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Cu2ZnSnSe4 films were prepared by selenization of metallic precursors obtained by a new wet process involving metal formates. Cu(HCOO)2 and Zn(HCOO)2 were used as copper and zinc sources respectively, while tin was introduced as a methoxide.The elemental analysis of the resulting absorber layers revealed a very low carbon content (less than 0.2wt%), which is believed to be a feature that chemical methods need to have in order to stand out as valuable alternatives to high-vacuum processes in this field. Solar cells with efficiencies of up to 2.39% with Voc of 207mV, a Jsc of 31.2mA/cm2 and a fill factor of 37.1% were achieved for these copper-poor CZTSe absorbers.

Organic-rich shales of the German Wealden, Lower Cretaceous, are a target for gas and oil shale exploration in Germany. Results of published organic petrographic investigations as well as oil shows and hydrocarbon gases extracted at the historical Lüdersfeld shaft of the Stadthagen syncline confirm the hydrocarbon potential of the Wealden sediments at the eastern margin of the Lower Saxony Basin. These former observations suggest that the shales of the eastern subbasin that comprise several hundreds of meters of thickness have reached thermal maturities compatible of the oil and gas generation windows. We present results of a surface geochemical study in which seventeen outcrop samples collected along a profile across the Stadthagen syncline (Bückeberge to Rehburg anticline) have been used for re-assessment of the hydrocarbon potential of the Wealden sub-basin. The analytical methods comprise porosity measurements, elemental analysis (x-ray fluorescence, total and organic carbon and total sulfur analyses), Rock- Eval pyrolysis, hydrocarbon extraction, fractionation of extracted hydrocarbons and gas chromatography on aliphatic fractions as well as stable carbon isotope analyses and gas geochemical investigations . The investigated Wealden sediments comprise sandstones and shales and the latter contain high relative concentrations of carbon with an average of 3.2 wt.-%. Rock-Eval pyrolysis suggests variable contributions of different types of organic organic matter (land plant, phytoplankton). The depositional environment of the sediments was predominantly oxic with the exception of three samples that were deposited under dysoxic to anoxic conditions. Thermal maturities range from the oil to the wet gas window (samples from the basin center). Two samples from the Rehburg anticline contain phytoplankton dominated kerogens and show thermal maturities of the oil window, the latter also confirmed by stable isotope geochemistry of extracted hydrocarbon gases. Hydrogen indi

The Maqarin site in Jordan has been investigated for three decades as a natural analogue for the long term changes of materials in contact with hyper-alkaline solutions. Similar processes are expected in radioactive waste disposal sites, where cement based materials are in contact with natural rocks or other e.g. clay based materials. In this context, a numerical reactive transport model was used to study local geochemical alterations and induced porosity changes for the Maqarin marl rock in contact with the hyper-alkaline solution. The geochemical setup for the rock mineralogy and the pore water was calibrated to match measurements from the Maqarin site. The setup includes several clay and zeolite minerals, considers cation exchange processes, and a state-of-the-art model for cement phases. Similar to earlier calculations by Steefel and Lichtner (1998) who used a much simpler geochemical model, the pore clogging occurred after several hundred years at a distance of 5–10 mm from the contact to the hyper-alkaline solution. In our calculations, this was caused by a massive precipitation of ettringite and C–S–H minerals. We performed a sensitivity study by varying the intrinsic diffusion coefficient, the Archie’s law exponential factor, and the mineral surface area available for dissolution and precipitation. We found that the dissolution of clay minerals controls the availability of Al, which is needed for ettringite and C–S–H phase precipitation. Thus, the amount and kinetically controlled dissolution of clay minerals controls the spatial and temporal evolution of porosity changes. The simulations reveal that neither cation exchange processes nor the formation of zeolite minerals strongly influence the geochemical evolution of the system.

