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Micro‐ R aman Imaging of Planetary Analogs: Nanoscale Characterization of Past and Current Processes

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Abstract

Raman spectroscopic imaging facilitates the detection of submicron‐scale features to identify their composition with the added benefit of visualizing their spatial relationships and textures. This powerful technique has proven useful in ascertaining the origins of and reconstructing the evolution of solar system materials through the characterization of macromolecular carbon and mineral assemblages in meteorites, interplanetary dust particles (IDPs), and terrestrial rocks. In Raman imaging microscopy the Raman instrument is mated with an optical microscope to achieve a spatial resolution ∼300 nm with the capability of resolving sample features on the micron and submicron spatial scales. In preparation for surface exploration and sample return missions of solar system bodies, planetary scientists rely on comparative analog studies of samples from terrestrial environments. Geologic deposits on Earth and other planetary bodies undergo several iterations of geochemical change over time resulting in often subtle structural and compositional differences that can obscure the origins of those deposits. The origins, formation mechanisms, and evolution of both terrestrial and planetary deposits may be recorded in different forms of organic compounds and mineral assemblages, often as barely discernible nanocrystalline phases, inclusions, and mineral intergrowths. Raman spectroscopic imaging is an excellent tool with which to visualize the relationships between different planetary minerals and to detect the subtle differences, especially when many of the same organic compounds and minerals occur in so many different types of planetary environments. It will certainly continue to play a significant role in new discoveries pertaining to understanding the evolution of the solar system, potentially habitable worlds, and life beyond Earth.

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... This could be an additional pathway involving mineral precipitation via both abiotic and biotic processes. This will be explored further with thin section analyses where these process-driven associations can be revealed in higher detail [45,46]. Microbial mats, lichen communities, and mosses all co-colonize the basalts along the edge of Hveragil stream, providing a consortium of potential cyanate producers and consumers. ...
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Carbonate rocks record the oldest forms of life on Earth, and their geologic reconstruction requires multiple methods to determine physical and chemical processes before conclusions of ancient biosignatures are made. Since crystal orientation within rock fabric may be used to infer geologic settings, we present here a complementary Raman method to study the orientation of calcite (CaCO3) and dolomite [CaMg (CO3)2] minerals. The relative peak intensity ratio of the carbonate lattice Eg modes T and L reveals the crystallographic orientation of calcite and dolomite with respect to the incident light polarization. Our results for calcite show that when the incident laser light propagates down the crystallographic a/b axis: (1) the L mode is always greater in intensity than the T mode (IT < IL), and (2) the spectra are most intense at 45° and least intense at 90° polarization angles measured from around the c axis. Our results for dolomite show that (1) IT > IL when the incident light propagation is down the crystallographic c axis and (2) IT < IL when the incident light propagation is down the crystallographic a/b axis. This study reveals mineral orientation variation related to deposition and paragenesis within limestone and dolostone samples. The method presented yields information related to growth and deformation during diagenetic and metamorphic alteration and may be used in research seeking to identify the fabric parameters of any calcite or dolomite containing rock. The compositional and structural data obtained from Raman mapping is useful in structural geology, materials science, and biosignature research.
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Raman spectroscopy was used to evaluate rank for a series of coals collected adjacent to an igneous intrusion. For these intruded coals, Raman parameters for collotelinite and its coked equivalent show complex changes during the transformation from low to very high levels of maturity (with vitrinite reflectance increasing from 0.55% to 5.0%). With increasing coal rank up to anthracite-level reflectance, the Raman spectra show a decrease in both G band full width at half maximum (FWHM) and D band intensity. The D band shape becomes increasingly asymmetric during the bituminization and de-bituminization stages, whereas in the anthracitization stage, the width of the D and G bands continues to decrease while D band intensity increases. In meta-anthracites (as seen in the ancillary Hunan samples), the G band has a low intensity and undergoes an apparent broadening due to the presence of the D2 band that occurs as a shoulder on the G band. Differences in Raman spectral parameters for vitrinite and inertinite macerals suggest differences in molecular structure between the macerals; as such, the heterogeneous nature of coal may affect Raman spectral results significantly if different maceral types are not considered. Within individual samples, Raman spectra indicate a high level of structural homogeneity between and within vitrinite particles, allowing assessment of differences between samples of different ranks. For vitrinite, the Raman spectral parameters G FWHM and DAs/GA (Area(1100-s)/Area(s-1650), s is the saddle point between 1100 cm⁻¹ and 1650 cm⁻¹) are highly correlated (R² > 0.9) with vitrinite reflectance (Rr) and maximum alteration temperature (Tpeak), and allow establishment of geothermometers over the temperature range of ~70–300 °C that can be used to evaluate temperatures attained in intruded coals.
