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

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

Phyllosilicate Diversity and Past Aqueous Activity Revealed at Mawrth Vallis, Mars

Observations 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 Fe^(2+) 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. Fe^(2+)-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

Mineralogy of Juventae Chasma: Sulfates in the light‐toned mounds, mafic minerals in the bedrock, and hydrated silica and hydroxylated ferric sulfate on the plateau

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A synthesis of Martian aqueous mineralogy after 1 Mars year of observations from the Mars Reconnaissance Orbiter

Martian 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 μm 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 Minéralogie, L'Eau, les Glaces et l'Activitié 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

Evidence for a sedimentary origin of a clay minerals in the Mawrth Vallis region, Mars

Clay minerals detected spectroscopically in the Mawrth Vallis region of Mars correspond to a complex, layered, thick (>600 m) stratigraphic section of ancient bedrock. Because the light-toned, clay-bearing rocks are lithologically diverse over a broad area (>80,000 km2), have significant internal layering and complexity, and contain buried impact craters within the section (demonstrating that they were deposited over a geologically significant duration of time), we interpret the host rocks as sedimentary or possibly pyroclastic. Crater counts date the claybearing rocks to early-middle Noachian time (estimated as 3.8-4.1 Ga). Geomorphic observations suggest that the rocks were lithified early and deeply eroded during the late Noachian-early Hesperian. The combination of a probable ancient sedimentary context of the clays and a moderate pH formation environment implied by the occurrence of smectites clearly places these rocks among the most important targets for future astrobiological exploration. © 2007 The Geological Society of America.Link_to_subscribed_fulltex