Multiple mineral horizons in layered outcrops at Mawrth Vallis, Mars, signify changing geochemical environments on early Mars

1,2Janice L.Bishop,2Christoph Gross,1,3 Jacob Danielsen,4Mario Parente,5Scott L.Murchie,6 Briony Horgan,7James J.Wray,6Christina Viviano,6Frank P.Seelos
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.113634]
1SETI Institute, Mountain View, CA, United States of America
2Freie Universität Berlin, Berlin, Germany
3San Jose State University, San Jose, CA, United States of America
4University of Massachusetts at Amherst, Amherst, MA, United States of America
5Johns Hopkins University Applied Physics Lab, Laurel, MD, United States of America
6Purdue University, West Lafayette, IN, United States of America
7Georgia Institute of Technology, Atlanta, GA, United States of America
Copyright Elsevier

Refined calibrations of CRISM images are enabling identification of smaller deposits of unique aqueous materials on Mars that reveal changing environmental conditions at the region surrounding Mawrth Vallis. Through characterization of these clay-sulfate assemblages and their association with the layered, phyllosilicate units of this region, more details of the aqueous geochemical history can be gleaned. A stratigraphy including five distinct mineral horizons is mapped using compositional data from CRISM over CTX and HRSC imagery across 100s of km and from CRISM over HiRISE imagery across 100s of meters. Transitions in mineralogic units were characterized using visible/near-infrared (VNIR) spectral properties and surface morphology. We identified and characterized complex “doublet” type spectral signatures with two bands between 2.2 and 2.3 μm at one stratigraphic horizon. Based on comparisons with terrestrial sites, the spectral “doublet” unit described here may reflect the remnants of a salty, evaporative period that existed on Mars during the transition from formation of Fe-rich phyllosilicates to Al-rich phyllosilicates. Layered outcrops observed at Mawrth Vallis are thicker than in other altered regions of Mars, but may represent processes that were more widespread in wet regions of the planet during its early history. The aqueous geochemical environments supporting the outcrops observed here include: (i) the formation of Fe3+-rich smectites in a warm and wet environment, (ii) overlain by a thin ferrous-bearing clay unit that could be associated with heating or reducing conditions, (iii) followed by a transition to salty and/or acidic alteration phases and sulfates (characterized by the spectral “doublet” shape) in an evaporative setting, (iv) formation of Al-rich phyllosilicates through pedogenesis or acid leaching, and (v) finally persistence of poorly crystalline aluminosilicates marking the end of the warm climate on early Mars. The “doublet” type units described here are likely composed of clay-sulfate assemblages formed in saline, acidic evaporative environments similar to those found in Western Australia and the Atacama desert. Despite the chemically extreme and variable waters present at these terrestrial, saline lake environments, active ecosystems are present; thus, these “doublet” type units may mark exciting areas for continued exploration important to astrobiology on Mars.

Determination of trace rare earth elements in rock samples including meteorites by ICP-MS coupled with isotope dilution and comparison methods

1Ebihara, M.,1Hayano,1K.,1Shirai, N.
Analytica Chimica Acta (in Press) Link to Article [DOI: 10.1016/j.aca.2019.12.031]
1Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, 1-1 Minami-osawa, Hachioji, Tokyo, 192-0397, Japan

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On impact and volcanism across the Cretaceous-Paleogene boundary

1Pincelli M. Hull et al. (>10)
Science 367, 266-272 Link to Article [DOI: 10.1126/science.aay5055]
1Department of Geology and Geophysics, Yale University, New Haven, CT 06511, USA.
Reprinted with Permission of AAAS

The cause of the end-Cretaceous mass extinction is vigorously debated, owing to the occurrence of a very large bolide impact and flood basalt volcanism near the boundary. Disentangling their relative importance is complicated by uncertainty regarding kill mechanisms and the relative timing of volcanogenic outgassing, impact, and extinction. We used carbon cycle modeling and paleotemperature records to constrain the timing of volcanogenic outgassing. We found support for major outgassing beginning and ending distinctly before the impact, with only the impact coinciding with mass extinction and biologically amplified carbon cycle change. Our models show that these extinction-related carbon cycle changes would have allowed the ocean to absorb massive amounts of carbon dioxide, thus limiting the global warming otherwise expected from postextinction volcanism.

