Fluid-dynamics driving saline water in the North East German Basin

In several areas of the North German Basin, saline water comes close to, or even reaches the surface. Available data from wells indicate that brine stratification is under unstable conditions in the deeper underground. In order to analyse the possible transport mechanisms, 3D thermohaline simulations have been carried out for two different scenarios. The 3D regional model (230×330 km) indicates that salty water is driven to the surface by hydrostatical forces from the surrounding highlands. In addition, a smaller scale model (10×10 km) has been constructed with a grid resolution accounting for possible convective flow. The results indicate that convective flow may play a dominant role in areas with minor topography. In summary, the complex pattern of near surface occurrences of saline water probably results from the interaction of hydrostatic and thermal forces.     

Geomorphic Signatures of Active Tectonic in Drainage Basins in the Southern Bolkar Mountain,Turkey

Bolkar Mountain forms the northeast extent of the Central Taurus Mountains, which are located north of the eastern Mediterranean Sea and consist of 3000 m or higher summits. The study area southern part of Bolkar Mt, has been investigated for geomorphic signatures of active tectonics using Geographical information system (GIS). The lower valley floor-to-width to height and elongation ratios, higher convexity, stream length-gradient (SL) indices, hypsometric integral and convex nature of the hypsometric curves and topographic asymmetry show that relative tectonic activity is greater in the eastern sector affected by Ecemiş fault. Spatial variations of tectonic activity along rivers studied point to a general trend of decreasing activity towards the west as well as tectonic activity again increase in the west. Westward migration of basin and range extension is consistent with the place of uplift in the southern Bolkar Mt. Topography of the southern sector is the result of Late Miocene-Early Pliocene extension related uplift. Drainage systems in the upper part of the central and western sectors are under the lithological control and karstic denudation; whereas the development of the drainage systems in the middle and outlet parts of all sectors depend on sea level changes and Late Quaternary tectonism. The development of drainage systems of the eastern sector depends mostly on fault tectonism and climatic changes in the Late Quaternary.     

Thermal tracer testing in a sedimentary aquifer: field experiment (Lauswiesen,Germany) and numerical simulation

An active and short-duration thermal tracer test (TTT) was conducted in a shallow sedimentary aquifer at the Lauswiesen test site, near Tübingen, Germany. By injecting 16  m³ of warm water at 22°C, a thermal anomaly was created, which propagated along the local groundwater flow direction. This was comprehensively monitored in five observation wells at a few meters distance. The purpose of this well-controlled experiment was to determine the practicability of such a TTT and its suitability to examine hydraulic characteristics of heterogeneous aquifers. The results showed that the thermal peak arrival times in the observation wells were consistent with previous observations from alternative field testing such as direct-push injection logging (DPIL). Combined analysis of depth-dependent temperatures and peak arrival times, and comparison with a numerical heat transport model, offers valuable insights into the natural flow field and spatial distribution of hydraulic conductivities. The study was able to identify vertical flow focusing and bypassing, which are attributed to preferential flow paths common in such sedimentary sand and gravel aquifers. These findings are fundamental for further development of experimental designs of active and short-duration TTTs and provide a basis for a more quantitative analysis of advective and conductive transport processes.     

Burial history and thermal evolution of Westphalian coal-bearing strata in the Campine Basin (NE Belgium)

A 1D-modelling program has been applied to reconstruct the burial and thermal histories of two exploration boreholes, KB172 and KB174, located in the Campine Basin. The results show differences in geological histories. The coalification of the Westphalian A and B strata in KB174 (0.66–0.98% R_o) was pre-Permian. Calculated maximum temperatures, based on borehole data and vitrinite reflectance, regional thicknesses and a heat flow of 84 mW/m² during the Late Westphalian, range from 110 °C at the top to 175 °C at the bottom of the Westphalian cored in this borehole. The high coalification (0.85–1.30% R_o) of the Westphalian C and D strata in KB172 could be the result of the deposition of 2500 m of Upper Permian to Middle Jurassic sediments in combination with elevated heat flows (71–80 mW/m²). Two coalification periods, i.e. Late Westphalian and Middle Jurassic, are suggested for this borehole. The simulated maximum temperatures range from 130 °C at the top to 175 °C at the bottom of the investigated Westphalian C and D. The differences in the burial and thermal histories of both boreholes can be related to the activity of the transversal Donderslag Fault, a major structural element in the Campine coalfield, and the Roer Valley Graben.     

