Hydrogen Variability in the Murray Formation, Gale Crater, Mars

1N.H. Thomas,1B.L. Ehlmann,1W. Rapin,2F. Rivera‐Hernández,1N.T. Stein,3J. Frydenvang,4T. Gabriel,5P.‐Y. Meslin,5S. Maurice,6R.C. Wiens
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2019JE006289]
1Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
2Dartmouth College, Hanover, NH, USA
3Natural History Museum, University of Copenhagen, Denmark
4Arizona State University, Tempe, AZ, USA
5Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, CNRS, UPS, CNES, Toulouse, France
6Los Alamos National Laboratory, Los Alamos, NM, USA
Published by arrangement with John Wiley & Sons

The Mars Science Laboratory (MSL) Curiosity rover is exploring the Murray formation, a sequence of heterolithic mudstones and sandstones recording fluvial deltaic and lake deposits that comprise over 350 meters of sedimentary strata within Gale crater. We examine >4500 Murray formation bedrock points, employing recent laboratory calibrations for ChemCam laser‐induced breakdown spectroscopy H measurements at millimeter scale. Bedrock in the Murray formation has an interquartile range of 2.3‐3.1 wt. % H2O, similar to measurements using the DAN and SAM instruments. However, specific stratigraphic intervals include high H targets (6‐18 wt. % H2O) correlated with Si, Mg, Ca, Mn, or Fe, indicating units with opal, hydrated Mg‐sulfates, hydrated Ca‐sulfates, Mn‐enriched units, and akageneite or other iron oxyhydroxides, respectively. One stratigraphic interval with higher hydrogen is the Sutton Island unit and Blunts Point unit contact, where higher hydrogen is associated with Fe‐rich, Ca‐rich, and Mg‐rich points. A second interval with higher hydrogen occurs in the Vera Rubin ridge portion of the Murray formation, where higher hydrogen is associated with Fe‐rich, Ca‐rich, and Si‐rich points. We also observe trends in the H signal with grain size, separate from chemical variation, whereby coarser‐grained rocks have higher hydrogen. Variability in the hydrogen content of rocks points to a history of water‐rock interaction at Gale crater that included changes in lake water chemistry during Murray formation deposition and multiple subsequent groundwater episodes.

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