Browsing by Author "Bibring, Jean-Pierre"
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ItemCharacterization of phyllosilicates observed in the central Mawrth Vallis region, Mars, their potential formational processes, and implications for past climate(2009) McKeown, Nancy K.; Bishop, Janice L.; Noe Dobrea, Eldar Z.; Ehlmann, Bethany L.; Parente, Mario; Mustard, John F.; Murchie, Scott L.; Swayze, Gregg A.; Bibring, Jean-Pierre; Silver, Eli A.Mawrth Vallis contains one of the largest exposures of phyllosilicates on Mars. Nontronite, montmorillonite, kaolinite, and hydrated silica have been identified throughout the region using data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). In addition, saponite has been identified in one observation within a crater. These individual minerals are identified and distinguished by features at 1.38-1.42, approximately 1.91, and 2.17-2.41 mu m. There are two main phyllosilicate units in the Mawrth Vallis region. The lowermost unit is nontronite bearing, unconformably overlain by an Al-phyllosilicate unit containing montmorillonite plus hydrated silica, with a thin layer of kaolinite plus hydrated silica at the top of the unit. These two units are draped by a spectrally unremarkable capping unit. Smectites generally form in neutral to alkaline environments, while kaolinite and hydrated silica typically form in slightly acidic conditions; thus, the observed phyllosilicates may reflect a change in aqueous chemistry. Spectra retrieved near the boundary between the nontronite and Al-phyllosilicate units exhibit a strong positive slope from 1 to 2 mu m, likely from a ferrous component within the rock. This ferrous component indicates either rapid deposition in an oxidizing environment or reducing conditions. Formation of each of the phyllosilicate minerals identified requires liquid water, thus indicating a regional wet period in the Noachian when these units formed. The two main phyllosilicate units may be extensive layers of altered volcanic ash. Other potential formational processes include sediment deposition into a marine or lacustrine basin or pedogenesis. ItemThe Mawrth Vallis region of Mars; a potential landing site for the Mars Science Laboratory (MSL) mission(2010) Michalski, Joseph R.; Bibring, Jean-Pierre; Poulet, Francois; Loizeau, D.; Mangold, Nicholas; Noe Dobrea, Eldar Z.; Bishop, Janice L.; Wray, James J.; McKeown, Nancy K.; Parente, Mario; Hauber, E.; Altieri, Francesca; Carrozzo, Filippo. Giacomo; Niles, Paul B.The primary objective of NASA's Mars Science Laboratory (MSL) mission, which will launch in 2011, is to characterize the habitability of a site on Mars through detailed analyses of the composition and geological context of surface materials. Within the framework of established mission goals, we have evaluated the value of a possible landing site in the Mawrth Vallis region of Mars that is targeted directly on some of the most geologically and astrobiologically enticing materials in the Solar System. The area around Mawrth Vallis contains a vast (>1 × 106 km2) deposit of phyllosilicate-rich, ancient, layered rocks. A thick (>150 m) stratigraphic section that exhibits spectral evidence for nontronite, montmorillonite, amorphous silica, kaolinite, saponite, other smectite clay minerals, ferrous mica, and sulfate minerals indicates a rich geological history that may have included multiple aqueous environments. Because phyllosilicates are strong indicators of ancient aqueous activity, and the preservation potential of biosignatures within sedimentary clay deposits is high, martian phyllosilicate deposits are desirable astrobiological targets. The proposed MSL landing site at Mawrth Vallis is located directly on the largest and most phyllosilicate-rich deposit on Mars and is therefore an excellent place to explore for evidence of life or habitability. ItemMineralogy and stratigraphy of phyllosilicate‐bearing and dark mantling units in the greater Mawrth Vallis/west Arabia Terra area: constraints on geological origin(2010) Noe Dobrea, Eldar Z.; Bishop, Janice L.; McKeown, Nancy K.; Fu, R.; Rossi, C. M.; Michalski, Joseph R.; Heinlein, C.; Hanus, V.; Poulet, Francois; Mustard, John F.; Murchie, Scott L.; McEwen, Alfred S.; Swayze, Gregg A.; Bibring, Jean-Pierre; Malaret, E.; Hash, C.Analyses of MRO/CRISM images of the greater Mawrth Vallis region of Mars affirm the presence of two primary phyllosilicate assemblages throughout a region ∼1000 × 1000 km. These two units consist of an Fe/Mg‐phyllosilicate assemblage overlain by an Al‐phyllosilicate and hydrated silica assemblage. The lower unit contains Fe/Mg‐ smectites, sometimes combined with one or more of these other Fe/Mg‐phyllosilicates: serpentine, chlorite, biotite, and/or vermiculite. It is more than 100 m thick and finely layered at meter scales. The upper unit includes Al‐smectite, kaolin group minerals, and hydrated silica. It is tens of