We present detailed stratigraphic and spectral analyses that focus on a region in northern Sinus Meridiani located between 1°N to 5°N latitude and 3°W to 1°E longitude. Several stratigraphically ...distinct units are defined and mapped using morphologic expression, spectral properties, and superposition relationships. Previously unreported exposures of hydrated sulfates and Fe/Mg smectites are identified using MRO CRISM and MEX OMEGA near‐infrared (1.0 to 2.5 μm) spectral reflectance observations. Layered deposits with monohydrated and polyhydrated sulfate spectral signatures that occur in association with a northeast‐southwest trending valley are reexamined using high‐resolution CRISM, HiRISE, and CTX images. Layers that are spectrally dominated by monohydrated and polyhydrated sulfates are intercalated. The observed compositional layering implies that multiple wetting events, brine recharge, or fluctuations in evaporation rate occurred. We infer that these hydrated sulfate‐bearing layers were unconformably deposited following the extensive erosion of preexisting layered sedimentary rocks and may postdate the formation of the sulfate‐ and hematite‐bearing unit analyzed by the MER Opportunity rover. Therefore, at least two episodes of deposition separated by an unconformity occurred. Fe/Mg phyllosilicates are detected in units that predate the sulfate‐ and hematite‐bearing unit. The presence of Fe/Mg smectite in older units indicates that the relatively low pH formation conditions inferred for the younger sulfate‐ and hematite‐bearing unit are not representative of the aqueous geochemical environment that prevailed during the formation and alteration of earlier materials. Sedimentary deposits indicative of a complex aqueous history that evolved over time are preserved in Sinus Meridiani, Mars.
The Sedimentary Cycle on Early Mars McLennan, Scott M; Grotzinger, John P; Hurowitz, Joel A ...
Annual review of earth and planetary sciences,
05/2019, Letnik:
47, Številka:
1
Journal Article
Recenzirano
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Two decades of intensive research have demonstrated that early Mars (
2 Gyr) had an active sedimentary cycle, including well-preserved stratigraphic records, understandable within a source-to-sink ...framework with remarkable fidelity. This early cycle exhibits first-order similarities to (e.g., facies relationships, groundwater diagenesis, recycling) and first-order differences from (e.g., greater aeolian versus subaqueous processes, basaltic versus granitic provenance, absence of plate tectonics) Earth's record. Mars' sedimentary record preserves evidence for progressive desiccation and oxidation of the surface over time, but simple models for the nature and evolution of paleoenvironments (e.g., acid Mars, early warm and wet versus late cold and dry) have given way to the view that, similar to Earth, different climate regimes on Mars coexisted on regional scales and evolved on variable timescales, and redox chemistry played a pivotal role. A major accomplishment of Mars exploration has been to demonstrate that surface and subsurface sedimentary environments were both habitable and capable of preserving any biological record.
Mars has an ancient sedimentary rock record with many similarities to but also many differences from Earth's sedimentary rock record.
Mars' ancient sedimentary cycle shows a general evolution toward more desiccated and oxidized surficial conditions.
Climatic regimes of early Mars were relatively clement but with regional variations leading to different sedimentary mineral assemblages.
Surface and subsurface sedimentary environments on early Mars were habitable and capable of preserving any biological record that may have existed.
Over the past decade, our knowledge of the geochemical and mineralogical diversity of Martian rocks has greatly increased. Rocks on the surface of Mars are older than most Martian meteorites and have ...a wider range in bulk chemistry (higher SiO2, higher total alkalis, and lower MgO contents). Recent Martian meteorite discoveries (NWA 7034, NWA 7635, and NWA 8159) are also significantly older than the shergottites and NWA 7034 contains clasts which have a similar range in chemistry of the surface basalts. In this invited review, I summarize what is known about the bulk chemistry (major elements) of Martian igneous rocks and use the chemistry to constrain the formation conditions in the interior, and how these conditions have changed through time.
The basalts at Gale Crater are consistent with forming from a metasomatized mantle source which affected not only the chemistry of the basalts, but also the formation conditions. Basalts at Gusev Crater, Bounce Rock at Meridiani Planum, and those basalts not affected by metasomatism like those at Gale Crater have a mantle potential temperature of ~1450°C for the Noachian. Conversely, Martian shergottites have a much higher mantle potential temperature (~1745°C), which has always been problematic to explain for such young rocks. New formation conditions calculations are consistent with previous models of formation by a hot mantle plume, but solve the pressure of formation paradox from the previous model. Combining the calculations for mantle potential temperature with previous estimates for GRS measurements of surface volcanics from the Hesperian and Amazonian, I calculate a baseline cooling curve and mantle melting conditions for the Martian interior through time.
