Synthesis and structural characterization of ferrous trioctahedral smectites: Implications for clay mineral genesis and detectability on Mars

Chemtob, S. M.; Nickerson, R. D.; Morris, R. V.; Agresti, D. G.; Catalano, Jeffrey G.

doi:10.1002/2014je004763

Cited by 56 publications

(113 citation statements)

References 84 publications

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“…Based on CheMin XRD data, the smectite in the Sheepbed Mudstone was previously interpreted as a ferrian (Fe 3+ > Fe 2+ ) saponite, largely because of equivalence in its (02 ℓ ) d‐spacing (4.59 Å) to the terrestrial Griffith saponite (Treiman et al, ). The (02 ℓ ) d‐spacing of our unaltered smectites C and D (4.60 and 4.58 Å, respectively; Table ) are within error of the spacing observed for the Sheepbed Mudstone saponite (Chemtob et al, ; Vaniman et al, ), suggesting that ferrous compositions (Fe 2+ > Fe 3+ ) are also permitted within the constraints of the XRD data. The composition of the Martian saponite could not be calculated independently, but the aggregate chemistry of the saponite plus the amorphous component is more consistent with Mg‐rich saponites like Griffith saponite and our two mixed Fe‐Mg smectites C and D as opposed to our high‐Fe ferrous smectites A and B (Vaniman et al, ).…”

Section: Discussionsupporting

confidence: 78%

“…A shoulder feature at a similar wavelength was previously observed in spectra of a Fe‐rich aluminous smectite by Bishop et al (). This band may represent an OH combination mode associated with Al clusters in the octahedral sheet and was previously assigned to AlAl‐OH by Chemtob et al (). In smectite C, the 2.191 μm feature diminished in intensity with recrystallization and reoxidation.…”

Section: Resultsmentioning

confidence: 88%

“…Postsynthesis oxidation of ferrous smectites in nominally anaerobic chambers is difficult to entirely prevent even at low O 2 concentrations if the reaction is kinetically favored, and we did encounter postsynthesis oxidation for some samples during Mössbauer measurements as previously reported (Chemtob et al, ). We also encountered unintentional oxidation under nominally anaerobic conditions in connection with this study (section 3.1); this oxidation complicated but did not obscure interpretation of results related to oxidation by aqueous air‐saturated and H 2 O 2 solutions.…”

Section: Methodsmentioning

confidence: 99%

“…Fe 2+ ‐Mg smectite formation by aqueous alteration of ferromagnesian minerals has been demonstrated experimentally to occur only under anoxic conditions (Dehouck et al, , ; Nickerson, Chemtob, & Catalano, ). Therefore, the detection of a trioctahedral, Fe 2+ ‐bearing smectite in sediments analyzed by the Curiosity rover at Yellowknife Bay in Gale Crater (Chemtob et al, ; Treiman et al, ; Vaniman et al, ) potentially supports anoxic conditions at the time of their formation in the late Noachian/early Hesperian.…”

Section: Introductionmentioning

confidence: 99%

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Oxidative Alteration of Ferrous Smectites and Implications for the Redox Evolution of Early Mars

Chemtob

Nickerson²,

Morris

et al. 2017

JGR Planets

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Surface conditions on early Mars were likely anoxic, similar to early Earth, but the timing of the evolution to oxic conditions characteristic of contemporary Mars is unresolved. Ferrous trioctahedral smectites are the thermodynamically predicted products of anoxic basalt weathering, but orbital analyses of Noachian‐aged terrains find primarily Fe3+‐bearing clay minerals. Rover‐based detection of Fe2+‐bearing trioctahedral smectites at Gale Crater suggests that ferrous smectites are the unoxidized progenitors of orbitally detected ferric smectites. To assess this pathway, we conducted ambient‐temperature oxidative alteration experiments on four synthetic ferrous smectites having molar Fe/(Mg + Fe) from 1.00 to 0.33. Smectite suspension in air‐saturated solutions produced incomplete oxidation (24–38% Fe3+/ΣFe). Additional smectite oxidation occurred upon reexposure to air‐saturated solutions after anoxic hydrothermal recrystallization, which accelerated cation and charge redistribution in the octahedral sheet. Oxidation was accompanied by contraction of the octahedral sheet (d(060) decreased from 1.53–1.56 Å to 1.52 Å), consistent with a shift toward dioctahedral structure. Ferrous smectite oxidation by aqueous hydrogen peroxide solutions resulted in nearly complete Fe2+ oxidation but also led to partial Fe3+ ejection from the structure, producing nanoparticulate hematite. Reflectance spectra of oxidized smectites were characterized by (Fe3+,Mg)2‐OH bands at 2.28–2.30 μm, consistent with oxidative formation of dioctahedral nontronite. Accordingly, ferrous smectites are plausible precursors to observed ferric smectites on Mars, and their presence in late‐Noachian sedimentary units suggests that anoxic conditions may have persisted on Mars beyond the Noachian.

