  The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) has returned
observations of the Nili Fossae region indicating the presence of Mg- carbonate
in small (<10km sq2), relatively bright rock units that are commonly fractured
(Ehlmann et al., 2008b). We have analyzed spectra from CRISM images and used
co-located HiRISE images in order to further characterize these
carbonate-bearing units. We applied absorption band mapping techniques to
investigate a range of possible phyllosilicate and carbonate minerals that
could be present in the Nili Fossae region. We also describe a clay-carbonate
hydrothermal alteration mineral assemblage in the Archean Warrawoona Group of
Western Australia that is a potential Earth analog to the Nili Fossae
carbonate-bearing rock units. We discuss the geological and biological
implications for hydrothermal processes on Noachian Mars.