Article
Ancient veins of calcium sulfate minerals (anhydrite, bassanite, and gypsum) deposited by subsurface aqueous fluids crosscut fluviolacustrine sedimentary rocks at multiple localities on Mars. Although these veins have been considered an attractive target for astrobiological investigation, their potential to preserve biosignatures is poorly understood. Here, we report the presence of biogenic authigenic pyrite in a fibrous gypsum vein of probable Cenozoic emplacement age from Permian lacustrine rocks in Northwest England. Pyrite occurs at the vein margins and displays a complex interfingering boundary with the surrounding gypsum suggestive of replacive authigenic growth. Gypsum-entombed carbonaceous material of probable organic origin was also identified by Raman spectroscopic microscopy in close proximity to the pyrite. Spatially resolved ion micro-probe (SIMS) measurements reveal that the pyrite sulfur isotope composition is consistently very light (d 34 S VCDT =-30.7&). Comparison with the sulfate in the vein gypsum (d 34 S VCDT = +8.5&) indicates a frac-tionation too large to be explained by nonbiological (thermochemical) sulfate reduction. We infer that the pyrite was precipitated by microorganisms coupling the reduction of vein-derived sulfate with the oxidation of wall-derived organic matter. This is the first evidence that such veins can incorporate biosignatures that remain stable over geological time, which could be detected in samples returned from Mars.
Article
This paper focuses on the post-accretion history of CV3 chondrites, through a combination of petrographic and mineralogical characterization, magnetic measurements, spectral (Raman and Infrared) and thermo-gravimetric analysis of 31 meteorites (including 7 falls, 21 Antarctic and 3 non-Antarctic finds) spanning a wide metamorphic range. We classify the 21 Antarctic chondrites and the Bukhara fall into the CVRed, CVOxA, and CVOxB subgroups. We establish quantitative parameters relevant for this sub-classification. In comparison to CVOx, CVRed chondrites are characterized by (i) a lower abundance of matrix, (ii) a higher abundance of metal, (iii) the presence of Ni-poor sulfides. In comparison to CVOxB, CVOxA are characterized by (i) similar matrix abundance, (ii) a higher abundance of metal, (iii) the presence of metal almost exclusively under the form of awaruite, (iv) lower Ni content of sulfides, (v) lower magnetic susceptibility and saturation remanence. Both CVOx (CVOxA and CVOxB) and CVRed experienced aqueous alteration, and contain oxyhydroxides and phyllosilicates. We show that the abundance of these hydrated secondary minerals observed today in individual CV chondrites decreases with their peak metamorphic temperature. This is interpreted either as partial dehydration of these secondary minerals or limited hydration due to the rapid exhaustion of the water reservoir during parent body thermal metamorphism. Moreover, the lower abundance of oxyhydroxides (that have a lower thermal stability than phyllosilicates and may in large part postdate the peak of thermal metamorphism) in more metamorphosed CV chondrites is interpreted as lower availability of aqueous fluids during retrograde metamorphism in these meteorites. Lastly, we show that in comparison to CVOxB, CVOxA are systematically (i) more metamorphosed, (ii) less hydrated, (iii) depleted in ferromagnetic minerals, (iv) but enriched in metal in the form of secondary awaruite. CVOxA may be thermally metamorphosed CVOxB. CVRed are significantly different from CVOx (matrix abundances, alteration products, opaque minerals), but span the same wide metamorphic range. This could be indicative of a laterally heterogeneous CV parent body, or suggest the existence of distinct parent bodies for CVOx and CVRed chondrites.
