¹Catherine M. Weitz,²Janice L. Bishop
¹Planetary Science Institute, Tucson, AZ
²SETI Institute, Mountain View, CA

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 2.2-2.3 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 both the eastern and western deposits dip towards the center of the trough, indicating they post-date 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.

Reference
Weitz CM, Bishop JL (2016) Stratigraphy and Formation of Clays, Sulfates, and Hydrated Silica within a Depression in Coprates Catena, Mars. Journal of Geophysical Research Planets (in Press)
Link to Article [DOI: 10.1002/2015JE004954]
Published by arrangement with John Wiley & Sons

¹James J. Wray et al. (>10)*
¹School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA
*Find the extensive, full author and affiliation list on the publishers website

Carbonates are key minerals for understanding ancient Martian environments because they are indicators of potentially habitable, neutral-to-alkaline water and may be an important reservoir for paleo-atmospheric CO₂. Previous remote sensing studies have identified mostly Mg-rich carbonates, both in Martian dust and in a Late Noachian rock unit circumferential to the Isidis basin. Here we report evidence for older Fe- and/or Ca-rich carbonates exposed from the subsurface by impact craters and troughs. These carbonates are found in and around the Huygens basin northwest of Hellas, in western Noachis Terra between Argyre basin and Valles Marineris, and in other isolated locations spread widely across the planet. In all cases they co-occur with or near phyllosilicates, and in Huygens basin specifically they occupy layered rocks exhumed from ~5 km depth. We discuss factors that might explain their observed regional distribution, arguments for why carbonates may be even more widespread in Noachian materials than presently appreciated, and what could be gained by targeting these carbonates for further study with future orbital or landed missions to Mars.

Reference
Wray JJ et al. (2016) Orbital evidence for more widespread carbonate-bearing rocks on Mars. Journal of Geophysical Research, Planets (in Press)
Link to Article [DOI: 10.1002/2015JE004972]
Published by arrangement with John Wiley & Sons