•Review of geochemistry of Martian basalts and formation conditions•Martian basalts are more chemically more diverse than represented by meteorites.•Gale Crater basalts are from a metasomatized mantle source.•Noachian basalts have a mantle potential temperature of ~1450°C.•Shergottites are from a deep, hot mantle source consistent with plume-style melting.
With Consolo's 'voices' Gianni Turchetta
Prassi ecdotiche della modernità letteraria,
09/2017
2
Journal Article
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The aesthetic and cognitive quality of the works of Vincenzo Consolo had benn askig for longtime an edition able to give it a stable presence in the canon of the great authors of the 20th century. On ...the other hand, the characteristics of Consolo's texts, with their well-known linguistic but also generally cultural complexity, asked the editor to modulate the apparatus so as to offer the reader the tools for an easier understanding. The systematic investigation in Consolo's Archivea has made it possible to face up to all the difficulties presented by the edition, achieving significant results both in terms of documentation and in terms of critical interpretation.
The objectives of this paper are twofold: first, to report our estimates of the meter‐to‐decameter‐scale topography and slopes of candidate landing sites for the Phoenix mission, based on analysis of ...Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) images with a typical pixel scale of 3 m and Mars Reconnaissance Orbiter (MRO) High Resolution Imaging Science Experiment (HiRISE) images at 0.3 m pixel−1 and, second, to document in detail the geometric calibration, software, and procedures on which the photogrammetric analysis of HiRISE data is based. A combination of optical design modeling, laboratory observations, star images, and Mars images form the basis for software in the U.S. Geological Survey Integrated Software for Imagers and Spectrometers (ISIS) 3 system that corrects the images for a variety of distortions with single‐pixel or subpixel accuracy. Corrected images are analyzed in the commercial photogrammetric software SOCET SET (® BAE Systems), yielding digital topographic models (DTMs) with a grid spacing of 1 m (3–4 pixels) that require minimal interactive editing. Photoclinometry yields DTMs with single‐pixel grid spacing. Slopes from MOC and HiRISE are comparable throughout the latitude zone of interest and compare favorably with those where past missions have landed successfully; only the Mars Exploration Rover (MER) B site in Meridiani Planum is smoother. MOC results at multiple locations have root‐mean‐square (RMS) bidirectional slopes of 0.8–4.5° at baselines of 3–10 m. HiRISE stereopairs (one per final candidate site and one in the former site) yield 1.8–2.8° slopes at 1‐m baseline. Slopes at 1 m from photoclinometry are also in the range 2–3° after correction for image blur. Slopes exceeding the 16° Phoenix safety limit are extremely rare.
The aim of the research was to analyze the possibilities of using deep learning methods for classifying multi-source image data for Mars. It should be emphasized that the main goal of the research ...was to develop a methodology for integrating image data acquired from orbiters (MRO mission's HIRISE camera) and in situ (Opportunity rover's NAVCAM camera) and to use their combined analytical potential. We used a VGG-16-based network for this study, which is well-characterized in the literature and has been successfully applied in a wide range of applications. The article proposes a methodology for the supervised classification of landforms on Mars. The proposed solution was evaluated using the Meridiani Planum area, utilizing neural network deep learning and was based on multi-source image data. We found that our approach classified aeolian reliefs correctly for more than 94% of the test dataset. The classification accuracy increased to almost 96% when using panoramas developed from Opportunity's images and the derivatives of the digital terrain models used during the classification process. It is possible to broaden the proposed concept of multi-source classification and the customized deep learning system to the analysis of other regions of Mars and to multispectral imaging without losing the generalizability of the solution.
The Meridiani Planum region of Mars has been identified as a region of past aqueous activity by a combination of orbital and in situ observations that revealed evidence for sulfate‐rich dirty ...evaporites formed in a playa setting. We investigate the hydrology and sedimentary record of this area using global and regional hydrological models in which groundwater flow is driven by a combination of precipitation, evaporation, and the surface topography. Groundwater evaporation results in evaporite precipitation and cementation of aeolian sediments, allowing the accumulation of deposits of substantial thickness, which then affect the subsequent patterns of groundwater flow. Hydrological activity is initially predicted to be isolated to the deepest craters and depressions, primarily within the Arabia Terra region surrounding Meridiani. As these depressions fill with sediments, the groundwater upwelling spreads laterally across broad regions of Arabia Terra, including Meridiani Planum, as well as regional topographic lows such as the northern lowlands and large impact basins. The model predictions are borne out by observations of large intracrater deposits, inverted valley networks, finely layered deposits, spectral evidence for hydrated sulfates, and pedestal craters that preserve the remnants of a much larger deposit that once covered much of Arabia Terra. The results suggest that the inferred playa at Meridiani was part of a regionally extensive zone of groundwater upwelling. This hydrological cycle requires that conditions in the late Noachian to early Hesperian must have been conducive to the existence of liquid water at the surface throughout much of the low latitudes of Mars.
