Rhine Graben Research Articles

Field Trip A (23 September 2018): geology and geomorphology of Giessen and its surrounding areas

Abstract. This field trip is intended to present an introduction to the geological and geomorphological evolution of Giessen and its surrounding areas (Fig. 1). The conference location of Giessen is located at the intersection of three major geological and morphological units: the Rheinisches Schiefergebirge (Rhenish Massif) to the west, the Hessische Senke (Hessian Depression) to the north and south and the Vogelsberg volcanic field to the east (Fig. 2). The rocks of the Rheinisches Schiefergebirge (Rhenish Massif) were formed during Paleozoic times, in the context of the Variscan orogeny. Dominant rock types include graywacke, slate, quartzite, and limestone, as well as mafic and felsic volcanics and their related pyroclastics. The area north and south of Giessen is dominated by the Hessische Senke (Hessian Depression), a north–south-trending subsidence area with several individual deposit segments. Due to Cenozoic tectonic activity, the Hessian Depression can be regarded as a connecting segment between the prominent Upper Rhine Graben and the smaller graben structures of northern Germany, and this is also documented by less consolidated Tertiary and Quaternary sediments. Long-lasting subsidence of the Hessian Depression, however, is indicated by the presence of Permian and Mesozoic sedimentary rocks. Rotliegend rocks are present towards the southwest rim of the Vogelsberg volcanic field and the Hanau-Seligenstädter Senke. Minor occurrences of Zechstein rocks are exposed along the Lahn valley between Giessen and Marburg. Mesozoic strata are dominated by Buntsandstein and are widespread in the Marburg area, with Muschelkalk and Keuper rocks being restricted to small erosional remnants in tectonic graben structures. The area to the east of Giessen is dominated by the Miocene Vogelsberg volcanic field, where an estimated area of 2500 km2 is covered by volcanic rocks of varying thickness, the Vogelsberg thus being the largest volcanic field of central Europe. The field trip provides an introduction to the geology, earth history and geomorphological characteristics of Giessen and its surrounding areas. We will therefore encounter rocks that formed in distinct geodynamic environments and within a timespan of roughly 400 Ma (Devonian to present).

Structure and nature of the\xa0Palaeozoic basement based on magnetic, gravimetric and seismic investigations in the\xa0central Upper Rhinegraben

New and old magnetic and gravimetric data acquired in the frame of a geothermal project have been processed in N. Vosges and the adjacent Rhinegraben in order to identify the nature and tectonic framework of the graben basement and to select areas with a geothermal potential. In maps, the ENE–WSW striking units of N. Vosges can be followed beneath the sedimentary cover as far as the N35°-striking Upper Rhenish Shear Zone, which shifts these units towards NE. The magnetic basement S and SW of Strasbourg is interpreted as akin to the southern Champ du Feu Massif, consisting of I-type granitoids. Combined with new and old reflection seismic sections, the data show that the petrologic and tectonic contexts in the Illkirch-Grafenstaden area, where a geothermal project is planned, which is similar to the deep geothermal wells of Soultz and Rittershoffen 70 km to the north. The target zone is a N–S fault, partly normal and partly transpressive, which offsets the magnetic, I-type granitoids with high contents of uranium and thorium by about 800 m. Further exploitation of oil along the N–S footwall block attests to the geothermal potential of the area. The NW–SE transpressional regime favours the formation of cracks and increases the porosity and consequently fluid convection. The close borehole ESC-7 and modelling of the temperature distribution lead to expectations of a temperature of at least 150 °C on top of the granite and show that the temperature anomaly results from the heat-productive granitoids and from the blanket effect of the low thermal conductivity tertiary sediments.

Upper Pleistocene and Holocene sedimentary sequences: recent data in the alsatian part of the upper Rhine graben (France)

Depuis les annees 1990 de nombreuses donnees stratigraphiques pour le Pleistocene en Alsace sont restees inedites en grande partie en raison de leur caractere epars et de leur contexte d’acquisition. Les coupes levees a l’occasion de diagnostics et de fouilles archeologiques et les datations radiocarbone associees sont regroupees dans cet article. Ceci permet de mettre en evidence l’existence de lambeaux de sols developpes a la fin du Pleistocene qui completent les donnees livrees par les grandes sequences stratigraphiques de reference sur le Quaternaire du Rift rhenan superieur. Pour le Tardiglaciaire, la disposition du reseau hydrographique et en particulier l’activite des rivieres vosgiennes est precisee. Enfin pour l’Holocene, les changements anterieurs a la Neolithisation sont abordes et permettent de fixer un cadre avant les grandes mutations liees a l’anthropisation.