Article
Earth's carbon budget is central to our understanding of the long-term co-evolution of life and the planet. Direct observations of surface reservoirs allow for the detailed quantification of their carbon content. However, the carbon content of Earth's deep interior remains poorly constrained. Here we study olivine-hosted melt inclusions from two Icelandic eruptions, with those from the Miðfell eruption allowing us to investigate the carbon content of the deep mantle. Comparison with the previously studied Borgarhraun eruption highlights the presence of deep, plume-sourced mantle material within the Miðfell source region. Miðfell contains trace element-depleted melt inclusions undersaturated in CO2, which have high CO2/Ba () and CO2/Nb (), though some inclusions preserve even greater relative carbon enrichment. These observations allow us to reconstruct the CO2 content of the bulk Miðfell source as being . By identifying that Miðfell is a mixture of depleted and deep mantle components, we can estimate a CO2 content for the deep mantle component of ; a concentration that is over ten times higher than depleted MORB mantle estimates. Assuming that the deep mantle component identified in Miðfell is representative of a global reservoir, then with our new CO2 estimate and by considering a range of representative mantle fractions for this reservoir, we calculate that it contains up to 14 times more carbon than that of the atmosphere, oceans, and crust combined. Our result of elevated CO2/Ba and CO2/Nb ratios, and carbon enrichment support geochemical bulk Earth carbon models that call for the presence of carbon-rich deep mantle domains to balance Earth's relatively carbon-poor upper mantle and surface environment.
Article
The Color Alteration Index (CAI) of conodont specimens is commonly used for identifying the maximum temperature to which units of sedimentary rock, particularly carbonates, have been heated. Observable color variations in these fossils are thought to be a result of the thermally-induced structural evolution of organic carbonaceous matter (CM). Such temperature history information is extremely valuable for applications in hydrocarbon exploration as well as for constraining other temperature-related geological processes in sedimentary systems. However, the identification of CAI depends on the qualitative visual assessment of color, which, along with a host of other potential complications, may yield inaccurate determinations of maximum temperature. Raman spectroscopy allows thermally-induced structural changes in CM to be quantified, and it has been used to estimate the thermal maturity in metasedimentary rocks for almost two decades. Here, we use Raman spectroscopy of carbonaceous material (RSCM) in conodont specimens and their Mississippian to Upper Triassic host rocks from British Columbia, Canada, to estimate maximum temperatures based on the transformation (structural reorganization) of disordered carbon to graphite. This study demonstrates that the maximum temperatures experienced by conodont specimens, as calculated from RSCM using the Iterative Fitting of Raman Spectra (IFORS) technique, correlate well with CAI but lie outside the suggested ranges in some instances. This may be due to complex thermal histories of these conodont specimens or the influence of diagenetic alteration, not thermal histories, on conodont color. We recommend the application of Raman spectroscopic analyses of CM in conodonts and their host rocks to obtain more confident, accurate, and precise estimations of maximum temperature that are independent of CAI.
Article
To date, only five natural carbonate minerals of calcite structure have been studied by Raman spectroscopy. These include calcite (CaCO3), magnesite (MgCO3), siderite (FeCO3), smithsonite (ZnCO3), and rhodochrosite (MnCO3). Thus far, only synthetic compounds of otavite (CdCO3), spherocobaltite (CoCO3), and gaspeite (NiCO3) have been investigated by Raman spectroscopy. However, the Raman spectra of natural otavite, spherocobaltite, and gaspeite have yet to be interpreted and compared with the Raman spectra of the other five natural carbonate minerals of calcite structure. This work has been undertaken to fill this gap and provide a comparison and interpretation of Raman spectra representative of all the eight natural carbonate minerals of calcite structure. The data here show that the carbonate Eg (T) phonon shifts are due to influences from the nearest neighbor distance; that is, M‐O, and different ionic radii of the divalent metal cation, as shown graphically by a strong correlation (r2 = 0.87 and 0.91, respectively). Using this graphical approach, we have developed a Raman spectroscopic model based on the equation, y = −2.067x + 356.2 (±5 pm) to calculate the ionic radii of the divalent metal cation present within the mineral and hence affording the identification and discrimination of calcite‐group minerals based on the band position of the Eg (T) mode. Only five natural carbonate minerals of calcite structure, that is calcite, magnesite, siderite, smithsonite, and rhodochrosite, have been studied by Raman spectroscopy. However, the Raman spectra of otavite and spherocobaltite have yet to be interpreted. Here we show that the carbonate Eg (T) phonon shifts are due to nearest neighbor distance and different ionic radii, which show strong correlation and can be used to identify carbonate minerals of calcite structure.
