Mineralogy of a Possible Ancient Lakeshore in the Sutton Island Member of Mt. Sharp, Gale Crater, Mars, From Mastcam Multispectral Images

Abstract

The Curiosity rover on the Mars Science Laboratory mission has found extensive evidence that Gale crater once hosted a habitable lacustrine environment; however, there are remaining questions about the chemistry and duration of the lake and the nature of the climate at the time. In this study, we use Mastcam multispectral data to investigate the mineralogy of the Sutton Island member of the Murray formation, a part of the basal layers of Mt. Sharp, which consists of heterolithic mudstone and sandstone that are distinct from the finely laminated mudstones that dominate much of the Murray. Sutton Island includes at least one instance of desiccation cracks, indicative of subaerial exposure, and uniquely irregular diagenetic features that may be related to local bedrock permeability. These features suggest that Sutton Island experienced a complex history of deposition and diagenesis which may be crucial for understanding changing water‐rock interactions within Gale. We find that most Mastcam bedrock spectra in this region lack the absorptions associated with hematite found throughout the Murray, and instead show deeper absorptions shifted toward longer wavelengths that are more consistent with Fe‐smectites such as nontronite. Elemental chemistry from ChemCam supports this interpretation, as SiO, MgO, Li, and the chemical index of alteration are elevated in this region. Combined with observations of bedrock sedimentology, this suggests that Sutton Island was deposited in a nearshore or low stand environment, and we hypothesize that the clay minerals were produced in this region due to sub‐aerial exposure and weathering in a semi‐arid climate.

The Distribution of Clay Minerals and Their Impact on Diagenesis in Glen Torridon, Gale Crater, Mars

“…However, ferric smectites are most plausible based on their strong detections in orbital observations of GT (Fraeman et al., 2016) and CheMin models of up to 34 wt.% phyllosilicates in GT drill samples (Bristow, Grotzinger, et al., 2021; Thorpe et al., 2021, 2022). Similar spectral signatures have been observed in the SI member below VRR (Haber et al., 2020) and in isolated cm‐scale patches within the VRR Jm (Horgan et al., 2020). The >900 nm band was observed in all types of ROIs (dusty bedrock, DRT spots, and drill tailings) and in all three stratigraphic members in Mastcam data, but not near the GT‐Stimson contact (Figures 7 and 8).…”

“…The clay minerals may have formed either through alteration in a lacustrine environment or laterally extensive surface weathering, whether the altered sediments were detrital or authigenic. Similar patchy clay and hematite spectral signatures in SI below VRR have been attributed to similar weathering and diagenetic processes (Haber et al, 2020). In contrast, the lack of clay spectral signatures on VRR may be due to destruction of clay minerals by late diagenetic alteration (e.g., Bristow, Grotzinger, et al, 2021;Horgan et al, 2020;.…”

“…Dark‐toned diagenetic features form due to concentrations of iron, which could be due to localized diagenesis, especially when associated with small‐scale bleached halos that form due to local iron remobilization (David et al., 2020; L’Haridon et al., 2020). Alternatively, these features can also form due to larger scale iron mobility as hypothesized for VRR (Bennett et al., 2021) and in SI (Haber et al., 2020). While FeO T wt.…”

Compositional Variations in Sedimentary Deposits in Gale Crater as Observed by ChemCam Passive and Active Spectra

“…7c), and a spectral maximum approaching 800 nm (Fig 7b). This is consistent with Mastcam observations which suggest a significant decrease in crystalline hematite relative to the rest of the Murray formation and an increase in other iron bearing phases with band centers past the wavelength range of ChemCam (~910-930 nm) such as Fe/Mg smectite, jarosite, and akaganeite (Haber et al, 2022). This compositional change is indicative of more surface exposure and a low stand environment as described in Rapin et al, 2019. In clearly identifying this important region, principal component analysis of passive spectra has demonstrated that it is a valuable tool for gaining additional geochemical insight from ChemCam data.…”

“…PCA of ChemCam passive spectra proved useful in highlighting geochemically distinct regions of the traverse. The Blunts Point-Sutton Island transition, which contains magnesium sulfate rich targets and has been proposed as an area of low lake level by Rapin et al (2019), was found to have zero 750 nm to 840 nm spectral slope (PC4) and weak 535 nm band depth (PC2), in agreement with Mastcam data from this interval (Haber et al, 2022). The Hutton interval (sol 2750-2800) was found to be spectrally distinct from the rest of the Mt.…”