APXS‐derived chemistry of the Bagnold dune sands: Comparisons with Gale Crater soils and the global Martian average

O’Connell‐Cooper, C. D.; Spray, John G.; Thompson, L. M.; Gellert, R.; Berger, J. A.; Boyd, Nicholas; Desouza, E.; Perrett, G. M.; Schmidt, M. E.; VanBommel, S. J.

doi:10.1002/2017je005268

Cited by 77 publications

(116 citation statements)

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“…SAM also found a low water content in the dunes (~1 wt %), which is about half the content measured at Rocknest sand shadow [ Sutter et al ., ]. The lower S and Cl LIBS signals are in agreement with the lower S and Cl abundances measured by the APXS [ O ' Connel‐Cooper et al ., ] and the smaller release of sulfur dioxide measured by SAM [ Sutter et al ., ].…”

Section: Discussionsupporting

confidence: 85%

Geochemistry of the Bagnold dune field as observed by ChemCam and comparison with other aeolian deposits at Gale Crater

et al. 2017

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The Curiosity rover conducted the first field investigation of an active extraterrestrial dune. This study of the Bagnold dunes focuses on the ChemCam chemical results and also presents findings on the grain size distributions based on the ChemCam Remote Micro‐Imager and Mars Hand Lens Imager images. These active dunes are composed of grains that are mostly <250 μm. Their composition is overall similar to that of the aeolian deposits analyzed all along the traverse (“Aeolis Palus soils”). Nevertheless, the dunes contain less volatiles (Cl, H, and S) than the Aeolis Palus soils, which appear to be due to a lower content of volatile‐rich fine‐grained particles (<100 μm) or a lower content of volatile‐rich amorphous component, possibly as a result of (1) a lower level of chemical alteration, (2) the removal of an alteration rind at the surface of the grains during transport, (3) a lower degree of interaction with volcanic gases/aerosols, or (4) physical sorting that removed the smallest and most altered grains. Analyses of the >150 μm grain‐size dump piles have shown that coarser grains (150–250 μm) are enriched in the mafic elements Fe and Mn, suggesting a larger content in olivine compared to smaller grains (<150 μm) of the Bagnold dunes. Moreover, the chemistry of soils analyzed in the vicinity of the dunes indicates that they are similar to the dune material. All these observations suggest that the olivine content determined by X‐ray diffraction of the <150 μm grain‐size sample should be considered as a lower limit for the Bagnold dunes.

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Section: Discussionsupporting

confidence: 85%

Geochemistry of the Bagnold dune field as observed by ChemCam and comparison with other aeolian deposits at Gale Crater

et al. 2017

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“…APXS data mostly fall into two clusters—coarser samples (darker circles) having elevated Fe and Mg and lower Si than the finer samples (pale circles)—which both fall within the most‐densely populated region above the plagioclase‐olivine join. Our inverted MAP at Namib Dune is close to the APXS cluster of coarser samples in this space [ Ehlmann et al , ; O'Connell‐Cooper et al , ]. The MAP results for the four locations (Figure ) do not trend along the plagioclase‐magnetite join but rather parallel a plagioclase‐olivine join in a trend most similar to that of the sand deposits of Stockstill‐Cahill et al [] (dark intracrater sand deposits in Amazonis Planitia, Mars) and Mangold et al [] (nonchemically weathered volcanic sand in Iceland).…”

Section: Discussionsupporting

confidence: 78%

Compositional variations in sands of the Bagnold Dunes, Gale crater, Mars, from visible‐shortwave infrared spectroscopy and comparison with ground truth from the Curiosity rover

et al. 2017

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During its ascent up Mount Sharp, the Mars Science Laboratory Curiosity rover traversed the Bagnold Dune Field. We model sand modal mineralogy and grain size at four locations near the rover traverse, using orbital shortwave infrared single‐scattering albedo spectra and a Markov chain Monte Carlo implementation of Hapke's radiative transfer theory to fully constrain uncertainties and permitted solutions. These predictions, evaluated against in situ measurements at one site from the Curiosity rover, show that X‐ray diffraction‐measured mineralogy of the basaltic sands is within the 95% confidence interval of model predictions. However, predictions are relatively insensitive to grain size and are nonunique, especially when modeling the composition of minerals with solid solutions. We find an overall basaltic mineralogy and show subtle spatial variations in composition in and around the Bagnold Dunes, consistent with a mafic enrichment of sands with cumulative aeolian‐transport distance by sorting of olivine, pyroxene, and plagioclase grains. Furthermore, the large variations in Fe and Mg abundances (~20 wt %) at the Bagnold Dunes suggest that compositional variability may be enhanced by local mixing of well‐sorted sand with proximal sand sources. Our estimates demonstrate a method for orbital quantification of composition with rigorous uncertainty determination and provide key constraints for interpreting in situ measurements of compositional variability within Martian aeolian sandstones.

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“…Figure shows the ChemCam 770/830 nm ratio compared to APXS S content for the Bagnold area samples [cf. O ' Connell‐Cooper et al ., ]. The S content decreases with increasing grain size of the sieved samples, consistent with the loss of dust and/or finer‐grained S‐bearing sulfate minerals.…”

Section: Discussionmentioning

confidence: 55%

Visible/near‐infrared spectral diversity from in situ observations of the Bagnold Dune Field sands in Gale Crater, Mars

et al. 2017

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As part of the Bagnold Dune campaign conducted by Mars Science Laboratory rover Curiosity, visible/near‐infrared reflectance spectra of dune sands were acquired using Mast Camera (Mastcam) multispectral imaging (445–1013 nm) and Chemistry and Camera (ChemCam) passive point spectroscopy (400–840 nm). By comparing spectra from pristine and rover‐disturbed ripple crests and troughs within the dune field, and through analysis of sieved grain size fractions, constraints on mineral segregation from grain sorting could be determined. In general, the dune areas exhibited low relative reflectance, a weak ~530 nm absorption band, an absorption band near 620 nm, and a spectral downturn after ~685 nm consistent with olivine‐bearing sands. The finest grain size fractions occurred within ripple troughs and in the subsurface and typically exhibited the strongest ~530 nm bands, highest relative reflectances, and weakest red/near‐infrared ratios, consistent with a combination of crystalline and amorphous ferric materials. Coarser‐grained samples were the darkest and bluest and exhibited weaker ~530 nm bands, lower relative reflectances, and stronger downturns in the near‐infrared, consistent with greater proportions of mafic minerals such as olivine and pyroxene. These grains were typically segregated along ripple crests and among the upper surfaces of grain flows in disturbed sands. Sieved dune sands exhibited progressive decreases in reflectance with increasing grain size, as observed in laboratory spectra of olivine size separates. The continuum of spectral features observed between the coarse‐ and fine‐grained dune sands suggests that mafic grains, ferric materials, and air fall dust mix in variable proportions depending on aeolian activity and grain sorting.

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APXS‐derived chemistry of the Bagnold dune sands: Comparisons with Gale Crater soils and the global Martian average

Cited by 77 publications

References 96 publications

Geochemistry of the Bagnold dune field as observed by ChemCam and comparison with other aeolian deposits at Gale Crater

Geochemistry of the Bagnold dune field as observed by ChemCam and comparison with other aeolian deposits at Gale Crater

Compositional variations in sands of the Bagnold Dunes, Gale crater, Mars, from visible‐shortwave infrared spectroscopy and comparison with ground truth from the Curiosity rover

Visible/near‐infrared spectral diversity from in situ observations of the Bagnold Dune Field sands in Gale Crater, Mars

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