Impure reworked evaporitic sandstones, preserved on Meridiani Planum, Mars, are mixtures of roughly equal amounts of altered siliciclastic debris, of basaltic provenance (40
±
10% by mass), and ...chemical constituents, dominated by evaporitic minerals (jarosite, Mg-, Ca-sulfates
±
chlorides
±
Fe-, Na-sulfates), hematite and possibly secondary silica (60
±
10%). These chemical constituents and their relative abundances are not an equilibrium evaporite assemblage and to a substantial degree have been reworked by aeolian and subaqueous transport. Ultimately they formed by evaporation of acidic waters derived from interaction with olivine-bearing basalts and subsequent diagenetic alteration. The rocks experienced an extended diagenetic history, with at least two and up to four distinct episodes of cementation, including stratigraphically restricted zones of recrystallization and secondary porosity, non-randomly distributed, highly spherical millimeter-scale hematitic concretions, millimeter-scale crystal molds, interpreted to have resulted from dissolution of a highly soluble evaporite mineral, elongate to sheet-like vugs and evidence for minor synsedimentary deformation (convolute and contorted bedding, possible teepee structures or salt ridge features). Other features that may be diagenetic, but more likely are associated with relatively recent meteorite impact, are meter-scale fracture patterns, veins and polygonal fractures on rock surfaces that cut across bedding. Crystallization of minerals that originally filled the molds, early cement and sediment deformation occurred syndepositionally or during early diagenesis. All other diagenetic features are consistent with formation during later diagenesis in the phreatic (fluid saturated) zone or capillary fringe of a groundwater table under near isotropic hydrological conditions such as those expected during periodic groundwater recharge. Textural evidence suggests that rapidly formed hematitic concretions post-date the primary mineral now represented by crystal molds and early pore-filling cements but pre-date secondary moldic and vug porosity. The second generation of cements followed formation of secondary porosity. This paragenetic sequence is consistent with an extended history of syndepositional through post-depositional diagenesis in the presence of a slowly fluctuating, chemically evolving, but persistently high ionic strength groundwater system.
The Opportunity Mars Exploration Rover found evidence for groundwater activity in the Meridiani Planum region of Mars in the form of aeolian and fluvial sediments composed of sulphate-rich grains. ...These sediments appear to have experienced diagenetic modification in the presence of a fluctuating water table. In addition to the extensive secondary aqueous alteration, the primary grains themselves probably derive from earlier playa evaporites. Little is known, however, about the hydrologic processes responsible for this environmental history-particularly how such extensive evaporite deposits formed in the absence of a topographic basin. Here we investigate the origin of these deposits, in the context of the global hydrology of early Mars, using numerical simulations, and demonstrate that Meridiani is one of the few regions of currently exposed ancient crust predicted to have experienced significant groundwater upwelling and evaporation. The global groundwater flow would have been driven primarily by precipitation-induced recharge and evaporative loss, with the formation of the Tharsis volcanic rise possibly playing a role through the burial of aquifers and induced global deformation. These results suggest that the deposits formed as a result of sustained groundwater upwelling and evaporation, rather than ponding within an enclosed basin. The evaporite formation coincided with a transition to more arid conditions that increased the relative impact of a deep-seated, global-scale hydrology on the surface evolution.
The Mössbauer (MB) spectrometer on Opportunity measured the Fe oxidation state, identified Fe‐bearing phases, and measured relative abundances of Fe among those phases at Meridiani Planum, Mars. ...Eight Fe‐bearing phases were identified: jarosite (K,Na,H3O)(Fe,Al)(OH)6(SO4)2, hematite, olivine, pyroxene, magnetite, nanophase ferric oxides (npOx), an unassigned ferric phase, and metallic Fe (kamacite). Burns Formation outcrop rocks consist of hematite‐rich spherules dispersed throughout S‐rich rock that has nearly constant proportions of Fe3+ from jarosite, hematite, and npOx (29%, 36%, and 20% of total Fe). The high oxidation state of the S‐rich rock (Fe3+/FeT ∼ 0.9) implies that S is present as the sulfate anion. Jarosite is mineralogical evidence for aqueous processes under acid‐sulfate conditions because it has structural hydroxide and sulfate and it forms at low pH. Hematite‐rich spherules, eroded from the outcrop, and their fragments are concentrated as hematite‐rich soils (lag deposits) on ripple crests (up to 68% of total Fe from hematite). Olivine, pyroxene, and magnetite are primarily associated with basaltic soils and are present as thin and locally discontinuous cover over outcrop rocks, commonly forming aeolian bedforms. Basaltic soils are more reduced (Fe3+/FeT ∼ 0.2–0.4), with the fine‐grained and bright aeolian deposits being the most oxidized. Average proportions of total Fe from olivine, pyroxene, npOx, magnetite, and hematite are ∼33%, 38%, 18%, 6%, and 4%, respectively. The MB parameters of outcrop npOx and basaltic‐soil npOx are different, but it is not possible to infer mineralogical information beyond octahedrally coordinated Fe3+. Basaltic soils at Meridiani Planum and Gusev crater have similar Fe‐mineralogical compositions.