Veins in clay-rich aquitards as records of deformation and fluid-flow events in northern Switzerland

The Jurassic clay-rich aquitard sequence underlying the Swiss Molasse Basin is locally penetrated by unusually frequent veins consisting of calcite ± celestite, in particular in the Schlattingen-1 and Oftringen drill cores. The veins are linked to extensional brittle structures, with shear senses ranging between dip-slip and strike-slip. Deformation triggered transient and localised events of fluid flow within the aquitard followed by sealing of the structures by the vein minerals. Vein calcite was dated by LA-ICP-MS analysis using the U/Pb method. While this was a demanding undertaking, given the low U and high common Pb contents of calcite, 9 significant ages could be obtained. Two groups of ages can be distinguished, namely 31–39 and 11–18 Ma. Both age groups are consistent with the known regional tectonic evolution. The older age group corresponds to the main phase of rifting in the Upper Rhine Graben, a major crustal discontinuity, whose effects were not limited to the graben proper but affected large parts of the Molasse Basin. The younger age group is linked to crustal tilting and related extensional deformation.Isotopic compositions of O and C in vein calcite from the Schlattingen-1 core show substantial variability but do not discriminate between veins of the two age groups. In contrast, 87Sr/86Sr ratios in veins show different signatures. The depth trend of 87Sr/86Sr ratios in veins fits well with that in pore water obtained by rock squeezing. The two data sets define a trend of values increasing with depth, connecting the current values in the embedding Malm and Keuper aquifer waters. This trend is best explained as a near-steady-state diffusion profile. While advective mixing of waters originating from the embedding aquifers to produce the veins, implying structures that cross cut the whole low-permeability sequence, cannot be discarded on the basis of existing data, it is considered more likely that the veins have local fluid sources. These are mixtures of local pore water with a possible contribution of water from the nearest aquifer, implying maximum vertical advection distances in the order of 50–100 m.

Comparative Analysis of the Effects of Stem Height and Artificial Pruning on Seasonal Radial Growth Dynamics of Wild Cherry (Prunus avium L.) and Sycamore (Acer pseudoplatanus L.) in a Widely Spaced System

Intensive artificial pruning of trees increases the proportion of high-value timber but simultaneously reduces the crown and consequently the capacity to assimilate photosynthates. Here, midterm effects of two intensive pruning treatments, a classical and a selective approach, on radial growth dynamics at different stem heights is comparatively analyzed for the broadleaved tree species sycamore (Acer pseudoplatanus L.) and wild cherry (Prunus avium L.) at a site in the upper Rhine valley in southwest Germany using high-resolution point-dendrometers starting three years after pruning. We fitted shape-constrained additive models to the dendrometer data and derived estimates of growth phenology and performance of individual trees over the 2010–2016 observation period. The statistical analysis based on linear mixed-effects models showed significantly later growth cessation and in individual years also higher rates of radial growth in sycamore compared to wild cherry. Growth onset for both tree species initiated systematically earlier at the higher dendrometer location compared to breast height. While no main effects of treatment or interactions of treatment with year were detected, we found significantly higher average daily growth rates and annual radial growth of wild cherry at the top dendrometer location compared to breast height in the selective pruning treatment. Our results provide new insights into seasonal growth patterns of sycamore and wild cherry in a widely spaced system and contribute to a better understanding of the effects of stem height, pruning treatment and climate on radial growth dynamics of valuable broadleaved tree species.

New geochemical results indicate a non-alpine provenance for the Alpine Spectrum (epidote, garnet, hornblende) in quaternary Upper Rhine sediment

The heavy mineral assemblage of late Pleistocene to Modern Rhine river sediment in the Upper Rhine Graben is dominated by garnet, green amphibole and epidote. This so-called Alpine Spectrum has been taken to indicate an exclusive derivation from the Alps and has hitherto been investigated with optical methods only. We present the first single-grain geochemical data set of garnet and amphibole from the upper Rhine river and some of its main tributaries. We use the new data to test the alleged Alpine provenance in the Rhine.Our results show that the provenance of garnet, mostly pyrope-rich almandine is grain-size dependent. Particularly the pyrope content indicates that the 0.063–0.25 mm size fraction has an Alpine provenance whereas 0.25–0.5 mm grains derived from the Black Forest and the Vosges, which flank the Upper Rhine Graben. They mainly comprise of Paleozoic metamorphic and igneous rocks supplying a suite of heavy minerals similar to the Alpine Spectrum to the Rhine river. Amphibole, mostly Mg-hornblende, has an increasing TiO2 content from the south to the north of the graben, which also indicates an input from the graben shoulders. The new data indicate that the so-called Alpine Spectrum of heavy minerals in Rhine river sediment of the upper Rhine derived to significant degrees from non-Alpine sources. Furthermore, our results indicate a relatively uniform provenance for the Rhine River system during the past 1 Ma.