Groundwater temperature evolution in the subsurface urban heat island of Cologne,Germany

Long‐term heating of shallow urban aquifers is observed worldwide. Our measurements in the city of Cologne, Germany revealed that the groundwater temperatures found in the city centre are more than 5 K higher than the undisturbed background. To explore the role of groundwater flow for the development of subsurface urban heat islands, a numerical flow and heat transport model is set up, which describes the hydraulic conditions of Cologne and simulates the transient evolution of thermal anomalies in the urban ground. A main focus is on the influence of horizontal groundwater flow, groundwater recharge and trends in local ground warming. To examine heat transport in groundwater, a scenario consisting of a local hot spot with a length of 1 km of long‐term ground heating was set up in the centre of the city. Groundwater temperature‐depth profiles at upstream, central and downstream locations of this hot spot are inspected. The simulation results indicate that the main thermal transport mechanisms are long‐term vertical conductive heat input, horizontal advection and transverse dispersion. Groundwater recharge rates in the city are low (<100 mm a^?1) and thus do not significantly contribute to heat transport into the urban aquifer. With groundwater flow, local vertical temperature profiles become very complex and are hard to interpret, if local flow conditions and heat sources are not thoroughly known. Copyright © 2014 John Wiley & Sons, Ltd.     

Modelle instabiler Kompaktionsverläufe unter Sedimentation

Zusammenfassung Am Beispiel der Kompaktion von Sedimenten werden Grenzen der Quantifizierung geologischer Vorgänge aufgezeigt. Prozesse, die dazu neigen instabil zu werden, sind vorwiegend durch topologische, nur noch qualitativ erfaßbare Eigenschaften bestimmt. Besonders deutlich wird dies bei fluidization und liquidization von Sedimenten unter Eigenlast. In diesem Zusammenhang kann man von einem sedimentologischen Paradoxon sprechen. Zur qualitativen Untersuchung werden Differentialgleichungen und Differenzengleichungen eingesetzt.

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By sedimentological examples it is shown that there are limits to quantify geological processes. Processes like fluidization and liquidization of sediments are dominated by topological qualitative properties rather than by quantitative parameters. The occurence of instabilities can be called a sedimentological paradoxon. The qualitative analysis is done by use of differential and difference equations.

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Résumé La consolidation au cours de la sédimentation mène souvent pour quelques sédiments á des transformations instables telles que la liquidisation et la fluidification. La simulation mathématique offre la possibilité d'étudier ce paradoxe sédimentologique de faÇon qualitative ou semi-quantitative á l'aide d'équations différentielles et de différence.

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Aus dem SFB 53 Tübingen, Fossil-Diagenese Nr. 30.     

Coalification anomalies induced by fluid flow at the Variscan thrust front: A numerical model of the palaeotemperature field

Geologie en Mijnbouw -     

Late Cretaceous–Cenozoic evolution of the North German Basin—results from 3-D geodynamic modelling

The Late Cretaceous–Cenozoic evolution of the North German Basin has been investigated by 3-D thermomechanical finite element modelling. The model solves the equations of motion of an elasto-visco-plastic continuum representing the continental lithosphere. It includes the variations of stress in time and space, the thermal evolution, surface processes and variations in global sea level.The North German Basin became inverted in the Late Cretaceous–Early Cenozoic. The inversion was most intense in the southern part of the basin, i.e. in the Lower Saxony Basin, the Flechtingen High and the Harz. The lower crustal properties vary across the North German Basin. North of the Elbe Line, the lower crust is dense and has high seismic velocity compared to the lower crust south of the Elbe Line. The lower crust with high density and high velocity is assumed to be strong. Lateral variations in lithospheric strength also arise from lateral variations in Moho depth. In areas where the Moho is deep, the upper mantle is warm and the lithosphere is thereby relatively weak.Compression of the lithosphere causes shortening, thickening and surface uplift of relatively weak areas. Tectonic inversion occurs as zones of preexisting weakness are shortened and thickened in compression. Contemporaneously, the margins of the weak zone subside. Cenozoic subsidence of the northern part of the North German Basin is explained as a combination of thermal subsidence and a small amount of deformation and surface uplift during compression of the stronger crust in the north.The modelled deformation patterns and resulting sediment isopachs correlate with observations from the area. This verifies the usefulness and importance of thermomechanical models in the investigation of intraplate sedimentary basin formation.