Tectonometamorphic evolution of the Koralm Complex (Eastern Alps): constraints from microstructures and textures of the ‘Plattengneis’ shear zone

Lattice preferred orientations (LPO) of quartz have been investigated along a south–north oriented section across the Plattengneis of the Koralm Complex (Eastern Alps). The Plattengneis forms an important shear zone within the Austroalpine nappe complex of the Eastern Alps, which has developed during the Cretaceous evolution of the Alpine orogen. The quartz c-axes form small circle distributions in the southernmost parts of the Koralm Complex, which represent the uppermost structural level of the Plattengneis. Further to the North two maxima between the Y and Z directions of the finite strain can be interpreted in terms of preferred slip on the rhomb planes. These fabrics continuously grade into (type I and type II crossed) girdle distributions in a northward direction. A strong maximum near the Y-axis with the tendency to be distributed along a single girdle, with three corresponding maxima of a-axes near the margin of the pole figure, can be observed in the central and northern parts. Such LPO are characteristic for both high grade metamorphic conditions and high finite strain. The microstructures display that the deformation within the Plattengneis shear zone was synmetamorphic. A continuous increase of peak temperatures (and pressure) from approximately 550 °C to approximately 750 °C from the South to the central parts can be inferred from geothermometric calculations. The temperatures then decrease to approximately 650 °C from the central parts to the North. The related pressures increase from 8 to 16 kbar, and then decrease to 10 kbar. The LPO changes that have been observed in the study area are best interpreted in terms of temperature dependence of the activation of glide systems within quartz aggregates. The temperature and pressure evolution may indicate that the central parts of the Koralm Complex have been exhumed by larger amounts than the northern and southern parts. This is also documented by the LPO evolution. Therefore, we assume that the Plattengneis shear zone formed during the exhumation of the Koralm Complex, and is related to the exhumation of high-pressure units in the footwall of this shear zone. Accordingly, the kinematics of the Plattengneis shear zone is rather extensional than thrust-related. The implications for the structural evolution of the Eastern Alps are shortly discussed.     

Facies architecture and sedimentology of a meandering fluvial system: a Palaeogene example from the Weisselster Basin, Germany

The Schleenhain open pit coal mine, located 30 km south of Leipzig, Germany, exposes Upper Eocene and Oligocene non-marine strata representing fluvial deposition in the centre of the Weisselster Basin. Active mining and successive cuts provided the rare opportunity to obtain a three-dimensional perspective of laterally extensive surface outcrops. These were used to construct a detailed fence diagram, which provided the basis for recognition of key architectural elements in the weakly consolidated meandering stream deposits. In addition to the eight basic architectural elements of Miall (1985 ), the element SL (shallow lake deposits) was newly defined and the element CH (channel) was subdivided into CHg (palaeo-river system) and CHk (small channel). The profiles contain parts of two fining-upward cycles, which are separated by an unconformity spanning the Early Oligocene. Deposits of the first cycle begin with transverse sand bars (downstream accretion deposits-DA) and point bars (lateral accretion deposits-LA). The upper part of the cycle is represented by overbank fines (OF) and the element SL, which consists of laterally discontinuous lenses of dark, plant-bearing, kaolinite-rich clays, that were deposited in shallow lakes adjacent to the active channel. Coal seams interlayered with palaeosols are the main constituents of element OF. Sheetlike bodies of medium to fine gravels (gravel bars and bedforms-GB) on an erosive coal surface mark the beginning of the second cycle. Dissolution of underlying Permian salts and sulphates prior to, during, and after the deposition of the Palaeogene strata caused the development of two synclines within the outcrop. Coal seams and clay horizons which thicken and dip towards the centre of the synclines, provide evidence for their chronological development.     