Lifetimes of interstellar dust from cosmic ray exposure ages of presolar silicon carbide

1,2,3Philipp R. Heck,1,2,3Jennika Greer,1,2,3Levke Kööp,4Reto Trappitsch,5,6Frank Gyngard,7Henner Busemann,7Colin Madeg,8Janaína N. Ávila,1,2,3,9Andrew M. Davis,7Rainer Wieler
Proceedings of the National Academy of Sciences of the United States of America (in Press) Link to Article [https://doi.org/10.1073/pnas.1904573117]
1Robert A. Pritzker Center for Meteoritics and Polar Studies, The Field Museum of Natural History, Chicago, IL 60605;
2Chicago Center for Cosmochemistry, The University of Chicago, Chicago, IL 60637;
3Department of the Geophysical Sciences, The University of Chicago, Chicago, IL 60637;
4Nuclear and Chemical Sciences Division, Lawrence Livermore National Laboratory, Livermore, CA 94550;
5Physics Department, Washington University, St. Louis, MO 63130;
6Center for NanoImaging, Harvard Medical School, Cambridge, MA 02139;
7Institute of Geochemistry and Petrology, ETH Zürich, 8092 Zürich, Switzerland;
8Research School of Earth Sciences, The Australian National University, Canberra, ACT 2601, Australia;
9Enrico Fermi Institute, The University of Chicago, Chicago, IL 60637

We determined interstellar cosmic ray exposure ages of 40 large presolar silicon carbide grains extracted from the Murchison CM2 meteorite. Our ages, based on cosmogenic Ne-21, range from 3.9 ± 1.6 Ma to ∼3 ± 2 Ga before the start of the Solar System ∼4.6 Ga ago. A majority of the grains have interstellar lifetimes of <300 Ma, which is shorter than theoretical estimates for large grains. These grains condensed in outflows of asymptotic giant branch stars <4.9 Ga ago that possibly formed during an episode of enhanced star formation ∼7 Ga ago. A minority of the grains have ages >1 Ga. Longer lifetimes are expected for large grains. We determined that at least 12 of the analyzed grains were parts of aggregates in the interstellar medium: The large difference in nuclear recoil loss of cosmic ray spallation products 3He and 21Ne enabled us to estimate that the irradiated objects in the interstellar medium were up to 30 times larger than the analyzed grains. Furthermore, we estimate that the majority of the grains acquired the bulk of their cosmogenic nuclides in the interstellar medium and not by exposure to an enhanced particle flux of the early active sun.

Heterogeneous accretion of Earth inferred from Mo-Ru isotope systematics

1,2Timo Hopp,1,3Gerrit Budde,1Thorsten Kleine
Earth and Planetary Science Letters 534, 116065 Link to Article [https://doi.org/10.1016/j.epsl.2020.116065]
1Institut für Planetologie, University of Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany
2Origins Laboratory, Department of Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, 5743 South Ellis Avenue, Chicago, IL 60637, USA.
3The Isotoparium, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA.
Copyright Elsevier

The Mo and Ru isotopic compositions of meteorites and the bulk silicate Earth (BSE) hold important clues about the provenance of Earth’s building material. Prior studies have argued that non-carbonaceous (NC) and carbonaceous (CC) meteorite groups together define a Mo-Ru ‘cosmic’ correlation, and that the BSE plots on the extension of this correlation. These observations were taken as evidence that the final 10–15% of Earth’s accreted material derived from a homogeneous inner disk reservoir with an enstatite chondrite-like isotopic composition. Here, using new Mo and Ru isotopic data for previously uninvestigated meteorite groups, we show that the Mo-Ru correlation only exists for NC meteorites, and that both the BSE and CC meteorites fall off this Mo-Ru correlation. These observations indicate that the final stages of Earth’s accretion were heterogeneous and consisted of a mixture of NC and CC materials. The Mo-Ru isotope systematics are best accounted for by either an NC heritage of the late veneer combined with a CC heritage of the Moon-forming giant impactor, or by mixed NC-CC compositions for both components. The involvement of CC bodies in the late-stage accretionary assemblage of Earth is consistent with chemical models for core-mantle differentiation, which argue for the addition of more oxidized and volatile-rich material toward the end of Earth’s formation. As such, this study resolves the inconsistencies between homogeneous accretion models based on prior interpretations of the Mo-Ru systematics of meteorites and the chemical evidence for heterogeneous accretion of Earth.