Article
An important question regarding the formation of the solar system is how planetary bodies developed from dust and ice into the planets and planetary bodies. A particularly interesting topic is the thermal evolution of carbonaceous chondrites and volatile-rich clasts that could have originated from CM- and CI-like parent bodies. Two types of these volatile-rich clasts, which are a particular type of dark clasts, can be found. These clasts are mineralogically very similar to CM and CI chondrites and can occasionally be found in achondritic meteorites. Mineral assemblages suggest that both CM and CI chondrites as well as volatile-rich clasts experienced low peak temperatures. However, these mineral assemblages only offer large estimated temperature ranges to describe the thermal history of CM and CI chondrites, and the thermal history of volatile-rich clasts has not been previously described. In this study, to gain a better understanding of the thermal history of both CM and CI chondrites and volatile-rich clasts, we estimated peak temperatures of 30 volatile-rich clasts (16 CI-, and 14 CM-like) in 10 different host meteorites (4 polymict ureilites, 5 polymict eucrites and 1 howardite) by Raman carbon thermometry. An automated method was developed in order to describe over 4000 collected Raman spectra using four pseudovoigt functions. The full width half maximum (FWHM) of the D1-band was then used to calculate peak temperatures. Results were then compared to Raman data of 8 different well-studied carbonaceous chondrites (including CI and CM chondrites) to evaluate the suggestion that volatile-rich clasts are composed of similar material to the equivalent CI and CM chondrites. Our results show that the peak temperatures experienced by CI-like clasts range between 30–110 °C with an average of about 65 ± 25 °C; the peak temperatures experienced by CM-like clasts range from 50 to 110 °C with an average of about 70 ± 25 °C. Six of the 8 studied carbonaceous chondrites (CM, CI, CR or C2ungr) also plot in the same low-temperature range between 50 °C and 75 °C and can thus be considered to have formed under similar temperature conditions as the volatile-rich clasts. This is in agreement with previous suggestions, based on their mineral compositions that volatile-rich clasts and CI and CM carbonaceous chondrites are composed of similar materials. The peak temperatures for carbonaceous chondrites determined in this study considerably reduce the range of temperature estimates proposed previously for these chondrites by different methods. By highlighting the ability of our methodology to evaluate data in an automated way, this study shows that Raman carbon thermometry is a good analytical technique for obtaining information about peak temperatures in small and delicate samples.
Article
Several of the Middle Ordovician polymetallic Zn-Pb-Cu-Ag volcanogenic massive sulfide deposits of the Bathurst Mining Camp (BMC), northern New Brunswick, Canada, were investigated using laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS). Quantitative and semi-quantitative analysis of a suite of fluid-mobile elements (As, Bi, Cd, Hg, In, Ga, Ge, Sb, Se, Sn, Te, and Tl) was conducted in pyrite, chalcopyrite, pyrrhotite, sphalerite, galena, arsenopyrite, and tetrahedrite-tennantite. The occurrence of fluid-mobile elements within different sulfide assemblages shows mineral-specific characteristics and genetically-controlled features. Our results show that subsequent metamorphism and deformation modified and redistributed the fluid-mobile elements at the mineral scale, which is texturally controlled. In addition, the fluid-mobile elements within sphalerite and chalcopyrite distinctly differentiate the hydrothermal facies. The chemical variation of sphalerite from the BMC is distinct in terms of metamorphic input compared to other VMS deposits at different metamorphic conditions.
Article
Measuring martian organics and methane The Curiosity rover has been sampling on Mars for the past 5 years (see the Perspective by ten Kate). Eigenbrode et al. used two instruments in the SAM (Sample Analysis at Mars) suite to catch traces of complex organics preserved in 3-billion-year-old sediments. Heating the sediments released an array of organics and volatiles reminiscent of organic-rich sedimentary rock found on Earth. Most methane on Earth is produced by biological sources, but numerous abiotic processes have been proposed to explain martian methane. Webster et al. report atmospheric measurements of methane covering 3 martian years and found that the background level varies with the local seasons. The seasonal variation provides an important clue for determining the origin of martian methane. Science , this issue p. 1096 , p. 1093 ; see also p. 1068
Article
We determined an empirical correlation that relates the Amide I vibrational band frequencies of the glutamine (Q) side chain to the strength of hydrogen bonding, van der Waals, and Lewis acid-base interactions of its primary amide carbonyl. We use this correlation to determine the Q side chain carbonyl interaction enthalpy (ΔHint) in monomeric and amyloid-like fibril conformations of D2Q10K2 (Q10). We independently verified these ΔHint values through molecular dynamics simulations that showed excellent agreement with experiments. We find that side chain-side chain and side chain-peptide backbone interactions in fibrils and monomers are more enthalpically favorable than are Q side chain-water interactions. Q10 fibrils also show a more favorable ΔHint for side chain-side chain interactions compared to backbone-backbone interactions. This work experimentally demonstrates that inter-amide side chain interactions are important in the formation and stabilization of polyQ fibrils.