meters thick and finely layered as well. A common phyllosilicate stratigraphy and morphology is observed throughout the greater region wherever erosional windows are present. This suggests that the geologic processes forming these units must have occurred on at least a regional scale. Sinuous ridges (interpreted to be inverted channels) and narrow channels cut into the upper clay‐bearing unit suggesting that aqueous processes were prevalent after, and possibly during, the deposition of the layered units. We propose that layered units may have been deposited at Mawrth Vallis and then subsequently altered to form the hydrated units. The Fe/Mg‐phyllosilicate assemblage is consistent with hydrothermal alteration or pedogenesis of mafic to ultramafic rocks. The Al‐phyllosilicate/hydrated silica unit may have formed through alteration of felsic material or via leaching of basaltic material through pedogenic alteration or a mildly acidic environment. These phyllosilicate‐bearing units are overlain by a darker, relatively unaltered, and indurated material that has probably experienced a complex geological history. ItemPhyllosilicate diversity and past aqueous activity revealed at Mawrth Vallis, Mars(2008) Bishop, Janice L.; Noe Dobrea, Eldar Z.; McKeown, Nancy K.; Parente, Mario; Ehlmann, Bethany L.; Michalski, Joseph R.; Milliken, Ralph E.; Poulet, Francois; Swayze, Gregg A.; Mustard, John F.; Murchie, Scott L.; Bibring, Jean-PierreObservations by the Mars Reconnaissance Orbiter/Compact Reconnaissance Imaging Spectrometer for Mars in the Mawrth Vallis region show several phyllosilicate species, indicating a wide range of past aqueous activity. Iron/magnesium (Fe/Mg)--smectite is observed in light-toned outcrops that probably formed via aqueous alteration of basalt of the ancient cratered terrain. This unit is overlain by rocks rich in hydrated silica, montmorillonite, and kaolinite that may have formed via subsequent leaching of Fe and Mg through extended aqueous events or a change in aqueous chemistry. A spectral feature attributed to an Fe²⁺ phase is present in many locations in the Mawrth Vallis region at the transition from Fe/Mg-smectite to aluminum/silicon (Al/Si)--rich units. Fe²⁺-bearing materials in terrestrial sediments are typically associated with microorganisms or changes in pH or cations and could be explained here by hydrothermal activity. The stratigraphy of Fe/Mg-smectite overlain by a ferrous phase, hydrated silica, and then Al-phyllosilicates implies a complex aqueous history. ItemA synthesis of Martian aqueous mineralogy after 1 Mars year of observations from the Mars Reconnaissance Orbiter(2009) Murchie, Scott L.; Mustard, John F.; Ehlmann, Bethany L.; Milliken, Ralph E.; Bishop, Janice L.; McKeown, Nancy K.; Noe Dobrea, Eldar Z.; Seelos, Frank P.; Buczkowski, Debra L.; Wiseman, Sandra M.; Arvidson, Raymond E.; Wray, James J.; Swayze, Gregg A.; Clark, Roger N.; Des Marais, David J.; McEwen, Alfred S.; Bibring, Jean-PierreMartian aqueous mineral deposits have been examined and characterized using data acquired during Mars Reconnaissance Orbiter's (MRO) primary science phase, including Compact Reconnaissance Imaging Spectrometer for Mars hyperspectral images covering the 0.4-3.9 mu m wavelength range, coordinated with higher-spatial resolution HiRISE and Context Imager images. MRO's new high-resolution measurements, combined with earlier data from Thermal Emission Spectrometer; Thermal Emission Imaging System; and Observatoire pour la Mineralogie, L'Eau, les Glaces et l'Activitie on Mars Express, indicate that aqueous minerals are both diverse and widespread on the Martian surface. The aqueous minerals occur in 9-10 classes of deposits characterized by distinct mineral assemblages, morphologies, and geologic settings. Phyllosilicates occur in several settings: in compositionally layered blankets hundreds of meters thick, superposed on eroded Noachian terrains; in lower layers of intracrater depositional fans; in layers with potential chlorides in sediments on intercrater plains; and as thousands of deep exposures in craters and escarpments. Carbonate-bearing rocks form a thin unit surrounding the Isidis basin. Hydrated silica occurs with hydrated sulfates in thin stratified deposits surrounding Valles Marineris. Hydrated sulfates also occur together with crystalline ferric minerals in thick, layered deposits in Terra Meridiani and in Valles Marineris and together with kaolinite in deposits that partially infill some highland craters. In this paper we describe each of the classes of deposits, review hypotheses for their origins, identify new questions posed by existing measurements, and consider their implications for ancient habitable environments. On the basis of current data, two to five classes of Noachian-aged deposits containing phyllosilicates and carbonates may have formed in aqueous environments with pH and water activities suitable for life.