2018, Grinat, Michael, Epping, Dieter, Meyer, Robert, Szymkiewicz, Adam, Sadurski, A., Jaworska-Szulc, B.

In September 2009 two newly developed vertical electrode systems were installed in boreholes in the water catchment areas Waterdelle and Ostland at the North Sea island Borkum to monitor possible changes of the transition zone between the freshwater lens and the underlying saltwater. The vertical electrode systems, which were both installed between 44 m and 65 m below ground level, are used for geoelectrical multi-electrode measurements carried out automatically several times per day; the measurements are still ongoing. The whole system consisting of a vertical electrode system in a borehole and the measuring unit at ground level is called SAMOS (Saltwater Monitoring System). At both locations the data show a clear resistivity decrease that indicates the transition zone between freshwater and saltwater. The depth of the transition zone as well as the kind of resistivity decrease is very stable since 2010. Temporal changes are visible if single depths are considered. In 2015 Miriam Ibenthal used a vertical 2D density-dependent groundwater flow model to explain the long-term resistivity measurements and showed that the temporal changes at CLIWAT 2 (Ostland) could be explained by variations of the groundwater level, changing groundwater recharge rates and changing pumping rates of the nearby located drinking water supply wells.

2018, Rahman, Mohammad Azizur, González, Eva, Wiederhold, Helga, Deus, Nico, Elbracht, Jörg, Siemon, Bernhard, Szymkiewicz, Adam, Sadurski, A., Jaworska-Szulc, B.

In this study, interdisciplinary approaches are considered to characterize the coastal zone aquifer of the Elbe-Weser region in the North of Lower Saxony, Germany. Geological, hydrogeological, geochemical and geophysical information have been considered to analyze the current status of the aquifers. All the information collectively states that the salinity distribution in the subsurface is heterogeneous both horizontally and vertically. Early age flooding also contributed to this heterogeneity. No general classification of groundwater quality (according to some piper diagrams) could be identified. Helicopter-borne electro-magnetic data clearly show the presence of freshwater reserves below the sea near the west coast. Groundwater recharge largely happens in the moraine ridges (west side of the area) where both the surface elevation and the groundwater level are high. Consequently, submarine groundwater discharge occurs from the same place. All these information will facilitate to develop the planned density driven groundwater flow and transport model for the study area.

2018, Budach, Ingmar, Moeck, Inga, Lüschen, Ewald, Wolfgramm, Markus

The structural evolution of faults in foreland basins is linked to a complex basin history ranging from extension to contraction and inversion tectonics. Faults in the Upper Jurassic of the German Molasse Basin, a Cenozoic Alpine foreland basin, play a significant role for geothermal exploration and are therefore imaged, interpreted and studied by 3D seismic reflection data. Beyond this applied aspect, the analysis of these seismic data help to better understand the temporal evolution of faults and respective stress fields. In 2009, a 27 km2 3D seismic reflection survey was conducted around the Unterhaching Gt 2 well, south of Munich. The main focus of this study is an in-depth analysis of a prominent v-shaped fault block structure located at the center of the 3D seismic survey. Two methods were used to study the periodic fault activity and its relative age of the detected faults: (1) horizon flattening and (2) analysis of incremental fault throws. Slip and dilation tendency analyses were conducted afterwards to determine the stresses resolved on the faults in the current stress field. Two possible kinematic models explain the structural evolution: One model assumes a left-lateral strike slip fault in a transpressional regime resulting in a positive flower structure. The other model incorporates crossing conjugate normal faults within a transtensional regime. The interpreted successive fault formation prefers the latter model. The episodic fault activity may enhance fault zone permeability hence reservoir productivity implying that the analysis of periodically active faults represents an important part in successfully targeting geothermal wells.