Article
UV resonance Raman (UVRR) spectroscopy is a powerful tool for investigating the structure of biological molecules, such as proteins. Numerous UVRR spectroscopic markers that provide information on the structure and environment of the protein backbone and of amino acid side chains have recently been discovered. Combining these UVRR markers with hydrogen-deuterium exchange and advanced statistics is a powerful tool for studying protein systems, including the structure and formation mechanism of protein aggregates and amyloid fibrils. These techniques allow crucial new insights into the structure and dynamics of proteins, such as polyglutamine peptides, which are associated with 10 different neurodegenerative diseases. Here we summarize the spectroscopic structural markers recently developed and the important insights they provide.
Article
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 (258C) and eogenetic conditions (378C, 708C, and 1008C). 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, b-carotene, and scytonemin were identified in the lower temperature regimes, but were not easily detected in the samples incubated at 1008C. 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.
Article
The Earth and other rocky bodies in the inner solar system contain significantly less carbon than the primordial materials that seeded their formation. These carbon-poor objects include the parent bodies of primitive meteorites, suggesting that at least one process responsible for solid-phase carbon depletion was active prior to the early stages of planet formation. Potential mechanisms include the erosion of carbonaceous materials by photons or atomic oxygen in the surface layers of the protoplanetary disk. Under photochemically generated favorable conditions, these reactions can deplete the near-surface abundance of carbon grains and polycyclic aromatic hydrocarbons by several orders of magnitude on short timescales relative to the lifetime of the disk out to radii of ~20-100+ au from the central star depending on the form of refractory carbon present. Due to the reliance of destruction mechanisms on a high influx of photons, the extent of refractory carbon depletion is quite sensitive to the disk's internal radiation field. Dust transport within the disk is required to affect the composition of the midplane. In our current model of a passive, constant-alpha disk, where alpha = 0.01, carbon grains can be turbulently lofted into the destructive surface layers and depleted out to radii of ~3-10 au for 0.1-1 um grains. Smaller grains can be cleared out of the planet-forming region completely. Destruction may be more effective in an actively accreting disk or when considering individual grain trajectories in non-idealized disks.
Article
The mineralogy and texture of shock-induced melt veinlets and melt pockets in silicate inclusions in the Elga IIE iron meteorite have been studied by reflected-light optical microscopy, EMPA, SEM, Raman spectroscopy and TEM. The results suggest that Elga experienced two discrete impact events. The earlier event involved the collision of a metallic projectile with a silicate target and resulted in partial melting and recrystallization of the silicate material, forming schreibersite and oxide rims between the metal and silicate. The later impact event resulted in melt pockets in the silicate inclusions and was associated with fragmentation , melting, and brecciation of the rims and displacement of some fragments into the melt pockets. These fragments are shown to contain carbon-bearing phases: siderite and amorphous sp 2 carbon, which form car-bon–oxide, siderite–oxide, and siderite–schreibersite associations. The fact that the carbon-bearing fragments are spatially constrained to shock breccia and melt zones indicates that these fragments are genetically related to the impact process and that their carbon-bearing phases are of cosmic origin. Keywords: Elga meteorite, melt pockets, brecciation, shock metamorphism, siderite in an IIE iron meteorite, amorphous carbon in an iron IIE meteorite, TEM, Raman spectroscopy
Article
This review is intended to summarize the current observations of reduced carbon in Martian meteorites, differentiating between terrestrial contamination and carbon that is indigenous to Mars. Indeed, the identification of Martian organic matter is among the highest priority targets for robotic spacecraft missions in the next decade, including the Mars Science Laboratory and Mars 2020. Organic carbon compounds are essential building blocks of terrestrial life, so the occurrence and origin (biotic or abiotic) of organic compounds on Mars is of great significance; however, not all forms of reduced carbon are conducive to biological systems. This paper discusses the significance of reduced organic carbon (including methane) in Martian geological and astrobiological systems. Specifically, it summarizes current thinking on the nature, sources, and sinks of Martian organic carbon, a key component to Martian habitability. Based on this compilation, reduced organic carbon on Mars, including detections of methane in the Martian atmosphere, is best described through a combination of abiotic organic synthesis on Mars and infall of extraterrestrial carbonaceous material. Although conclusive signs of Martian life have yet to be revealed, we have developed a strategy for life detection on Mars that can be utilized in future life-detection studies.