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Section: Discussionsupporting

confidence: 78%

Section: Resultsmentioning

confidence: 88%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Oxidative Alteration of Ferrous Smectites and Implications for the Redox Evolution of Early Mars

Chemtob

Nickerson²,

Morris

et al. 2017

JGR Planets

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“…[], as well as ferrous saponites measured in a Mars‐like environment from Chemtob et al . []. In the case of our detections, the shorter wavelength absorption is more diagnostic of mineral composition since it has a broader range.…”

Section: Discussionmentioning

confidence: 68%

Mineralogy and stratigraphy of the Gale crater rim, wall, and floor units

et al. 2017

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The Curiosity rover has detected diverse lithologies in float rocks and sedimentary units on the Gale crater floor, interpreted to have been transported from the rim. To understand their provenance, we examine the mineralogy and geology of Gale's rim, walls, and floor, using high‐resolution imagery and infrared spectra. While no significant differences in bedrock spectral properties were observed within most Thermal Emission Imaging System and Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) scenes, some CRISM scenes of rim and wall rocks showed olivine‐bearing bedrock accompanied by Fe/Mg phyllosilicates. Hydrated materials with 2.48 μm absorptions in Gale's eastern walls are spectrally similar to the sulfate unit in Mount Sharp (Aeolis Mons). Sedimentary strata on the Gale floor southwest of the landing site, likely coeval with the Bradbury units explored by Curiosity, also are hydrated and/or have Fe/Mg phyllosilicates. Spectral properties of these phyllosilicates differ from the Al‐substituted nontronite detected by CRISM in Mount Sharp, suggesting formation by fluids of different composition. Geologic mapping of the crater floor shows that the hydrated or hydroxylated materials are typically overlain by spectrally undistinctive, erosionally resistant, cliff‐forming units. Additionally, a 4 km impact crater exposes >250 m of the Gale floor, including finely layered units. No basement rocks are exposed, thus indicating sedimentary deposits ≥250 m beneath strata studied by Curiosity. Collectively, the data indicate substantial sedimentary infill of Gale crater, including some materials derived from the crater rim. Lowermost thin layers are consistent with deposition in a lacustrine environment; interbedded hydrated/hydroxylated units may signify changing environmental conditions, perhaps in a drying or episodically dry lake bed.

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The stratigraphy and evolution of lower Mount Sharp from spectral, morphological, and thermophysical orbital data sets

et al. 2016

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We have developed a refined geologic map and stratigraphy for lower Mount Sharp using coordinated analyses of new spectral, thermophysical, and morphologic orbital data products. The Mount Sharp group consists of seven relatively planar units delineated by differences in texture, mineralogy, and thermophysical properties. These units are (1–3) three spatially adjacent units in the Murray formation which contain a variety of secondary phases and are distinguishable by thermal inertia and albedo differences, (4) a phyllosilicate‐bearing unit, (5) a hematite‐capped ridge unit, (6) a unit associated with material having a strongly sloped spectral signature at visible near‐infrared wavelengths, and (7) a layered sulfate unit. The Siccar Point group consists of the Stimson formation and two additional units that unconformably overlie the Mount Sharp group. All Siccar Point group units are distinguished by higher thermal inertia values and record a period of substantial deposition and exhumation that followed the deposition and exhumation of the Mount Sharp group. Several spatially extensive silica deposits associated with veins and fractures show that late‐stage silica enrichment within lower Mount Sharp was pervasive. At least two laterally extensive hematitic deposits are present at different stratigraphic intervals, and both are geometrically conformable with lower Mount Sharp strata. The occurrence of hematite at multiple stratigraphic horizons suggests redox interfaces were widespread in space and/or in time, and future measurements by the Mars Science Laboratory Curiosity rover will provide further insights into the depositional settings of these and other mineral phases.

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Synthesis and structural characterization of ferrous trioctahedral smectites: Implications for clay mineral genesis and detectability on Mars

Cited by 56 publications

References 84 publications

Oxidative Alteration of Ferrous Smectites and Implications for the Redox Evolution of Early Mars

Oxidative Alteration of Ferrous Smectites and Implications for the Redox Evolution of Early Mars

Mineralogy and stratigraphy of the Gale crater rim, wall, and floor units

The stratigraphy and evolution of lower Mount Sharp from spectral, morphological, and thermophysical orbital data sets

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