2018, Oppermann, Frank, Günther, Thomas

We present a new versatile datalogger that can be used for a wide range of possible applications in geosciences. It is adjustable in signal strength and sampling frequency, battery saving and can remotely be controlled over a Global System for Mobile Communication (GSM) connection so that it saves running costs, particularly in monitoring experiments. The internet connection allows for checking functionality, controlling schedules and optimizing pre-amplification. We mainly use it for large-scale electrical resistivity tomography (ERT), where it independently registers voltage time series on three channels, while a square-wave current is injected. For the analysis of this time series we present a new approach that is based on the lock-in (LI) method, mainly known from electronic circuits. The method searches the working point (phase) using three different functions based on a mask signal, and determines the amplitude using a direct current (DC) correlation function. We use synthetic data with different types of noise to compare the new method with existing approaches, i.e. selective stacking and a modified fast Fourier transformation (FFT)-based approach that assumes a 1∕f noise characteristics. All methods give comparable results, but the LI is better than the well-established stacking method. The FFT approach can be even better but only if the noise strictly follows the assumed characteristics. If overshoots are present in the data, which is typical in the field, FFT performs worse even with good data, which is why we conclude that the new LI approach is the most robust solution. This is also proved by a field data set from a long 2-D ERT profile.

2018, Wiederhold, Helga, Scheer, Wolfgang, Kirsch, Reinhard, Azizur Rahman, M., Ronczka, Mathias, Szymkiewicz, Adam, Sadurski, A., Jaworska-Szulc, B.

Climate change will result in rising sea level and, at least for the North Sea region, in rising groundwater table. This leads to a new balance at the fresh–saline groundwater boundary and a new distribution of saltwater intrusions with strong regional differentiations. These effects are investigated in several research projects funded by the European Union and the German Federal Ministry of Education and Research (BMBF). Objectives and some results from the projects TOPSOIL and go-CAM are presented in this poster.

2018, Winsemann, Jutta, Lang, Jörg, Polom, Ulrich, Loewer, Markus, Igel, Jan, Pollok, Lukas, Brandes, Christian

This study presents a synthesis of the geomorphology, facies variability and depositional architecture of ice-marginal deltas affected by rapid lake-level change. The integration of digital elevation models, outcrop, borehole, ground-penetrating radar and high-resolution shear-wave seismic data allows for a comprehensive analysis of these delta systems and provides information about the distinct types of deltaic facies and geometries generated under different lake-level trends. The exposed delta sediments record mainly the phase of maximum lake level and subsequent lake drainage. The stair-stepped profiles of the delta systems reflect the progressive basinward lobe deposition during forced regression when the lakes successively drained. Depending on the rate and magnitude of lake-level fall, fan-shaped, lobate or more digitate tongue-like delta morphologies developed. Deposits of the stair-stepped transgressive delta bodies are buried, downlapped and onlapped by the younger forced regressive deposits. The delta styles comprise both Gilbert-type deltas and shoal-water deltas. The sedimentary facies of the steep Gilbert-type delta foresets include a wide range of gravity-flow deposits. Delta deposits of the forced-regressive phase are commonly dominated by coarse-grained debrisflow deposits, indicating strong upslope erosion and cannibalization of older delta deposits. Deposits of supercritical turbidity currents are particularly common in sand-rich Gilbert-type deltas that formed during slow rises in lake level and during highstands. Foreset beds consist typically of laterally and vertically stacked deposits of antidunes and cyclic steps. The trigger mechanisms for these supercritical turbidity currents were both hyperpycnal meltwater flows and slope-failure events. Shoal-water deltas formed at low water depths during both low rates of lake-level rise and forced regression. Deposition occurred from tractional flows. Transgressive mouthbars form laterally extensive sand-rich delta bodies with a digitate, multi-tongue morphology. In contrast, forced regressive gravelly shoal-water deltas show a high dispersion of flow directions and form laterally overlapping delta lobes. Deformation structures in the forced-regressive ice-marginal deltas are mainly extensional features, including normal faults, small graben or half-graben structures and shear-deformation bands, which are related to gravitational delta tectonics, postglacial faulting during glacial-isostatic adjustment, and crestal collapse above salt domes. A neotectonic component cannot be ruled out in some cases. © 2018 The Authors. Boreas published by John Wiley & Sons Ltd on behalf of The Boreas Collegium

2018, Stevens, T., Buylaert, J.-P., Thiel, C., Újvári, G., Yi, S., Murray, A.S., Frechen, M., Lu, H.