Overview of naturally permeable fractured reservoirs in the central and southern Upper Rhine Graben: Insights from geothermal wells

Since the 1980′s, more than 15 geothermal wells have been drilled in the Upper Rhine Graben (URG), representing more than 60 km of drill length. Although some early concepts were related to purely matrix-porosity reservoirs or Hot Dry Rock systems, most projects in the URG are currently exploiting the geothermal resources that are trapped in fracture networks at the base of the sedimentary cover and in the granitic basement. Lessons-learnt from the European EGS reference site at Soultz-sous-Forêts reveal highest natural permeability in the uppermost altered crystalline basement.Here, we present a compilation of related information to examine a more general validity of this hypothesis for the central URG. In this respect, 15 geothermal wells were analyzed concerning their lithologies, temperature distribution with depth, and their hydraulic yields. Among others, permeable fractures in Triassic sediments were observed among others during drilling operations at Soultz-sous-Forêts, Rittershoffen, Cronenbourg (France), Landau, Insheim, Bruchsal and Brühl (Germany). The geothermal wells at Soultz-sous-Forêts, Rittershoffen (France), Landau and Insheim (Germany) also intersect well-connected fracture networks in the uppermost altered granitic basement. Permeable fractures are intersected to a depth of 5 km at Soultz-sous-Forêts (France) and Basel (Switzerland).The compilation of geologic, hydraulic and thermal data of 15 geothermal wells shows permeability variation among the lithologies with the maximum observed at the top of the hydrothermally altered granite. This higher permeability is likely due to the intense fracture density in the fault core of the fracture zone and the large porous and altered damage zone which allow connection with the reservoir.

The incipient flash melting of scapolite and plagioclase megacrysts in alkali basalts of the Olot suite, Catalunya, Spain, and at Chuquet Genestoux, Puy-de-Dôme, France

Megacryst-bearing alkaline basic rocks of Cenozoic age occur in scattered centers in western Europe, from the Rhine graben to southern Spain. We focus on two volcanic fields, La Garrotxa in northeastern Spain, and in particular the Pomareda and Roca Negra monogenetic cones in the Olot suite, and the Chuquet Genestoux occurrence, Puy-de-Dome, France. The explosive emplacement of the basanitic magma favored the entrainment of xenoliths of clearly crustal and mantle origin in both suites. We seek to characterize the megacrysts of scapolite and andesine. The sulfate-bearing scapolite crystallized in space group I 4/ m rather than the expected P 4 2 / n , likely because of disorder in the sulfate groups. The megacrysts in both suites are part of an igneous mantle-derived assemblage, to judge from δ 18 O values, supported by δ 13 C and δ 34 S values of the sulfate-bearing scapolite. We document signs of flash melting in both scapolite and plagioclase megacrysts from Pomareda. A white rim of up to 2 mm on the scapolite megacrysts consists of skeletal individuals of calcic plagioclase; these crystals contain wollastonite, silvialite, diopside, and myriads of vacuoles. The andesine megacryst also underwent melting at its margin, to a sieve-textured assemblage of neoformed labradorite, glass, and free silica. The flash melting of individual megacrysts encapsulated in basanitic melt, documented here for the first time, has produced metastable products. Progress of the melting reactions was arrested by a thermal quench upon eruption.

Plasticulture changes soil invertebrate assemblages of strawberry fields and decreases diversity and soil microbial activity

