Evolved Gas Analyses of Sedimentary Rocks From the Glen Torridon Clay‐Bearing Unit, Gale Crater, Mars: Results From the Mars Science Laboratory Sample Analysis at Mars Instrument Suite

Abstract

Evolved gas analysis (EGA) data from the Sample Analysis at Mars (SAM) instrument suite indicated Fe-rich smectite, carbonate, oxidized organics, Fe/Mg sulfate, and chloride in sedimentary rocks from the Glen Torridon (GT) region of Gale crater that displayed phyllosilicate spectral signatures from orbit. SAM evolved H 2 O data indicated that the primary phyllosilicate in all GT samples was an Fe-rich dioctahedral smectite (e.g., nontronite) with lesser amounts of a phyllosilicate such as mixed layer talc-serpentine or greenalite-minnesotaite. CO 2 data supported the identification of siderite in several samples, and CO 2 and CO data was also consistent with trace oxidized organic compounds such as oxalate salts. SO 2 data indicated trace and/or amorphous Fe sulfates in all samples and one sample may contain Fe sulfides. SO 2 data points to significant Mg sulfates in two samples, and lesser amounts in several other samples. A lack of evolved O 2 indicated the absence of oxychlorine salts and Mn 3+ /Mn 4+ oxides. The lack of, or very minor, evolved NO revealed absent or very trace nitrate/nitrite salts. HCl data suggested chloride salts in GT samples. Constraints from EGA data on mineralogy and chemistry indicated that the environmental history of GT involved alteration with fluids of variable redox potential, chemistry and pH under a range of fluid-to-rock ratio conditions. Several of the fluid episodes could have provided habitable environmental conditions and carbon would have been available to any past microbes though the lack of significant N could have been a limiting factor for microbial habitability in the GT region. Plain Language SummaryThe Mars Science Laboratory Curiosity rover carried out a comprehensive investigation of the sedimentary rocks in the Glen Torridon (GT) region in Gale crater, Mars, to better understand Martian geologic history. The rover's Sample Analysis at Mars instrument suite was used to heat samples from GT and detect gases that were evolved to help identify the volatile-bearing mineralogy of the samples. Results indicated the presence of Fe-rich smectite, carbonate, oxidized organics, Fe and Mg sulfate, and chloride while oxychlorine salts, Mn 3+ /Mn 4+ oxides, and nitrate/nitrite salts were either not detected or occurred in trace amounts. This mineralogy data implied that geochemical conditions and fluid-to-rock ratios varied over time and that the conditions of GT depositional and diagenetic environments would have been amenable to microbial life with sufficient carbon but nitrogen abundances could have been limiting.

Geology and Stratigraphic Correlation of the Murray and Carolyn Shoemaker Formations Across the Glen Torridon Region, Gale Crater, Mars

“…Bedding in this location is less than about 10 cm thick and consists of stacked toesets of tabular‐tangential cross‐stratification. The top of this unit was drilled (Glen Etive) and studied extensively for (Dehouck et al., 2022; O’Connell‐Cooper et al., 2022) and potential preserved organics (McAdam et al., 2022). While grain‐size is difficult to determine through this interval, high‐resolution MAHLI mosaics taken from centimeters from the outcrop surface, along with ChemCam RMI image mosaics, locally show dimpled outcrop textures suggestive of fine‐to‐medium sand.…”

Sedimentary Organics in Glen Torridon, Gale Crater, Mars: Results From the SAM Instrument Suite and Supporting Laboratory Analyses

“…The sedimentary rocks of Glen Torridon have experienced a complex authigenic/diagenetic history involving fluids with varying pH and redox composition (McAdam et al, 2022). Diagenetic fluid chemistry could have influenced the change in sulfur mineralogy from KM and the GE/MA drill samples up-section to the Glasgow member, which includes the GG and HU samples.…”

Surface Kinetic Temperatures and Nontronite Single Scattering Albedo Spectra From Mars Reconnaissance Orbiter CRISM Hyperspectral Imaging Data Over Glen Torridon, Gale Crater, Mars

“…The presence of ferric smectite (including nontronite) in drill samples Kilmarie, Glen Etive 1,and Glen Etive 2 is also supported by evolved gas analysis by the SAM instrument (Aberlady not analyzed). Evolved H 2 O in the temperature interval approximately bounded by 400°C and 550°C is interpreted as thermal dehydroxylation of ferric smectite (e.g., Bristow et al., 2021; McAdam et al., 2022). By extension, the CRISM RU_a spectra (Figures 19 and 20) are best explained by the presence of desiccated nontronite.…”