UNDERSTANDING THE SEDIMENTARY RECORD OF MARS THROUGH GLOBAL STRATIGRAPHY AND ORBITAL FACIES
We have developed a suite of ‘orbital facies’ that are defined by specific morphologic and mineralogical characteristics as observed from orbital data. They include Massive Breccia (MBR), Complexly Stratified Clays (CSC), Laterally Continuous Sulfates (LCS), Laterally Continuous Heterolithic (LCH), Distributary Networks (DNW), and Rhythmite (RHY) facies. We have also identified a number of stratigraphic sections across the planet that may be useful reference sections for global scale correlation. The most ancient terrains are dominated by MBR and CSC facies, with impact cratering being an important process for some occurrences of these facies. In contrast, Hesperian terrains are characterized by LCS, DNW, and, to a lesser extent, the CSC facies. RHY occurrences are commonly associated with post-Noachian terrains and may record sediment accumulation linked to orbital forcing. These results indicate that transitions in mineralogy and any associated changes in climate may have been slower-paced or more spatially restricted than previously recognized. The data largely support a gradual desiccation of Mars, but the timing, duration, and mineralogical record of this process may be better constrained through global-scale application of an objective classification scheme that is ultimately evaluated in multiple locations by future landed missions.