Leonardo Sciascia and Danilo Dolci, two of the most important Italian intellectuals, have lived and operated in the same zone in Sicily for a long time, analyzing the same enemy, both writing on that ...kind of violence traditionally called «mafia». Nevertheless, they didn't agree with each other on the method to be used for people's emancipation from such Sicilian drama. Sciascia is persuaded that try to solve Sicilian violence by non-violent methods, as Dolci supposes, is an illusion. Dolci, on the contrary, believes that non-violence is actually the only solution to face it. Understanding this dispute can stimulate our points of view on the Sicilian history of violence, prevalently identified with that organized shape of violence better known as mafia; but it can also encourage our perspectives and purposes on non-violent action and researches.
Spectral reflectance properties of nontronite a phyllosilicate with an ideal formula of Na0.3Fe23+(Si,Al)4O10(OH)2·nH2O were investigated under simulated Mars surface conditions of atmospheric ...pressure and composition, and after heating to 110°, 180°, and 300 °C. The data can be used to determine the conditions to which nontronites on the martian surface may have been subjected. Nontronite's spectral features include Fe3+ associated absorption features below 1000 nm, H2O/OH features near 1400 nm, H2O features near 1900 nm, a characteristic metal-OH (Fe3+) feature in the 2280–2290 nm region, and an additional Fe-OH absorption feature near 2400 nm. Heating in a low-pressure CO2 environment leads to the loss of Fe-OH-associated features below 1000 nm at temperatures as low as 110 °C. Both OH and H2O are progressively lost upon heating to 300 °C, but small, spectrally-detectable amounts remain at 300 °C. The longer wavelength Fe-OH absorption bands in the 2280 and 2400 nm region persist up to these temperatures. Comparison to other smectites and Fe-rich phyllosilicates show that a strong 2280–2290 nm absorption feature and weak or absent ∼2320 nm feature are unique to nontronite. A broader absorption feature in the 2300 nm region suggests the presence of nontronite and one or more Mg-bearing phyllosilicate(s). A Mg+Fe3+ phyllosilicate is implausible because of the difficulty in incorporating Mg2+ into the dioctahedral structure of nontronite. With increasing grain size, nontronite spectra become darker and progressively more blue-sloped beyond ∼1500 nm with absorption bands showing increasing depth until saturation is reached for some of them beyond a few hundred-micron grain size. The spectral changes documented in this study, as well as a comparison to previous studies, suggest that the absorption features associated with nontronite can be used to place constraints on conditions that nontronite may have been exposed to in the past. This study demonstrates that dehydration as well as dehydroxylation can occur at temperatures <300 °C.
•A suite of nontronite samples was characterized compositionally, structurally, and by reflectance spectroscopy•Nontronite reflectance spectra are characterized by several diagnostic Fe-OH absorption bands, at ∼2280 and ∼2400 nm•The 2280 nm absorption feature and the absence of a strong ∼2320 nm absorption band are unique to nontronites•Heating up to 300°C in a Mars-like atmosphere demonstrates the spectral robustness of the ∼2280-2290 nm absorption feature
•Grasberg and Burns rocks had very similar chemical compositions prior to diagenesis.•Grasberg rocks experienced diagenetic loss of MgSO4 similar to some Burns rocks.•Grasberg rocks and Burns rocks ...near the contact also had diagenetic loss of Mn.•Similar compositions suggest sediment sources for both units were closely related.
The hematite-bearing, sulfate-rich sandstones of the Burns formation at Meridiani Planum are underlain by a thin stratigraphic unit referred to as the Grasberg formation. The sulfate-bearing Grasberg rocks are fine-grained and lack bedding structures, and were previously interpreted to be a distinct lithologic unit based on morphological and chemical differences from the overlying Burns formation. However, reanalysis of the data indicates that, except for variable amounts of Mg, Ni, SO3 and Mn, the chemical compositions of the Grasberg and Burns rocks are very similar. The relatively low levels of Mg, Ni, and SO3 in the Grasberg rocks indicates that they have experienced diagenetic loss of Mg sulfates similar to that observed in a subset of eleven Burns formation rocks depleted in the same elements, including two Burns rocks immediately above the Grasberg contact. The Grasberg formation and Burns rocks near the contact have also evidently lost Mn during diagenesis. When compensated for diagenetic losses, rocks from the Grasberg and Burns formations are found to have nearly identical chemical compositions, albeit Grasberg rocks contained a few wt.% less SO3. These observations suggest that the sediment sources for the Grasberg and Burns formations are genetically related, and that both formations experienced some of the same diagenetic processes after deposition. Furthermore, the apparent loss of Mg, Ni, SO3, and Mn from the Grasberg formation and immediately overlying Burns rocks is mirrored by enrichments of these same elements in fractures within the underlying Shoemaker formation, suggesting downward movement of fluids during some diagenetic events.
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