title: Orbital identification of carbonate-bearing rocks on Mars.
abstract: Geochemical models for Mars predict carbonate formation during aqueous alteration. Carbonate-bearing rocks had not previously been detected on Mars' surface, but Mars Reconnaissance Orbiter mapping reveals a regional rock layer with near-infrared spectral characteristics that are consistent with the presence of magnesium carbonate in the Nili Fossae region. The carbonate is closely associated with both phyllosilicate-bearing and olivine-rich rock units and probably formed during the Noachian or early Hesperian era from the alteration of olivine by either hydrothermal fluids or near-surface water. The presence of carbonate as well as accompanying clays suggests that waters were neutral to alkaline at the time of its formation and that acidic weathering, proposed to be characteristic of Hesperian Mars, did not destroy these carbonates and thus did not dominate all aqueous environments.
authors.affiliation: Department of Geological Sciences, Brown University, Providence, RI02912, USA.
authors.forename: Bethany L
authors.initials: BL
authors.lastname: Ehlmann
authors.forename: John F
authors.initials: JF
authors.lastname: Mustard
authors.forename: Scott L
authors.initials: SL
authors.lastname: Murchie
authors.forename: Francois
authors.initials: F
authors.lastname: Poulet
authors.forename: Janice L
authors.initials: JL
authors.lastname: Bishop
authors.forename: Adrian J
authors.initials: AJ
authors.lastname: Brown
authors.forename: Wendy M
authors.initials: WM
authors.lastname: Calvin
authors.forename: Roger N
authors.initials: RN
authors.lastname: Clark
authors.forename: David J Des
authors.initials: DJ
authors.lastname: Marais
authors.forename: Ralph E
authors.initials: RE
authors.lastname: Milliken
authors.forename: Leah H
authors.initials: LH
authors.lastname: Roach
authors.forename: Ted L
authors.initials: TL
authors.lastname: Roush
authors.forename: Gregg A
authors.initials: GA
authors.lastname: Swayze
authors.forename: James J
authors.initials: JJ
authors.lastname: Wray
mesh_terms: D005118:Extraterrestrial Environment; D058085:Iron Compounds; D008274:Magnesium; D017616:Magnesium Compounds; D018535:Mars; D017640:Silicates; D018531:Spacecraft; D013057:Spectrum Analysis; D013696:Temperature; D014867:Water
chemical_list: D058085:Iron Compounds; D017616:Magnesium Compounds; D017640:Silicates; D014867:Water; C005479:magnesium carbonate; C034475:olivine; C033214:Smectite; D008274:Magnesium