The International Commission on Stratigraphy (ICS) utilises benchmark chronostratigraphies to divide geologic time. The reliability of these records is fundamental to understand past global change. Here we use the most detailed luminescence dating age model yet published to show that the ICS chronology for the Quaternary terrestrial type section at Jingbian, desert marginal Chinese Loess Plateau, is inaccurate. There are large hiatuses and depositional changes expressed across a dynamic gully landform at the site, which demonstrates rapid environmental shifts at the East Asian desert margin. We propose a new independent age model and reconstruct monsoon climate and desert expansion/contraction for the last ~250 ka. Our record demonstrates the dominant influence of ice volume on desert expansion, dust dynamics and sediment preservation, and further shows that East Asian Summer Monsoon (EASM) variation closely matches that of ice volume, but lags insolation by ~5 ka. These observations show that the EASM at the monsoon margin does not respond directly to precessional forcing.

2018, Schneider, A., Zhao, H., Wolf, J., Logashenko, D., Reiter, S., Howahr, M., Eley, M., Gelleszun, M., Wiederhold, H., Szymkiewicz, Adam, Sadurski, A., Jaworska-Szulc, B.

A 3d regional density-driven flow model of a heterogeneous aquifer system at the German North Sea Coast is set up within the joint project NAWAK (“Development of sustainable adaption strategies for the water supply and distribution infrastructure on condition of climatic and demographic change”). The development of the freshwater-saltwater interface is simulated for three climate and demographic scenarios. Groundwater flow simulations are performed with the finite volume code d3f++ (distributed density driven flow) that has been developed with a view to the modelling of large, complex, strongly density-influenced aquifer systems over long time periods.

2018, Agemar, Thorsten, Weber, Josef, Moeck, Inga S.

Any geothermal resource assessment requires consistent and widely accepted terminology, methods, and reporting schemes that facilitate the comparison of geothermal resource estimates. This paper reviews common resource assessment methods, as well as reporting codes and terminology. Based on a rigorous analysis of the portrayed concepts and methods, it discusses the appropriateness of the existing reporting codes for sustainable utilization of geothermal resources in Germany. Since the last quantitative geothermal resource assessment in Germany was done 15 years ago, a revised report is overdue. Unlike fossil energy commodities, geothermal energy replenishes naturally and heat recuperation increases in created heat sinks. This replenishment process offers the opportunity for sustainable reservoir management in the case of moderate production rates or cyclic operation. Existing reporting codes, however, regard geothermal resources in a similar way to fossil resources or focus too much on field development rather than on the whole assessment process. In order to emphasize the renewability of geothermal energy, we propose the reporting of geothermal capacities (per doublet or per km2) instead of recoverable heat energy which depends very much on project lifetime and other factors. As a first step, a new classification scheme for geothermal resources and reserves is outlined.

2018, Burschil, Thomas, Buness, Hermann, Tanner, David C., Wielandt‐Schuster, Ulrike, Ellwanger, Dietrich, Gabriel, Gerald

Over-deepened basins exist throughout the Alpine realm. Improving our knowledge on these basins is of high social relevance, since these areas are often well-populated and they possess, for instance, unusual hydrological settings. Nonetheless, geophysical and sedimentological investigations of over-deepened basins are rare. We analyse the sedimentary succession of such a basin, the Tannwald Basin, through geological interpretation of seismic reflection profiles. The basin is located approximately 60 km north of the European Alps. It was incised into Tertiary molasse sediments by the Rhine Glacier and later filled by glacial, fluvial, and lacustrine deposits of 250 m thickness. The Leibniz Institute for Applied Geophysics acquired a grid of five high-resolution seismic reflection lines that imaged till the deepest parts of the Tannwald Basin. The seismic profiles, processed to a pre-stack depth migration level, allow a detailed geological interpretation that is calibrated with the help of a nearby borehole. We determine the structure and the seismic facies of the sediment succession in the basin and presume the following hypothesis of the evolution of the basin: sub-glacial erosion comprises the excavation of the over-deepened basin as well as detachment of large fragments of molasse material. These molasse slabs were deposited within the basin in a layer of basal till that graded upwards in water-lain till and fine-grained deposits. During the last two glaciations, the basinal structure became buried by till sequences and glacio-fluvial sediments.