Stratigraphy and formation of clays, sulfates, and hydrated silica within a depression in Coprates Catena, Mars
We investigate the morphology, mineralogy, and stratigraphy of light-toned layered deposits within a trough of Coprates Catena, centered at -15°N, 300°E. One of the deposits in the eastern portion of the trough contains numerous hydrated minerals, including Al-phyllosilicates, Fe/Mg-phyllosilicates, hydrated silica, hydrated sulfates, jarosite and acid alteration products characterized by a spectral doublet between 2.2 and 2.3 µm, and weakly hydrated materials. The Al-phyllosilicates are observed both stratigraphically above and below the Fe/Mg-phyllosilicate unit, which is a rare and perhaps unique association on Mars. Most of the western light-toned layered deposit underlies a terraced fan. This deposit contains hydrated materials, including Al-phyllosilicates and Fe/Mg-phyllosilicates. Dip measurements indicate that both the eastern and western deposits dip toward the center of the trough, indicating that they postdate formation of the trough and are consequently Late Hesperian or younger in age. Volcanic ash, most likely erupted during formation of the pit crater in the eastern portion of the trough, seems to best explain our observations for several of the units. Valleys sourced from water along the plateau may have flowed into the trough and altered the sediments, with changing aqueous chemistries over time resulting in the diverse range of mineralogies now observed in the eastern light-toned deposit. Our results reveal a complex sedimentary and aqueous history within the Coprates Catena trough, indicating that localized habitable conditions were possible relatively late in Martian history at a time when colder, drier conditions likely dominated the majority of the planet.