¹A. Bouvier, ²M. Boyet
Nature 537, 399–402   Link to Article  [doi:10.1038/nature19351]
¹University of Western Ontario, Department of Earth Sciences, Centre for Planetary Science and Exploration, London, Ontario N6A 3K7, Canada
²Clermont Université, Université Blaise Pascal, Laboratoire Magmas et Volcans, UMR CNRS 6524, Campus Universitaire des Cézeaux, 6 avenue Blaise Pascal, 63178 Aubière Cedex, France

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^1,2C. Burkhardt, ³L. E. Borg, ^2,3G. A. Brennecka, ^2,3Q. R. Shollenberger, ¹N. Dauphas ²T. Kleine
Nature 537, 394–398 Link to Article [doi:10.1038/nature18956]
¹Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, 5734 South Ellis Avenue, Chicago, Illinois 60637, USA
²Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm Klemm-Strasse 10, 48149 Münster, Germany
³Lawrence Livermore National Laboratory, L231, Livermore, California 94550, USA

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^1,2Guénon, S., ^1,3Ramírez, J.G., ^1,4Basaran, A.C., ¹Wampler, J., ⁵Thiemens, M., ¹Schuller, I.K.
Journal of Superconductivity and Novel Magnetism (in Press) Link to Article [doi:10.1007/s10948-016-3708-7]
¹Department of Physics and Center for Advanced Nanoscience, University of California, La Jolla, San Diego, CA, United States
²CQ Center for Collective Quantum Phenomena and their Applications in LISA +, Physikalisches Institut, Eberhard Karls Universität Tübingen, Auf der Morgenstelle 14, Tübingen, Germany
³Department of Physics, Universidad de los Andes, Bogotá, Colombia
⁴Department of Physics, Gebze Technical University, Gebze, Kocaeli, Turkey
⁵Department of Chemistry and Biochemistry, University of California, La Jolla, San Diego, CA, United States

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¹C.D. Cino, ¹E. Dehouck, ¹S.M. McLennan
Icarus (in Press) Link to Article [http://dx.doi.org/10.1016/j.icarus.2016.08.029]
¹Department of Geosciences, State University of New York at Stony Brook, Stony Brook NY, 11794-2100, USA
Copyright Elsevier

Burns formation sandstones, deposited by aeolian processes and preserved at Meridiani Planum, Mars, contain abundant sulfate minerals. These sedimentary rocks are thought to be representative of a sulfate-rich geological epoch during late Noachian – early Hesperian time that followed an earlier clay-rich epoch. Twenty Burns formation targets, abraded by the Rock Abrasion Tool (RAT) and for which alpha-particle X-ray spectrometry (APXS) and Mössbauer spectroscopy data are available, were selected for geochemical modeling. A linear unmixing modeling approach was employed. Mineralogical constituents quantitatively constrained by Mössbauer and Mini-TES spectroscopy and interpreted to be chemically precipitated from aqueous fluids during deposition and/or early diagenesis were subtracted from the bulk chemistry. Resulting residual chemical compositions, interpreted to be dominated by detrital siliciclastic components and representing ∼21–35% of the rocks, were then geochemically evaluated to constrain the potential for the presence of clay minerals or their poorly-crystalline or non-crystalline precursors/chemical equivalents. Calculations incorporated a robust estimate of the uncertainties in mineral abundances. On Al2O3 – (CaO+Na2O) – K2O (A-CN-K) and Al2O3 – (CaO+Na2O+K2O) – (FeOtotal+MgO) (A-CNK-FM) molar ternary diagrams, removal of chemical constituents resulted in a shift from igneous–like compositions to compositions consistent with secondary mineral assemblages containing significant aluminous clay mineral components. All of the residual compositions are corundum-normative, further supportive of the presence of highly aluminous phases. On the A-CNK-FM diagram, clay minerals plotting closest to the residual field are natural montmorillonites but could also represent mixtures of various Mg/Fe-rich phyllosilicates, such as nontronite or saponite, and other more Al-rich minerals such as Al-montmorillonite, kaolinite or illite. Depending on the age of clay mineral formation, occurrence of clay minerals or their poorly crystalline precursors/chemical equivalents in the Burns formation could suggest that any global transition from clay-rich to sulfate-rich environments on early Mars was more complex than previously recognized. Results are also consistent with models for the Burns formation aqueous history in which acidic conditions were more restricted in time and/or space than previously thought and thus may also be consistent with growing evidence that changing redox conditions, rather than global pH variations, was an important factor in the environmental evolution of early Mars.