Spectral Stratigraphy of Phyllosilicate-Bearing Terrains in Mawrth Vallis and Terra Meridiani

Layered phyllosilicate-bearing rocks have been observed near Mawrth Vallis (MV) (centered at approximately 20° W and 23° N) and scattered exposures have been observed over Terra Meridiani (TM) to the southwest. TM has more prominent exposures of sulfate-bearing rocks and, in its southwest has coarsely crystalline hematite bearing plains explored in part by the Opportunity rover. The phyllosilicate-bearing strata in TM underlie the sulfate-bearing rocks. Exposures of sulfate-bearing rocks have not been observed at MV. We have examined these regions using data from Mars Express HRSC and OMEGA, MRO CRISM and HiRISE, Mars Odyssey THEMIS, and MGS TES. While imaging data indicates that the phyllosilicate minerals at MV reside in light-toned strata; target transformation analysis of TES data paradoxically indicate better matches with powdered phyllosilicate minerals although this result may be more indicative of rough textured outcrop rather than the physical state of the clay minerals. MV has greater mineralogic variability than the phyllosilicate exposures in TM with exposures of materials with 1900 nm bound water features, a 2200 nm Al-OH feature and a 2300 nm Mg or Fe-OH band. At MV, strata with the 2200 nm feature overlie those with the 2300 nm feature while at TM only the 2300 nm feature is observed. Four band HRSC data also indicate greater VNIR color variability over the MV phyllosilicate-bearing terrains than in the TM equivalents. Estimates for the thickness of the light-toned rocks at MV range from over 100 to over 600 m. Our own examination indicates a minimum thickness of 140 m which is nearly equally divided between materials displaying primarily the 2300 nm band and those displaying primarily the 2200 nm band. In this paper, we further examine similarities and differences between the MV and TM layered terrains and examine spectral stratigraphy within the broader MV region.