Geologic Context of Al-rich Phyllosilicate Deposits in Meridiani

Exposures of Al-rich phyllosilicate-bearing deposits are detected using MRO CRISM spectral data in fluvially dissected cratered terrain to the south of the sulfate and hematite-bearing plains unit analyzed by the Opportunity rover. Specifically, Al-rich phyllosilicates, including montmorillonite and kaolinite, are identified in association with Fe/Mg smectites. Although Fe/Mg smectites have been previously detected in Sinus Meridiani using OMEGA and CRISM images, this is the first identification of Al-rich phyllosilicates in this region. Al and Fe/Mg phyllosilicates have been identified in relatively large, compositionally stratified deposits within Mawrth Vallis. Although the Meridiani phyllosilicate deposits are exposed over a more limited area than the Mawrth deposits, initial analyses suggest that the Meridiaini phyllosilicate deposits are also compositionally stratified. The phyllosilicates occur in remnants of higher standing terrain. Analysis of superposition relationships using image and topographic data demonstrate that, after formation, the phyllosilicate deposits were incised via fluvial erosion and later embayed by the hematite-bearing plains unit.