¹S. Czarnecki,¹C. Hardgrove,²R. E. Arvidson,²M. N. Hughes,³M. E. Schmidt,³T. Henley,⁴L. M. Martinez Sierra,⁴I. Jun,⁵M. Litvak,⁵I. Mitrofanov
Journal of Geophysical (Planets)(in Press) Link to Article [https://doi.org/10.1029/2021JE007104]
¹School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA
²Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, MO, USA
³Department of Earth Sciences, Brock University, St. Catharines, ON, Canada
⁴Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
⁵Space Research Institute, Russian Academy of Sciences, Moscow, Russia
Published by arrangement with John Wiley & Sons

Glen Torridon (GT) is a geomorphic feature of Aeolis Mons (informally Mt. Sharp) in Gale crater, Mars, variably covered by local regolith and wind-blown basaltic sands. The Mars Reconnaissance Orbiter’s Compact Imaging Spectrometer for Mars (CRISM) detected clay minerals in GT, making GT a target of investigation by the Mars Science Laboratory (MSL) rover, Curiosity, which confirmed a large abundance of clays. The MSL Dynamic Albedo of Neutrons (DAN) instrument observed enrichments in bulk subsurface ( < 50 cm) hydration along the rover traverse compared to lower stratigraphic sections of Mt. Sharp. Here, we investigate the relationship between the CRISM 3 μm hydration index and DAN results, taking into consideration the different spatial scales and effective depths of these two instruments. We show that the elevated hydration observed by CRISM in one area of GT corresponds to elevated DAN-derived hydration, while the lower CRISM hydration in another area of GT does not correspond to a significantly lower DAN-derived hydration. We find that CRISM measured lower hydration in areas with rough surface texture and sand cover, while DAN bulk hydration is relatively insensitive to these characteristics. DAN active neutron results also show that the stratigraphically higher section of GT has significantly higher neutron absorption, which could be due to Fe- and Mn-rich diagenetic features. Additionally, DAN results show that GT is enriched in hydrogen with respect to other, less clay-rich units observed throughout the traverse, suggesting that subsurface clay minerals could be a significant reservoir for the hydration measured by DAN in GT.

¹Michael T. Thorpe et al. (>10)
Journal of Geophysical Research (Planets)(in Press) Link to Article [https://doi.org/10.1029/2021JE007099]
¹Texas State University, JETS, at NASA Johnson Space Center, Houston, TX, 77058 USA
Published by arrangement with John Wiely & Sons

The Glen Torridon (GT) region in Gale crater, Mars is a region with strong clay mineral signatures inferred from orbital spectroscopy. The CheMin X-ray diffraction (XRD) instrument onboard the Mars Science Laboratory rover, Curiosity, measured some of the highest clay mineral abundances to date within GT, complementing the orbital detections. GT may also be unique because in the XRD patterns of some samples, CheMin identified new phases, including: (i) Fe-carbonates, and (ii) a phase with a novel peak at 9.2 Å. Fe-carbonates have been previously suggested from other instruments onboard, but this is the first definitive reporting by CheMin of Fe-carbonate. This new phase with a 9.2 Å reflection has never been observed in Gale crater and may be a new mineral for Mars, but discrete identification still remains enigmatic because no single phase on Earth is able to account for all of the GT mineralogical, geochemical, and sedimentological constraints. Here, we modeled XRD profiles and propose an interstratified clay mineral, specifically greenalite-minnesotaite, as a reasonable candidate. The coexistence of Fe-carbonate and Fe-rich clay minerals in the GT samples supports a conceptual model of a lacustrine groundwater mixing environment. Groundwater interaction with percolating lake waters in the sediments is common in terrestrial lacustrine settings, and the diffusion of two distinct water bodies within the subsurface can create a geochemical gradient and unique mineral front in the sediments. Ultimately, the proximity to this mixing zone may have controlled the secondary minerals preserved in sedimentary rocks exposed in GT.