Geochemistry of the Bagnold dune field as observed by ChemCam and comparison with other aeolian deposits at Gale crater
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.
© 2017 American Geophysical Union. Received 9 JAN 2017; Accepted 20 JUN 2017; Accepted article online 27 JUN 2017; Published online 23 OCT 2017. We are grateful to the MSL science and operation teams who developed the rover and contributed to collecting the Bagnold dune data set. All the data sets used in this paper are released and can be found on the Planetary Data Science (http://pdsgeosciences.wustl.edu/missions/msl/.htm). We also thank S. Karunatillake and S. Ruff for their helpful and constructive comments, which improved the manuscript. We would also like to express our sincere gratefulness to Nathan Bridges for his enthusiasm and huge implication for the Bagnold Dunes Campaign. This work was supported by the CNES in France and by the NASA Mars Exploration Program in the U.S.
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