Formation of secondary carbonates and native sulphur in sulphate-rich Messinian strata, Sicily

Microbially formed authigenic carbonates accompanied by native sulphur are present in the ‘Calcare Solfifero’ below a thick succession of gypsum deposited during the Messinian salinity crisis in Sicily. We sampled these carbonates and associated sulphur in five former sulphur mines to subject them to a detailed petrographic and geochemical study in order to explore their different modes of formation. Native sulphur formed in conjunction with microbial sulphate reduction,which is reflected in its depletion in 34S (δ34Svaluesas lowas−2‰vs. V-CDT) and an enrichment of 34S in the residual sulphate (δ34S values as high as+61‰). The oxidation of organic matter by sulphate reduction increased alkalinity, inducing precipitation of secondary carbonate minerals. A set of authigenic limestones lacking sulphate minerals, but characterized by pseudomorphs after gypsumand high δ18O values (as high as +9‰ vs. V-PDB) reflects syngenetic mineral formation within evaporitic settings. Low δ13C values (as low as −52‰ vs. V-PDB) reveal that these carbonate phases were formed by microbial sulphate reduction coupled to the oxidation of biogenic methane. Another set of authigenic carbonates that replaced sulphate minerals is typified by lowδ18O values (as lowas−4‰). These carbonates formed epigenetically during later diagenesis following compaction. Dissolution of gypsum or anhydrite by meteoric waters delivered the sulphate for microbial sulphate reduction. Lowcarbon isotope values of these carbonates (−29 to−5‰) indicate that carbonatewas derived fromthe oxidation of crude oil and possibly minormethane, partly involving different degrees of admixture of dissolved carbonate from other sources. Although the studied rocks with their vast amounts of secondary carbonate minerals and sulphur seem to indicate a similar genesis at first glance – having formed by biogeochemical transformations of sulphate and hydrocarbons – this study reveals that these processes can occur at different times in variable geological environments

Sedimentologic to metamorphic processes recorded in the high-pressure/low-temperature Mesozoic Rosetta Marble of Anatolia

© 2015, Springer-Verlag Berlin Heidelberg. Anatolia’s high-pressure metamorphic belts are characterized in part by a Neotethyan stratigraphic succession that includes a mid-Cretaceous hemi-pelagic marble sequence. This unit contains, towards its stratigraphic top, dm-to-m-long radiating calcitic rods forming rosette-like textures. Here, we refer to these features as “Rosetta Marble”. The remarkable textural similarity of non-metamorphic selenite crystals and radiating calcite rods in the Rosetta Marble strongly suggests that these textures represent pseudomorphs after selenites. Metamorphosed hemi-pelagic limestones, dominated by Rosetta selenite pseudomorphs, are alternating with siliceous meta-sediments containing relictic radiolaria tests. This stratigraphic pattern is indicative of transient phases characterized by evaporites precipitated from basinal brines alternating with non-evaporative hemi-pelagic deposition from normal-marine seawater. The regional distribution of Rosetta Marble exposures over 600 km is indicative of basin-scale evaporitic intervals. High-pressure, low-temperature metamorphism of these rocks is witnessed by Sr-rich (up to 3500 ppm), fibrous calcite pseudomorphs after aragonite and isolated aragonite inclusions in quartz. Peak metamorphic conditions of 1.2 GPa and 300–350 °C are attested by high-Si white mica thermobarometry. The Rosetta Marble case example examines the potential to unravel the complete history from deposition to diagenesis and metamorphism of meta-sedimentary rocks

Methanogens and Methanogenesis in Hypersaline Environments

Methanogenesis is controlled by redox potential and permanency of anaerobic conditions; and in hypersaline environments, the high concentration of terminal electron acceptors, particularly sulfate, is an important controlling factor. This is because sulfate-reducing microbes, compared with methanogens, have a greater affinity for, and energy yield from, competitive substrates like hydrogen and acetate. However, hypersalinity is not an obstacle to methylotrophic methanogenesis; in many cases hypersaline environments have high concentrations of noncompetitive substrates like methylamines, which derive from compatible solutes such as glycine betaine that is synthesized by many microbes inhabiting hypersaline environments. Also, depletion of sulfate, as may occur in deeper sediments, allows increased methanogenesis. On the other hand, increasing salinity requires methanogens to synthesize or take up more compatible solutes at a significant energetic cost. Acetoclastic and hydrogenotrophic methanogens, with their lower energetic yields, are therefore more susceptible than methylotrophic methanogens, which further explains the predominance of methylotrophic methanogens like Methanohalophilus and Methanohalobium spp. in hypersaline environments. There are often deviations from the picture outlined above, which are sometimes difficult to explain. Identifying the role of uncultivated Euryarchaeota in hypersaline environments, elucidating the effects of different ions (which have differential stress effects and potential as electron acceptors), and understanding the effects of salinity on all microbes involved in methane cycling will help us to understand and predict methane production in hypersaline environments. A good demonstration of this is a recent discovery of extremely haloalkaliphilic methanogens living in hypersaline lakes, which utilize the methyl-reducing pathway and form a novel class “Methanonatronarchaeia” in the Euryarchaeota

Frutexites-like structures formed by iron oxidizing biofilms in the continental subsurface (Äspö Hard Rock Laboratory, Sweden)

Stromatolitic iron-rich structures have been reported from many ancient environments and are often described as Frutexites, a cryptic microfossil. Although microbial formation of such structures is likely, a clear relation to a microbial precursor is lacking so far. Here we report recent iron oxidizing biofilms which resemble the ancient Frutexites structures. The living Frutexites-like biofilms were sampled at 160 m depth in the Äspö Hard Rock Laboratory in Sweden. Investigations using microscopy, 454 pyrosequencing, FISH, Raman spectroscopy, biomarker and trace element analysis allowed a detailed view of the structural components of the mineralized biofilm. The most abundant bacterial groups were involved in nitrogen and iron cycling. Furthermore, Archaea are widely distributed in the Frutexites-like biofilm, even though their functional role remains unclear. Biomarker analysis revealed abundant sterols in the biofilm most likely from algal and fungal origins. Our results indicate that the Frutexites-like biofilm was built up by a complex microbial community. The functional role of each community member in the formation of the dendritic structures, as well as their potential relation to fossil Frutexites remains under investigation.Open-Access-Publikationsfonds 201

Flow Chemistry Approaches Applied to the Synthesis of Saturated Heterocycles

Continuous-flow processing approaches are having a significant impact on the way we devise and perform chemical synthesis. Flow chemistry has repeatedly demonstrated numerous improvements with respect to synthesis efficiency, process safety and ease of reaction scale-up. In recent years flow chemistry has been applied with remarkable success to the generation of valuable target structures across a range of industries from basic bulk chemical manufacture and materials development to flavours, food and cosmetic applications. However, due to its earlier implementation, it has found so far many more advocates in areas of medicinal and agrochemical research and manufacture. In this review article, we summarise the key developments that continuous-flow synthesis has had in the area of saturated heterocycles, specifically focusing on approaches that generate these important entities from acyclic precursors