Orbital Identification of Carbonate-Bearing Rocks on Mars

Department of Geological Sciences, Brown University, Providence, RI02912, USA.
Science (Impact Factor: 31.48). 01/2009; 322(5909):1828-32. DOI: 10.1126/science.1164759
Source: PubMed

ABSTRACT Geochemical models for Mars predict carbonate formation during aqueous alteration. Carbonate-bearing rocks had not previously
been detected on Mars' surface, but Mars Reconnaissance Orbiter mapping reveals a regional rock layer with near-infrared spectral
characteristics that are consistent with the presence of magnesium carbonate in the Nili Fossae region. The carbonate is closely
associated with both phyllosilicate-bearing and olivine-rich rock units and probably formed during the Noachian or early Hesperian
era from the alteration of olivine by either hydrothermal fluids or near-surface water. The presence of carbonate as well
as accompanying clays suggests that waters were neutral to alkaline at the time of its formation and that acidic weathering,
proposed to be characteristic of Hesperian Mars, did not destroy these carbonates and thus did not dominate all aqueous environments.

Download full-text


Available from: John F. Mustard, Jul 27, 2015
  • Source
    • "face reduces the spectral information from minerals beyond the range of 2 . 6 lm wavelength . The contribution of ther - mal emissions and the lower signal - to - noise ratio of the detector have also been found around 3 lm and can also diminish impor - tant information from spectral signatures ( Wagner and Schade , 1996 ; Murchie et al . , 2007 ; Ehlmann et al . , 2008 ) . Therefore , in general , limited spectral range up to 2 . 6 lm was used in the pres - ent study to avoid the effect of the thermal emission of the surface and low signal - to - noise ratio of the detector . However , since some aqueous minerals such as hydrous silicates and carbonates also have diagnostic absorptions between the ran"
    [Show abstract] [Hide abstract]
    ABSTRACT: Spectral reflectance data from the MRO-CRISM (Mars Reconnaissance Orbiter-Compact Reconnaissance Imaging Spectrometer for Mars) of Capri Chasma, a large canyon within Valles Marineris on Mars, have been studied. Results of this analysis reveal the presence of minerals, such as, phyllosilicates (illite, smectite (montmorillonite)) and carbonates (ankerite and manganocalcite). These minerals hint of the aqueous history of Noachian time on Mars. Phyllosilicates are products of chemical weathering of igneous rocks, whereas carbonates could have formed from local aqueous alteration of olivine and other igneous minerals. Four different locations within the Capri Chasma region were studied for spectral reflectance based mineral detection. The study area also shows the spectral signatures of iron-bearing minerals, e.g. olivine with carbonate, indicating partial weathering of parent rocks primarily rich in ferrous mineral. The present study shows that the minerals of Capri Chasma are characterized by the presence of prominent spectral absorption features at 2.31 μm, 2.33 μm, 2.22 μm, 2.48 μm and 2.52 μm wavelength regions, indicating the existence of hydrous minerals, i.e., carbonates and phyllosilicates. The occurrence of carbonates and phyllosilicates in the study area suggests the presence of alkaline environment during the period of their formation. Results of the study are important to understand the formation processes of these mineral assemblages on Mars, which may help in understanding the evolutionary history of the planet.
    Icarus 04/2015; 250. DOI:10.1016/j.icarus.2014.11.018 · 2.84 Impact Factor
  • Source
    • "Recently, Mumma et al. (2009) reported that a notable enrichment of methane was detected over several localized areas, including Syrtis Major and Nili Fossae regions, which correspond to areas where deep crustal carbonates have been found (Ehlmann et al., 2008; Michalski and Niles, 2010), although high levels of methane have not been confirmed by in situ measurement (Mahaffy et al., 2013; Webster et al., 2013). The presence of organic compounds have also been recognized in martian meteorites (Clemett et al., 1998; Becker et al., 1999; Sephton et al., 2002). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Experiments were performed to better understand the role of environmental factors on reaction pathways and corresponding carbon isotope fractionations during abiotic hydrothermal synthesis of organic compounds using piston cylinder apparatus at 750 °C and 5.5 kbars. Chemical compositions of experimental products and corresponding carbon isotopic values were obtained by a Pyrolysis-GC-MS-IRMS system. Alkanes (methane and ethane), straight-chain saturated alcohols (ethanol and n-butanol) and monocarboxylic acids (formic and acetic acids) were generated with ethanol being the only organic compound with higher 13C than CO2. CO was not detected in experimental products owing to the favorable water-gas shift reaction under high water pressure conditions. The pattern of δ13C values of CO2, carboxylic acids and alkanes are consistent with their equilibrium isotope relationships: CO2 > carboxylic acids > alkanes, but the magnitude of the fractionation among them is higher than predicted isotope equilibrium values. In particular, the isotopic fractionation between CO2 and CH4 remained constant at ∼31‰, indicating a kinetic effect during CO2 reduction processes. No “isotope reversal” of δ13C values for alkanes or carboxylic acids was observed, which indicates a different reaction pathway than what is typically observed during Fischer-Tropsch synthesis under gas phase conditions. Under constraints imposed in experiments, the anomalous 13C isotope enrichment in ethanol suggests that hydroxymethylene is the organic intermediate, and that the generation of other organic compounds enriched in 12C were facilitated by subsequent Rayleigh fractionation of hydroxymethylene reacting with H2 and/or H2O. Carbon isotope fractionation data obtained in this study are instrumental in assessing the controlling factors on abiotic formation of organic compounds in hydrothermal systems. Knowledge on how environmental conditions affect reaction pathways of abiotic synthesis of organic compounds is critical for understanding deep subsurface ecosystems and the origin of organic compounds on Mars and other planets.
    Geochimica et Cosmochimica Acta 01/2015; 154. DOI:10.1016/j.gca.2015.01.027 · 4.25 Impact Factor
  • Source
    • "Recently, carbonates have been detected at several sites on Mars, such as in the Nili Fossae region (Ehlmann et al. 2008), in the Columbia Hills of Gusev crater (Morris et al. 2010) and in Leighton crater (Michalski & Niles 2010). Carbonates have also been detected in Martian meteorite ALH84001, and have been thought to be of biological origin (McKay et al. 1996), however not without dispute (e.g. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The ability to discriminate biogenic from abiogenic calcium carbonate (CaCO3) would be useful in the search for extant or extinct life, since CaCO3 can be produced by both biotic and abiotic processes on Earth. Bioprecipitated CaCO3 material was produced during the growth of heterotrophic microbial isolates on medium enriched with calcium acetate or calcium citrate. These biologically produced CaCO3, along with natural and synthetic non-biologically produced CaCO3 samples, were analysed by reflectance spectroscopy (0.35–2.5 μm), Raman spectroscopy (532 and 785 nm), and laser-induced fluorescence spectroscopy (365 and 405 nm excitation). Optimal instruments for the discrimination of biogenic from abiogenic CaCO3 were determined to be reflectance spectroscopy, and laser-induced fluorescence spectroscopy. Multiple absorption features in the visible light region occurred in reflectance spectra for most biogenic CaCO3 samples, which are likely due to organic pigments. Multiple fluorescence peaks occurred in emission spectra (405 nm excitation) of biogenic CaCO3 samples, which also are best attributed to the presence of organic compounds; however, further analyses must be performed in order to better determine the cause of these features to establish criteria for confirming the origin of a given CaCO3 sample. Raman spectroscopy was not useful for discrimination since any potential Raman peaks in spectra of biogenic carbonates collected by both the 532 and 785 nm lasers were overwhelmed by fluorescence. However, this also suggests that biogenic carbonates may be identified by the presence of this organic-associated fluorescence. No reliable spectroscopic differences in terms of parameters such as positions or widths of carbonate-associated absorption bands were found between the biogenic and abiogenic carbonate samples. These results indicate that the presence or absence of organic matter intimately associated with carbonate minerals is the only potentially useful spectral discriminator for the techniques that were examined, and that multiple spectroscopic techniques are capable of detecting the presence of associated organic materials. However, the presence or absence of intimately associated organic matter is not, in itself, an indicator of biogenicity.
    International Journal of Astrobiology 08/2014; DOI:10.1017/S1473550414000366 · 0.83 Impact Factor
Show more