The landforms of northern Gale crater on Mars expose thick sequences of sedimentary rocks. Based on images obtained by the Curiosity rover, we interpret these outcrops as evidence for past fluvial, ...deltaic, and lacustrine environments. Degradation of the crater wall and rim probably supplied these sediments, which advanced inward from the wall, infilling both the crater and an internal lake basin to a thickness of at least 75 meters. This intracrater lake system probably existed intermittently for thousands to millions of years, implying a relatively wet climate that supplied moisture to the crater rim and transported sediment via streams into the lake basin. The deposits in Gale crater were then exhumed, probably by wind-driven erosion, creating Aeolis Mons (Mount Sharp).
The first four rocks examined by the Mars Science Laboratory Alpha Particle X‐ray Spectrometer indicate that Curiosity landed in a lithologically diverse region of Mars. These rocks, collectively ...dubbed the Bradbury assemblage, were studied along an eastward traverse (sols 46–102). Compositions range from Na‐ and Al‐rich mugearite Jake_Matijevic to Fe‐, Mg‐, and Zn‐rich alkali‐rich basalt/hawaiite Bathurst_Inlet and span nearly the entire range in FeO* and MnO of the data sets from previous Martian missions and Martian meteorites. The Bradbury assemblage is also enriched in K and moderately volatile metals (Zn and Ge). These elements do not correlate with Cl or S, suggesting that they are associated with the rocks themselves and not with salt‐rich coatings. Three out of the four Bradbury rocks plot along a line in elemental variation diagrams, suggesting mixing between Al‐rich and Fe‐rich components. ChemCam analyses give insight to their degree of chemical heterogeneity and grain size. Variations in trace elements detected by ChemCam suggest chemical weathering (Li) and concentration in mineral phases (e.g., Rb and Sr in feldspars). We interpret the Bradbury assemblage to be broadly volcanic and/or volcaniclastic, derived either from near the Gale crater rim and transported by the Peace Vallis fan network, or from a local volcanic source within Gale Crater. High Fe and Fe/Mn in Et_Then likely reflect secondary precipitation of Fe3+ oxides as a cement or rind. The K‐rich signature of the Bradbury assemblage, if igneous in origin, may have formed by small degrees of partial melting of metasomatized mantle.
Key Points
Rocks at the MSL landing site are diverse and alkali‐ and volatile metal‐rich.
Three of the first four rocks studied by APXS form a mixing line in element plots.
The alkali‐rich nature reflects an igneous source affected by metasomatism.
We describe and model the evolution of a recent landslide, tsunami, outburst flood, and sediment plume in the southern Coast Mountains, British Columbia, Canada. On November 28, 2020, about 18 ...million m3 of rock descended 1,000 m from a steep valley wall and traveled across the toe of a glacier before entering a 0.6 km2 glacier lake and producing >100‐m high run‐up. Water overtopped the lake outlet and scoured a 10‐km long channel before depositing debris on a 2‐km2 fan below the lake outlet. Floodwater, organic debris, and fine sediment entered a fjord where it produced a 60+km long sediment plume and altered turbidity, water temperature, and water chemistry for weeks. The outburst flood destroyed forest and salmon spawning habitat. Physically based models of the landslide, tsunami, and flood provide real‐time simulations of the event and can improve understanding of similar hazard cascades and the risk they pose.
Plain Language Summary
Glacier retreat exposes unstable slopes that can suddenly fail. We describe and model one such event with far‐reaching consequences. The landslide mass (50 million tonnes, equivalent to the combined mass of all Canadian automobiles) entered and suddenly drained a 0.6‐km2 alpine lake in the southern Coast Mountains of British Columbia. Displaced water destroyed salmon‐spawning habitat over a distance of 8.5 km and created a plume of sediment and organic matter more than 60 km from the head of the fjord into which the floodwaters discharged. Physically based models are able to simulate the hazard cascade, and such models could be used to improve hazard and risk assessments of these events under future climate change.
Key Points
Rapid glacier retreat created conditions that allowed a geohazard cascade to occur in a steep mountain valley
We describe and model a recent landslide, tsunami, and outburst flood that typifies a deglacial geohazard cascade
Future work should predict new glacial lakes and use physically based models to simulate the slope, tsunami, and outburst flood hazards
•ChemCam/Curiosity provides elemental composition at Gale crater’ lower Mt Sharp.•Diagenetic features in fine-grained sediments show diverse textures and compositions.•Presence of Mg-, Fe-, ...Ca-sulfates and fluorite is deduced from ChemCam chemistry.•Multiple phases of aqueous alteration suggest a complex post-depositional history.
