Variability in the sulfur isotopic composition in sediments can reflect atmospheric, geologic and biological processes. Evidence for ancient fluvio-lacustrine environments at Gale crater on Mars and a lack of efficient crustal recycling mechanisms on the planet suggests a surface environment that was once warm enough to allow the presence of liquid water, at least for discrete periods of time, and implies a greenhouse effect that may have been influenced by sulfur-bearing volcanic gases. Here we report in situ analyses of the sulfur isotopic compositions of SO2 volatilized from ten sediment samples acquired by NASA's Curiosity rover along a 13 km traverse of Gale crater. We find large variations in sulfur isotopic composition that exceed those measured for Martian meteorites and show both depletion and enrichment in S-34. Measured values of delta S-34 range from -47 +/- 14 parts per thousand to 28 +/- 7 parts per thousand h, similar to the range typical of terrestrial environments. Although limited geochronological constraints on the stratigraphy traversed by Curiosity are available, we propose that the observed sulfur isotopic signatures at Gale crater can be explained by equilibrium fractionation between sulfate and sulfide in an impact-driven hydrothermal system and atmospheric processing of sulfur-bearing gases during transient warm periods.

Cyanobacteria are ubiquitous in a variety of modern habitats, and siliciclastic sediments in particular are home to a wide diversity of microbial communities. Benthic microbial mats, typically established by cyanobacteria on modern Earth, were likely prevalent on Archean Earth, yet explicit traces of their ancestors in Archean siliciclastic rocks are difficult to detect. To understand the taphonomy of benthic microbial mats in sandy, subaquatic environments, cyanobacterial mats were incubated for five months under a range of temperatures representative of ambient (25 degrees C) and eogenetic conditions (37 degrees C, 70 degrees C, and 100 degrees C). Cyanobacterial materials including trichomes, sheaths, and extracellular polymeric substances (EPS) were analyzed using scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and micro Raman spectroscopy. Textures were permineralized in all temperature regimes with phases that included mixed silicates, Na-carbonate, clays, gypsum-anhydrite, pyrrhotite, anatase, akaganeite, magnetite, natrojarosite, and ankerite. Pigments including chlorophyll, beta-carotene, and scytonemin were identified in the lower temperature regimes, but were not easily detected in the samples incubated at 100 degrees C. The morphological characteristics of trichomes and sheaths were maintained to some degree in all temperature regimes, but there was a higher relative abundance of EPS as temperatures increased. The profusion of EPS obscured the absolute differentiation between individual trichomes and sheaths at higher temperatures. The results indicate that over time, morphological, mineralogical, and carbonaceous features that formed at the end of these incubation experiments could collectively create the laminations characteristic of fossilized microbial mats found in sandstones throughout the geologic record. In Archean sandstones, where very little is preserved, these collective features may prove to be especially important in the detection of ancient life.

We describe the current state of the search for direct, surviving samples of early, inner Solar System fluids-fluid inclusions in meteorites. Meteoritic aqueous fluid inclusions are not rare, but they are very tiny and their characterization is at the state of the art for most analytical techniques. Meteoritic fluid inclusions offer us a unique opportunity to study early Solar System brines in the laboratory. Inclusion-by-inclusion analyses of the trapped fluids in carefully selected samples will, in the immediate future, provide us detailed information on the evolution of fluids as they interacted with anhydrous solid materials. Thus, real data can replace calculated fluid compositions in thermochemical calculations of the evolution of water and aqueous reactions in comets, asteroids, moons and the terrestrial planets.

The sample analysis at Mars instrument evolved gas analyzer (SAM-EGA) has detected evolved water, H-2, SO2, H2S, NO, CO2, CO, O-2, and HCl from two eolian sediments and nine sedimentary rocks from Gale Crater, Mars. These evolved gas detections indicate nitrates, organics, oxychlorine phase, and sulfates are widespread with phyllosilicates and carbonates occurring in select Gale Crater materials. Coevolved CO2 (160248-2373820gC((CO2))/g) and CO (113-320130 gC((CO))/g) suggest that organic C is present in Gale Crater materials. Five samples evolved CO2 at temperatures consistent with carbonate (0.32 +/- 0.05-0.70 +/- 0.1wt% CO3). Evolved NO amounts to 0.002 +/- 0.007-0.06 +/- 0.03wt% NO3. Evolution of O-2 suggests that oxychlorine phases (chlorate/perchlorate) (0.05 +/- 0.025-1.05 +/- 0.44wt% ClO4) are present, while SO2 evolution indicates the presence of crystalline and/or poorly crystalline Fe and Mg sulfate and possibly sulfide. Evolved H2O (0.9 +/- 0.3-2.5 +/- 1.6wt% H2O) is consistent with the presence of adsorbed water, hydrated salts, interlayer/structural water from phyllosilicates, and possible inclusion water in mineral/amorphous phases. Evolved H-2 and H2S suggest that reduced phases occur despite the presence of oxidized phases (nitrate, oxychlorine, sulfate, and carbonate). SAM results coupled with CheMin mineralogical and Alpha-Particle X-ray Spectrometer elemental analyses indicate that Gale Crater sedimentary rocks have experienced a complex authigenetic/diagenetic history involving fluids with varying pH, redox, and salt composition. The inferred geochemical conditions were favorable for microbial habitability and if life ever existed, there was likely sufficient organic C to support a small microbial population.

Bobdownsite, IMA number 2008-037, was approved as a new mineral by the Commission on New Minerals, Nomenclature and Classification (CNMNC) as the fluorine end-member of the mineral whitlockite. The type locality of bobdownsite is in Big Fish River, Yukon, Canada, and bobdownsite was reported to be the first mineral with essential monofluorophosphate (PO3F2-). The type specimen of bobdownsite has been reinvestigated by electron probe microanalysis (EPMA), and our data indicate that fluorine abundances are below detection in the mineral. In addition, we conducted detailed analysis of bobdownsite from the type locality by gas chromatography isotope ratio mass spectrometry, Raman spectroscopy, EPMA, and NMR spectroscopy. These data were compared with previously published data on synthetic monofluorophosphate salts. Collectively, these data indicate that bobdownsite is indistinguishable from whitlockite with a composition along the whitlockite-merrillite solid solution. Bobdownsite is therefore discredited as a valid mineral species. An additional mineral, krasnoite, has been purported to have monofluorophosphate components in its structure, but reexamination of those data indicate that F-in krasnoite forms bonds with Al, similar to OH-bonded to Al in perhamite. Consequently, krasnoite also lacks monofluorophosphate groups, and there are currently no valid mineral species with monofluorophosphate in their structure. We recommend that any future reports of new minerals that contain essential monofluorophosphate anions be vetted by abundance measurements of fluorine, vibrational spectroscopy (both Raman and FTIR), and where paramagnetic components are permissibly low, NMR spectroscopy. Furthermore, we emphasize the importance of using synthetic compounds containing monofluorophosphate anions as a point of comparison in the identification of minerals with essential monofluorophosphate. Structural data that yield satisfactory P-F bond lengths determined by X-ray crystallography, coupled with direct chemical analyses of fluorine in a material do not constitute sufficient evidence alone to identify a new mineral with essential monofluorophosphate.