Transfer of results from reed research into practice as illustrated by reed protection measures in Berlin

There is great interest in solving the question of how far the successful establishment of common reed for shore restoration is influenced by genetically determined characteristics of different reed clones. For this purpose, ten reed clones were planted at six artificial sand banks in 1995, according to a special planting design. The growth and expansion performance of the clones was compared.The reed plants grew without significant stress in the first vegetation period, resulting in newly established reed stands in a very good condition at the end of the season. Despite the same site conditions at the experimental plots, the planted clones differed significantly in their morphology and stand structure. By comparison, reed plants of the same clone exhibited strong similarity on all experimental plots. These results appear to justify the assertion that, at least during the initial phase of establishing a reed stand, the development of stand structure is determined more by genetically controlled programmes than by site conditions. Only long-term investigations will be able to clarify to what extent stable stand structures are formed by genetically controlled programmes after polycormons reach maturity.     

A sequence stratigraphic model for the Lower Coal Measures (Upper Carboniferous) of the Ruhr district, north-west Germany

Upper Carboniferous Coal Measures strata have been interpreted traditionally in terms of cyclothems bounded by marine flooding surfaces (marine bands) and coal seams. Correlation of such cyclothems in an extensive grid of closely spaced coal exploration boreholes provides a robust stratigraphic framework in which to study the Lower Coal Measures (Namurian C–Westphalian A) of the Ruhr district, north-west Germany. Three distinct types of cyclothem are recognized, based on their bounding surfaces and internal facies architecture. (1) Type 1 cyclothems are bounded by marine bands. Each cyclothem comprises a thick (30–80 m), regionally extensive, coarsening-upward delta front succession of interbedded shales, siltstones and sandstones, which may be deeply incised by a major fluvial sandstone complex. The delta front succession is capped by a thin (<1 m), regionally extensive coal seam and an overlying marine band defining the top of the cyclothem. (2) Type 2 cyclothems are bounded by thick (≈1 m), regionally extensive coal seams with few splits. The basal part of a typical cyclothem comprises a thick (15–50 m), widespread, coarsening-upward delta front or lake infill succession consisting of interbedded shales, siltstones and sandstones. Networks of major (>5 km wide, 20–40 m thick), steep-sided, multistorey fluvial sandstone complexes erode deeply into and, in some cases, through these successions and are overlain by the coal seam defining the cyclothem top. (3) Type 3 cyclothems are bounded by regionally extensive coal seam groups, characterized by numerous seam splits on a local (0·1–10 km) scale. Intervening strata vary in thickness (15–60 m) and are characterized by strong local facies variability. Root-penetrated, aggradational floodplain heteroliths pass laterally into single-storey fluvial channel-fill sandstones and coarsening-upward, shallow lake infill successions of interbedded shales, siltstones and sandstones over distances of several hundred metres to a few kilometres. Narrow (<2 km) but thick (20–50 m) multistorey fluvial sandstone complexes are rare, but occur in a few type 3 cyclothems. Several cyclothems are observed to change character from type 1 to type 2 and from type 2 to type 3 up the regional palaeoslope. Consequently, we envisage a model in which each cyclothem type represents a different palaeogeographic belt within the same, idealized delta system, subject to the same allogenic and autogenic controls on facies architecture. Type 1 cyclothems are dominated by deltaic shorelines deposited during a falling stage and lowstand of sea level. Type 2 cyclothems represent the coeval lower delta plain, which was deeply eroded by incised valleys that fed the falling stage and lowstand deltas. Type 3 cyclothems comprise mainly upper delta plain deposits in which the allogenic sea-level control was secondary to autogenic controls on facies architecture. The marine bands, widespread coals and coal seam groups that bound these three cyclothem types record abandonment of the delta system during periods of rapid sea-level rise. The model suggests that the extant cyclothem paradigm does not adequately describe the detailed facies architecture of Lower Coal Measures strata. Instead, these architectures may be better understood within a high-resolution stratigraphic framework incorporating sequence stratigraphic key surfaces, integrated with depositional models derived from analogous Pleistocene–Holocene fluvio-deltaic strata.     