•Potential desiccation polygons (PDPs) are common on Mars.•PDPs are associated with ancient phyllosilicates and chlorides.•PDPs can be markers of smectites deposited in paleolacustrine ...environments.•PDPs may indicate warmer and hydrologically-active ancient climates.
Potential desiccation polygons (PDPs) are polygonal surface patterns that are a common feature in Noachian-to-Hesperian-aged phyllosilicate- and chloride-bearing terrains and have been observed with size scales that range from cm-wide (by current rovers) to 10s of meters-wide. The global distribution of PDPs shows that they share certain traits in terms of morphology and geologic setting that can aid identification and distinction from fracturing patterns caused by other processes. They are mostly associated with sedimentary deposits that display spectral evidence for the presence of Fe/Mg smectites, Al-rich smectites or less commonly kaolinites, carbonates, and sulfates. In addition, PDPs may indicate paleolacustrine environments, which are of high interest for planetary exploration, and their presence implies that the fractured units are rich in smectite minerals that may have been deposited in a standing body of water. A collective synthesis with new data, particularly from the HiRISE camera suggests that desiccation cracks may be more common on the surface of Mars than previously thought. A review of terrestrial research on desiccation processes with emphasis on the theoretical background, field studies, and modeling constraints is presented here as well and shown to be consistent with and relevant to certain polygonal patterns on Mars.
The geomorphology and geochemistry data gathered by the MER Opportunity at Meridiani Planum is a rich data set relevant to soil research on Mars. Many of the data, particularly with respect to ...outcrops at Victoria Crater, have been only partially analyzed. Here, the previously published geochemical profile of Endurance Crater is compared to that of Victoria Crater, to understand aspects of the post-depositional aqueous and chemical alteration of the Meridiani land surface. The landsurface bears cracking patterns similar to those produced by multiple episodes of wetting and drying in expansive materials on Earth. The geochemical profiles at both craters are nearly identical, suggesting (using mass balance methods) that a very chemically homogenous sedimentary deposit has been engulfed by the apparent surficial addition of S, Cl, and Br (and associated cations) since exposure to the atmosphere. The chemistry and mineralogy at both locations is one where the most insoluble of the added components resides near the land surface (Ca sulfates), and the more soluble components are concentrated at greater depths in a vertical pattern consistent with their solubility in water. The profiles, when compared to those on Earth (and to physical constraints), are most similar those generated by the downward movement of meteoric water. When this aqueous alteration and soil formation occurred is not well constrained, but the processes occurred between late Noachian (?) to late Amazonian times. The exposure of the Victoria crater walls, which occurred likely less than 107 y ago (late Amazonian), shows the accumulation of dust as well as evidence for aqueous concentration of NaBr and/or CaBr, possibly by deliquescence. By direct comparison to Earth, the regional soil at Meridiani Planum is a Typic Petrogypsid (a sulfate cemented arid soil), bearing similarities to very ancient soils formed in the Atacama Desert of Chile. The amount of water required to produce the soils ranges from a very low (and physically unlikely) quantity of 2–4 m, to possibly (and more likely) kilometers of water that were added in small individual increments over long spans of geological time.
•The geochemical profiles of Endurance and Victoria craters on Mars are found to be nearly identical.•The chemical profiles appear to have formed by meteoric water over long times spans.•There is evidence for minor aqueous alteration of crater walls during the past few million years.
The Mars Exploration Rover Opportunity has investigated the landing site in Eagle crater and the nearby plains within Meridiani Planum. The soils consist of fine-grained basaltic sand and a surface ...lag of hematite-rich spherules, spherule fragments, and other granules. Wind ripples are common. Underlying the thin soil layer, and exposed within small impact craters and troughs, are flat-lying sedimentary rocks. These rocks are finely laminated, are rich in sulfur, and contain abundant sulfate salts. Small-scale cross-lamination in some locations provides evidence for deposition in flowing liquid water. We interpret the rocks to be a mixture of chemical and siliciclastic sediments formed by episodic inundation by shallow surface water, followed by evaporation, exposure, and desiccation. Hematite-rich spherules are embedded in the rock and eroding from them. We interpret these spherules to be concretions formed by postdepositional diagenesis, again involving liquid water.
