Spectral, Compositional, and Physical Properties of the Upper Murray Formation and Vera Rubin Ridge, Gale Crater, Mars

Jacob, Samantha; Wellington, Danika; Fraeman, A. A.; Achilles, C. N.; Horgan, B.; Johnson, J. R.; Maurice, S.; Peters, G. H.; Rampe, E. B.; Thompson, L. M.; Wiens, R. C.

doi:10.1029/2019je006290

Cited by 23 publications

(62 citation statements)

References 60 publications

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“…Because of these effects, hematite is the main contributor to Mastcam spectral signatures across VRR, even though the actual abundance of crystalline hematite varies substantially across the three VRR samples analyzed by CheMin (Rampe et al, 2020)—14.7% hematite in ST (Pettegrove Point), 2.9% in RH (red Jura), and 8.5% in HF (gray Jura). Other minerals detected on VRR that could be spectrally detectable by Mastcam include pyroxene (3–9%), akaganeite (0–6%), magnetite (0–0.5%), jarosite (0–2%), and ferric smectite (5–13%); however, these minerals can likely all be spectrally masked by hematite (e.g., Jacob et al, 2020; Morris & Neely, 1982; Townsend, 1987).…”

Section: Discussionmentioning

confidence: 99%

“…Diagenesis may also have affected the strength or hardness of VRR rocks, as defined by drill percussion energy (Fraeman, Edgar, et al, 2020; Jacob et al, 2020). DU and RH required lower percussive energies for the drill to make sufficient rates of progress during drilling, whereas ST and HF both required the maximum percussive energy allowed to make sufficient forward progress during drilling.…”

Section: Discussionmentioning

confidence: 99%

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Diagenesis of Vera Rubin Ridge, Gale Crater, Mars, From Mastcam Multispectral Images

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Images from the Mars Science Laboratory (MSL) mission of lacustrine sedimentary rocks of Vera Rubin ridge on "Mt. Sharp" in Gale crater, Mars, have shown stark color variations from red to purple to gray. These color differences crosscut stratigraphy and are likely due to diagenetic alteration of the sediments after deposition. However, the chemistry and timing of these fluid interactions is unclear. Determining how diagenetic processes may have modified chemical and mineralogical signatures of ancient Martian environments is critical for understanding the past habitability of Mars and achieving the goals of the MSL mission. Here we use visible/near-infrared spectra from Mastcam and ChemCam to determine the mineralogical origins of color variations in the ridge. Color variations are consistent with changes in spectral properties related to the crystallinity, grain size, and texture of hematite. Coarse-grained gray hematite spectrally dominates in the gray patches and is present in the purple areas, while nanophase and fine-grained red crystalline hematite are present and spectrally dominate in the red and purple areas. We hypothesize that these differences were caused by grain-size coarsening of hematite by diagenetic fluids, as observed in terrestrial analogs. In this model, early primary reddening by oxidizing fluids near the surface was followed during or after burial by bleaching to form the gray patches, possibly with limited secondary reddening after exhumation. Diagenetic alteration may have diminished the preservation of biosignatures and changed the composition of the sediments, making it more difficult to interpret how conditions evolved in the paleolake over time. Plain Language Summary Sedimentary rocks found in deserts on Earth often exhibit striking color differences from red and purple to white, which are caused by groundwater dissolving and reprecipitating iron oxides within the rocks. NASA's Mars Science Laboratory (MSL) mission has observed similar color differences on Mars within the sedimentary rocks of Vera Rubin ridge in Gale crater, which were laid down in an ancient lake. We use color images and spectral data from the Mastcam cameras on MSL to investigate the origin of these color differences and find that they are consistent with changes in iron oxides through the ridge. This variation in iron oxides suggests that groundwater flowed through and altered these rocks multiple times before and after they were buried by later sediments. The MSL mission has shown that habitable lake environments once existed in Gale crater, through detections of the building blocks of life, including organic molecules, and by showing that conditions that existed in the lake were clement for life. However, later alteration by groundwater may have diminished the preservation of organics and changed the composition of these rocks, making it more difficult to interpret the details of how conditions evolved in the lake over time.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Diagenesis of Vera Rubin Ridge, Gale Crater, Mars, From Mastcam Multispectral Images

et al. 2020

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“…Alternative interpretations, however, cannot be ruled out. Jacob et al (2020) demonstrate that the presence of Fe 3+ ‐phyllosilicates also influences the depth of the 867 nm absorption measured by Mastcam multispectral data on VRR. Importantly, the types and abundance of ferric materials in the X‐ray amorphous component of the drilled samples is also largely unknown (Rampe et al, 2020), and these materials could have a strong influence on bedrock spectral properties.…”