Heterogeneity preserving upscaling for heat transport in fractured geothermal reservoirs

In simulation of fluid injection in fractured geothermal reservoirs, the characteristics of the physical processes are severely affected by the local occurence of connected fractures. To resolve these structurally dominated processes, there is a need to develop discretization strategies that also limit computational effort. In this paper, we present an upscaling methodology for geothermal heat transport with fractures represented explicitly in the computational grid. The heat transport is modeled by an advection-conduction equation for the temperature, and solved on a highly irregular coarse grid that preserves the fracture heterogeneity. The upscaling is based on different strategies for the advective term and the conductive term. The coarse scale advective term is constructed from sums of fine scale fluxes, whereas the coarse scale conductive term is constructed based on numerically computed basis functions. The method naturally incorporates the coupling between solution variables in the matrix and in the fractures, respectively, via the discretization. In this way, explicit transfer terms that couple fracture and matrix solution variables are avoided. Numerical results show that the upscaling methodology performs well, in particular for large upscaling ratios, and that it is applicable also to highly complex fracture networks.     

A new scenario framework for climate change research: background,process, and future directions

The scientific community is developing new global, regional, and sectoral scenarios to facilitate interdisciplinary research and assessment to explore the range of possible future climates and related physical changes that could pose risks to human and natural systems; how these changes could interact with social, economic, and environmental development pathways; the degree to which mitigation and adaptation policies can avoid and reduce risks; the costs and benefits of various policy mixes; and the relationship of future climate change adaptation and mitigation policy responses with sustainable development. This paper provides the background to and process of developing the conceptual framework for these scenarios, as described in the three subsequent papers in this Special Issue (Van Vuuren et al., 2013; O’Neill et al., 2013; Kriegler et al., Submitted for publication in this special issue). The paper also discusses research needs to further develop, apply, and revise this framework in an iterative and open-ended process. A key goal of the framework design and its future development is to facilitate the collaboration of climate change researchers from a broad range of perspectives and disciplines to develop policy- and decision-relevant scenarios and explore the challenges and opportunities human and natural systems could face with additional climate change.     

High resolution regional climate model simulations for Germany: part I—validation

A five-member ensemble of regional climate model (RCM) simulations for Europe, with a high resolution nest over Germany, is analysed in a two-part paper: Part I (the current paper) presents the performance of the models for the control period, and Part II presents results for near future climate changes. Two different RCMs, CLM and WRF, were used to dynamically downscale simulations with the ECHAM5 and CCCma3 global climate models (GCMs), as well as the ERA40-reanalysis for validation purposes. Three realisations of ECHAM5 and one with CCCma3 were downscaled with CLM, and additionally one realisation of ECHAM5 with WRF. An approach of double nesting was used, first to an approximately 50 km resolution for entire Europe and then to a domain of approximately 7 km covering Germany and its near surroundings. Comparisons of the fine nest simulations are made to earlier high resolution simulations for the region with the RCM REMO for two ECHAM5 realisations. Biases from the GCMs are generally carried over to the RCMs, which can then reduce or worsen the biases. The bias of the coarse nest is carried over to the fine nest but does not change in amplitude, i.e. the fine nest does not add additional mean bias to the simulations. The spatial pattern of the wet bias over central Europe is similar for all CLM simulations, and leads to a stronger bias in the fine nest simulations compared to that of WRF and REMO. The wet bias in the CLM model is found to be due to a too frequent drizzle, but for higher intensities the distributions are well simulated with both CLM and WRF at the 50 and 7 km resolutions. Also the spatial distributions are close to high resolution gridded observations. The REMO model has low biases in the domain averages over Germany and no drizzle problem, but has a shift in the mean precipitation patterns and a strong overestimation of higher intensities. The GCMs perform well in simulating the intensity distribution of precipitation at their own resolution, but the RCMs add value to the distributions when compared to observations at the fine nest resolution.     

