Characterization of phyllosilicates observed in the central Mawrth Vallis region, Mars, their potential formational processes, and implications for past climate

By N. K. McKeown, Janice L. Bishop, E. Dobrea, Bethany L. Ehlmann, Mario Parente, J. F. Mustard, Scott L. Murchie, G. Swayze, J. Bibring, E. Silver. 2009

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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, ∼1.91, and 2.17–2.41 μm. 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 μm, 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.

Subfields: Aerospace Engineering, Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/9c8043cc366834951ceb71433439db6d595fbff3

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Citations in the corpus

A synthesis of Martian aqueous mineralogy after 1 Mars year of observations from the Mars Reconnaissance Orbiter (2009, background): “…clays exhibiting coarse polygonal fractures tens of meters apart, the Al smectite clays exhibiting more closely spaced fractures, and the kaolinite-group-and silica-bearing layers exhibiting a smooth texture at meters scale [Wray et al., 2007, 2008a; Bishop et al., 2008; McKeown et al., 2009].”
Compact Reconnaissance Imaging Spectrometer for Mars investigation and data set from the Mars Reconnaissance Orbiter's primary science phase (2009, background): “In the Mawrth Valles region, coordinated targeted observations reveal vertical layering of phyllosilicate composition consistent over hundreds of thousands of square kilometers [Bishop et al., 2008; McKeown et al., 2009 ].”
The High Resolution Stereo Camera (HRSC) of Mars Express and its approach to science analysis and mapping for Mars and its satellites (2016, background): “…Vallis has identified extensive deposits rich in clay minerals, where two main species have been identified, one richer in Al, the other richer in Fe/Mg, using distinctive absorption bands in the NIR domain (Poulet et al., 2005; Loizeau et al., 2007; Bishop et al., 2008; McKeown et al., 2009).”
3D modelling of the early Martian Climate under a denser CO2 atmosphere: Temperatures and CO2 ice clouds. (2012, background): “l erosion rate inferred for the early Noachian period, or the formation of extensive deposits of phyllosilicates like in the Mawrth Vallis region (e.g. Craddock and Howard, 2002, Bibring et al. 2006, McKeown et al. 2009). In any case, there is no doubt that conditions on Mars during the ﬁrst billion”