The Curiosity rover's campaign at Pahrump Hills provides the first analyses of lower Mount Sharp strata. Here we report ChemCam elemental composition of a diverse assemblage of post-depositional features embedded in, or cross-cutting, the host rock. ChemCam results demonstrate their compositional diversity, especially compared to the surrounding host rock: (i) Dendritic aggregates and relief enhanced features, characterized by a magnesium enhancement and sulfur detection, and interpreted as Mg-sulfates; (ii) A localized observation that displays iron enrichment associated with sulfur, interpreted as Fe-sulfate; (iii) Dark raised ridges with varying Mg- and Ca-enriched compositions compared to host rock; (iv) Several dark-toned veins with calcium enhancement associated with fluorine detection, interpreted as fluorite veins. (v) Light-toned veins with enhanced calcium associated with sulfur detection, and interpreted as Ca-sulfates. The diversity of the Pahrump Hills diagenetic assemblage suggests a complex post-depositional history for fine-grained sediments for which the origin has been interpreted as fluvial and lacustrine. Assessment of the spatial and relative temporal distribution of these features shows that the Mg-sulfate features are predominant in the lower part of the section, suggesting local modification of the sediments by early diagenetic fluids. In contrast, light-toned Ca-sulfate veins occur in the whole section and cross-cut all other features. A relatively late stage shift in geochemical conditions could explain this observation. The Pahrump Hills diagenetic features have no equivalent compared to targets analyzed in other locations at Gale crater. Only the light-toned Ca-sulfate veins are present elsewhere, along Curiosity's path, suggesting they formed through a common late-stage process that occurred at over a broad area.
Martian Eolian Dust Probed by ChemCam Lasue, J.; Cousin, A.; Meslin, P.‐Y. ...
Geophysical research letters,
28 October 2018, Letnik:
45, Številka:
20
Journal Article
Recenzirano
Odprti dostop
The ubiquitous eolian dust on Mars plays important roles in the current sedimentary and atmospheric processes of the planet. The ChemCam instrument retrieves a consistent eolian dust composition at ...the submillimeter scale from every first laser shot on Mars targets. Its composition presents significant differences with the Aeolis Palus soils and the Bagnold dunes as it contains lower CaO and higher SiO2. The dust FeO and TiO2 contents are also higher, probably associated with nanophase oxide components. The dust spectra show the presence of volatile elements (S and Cl), and the hydrogen content is similar to Bagnold sands but lower than Aeolis Palus soils. Consequently, the dust may be a contributor to the amorphous component of soils, but differences in composition indicate that the two materials are not equivalent.
Plain Language Summary
Eolian dust on Mars is very fine dust that covers the entire surface of the planet, gives it its typical red hue, and is mobilized by wind. It plays a significant role in the current rock cycle of the planet and for the temperature of the atmosphere. ChemCam uses a series of pulsed laser shots to analyze the chemical composition of target materials. Each first laser shot by ChemCam gives the composition of the deposited dust. These measurements have been constant over the duration of the Mars Science Laboratory mission. The dust is homogeneous at the millimeter scale (approximately the size of the ChemCam analysis spot). Compared to local soils and sands at Gale crater, the dust contains higher levels of iron and titanium, associated with volatile elements like hydrogen, sulfur, and chlorine. We infer from this difference that the dust does not entirely originate locally and may be part of a separate global cycle.
Key Points
The martian eolian dust chemical composition is homogeneous at the submillimeter scale
The dust composition is different from the Aeolis Palus soils and Bagnold sands with a larger content of FeO and TiO2 and lower hydration
Although dust may be a contributor to the amorphous component of soils, its composition indicates that the two materials are not equivalent
The ChemCam instrument package on the Mars Science Laboratory rover, Curiosity, is the first planetary science instrument to employ laser-induced breakdown spectroscopy (LIBS) to determine the ...compositions of geological samples on another planet. Pre-processing of the spectra involves subtracting the ambient light background, removing noise, removing the electron continuum, calibrating for the wavelength, correcting for the variable distance to the target, and applying a wavelength-dependent correction for the instrument response. Further processing of the data uses multivariate and univariate comparisons with a LIBS spectral library developed prior to launch as well as comparisons with several on-board standards post-landing. The level-2 data products include semi-quantitative abundances derived from partial least squares regression.