Synsedimentary faults and amalgamated unconformities: Insights from 3D-seismic and core analysis of the Lower Triassic Middle Buntsandstein, Ems Trough, north-western Germany

The Late Permian/Early Triassic succession of the Central European Basin (CEB) was repeatedly affected by the tectonic pulses associated with the earliest phases of Tethyan and Arctic–North Atlantic rifting. Effects of the differential tectonic subsidence are particularly well recorded by unconformities, which form widespread sequence boundaries. Such unconformities are most obvious in areas occupied by fault-controlled intra-basinal highs (swells). In that areas, stratigraphic loss may comprise entire Lower and Middle Buntsandstein formations and in places remnant Middle Buntsandstein successions directly rest on Permian strata. Analysis of 3D-seismic data and well logs combined with high-resolution sedimentological logging of drillcores at the western margin of the Ems Trough (NW Germany) reveals details of synsedimentary tectonic control on sequence development. Early Triassic extensional faulting of basement blocks provided stepwise addition of accommodation space for continental sequences by growth faulting along north–south oriented fault zones blocks on the flanks of the East Netherlands High. This process is most evident during the development of the Hardegsen Unconformity, which is characterised by an amalgamation of succeeding unconformity surfaces in areas of structurally controlled intrabasinal highs.     

Molecular characterization of uranium(VI) sorption complexes on iron(III)-rich acid mine water colloids

A mixing of metal-loaded acid mine drainage with shallow groundwater or surface waters usually initiates oxidation and/or hydrolysis of dissolved metals such as iron (Fe) and aluminum (Al). Colloidal particles may appear and agglomerate with increasing pH. Likewise chemical conditions may occur while flooding abandoned uranium mines. Here, the risk assessment of hazards requires reliable knowledge on the mobility of uranium (U). A flooding process was simulated at mesocosm scale by mixing U-contaminated acid mine water with near-neutral groundwater under oxic conditions. The mechanism of U-uptake by fresh precipitates and the molecular structure of U bonding were determined to estimate the mobility of U(VI). Analytical and spectroscopic methods such as Extended X-ray Absorption Fine-Structure (EXAFS) spectroscopy at the Fe K-edge and the U L_III-edge, and Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy were employed. The freshly formed precipitate was identified as colloidal two-line ferrihydrite. It removed U(VI) from solution by sorption processes, while surface precipitation or structural incorporation of U was not observed. EXAFS data suggest a mononuclear inner-sphere, edge-sharing complex of U(VI) with ferrihydrite in the absence of dissolved carbonate. By employing a novel EXAFS analysis method, Monte Carlo Target Transformation Factor Analysis, we could for the first time ascertain a 3-D configuration of this sorption complex without the necessity to invoke formation of a ternary complex. The configuration suggests a slightly tilted position of the adsorbed unit relative to the edge-sharing Fe(O, OH)₆ octahedra. In the presence of dissolved carbonate and at pH ∼8.0, a distal carbonate O-atom at ∼4.3 Å supports formation of ternary U(VI)-carbonato surface complexes. The occurrence of these complexes was also confirmed by ATR-FTIR. However, in slightly acidic conditions (pH 5-6) in equilibrium with atmospheric CO₂, the U(VI) sorption on ferrihydrite was dominated by the binary complex species Fe(O)₂UO₂, whereas ternary U(VI)-carbonato surface complexes were of minor relevance. While sulfate and silicate were also present in the mine water, they had no detectable influence on U(VI) surface complexation. Our experiments demonstrate that U(VI) forms stable inner-sphere sorption complexes even in the presence of carbonate and at slightly alkaline pH, conditions which previously have been assumed to greatly accelerate the mobility of U(VI) in aqueous environments. Depending on the concentrations of U(VI) and carbonate, the type of surface complexes may change from binary uranyl-ferrihydrite to ternary carbonato-uranyl-ferrihydrite complexes. These different binding mechanisms are likely to influence the binding stability and retention of U(VI) at the macroscopic level.