The chemical case for Mercury mantle stripping

1Helffrich, G.,1Brasser, R.,2Shahar, A.
Progress in Earth and Planetary Science 6, 66 Link to Article [DOI: 10.1186/s40645-019-0312-z]
1Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo, 152-8550, Japan
2Geophysical Laboratory, Carnegie Institution for Science, 5251 Broad Branch Road NW, Washington, DC 20015, United States

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Geochemical variation in the Stimson formation of Gale crater: Provenance, mineral sorting, and a comparison with modern Martian dunes

1,2C.C.Bedford,3S.P.Schwenzer,4J.C.Bridges,5S.Banham,6R.C.Wiens,7O.Gasnault,2 E.B.Rampe,8J.Frydenvang,6P.J.Gasda
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.113622]
1Lunar and Planetary Institute, Universities Space Research Association, 3600 Bay Area Blvd., Houston, TX, USA
2Astromaterials and Exploration Science, NASA Johnson Space Center, Houston, TX, USA
3School of Environment, Earth and Ecosystem Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
4Space Research Centre, School of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK
5Imperial College London, London, UK
6Los Alamos National Laboratory, Los Alamos, NM, USA
7Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, CNRS, CNES, France
8Natural History Museum of Denmark, University of Copenhagen, Copenhagen, Denmark
Copyright Elsevier

The Mars Science Laboratory Curiosity rover has encountered both ancient lithified and modern active aeolian dune deposits within Gale crater, providing an opportunity to study how aeolian processes have changed during Gale crater’s geological history. This study uses data from the Chemistry and Camera (ChemCam) and Chemistry and Mineralogy (CheMin) instrument suites onboard Curiosity to; (1) constrain the diagenetic processes that lithified and altered the ancient aeolian Stimson formation, (2) investigate whether the geochemical signature in the Stimson formation is consistent with the aeolian mafic-felsic mineral sorting trend identified in the modern Bagnold dune fields in Gale crater, and (3) discuss the provenance of the Stimson sediments, comparing it to those identified in the ancient river and lake deposits also analyzed along Curiosity’s traverse.
The ancient Stimson dune deposits that stratigraphically overlie the Gale fluvio-lacustrine units were analyzed in two locations; the Emerson and the Naukluft plateaus. ChemCam data show that the Stimson formation has subtle variations in MgO, Al2O3, Na2O and K2O between the two localities. An agglomerative cluster analysis of the constrained Stimson dataset reveals five clusters, four of which relate to different proportions of mafic and felsic minerals analyzed by ChemCam. In general, the cluster analysis shows that the Emerson plateau has a greater proportion of mafic minerals and fewer coarse, felsic grains relative to the Naukluft plateau. This variation in mafic and felsic minerals between localities suggests a southwest to northeast net sediment transport direction due to aeolian mineral sorting dynamics preferentially transporting mafic minerals that are easier to saltate than the elongate, often coarser, felsic minerals. This derived transport direction for the Stimson formation supports that determined by sedimentological evidence and is opposite to that previously determined for the active Bagnold dunes inferring a change in the wind regime with time. An opposite sediment transport direction between the ancient and modern dunes in Gale crater further supports geochemical and mineralogical evidence that suggests different basaltic source regions. Compositionally, the bulk Stimson formation is most similar to the subalkaline basalt source region that is inferred to be the dominant sediment source of the fluvio-lacustrine Bradbury group. This is likely the result of the Stimson formation and basaltic Bradbury group sediments sharing a similar local basaltic source region such as the rim and walls of Gale crater.