A LIBS spectral library was developed using 69 rock standards in the form of pressed powder disks, glasses, and ceramics to minimize heterogeneity on the scale of the observation (350–550μm dia.). The standards covered typical compositional ranges of igneous materials and also included sulfates, carbonates, and phyllosilicates. The provenance and elemental and mineralogical compositions of these standards are described. Spectral characteristics of this data set are presented, including the size distribution and integrated irradiances of the plasmas, and a proxy for plasma temperature as a function of distance from the instrument. Two laboratory-based clones of ChemCam reside in Los Alamos and Toulouse for the purpose of adding new spectra to the database as the need arises. Sensitivity to differences in wavelength correlation to spectral channels and spectral resolution has been investigated, indicating that spectral registration needs to be within half a pixel and resolution needs to match within 1.5 to 2.6pixels. Absolute errors are tabulated for derived compositions of each major element in each standard using PLS regression. Sources of errors are investigated and discussed, and methods for improving the analytical accuracy of compositions derived from ChemCam spectra are discussed.
► We describe a LIBS spectral training set of 69 geological standards. ► ChemCam Mars LIBS data processing is described. Detection limits are given. ► Laser coupling, plasma temperature, accuracy, and precision are detailed.
Nearly all cases of melioidosis in the continental United States are related to international travel to areas to which Burkholderia pseudomallei, the bacterium that causes melioidosis, is endemic. We ...report the diagnosis and clinical course of melioidosis in a patient from the United States who had no international travel history and the public health investigation to determine the source of exposure. We tested environmental samples collected from the patient’s home for B. pseudomallei by PCR and culture. Whole-genome sequencing was conducted on PCR-positive environmental samples, and results were compared with sequences from the patient’s clinical specimen. Three PCR-positive environmental samples, all collected from a freshwater home aquarium that had contained imported tropical fish, were a genetic match to the clinical isolate from the patient. This finding suggests a novel route of exposure and a potential for importation of B. pseudomallei, a select agent, into the United States from disease-endemic areas.
The US Public Health Emergency Medical Countermeasures Enterprise convened subject matter experts at the 2010 HHS Burkholderia Workshop to develop consensus recommendations for postexposure ...prophylaxis against and treatment for Burkholderia pseudomallei and B. mallei infections, which cause melioidosis and glanders, respectively. Drugs recommended by consensus of the participants are ceftazidime or meropenem for initial intensive therapy, and trimethoprim/sulfamethoxazole or amoxicillin/clavulanic acid for eradication therapy. For postexposure prophylaxis, recommended drugs are trimethoprim/sulfamethoxazole or co-amoxiclav. To improve the timely diagnosis of melioidosis and glanders, further development and wide distribution of rapid diagnostic assays were also recommended. Standardized animal models and B. pseudomallei strains are needed for further development of therapeutic options. Training for laboratory technicians and physicians would facilitate better diagnosis and treatment options.
The Sheepbed member of the Yellowknife Bay formation in Gale crater contains millimeter‐scale nodules that represent an array of morphologies unlike those previously observed in sedimentary deposits ...on Mars. Three types of nodules have been identified in the Sheepbed member in order of decreasing abundance: solid nodules, hollow nodules, and filled nodules, a variant of hollow nodules whose voids have been filled with sulfate minerals. This study uses Mast Camera (Mastcam) and Mars Hand Lens Imager (MAHLI) images from the Mars Science Laboratory Curiosity rover to determine the size, shape, and spatial distribution of the Sheepbed nodules. The Alpha Particle X‐Ray Spectrometer (APXS) and ChemCam instruments provide geochemical data to help interpret nodule origins. Based on their physical characteristics, spatial distribution, and composition, the nodules are interpreted as concretions formed during early diagenesis. Several hypotheses are considered for hollow nodule formation including origins as primary or secondary voids. The occurrence of concretions interpreted in the Sheepbed mudstone and in several other sedimentary sequences on Mars suggests that active groundwater systems play an important role in the diagenesis of Martian sedimentary rocks. When concretions are formed during early diagenetic cementation, as interpreted for the Sheepbed nodules, they have the potential to create a taphonomic window favorable for the preservation of Martian organics.
Key Points
Three types of nodules are observed in the Sheepbed mudstoneSheepbed nodules are interpreted as early diagenetic concretionsAuthigenic mineral precipitation was an important diagenetic process on Mars
To our knowledge, environmental isolation of Burkholderia pseudomallei, the causative agent of melioidosis, from the continental United States has not been reported. We report a case of melioidosis ...in a Texas resident. Genomic analysis indicated that the isolate groups with B. pseudomallei isolates from patients in the same region, suggesting possible endemicity to this region.
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