Article
Carbonates are key minerals for understanding ancient Martian environments because they are indicators of potentially habitable, neutral-to-alkaline water and may be an important reservoir for paleoatmospheric CO2. Previous remote sensing studies have identified mostly Mg-rich carbonates, both in Martian dust and in a Late Noachian rock unit circumferential to the Isidis basin. Here we report evidence for older Fe- and/or Ca-rich carbonates exposed from the subsurface by impact craters and troughs. These carbonates are found in and around the Huygens basin northwest of Hellas, in western Noachis Terra between the Argyre basin and Valles Marineris, and in other isolated locations spread widely across the planet. In all cases they cooccur with or near phyllosilicates, and in Huygens basin specifically they occupy layered rocks exhumed from up to ~5 km depth. We discuss factors that might explain their observed regional distribution, arguments for why carbonates may be even more widespread in Noachian materials than presently appreciated and what could be gained by targeting these carbonates for further study with future orbital or landed missions to Mars.
Article
This is the final report on the nomenclature of pyroxenes by the Subcommittee on Pyroxenes established by the Commission on New Minerals and Mineral Names of the International Mineralogical Association. The recommendations of the Subcommittee as put forward in this report have been formally accepted by the Commission. Accepted and widely used names have been chemically defined, by combining new and conventional methods, to agree as far as possible with the consensus of present use. Twenty names are formally accepted, among which thirteen are used to represent the end-members of definite chemical compositions. In common binary solid-solution series, species names are given to the two end-members by the “50% rule”. Adjectival modifiers for pyroxene mineral names are defined to indicate unusual amounts of chemical constituents. This report includes a list of 105 previously used pyroxene names that have been formally discarded by the Commission.
Article
Stromatolites composed of apatite occur in post-Lomagundi-Jatuli successions (late Palaeoproterozoic) and suggest the emergence of novel types of biomineralization at that time. The microscopic and nanoscopic petrology of organic matter in stromatolitic phosphorites might provide insights into the suite of diagenetic processes that formed these types of stromatolites. Correlated geochemical micro-analyses of the organic matter could also yield molecular, elemental and isotopic compositions and thus insights into the role of specific micro-organisms among these communities. Here, we report on the occurrence of nanoscopic disseminated organic matter in the Palaeoproterozoic stromatolitic phosphorite from the Aravalli Supergroup of north-west India. Organic petrography by micro-Raman and Transmission Electron Microscopy demonstrates syngeneity of the organic matter. Total organic carbon contents of these stromatolitic phosphorite columns are between 0.05 and 3.0 wt% and have a large range of δ(13) Corg values with an average of -18.5‰ (1σ = 4.5‰). δ(15) N values of decarbonated rock powders are between -1.2 and +2.7‰. These isotopic compositions point to the important role of biological N2 -fixation and CO2 -fixation by the pentose phosphate pathway consistent with a population of cyanobacteria. Microscopic spheroidal grains of apatite (MSGA) occur in association with calcite microspar in microbial mats from stromatolite columns and with chert in the core of diagenetic apatite rosettes. Organic matter extracted from the stromatolitic phosphorites contains a range of molecular functional group (e.g. carboxylic acid, alcohol, and aliphatic hydrocarbons) as well as nitrile and nitro groups as determined from C- and N-XANES spectra. The presence of organic nitrogen was independently confirmed by a CN(-) peak detected by ToF-SIMS. Nanoscale petrography and geochemistry allow for a refinement of the formation model for the accretion and phototrophic growth of stromatolites. The original microbial biomass is inferred to have been dominated by cyanobacteria, which might be an important contributor of organic matter in shallow-marine phosphorites.