Mars Science Laboratory CheMin Data From the Glen Torridon Region and the Significance of Lake‐Groundwater Interactions in Interpreting Mineralogy and Sedimentary History

Abstract

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: (a) Fe-carbonates, and (b) 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. Plain Language SummaryThe Glen Torridon (GT) region on the lower slopes of the sedimentary mound in Gale Crater, Mars is characterized by terrains with enhanced clay mineral spectral signatures, as identified from orbit. This regional distinction in the landscape was confirmed on the ground with some of the highest clay mineral abundances measured to date by the CheMin X-ray diffraction instrument onboard the Mars Science Laboratory rover, Curiosity. In addition to clay minerals, this region is unique because of two new phase identifications for CheMin: (a) Fe-carbonates, which have been previously suggested from other instruments onboard Curiosity, but definitively identified for the first time with CheMin and (b) a new phase that has never been detected before on Mars. Even on Earth, few examples of this enigmatic phase exist, but here we modeled a mixture of clay minerals that were able to replicate the novel CheMin observations. Conceptually, a lake environment that interacts with discharging groundwater in the subsurface is an ideal setting to form the observed mineralogical trends in the GT region. Ancient lake and ground waters would have THORPE ET AL.

An Insight Into Ancient Aeolian Processes and Post‐Noachian Aqueous Alteration in Gale Crater, Mars, Using ChemCam Geochemical Data From the Greenheugh Capping Unit

“…The Greenheugh pediment capping unit has more MgO relative to the other Stimson localities (Figures 6 and 11), in addition to a greater abundance of Clusters 2 and 5 (Figure 11), indicative of higher abundances of mafic minerals. This is supported by the mineralogical results from CheMin that show a relatively high concentration of olivine (Rampe, Yen et al., 2020; Thorpe et al., 2022), indicating that the Greenheugh capping unit may be enriched in mafic components as a result of mineral sorting during transportation, assuming that the sands were derived from the same sediment source. If this is the case, the Greenheugh capping unit would have been deposited farther from the source than the Stimson formation at the Emerson and Naukluft plateaus that respectively show an increase in the felsic Clusters 3 and 4 (Figure 10).…”

“…The geochemical trends of the majority of ChemCam data between mafic and felsic minerals, and the similarity in composition between concretionary and non‐concretionary bedrock, also suggests that alteration was likely minimal away from the unconformity for the Greenheugh pediment capping unit. Minimal alteration at Greenheugh is further supported by the presence of 8 wt% olivine in the Edinburgh drilled sample (Rampe, Yen et al., 2020; Thorpe et al, 2022), which is only slightly less than the olivine abundances for the active aeolian sands at the Bagnold Dunes (e.g., 9.6 wt% at Ogunquit Beach; Rampe et al., 2018). This, in addition to the low degree of chemical weathering during transportation for dry aeolian systems (Jiang and Yang, 2019; Zhu and Yang, 2009), suggests that the geochemistry of the Stimson formation at the Greenheugh pediment capping unit is likely to be representative of the mineralogy of the dune sands at the time of deposition.…”

“…This can be indicative of calcium sulfate cement which has been largely detected by the ChemCam instrument and correlated to light-toned cements in MAHLI images acquired in the traverse leading up to the Greenheugh pediment (Gasda et al, 2022;Nellessen et al, 2019). However, the mineralogy of the Hutton drilled sample acquired below the capping unit only contains 0.6 wt% anhydrite (Thorpe et al, 2022), which is some of the lowest abundances of crystalline calcium sulfate detected in the Mt Sharp group since the drilled samples of the Pahrump Hills (Rampe et al, 2017), and sulfur is not detected here with APXS (Thompson et al, 2022). F abundances also increase in the Carolyn Shoemaker formation below the unconformity at the Hutton drill site (Dehouck et al, 2022; Figure 8b), including for alteration features such as veins and raised ridges (Gasda et al, 2022).…”

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

“…If the 9.2 Å phase is an authigenic clay mineral such as mixed layer G‐M hypothesized by Thorpe et al. (2022) the siderite may have been deposited from the same fluids as formed the G‐M, since these minerals are known to occur together in terrestrial settings.…”

“…This process could have also contributed to the heterogeneity in siderite abundances now observed in Jm and KHm rocks. If the 9.2 Å phase is an authigenic clay mineral such as mixed layer G-M hypothesized by Thorpe et al (2022) the siderite may have been deposited from the same fluids as formed the G-M, since these minerals are known to occur together in terrestrial settings. 3.…”