably formed via aqueous alteration of basalt of the ancient cratered terrain. This unit is overlain by rocks rich in hydrated silica, montmorillonite, and kaolinite that may have formed via subsequent leaching of Fe and Mg through extended aqueous events or a change in aqueous chemistry. A spectral feature attributed to an Fe2+ phase is present in many locations in the Mawrth Vallis region at the transition from Fe/Mg-smectite to aluminum/silicon (Al/Si)-rich units. Fe2+-bearing materials in terrestrial sediments are typically associated with microorganisms or changes in pH or cations and could be explained here by hydrothermal activity. The stratigraphy of Fe/Mg-smectite overlain by a ferrous phase, hydrated silica, and then Al-phyllosilicates implies a complex aqueous history.
authors.affiliation: SETI Institute and NASA Ames Research Center, Mountain View, CA 94043, USA. jbishop@seti.org
authors.forename: Janice L
authors.initials: JL
authors.lastname: Bishop
authors.forename: Eldar Z Noe
authors.initials: EZ
authors.lastname: Dobrea
authors.forename: Nancy K
authors.initials: NK
authors.lastname: McKeown
authors.forename: Mario
authors.initials: M
authors.lastname: Parente
authors.forename: Bethany L
authors.initials: BL
authors.lastname: Ehlmann
authors.forename: Joseph R
authors.initials: JR
authors.lastname: Michalski
authors.forename: Ralph E
authors.initials: RE
authors.lastname: Milliken
authors.forename: Francois
authors.initials: F
authors.lastname: Poulet
authors.forename: Gregg A
authors.initials: GA
authors.lastname: Swayze
authors.forename: John F
authors.initials: JF
authors.lastname: Mustard
authors.forename: Scott L
authors.initials: SL
authors.lastname: Murchie
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Bibring
mesh_terms: D005118:Extraterrestrial Environment; D007501:Iron / Q000032:analysis; D008274:Magnesium / Q000032:analysis; D018535:Mars; D017640:Silicates / Q000032:analysis*; D013057:Spectrum Analysis; D014867:Water
chemical_list: D017640:Silicates; D014867:Water; C033214:Smectite; D007501:Iron; D008274:Magnesium