Section: Discussionmentioning

confidence: 99%

Synergistic Ground and Orbital Observations of Iron Oxides on Mt. Sharp and Vera Rubin Ridge

Fraeman

Johnson

Arvidson³

et al. 2020

JGR Planets

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Visible/short‐wave infrared spectral data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) show absorptions attributed to hematite at Vera Rubin ridge (VRR), a topographic feature on northwest Mt. Sharp. The goals of this study are to determine why absorptions caused by ferric iron are strongly visible from orbit at VRR and to improve interpretation of CRISM data throughout lower Mt. Sharp. These goals are achieved by analyzing coordinated CRISM and in situ spectral data along the Curiosity Mars rover's traverse. VRR bedrock within areas that have the deepest ferric absorptions in CRISM data also has the deepest ferric absorptions measured in situ. This suggests strong ferric absorptions are visible from orbit at VRR because of the unique spectral properties of VRR bedrock. Dust and mixing with basaltic sand additionally inhibit the ability to measure ferric absorptions in bedrock stratigraphically below VRR from orbit. There are two implications of these findings: (1) Ferric absorptions in CRISM data initially dismissed as noise could be real, and ferric phases are more widespread in lower Mt. Sharp than previously reported. (2) Patches with the deepest ferric absorptions in CRISM data are, like VRR, reflective of deeper absorptions in the bedrock. One model to explain this spectral variability is late‐stage diagenetic fluids that changed the grain size of ferric phases, deepening absorptions. Curiosity's experience highlights the strengths of using CRISM data for spectral absorptions and associated mineral detections and the caveats in using these data for geologic interpretations and strategic path planning tools.

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“…The return to drilling was marked with a sample called “Duluth” collected from the Blunts Point member on Sol 2057 at an elevation of −4192.5 m. The “Stoer” sample was collected on Sol 2136 at an elevation of −4169.9 m from the Pettegrove Point member near some of the strongest hematite spectral signatures observed from orbit. The science team attempted to drill samples from Pettegrove Point within the pixels with the deepest hematite‐related absorptions in CRISM‐based maps, but these locations proved too hard to drill to the optimum sampling depth of ~4 cm (e.g., Jacob et al, 2020). As a result, Stoer came from a region without a strong orbital hematite signature.…”

Section: Methodsmentioning

confidence: 99%

Mineralogy of Vera Rubin Ridge From the Mars Science Laboratory CheMin Instrument

et al. 2020

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Vera Rubin ridge (VRR) is an erosion‐resistant feature on the northwestern slope of Mount Sharp in Gale crater, Mars, and orbital visible/shortwave infrared measurements indicate it contains red hematite. The Mars Science Laboratory Curiosity rover performed an extensive campaign on VRR to study its mineralogy, geochemistry, and sedimentology to determine the depositional and diagenetic history of the ridge and constrain the processes by which the hematite could have formed. X‐ray diffraction (XRD) data from the CheMin instrument of four samples drilled on and below VRR demonstrate differences in iron, phyllosilicate, and sulfate mineralogy and hematite grain size. Hematite is common across the ridge, and its detection in a gray outcrop suggest localized regions with coarse‐grained hematite, which commonly forms from warm fluids. Broad XRD peaks for hematite in one sample below VRR and the abundance of FeOT in the amorphous component suggest the presence of nanocrystalline hematite and amorphous Fe oxides/oxyhydroxides. Well crystalline akaganeite and jarosite are present in two samples drilled from VRR, indicating at least limited alteration by acid‐saline fluids. Collapsed nontronite is present below VRR, but samples from VRR contain phyllosilicate with d(001) = 9.6 Å, possibly from ferripyrophyllite or an acid‐altered smectite. The most likely cementing agents creating the ridge are hematite and opaline silica. We hypothesize late diagenesis can explain much of the mineralogical variation on the ridge, where multiple fluid episodes with variable pH, salinity, and temperature altered the rocks, causing the precipitation and crystallization of phases that are not otherwise in equilibrium.

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Spectral, Compositional, and Physical Properties of the Upper Murray Formation and Vera Rubin Ridge, Gale Crater, Mars

Cited by 23 publications

References 60 publications

Diagenesis of Vera Rubin Ridge, Gale Crater, Mars, From Mastcam Multispectral Images

Diagenesis of Vera Rubin Ridge, Gale Crater, Mars, From Mastcam Multispectral Images

Synergistic Ground and Orbital Observations of Iron Oxides on Mt. Sharp and Vera Rubin Ridge

Mineralogy of Vera Rubin Ridge From the Mars Science Laboratory CheMin Instrument

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