Characterization of Sulfate Minerals in Juventae Chasma from CRISM images

We are investigating the mineralogy of the Juventae Chasma region that lies north-east of Valles Marineris. The OMEGA investigation on the Mars Express spacecraft identified sulfates in the light-toned outcrops inside Juventae Chasma (Gendrin et al 2005). In particular they observed spectral features attributed to gypsum and kieserite in the mound labelled B by Catling et al (2006). This study analyzed the geomorphology using MOC, MOLA, TES and THEMIS data and formulated hypotheses on the formation of light-toned layered outcrops labeled A to D from the South-West to the North rim of Juventae Chasma. The order of magnitude increase in spatial resolution of the CRISM instrument on Mars Reconnaissance Orbiter over OMEGA is used here to assess mineralogic diversity and to analyze stratigraphic relationships between the mounds and the surrounding Chasma walls. CRISM data show evidence for diagnostic sulfate absorptions in a few locations. These are consistent with monohydrated sulfates such as kieserite and szomolnokite as well as polyhydrated sulfates such as starkeyite. The strongest occurrences of sulfates appear at the location occupied by the light-toned outcrops, in particular mound "A". A mobile basaltic sand sheet covers much of the chasma floor. Patches of olivine and pyroxene are observed in the chasma wall rock but require further spectroscopic study to assess their extent and stratigraphic relationship with the mounds. The detection of sulfate bands in the exposed light-toned material in the mounds, which date back to late - noachian / early hesperian (Catling et al. 2006), indicates the presence of an early acidic environment in the Chasma and probable evaporitic processes. The "sulfate" layered mounds present evidence of high erosion and in some regions of exhumation from the west wall of the chasma and the hummochy terrains in the north, as visible from ConText Imager (CTX) and HiRISE data. References: Gendrin A., et al.(2005). Science, 307, 1587-1591. Catling, D.C. et al. (2006). Icarus, 181,26-51.