Four seep sites located within an 20 km2 area offshore Georgia (Batumi seep area, Pechori Mound, Iberia Mound, and Colkheti Seep) show characteristic differences with respect to element concentrations, and oxygen, hydrogen, strontium, and chlorine isotope signatures in pore waters, as well as impregnation of sediments with petroleum and hydrocarbon potential. All seep sites have active gas seepage, near surface authigenic carbonates and gas hydrates. Cokheti Seep, Iberia Mound, and Pechori Mound are characterized by oil-stained sediments and gas seepage decoupled from deep fluid advection and bottom water intrusion induced by gas bubble release. Pechori Mound is further characterized by deep fluid advection of lower salinity pore fluids. The Pechori Mound pore fluids are altered by mineral/water reactions at elevated temperatures (between 60 and 110 °C) indicated by heavier oxygen and lighter chlorine isotope values, distinct Li and B enrichment, and K depletion. Strontium isotope ratios indicate that fluids originate from late Oligocene strata. This finding is supported by the occurrence of hydrocarbon impregnations within the sediments. Furthermore, light hydrocarbons and high molecular weight impregnates indicate a predominant thermogenic origin for the gas and oil at Pechori Mound, Iberia Mound, and Colkheti Seep. C15+ hydrocarbons at the oil seeps are allochtonous, whereas those at the Batumi seep area are autochthonous. The presence of oleanane, an angiosperm biomarker, suggests that the hydrocarbon source rocks belong to the Maikopian Formation. In summary, all investigated seep sites show a high hydrocarbon potential and hydrocarbons of Iberia Mound, Colkheti Seep, and Pechori Mound are predominantly of thermogenic origin. However, only at the latter seep site advection of deep pore fluids is indicated.

Clays and clay rocks are considered viable geotechnical barriers in radioactive waste disposal. One reason for this is the propensity for cation exchange reactions in clay minerals to retard the migration of radionuclides. Although another retardation mechanism, namely the incorporation of radionuclides into sulfate or carbonate solid solutions, has been known for a long time, only recently has it been examined systematically. In this work, we investigate the competitive effect of both mechanisms on the transport of radium (Ra) in the near-field of a low- and intermediate level nuclear waste repository. In our idealized geochemical model, numerical simulations show that barium (Ba) and strontium (Sr) needed for Ra sulfate solid solutions also partition to the cation exchange sites of montmorillonite (Mont), which is the major mineral constituent of bentonite that is used for tunnel backfill. At high Mont content, most Ra tends to attach to Mont, while incorporation of Ra in sulfate solid solutions is more important at low Mont content. To explore the effect of the Mont content on the transport of radium, a multi-component reactive transport model was developed and implemented in the scientific software OpenGeoSys-GEM. It was found that a decrease of fixation capacity due to low Mont content is compensated by the formation of solid solutions and that the migration distance of aqueous Ra is similar at different Mont/water ratios.

The Makran accretionary complex shows a distinct bottom-simulating reflector, indicating a thick gas-hydrate-bearing horizon between the deformational front and about 1350 m water depth which seals off the upward flow of gas-charged fluids. A field of presently inactive mud diapirs with elevations up to 65 m was discovered in the abyssal plain seawards of the deformation front, suggesting that in the past conditions were favorable for periodic but localized vigorous mud diapirism. Regional destabilization of the gas hydrate leading to focused flow was observed where deep-penetrating, active faults reach the base of the gas-hydrate layer, as in a deeply incised submarine canyon (2100–2500 m water depth). At this location we discovered seeps of methane and H2S-rich fluids associated with chemoautotrophic vent faunas (e.g., Calyptogena sp.). Driven by the accretionary wedge dynamics, the landward part of the gas-hydrate layer below the Makran margin is being progressively uplifted. Due to reduced hydrostatic pressure and rising ocean bottom-water temperatures, gas hydrates are progressively destabilized and dissociated into hydrate water, methane and H2S. Sediment temperatures lie outside the methane stability field wherever water depth is less than 800 m. Above this depth, upward migration of fluids to the seafloor is unimpeded, thus explaining the abundance of randomly distributed gas seeps observed at water depths of 350 to 800 m.

During the period 1978-1988, the research vessel SONNE made ten cruises studying the geological structure, the geological development and the hydrocarbon potential of continental margins and of marginal seas in the following areas: Western Coral Sea, Arafura Sea, Lord Howe Rise, Makassar Strait, West Tasmania, South Tasman Rise, East China Sea, Red Sea, South China Sea, Sulu Sea and Celebes Sea., During the period 1978-1988, the research vessel SONNE made ten cruises studying the geological structure, the geological development and the hydrocarbon potential of continental margins and of marginal seas in the following areas: Western Coral Sea, Arafura Sea, Lord Howe Rise, Makassar Strait, West Tasmania, South Tasman Rise, East China Sea, Red Sea, South China Sea, Sulu Sea and Celebes Sea.