The Terra Sirenum region of Mars, located in the Noachian southern highlands, is mineralogically diverse, providing unique insight into ancient aqueous processes. Analyses of remote sensing data over ...the region indicate the presence of both Fe‐ or Mg‐rich phyllosilicates and a spectrally unique deposit interpreted to be rich in chloride salts. The stratigraphic relationships indicate that the phyllosilicates are part of the ancient highland crust and that the salts were deposited at a later time. In some instances, there is clear morphological evidence that salts were mobilized and deposited by near‐surface waters.
•Pancam estimates the Lambert albedo at Gusev crater and Meridiani Planum, Mars.•Albedo varies on small spatial/temporal scales due to localized wind events.•Albedo measurements from Pancam, MOC, CTX ...and HiRISE agree to within 15%.
The Mars Exploration Rovers (MER) Spirit and Opportunity have systematically used their Panoramic Camera (Pancam) instruments to estimate the Lambert albedo of the surface across their traverses in Gusev crater and Meridiani Planum. The 360˚ “albedo pan” observations acquired with Pancam's broadband (739 ± 338 nm) L1 filter allow for quantitative estimates of the overall surface albedo and measurements of individual surface features. As of November 2016, over nearly six Mars years of the MER mission, Spirit acquired 20 albedo pans (over 7,730 m of traverse distance) and Opportunity acquired 117 albedo pans (over 42,368 m of traverse distance). For Spirit, this comprises the rover's complete dataset. The ranges of Pancam-derived albedos at Gusev crater (0.14–0.24) and at Meridiani Planum (0.11–0.22, with one anomalously high measurement of 0.27 during the July 2007 global dust storm) are consistent with large-scale albedos of the sites as previously determined by the Viking Orbiter Infrared Thermal Mapper (IRTM), Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES), MGS Mars Orbiter Camera (MOC), Mars Odyssey Thermal Emission Imaging System (THEMIS), Mars Reconnaissance Orbiter (MRO) Context Camera (CTX) and MRO Mars Color Imager (MARCI) instruments. Through comparisons with atmospheric opacity measurements, temporal changes in Pancam albedo values provide insights into interactions between the Martian surface and atmosphere. Pancam observations are also used to “ground truth” measurements from orbit and validate radiometric calibrations, and we present comparisons across the full rover traverses to MOC, CTX, and MRO High Resolution Imaging Science Experiment (HiRISE) data. Albedo averages from the same regions observed by Pancam and all three orbital instruments generally agree to within ± 15%. The few instances found where cross-instrument comparisons exceed the estimated instrument calibration uncertainties can be attributed to atmospheric effects and/or differences in viewing geometries.
Preferred orientations of cracks in surface clasts have been reported on Earth and on Mars. This paper uses a 2D radiative transfer algorithm to simulate the Martian atmosphere, in combination with ...an original geometric code to determine the levels of differential insolation received by cracks as a function of season, latitude, and crack morphology on the surface of Mars. We find significant variation in preferred orientation both as a function of latitude and relative crack depth. Crack shape has little effect on the overall preferred orientation. The effect of requiring a minimum energy threshold to mobilize water is found to also affect the preferred direction, suppressing the E–W direction and somewhat promoting cross-modes. Crack orientations observed along the Spirit traverse can only be recreated by restricting growth propagation to mornings in the local autumn/winter season.
This paper describes karst landforms observed in the northern Sinus Meridiani region of Mars, located between 1°20′–2°20′ N and 2°50′ W–1°E and covering an area of about 20,000km2.The karst is ...characterised by spectral signatures of mono- and poly-hydrated sulphates. A morphologic and morphometric survey of the study area was performed through an integrated analysis of 18 Mars Reconnaissance Orbiter High Resolution Imaging Science Experiment. Four distinct karst terrains were observed in the study area; they resemble landforms in a variety of karst terrains on Earth. The Martian landforms are characterised by different doline depression features and display different kinds and degrees of karstification. This variation seems to indicate differences in relative karst susceptibility due to the solutional properties of the four units, and enables the use of the karst landforms as significant geomorphic markers to distinguish units compositionally and/or mineralogically in the Sinus Meridiani area.
► Four distinct karst terrains (KTs) are exposed at different stratigraphic levels throughout northern Sinus Meridiani. ► The KTs are characterised by different kinds and degrees of karstification. ► The differences among terrains as the result of different relative karst susceptibility. ► The karst landforms can be used as significant geomorphic markers.
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