In agriculture, the use of plastic mulch (plasticulture) is globally increasing. Besides beneficial effects on crop yield and quality, possible adverse environmental effects associated with plastic mulch are currently under debate. Aside from the obvious disadvantages of substantial amounts of (micro)plastic waste, adverse effects on soil quality and biodiversity might be assumed. We compared the effect of plastic mulch and organic mulch (straw) systems in strawberry cultivation on soil invertebrates and biological activity in an observational field study in the Upper Rhine valley, Germany. Soil invertebrates were collected using pitfall traps and Berlese-Tullgren-funnels, earthworms by hand sorting. Soil biological activity was determined using bait-lamina sticks and the MicroResp™ system. Soil samples from test fields were analysed for physicochemical and microbial parameters. Despite minor effects on soil physicochemical parameters, our results showed that the mulch system had a significant effect on the community structure of soil invertebrates. In strawberry fields with plastic mulch we found a decreased taxonomic richness and taxonomic richness decreased with increasing soil temperature. About 50% of the analysed taxa had significantly lower abundances in plastic mulched fields compared to fields with organic mulch. No investigated taxon had a higher abundance in plastic mulched fields. Soil moisture was the most important environmental variable in explaining invertebrate abundances. The soil microbial activity was significantly lower in plastic mulched fields than in fields with organic mulch. Our results indicate that even little shifts in abiotic (e.g. temperature, water content) and biotic (e.g. food availability) conditions associated with the plastic mulch system can have strong effects on soil invertebrates and soil microbial activity. Hence, plastic mulch might pose a threat to soil biodiversity and related ecosystem functions in agroecosystems. We call for further studies analysing the influence of plasticulture, to better evaluate the long-term consequences on agrobiodiversity and soil quality as well as sustainability.

Multi-reservoir fluid mixing processes in rift-related hydrothermal veins, Schwarzwald, SW-Germany

Fluid mixing is an important process in the formation of many hydrothermal vein-type deposits. Here, we present evidence from hydrothermal fluorite-barite-quartz veins with Pb-Zn-Cu-(Ag)-sulfides and associated mineralization, indicating that mineral precipitation was initiated by mixing of fluids derived from multiple sources, including mixing between more than two end-member fluid compositions. Based on our observations, we relate the diversity of the hydrothermal veins of the Schwarzwald mining district in terms of mineral assemblage and fluid inclusion chemistry to the disturbed and transient geological environment during ongoing rifting. Literature data on the regional geology, current groundwater reservoirs, formation processes and hydraulic features are augmented by new fluid inclusion analyses from post-Cretaceous, hydrothermal vein minerals including microthermometry, crush leach, Microraman and LA-ICP-MS analyses of individual fluid inclusions.Petrography and microthermometry of fluid inclusions show complex sequences of alternating fluid signatures within different growth zones of one crystal. High (20–26wt% NaCl+CaCl2), moderate (5–20wt% NaCl+CaCl2) and low salinity (<5wt% NaCl+CaCl2), sulfate- and/or CO2-bearing primary fluids were trapped during crystal growth. Such variations are commonly observed in minerals from different localities. Bulk crush leach analyses show significant variations in major element composition of the trapped fluids, within the overall Na-Ca-Cl-SO4-HCO3-system. These variations are caused by mixing of fluids from different aquifers and in various proportions. Ancient fluids show chemical similarities to modern groundwater aquifers that are available for direct sampling, such as granitic basement, Lower Triassic sandstones or Middle Triassic limestones and evaporites. Analyses of individual fluid inclusions by LA-ICP-MS support this interpretation and document the multi-component fluid mixing processes at individual localities recorded on the scale of single crystal growth zones. The latter data are used in a diffusion model to obtain the duration of mineral growth (before the fluid is homogenized), which implies very short-lived fluid events on the order of seconds to hours.By defining end member fluids and their proportions, we show that nearly all fluid mixtures are saturated with respect to barite. By contrast, fluorite-saturated fluids can only be modelled by mixing of a basement brine with fluids from Triassic sandstones. All fluid mixtures are strongly undersaturated with respect to galena, chalcopyrite and sphalerite, the most commonly observed ore minerals in the hydrothermal veins. As the calculated fluid mixtures are typically relatively oxidized and contain high sulfate/sulfide ratios, precipitation of sulfides was probably related to short-lived reduction events caused by an influx of hydrocarbons, by reactions with graphitic wall rocks in fractures by sulfidation related to fluid-rock reaction with the surrounding host rocks or an external influx of hydrocarbon-bearing fluids. The multi-aquifer fluid mixing processes involving aquifers of different chemical and physical constitution were triggered by brittle deformation related to rifting of the Rhine graben. This appears to be essential for the formation of a large number of mineralogically diverse hydrothermal ore deposits.

Influence of wind turbines on seismic stations in the upper rhine graben, SW Germany

By analysing long- and short-term seismological measurements at wind farms close to the town of Landau, SW Germany, we present new insights into ground motion signals from wind turbines (WTs) at local seismic stations. Because of their need to be located in similar regions with sparsely anthropogenic activities, wind turbines impact seismic stations and their recordings in a way that is not yet fully understood by researchers. To ensure the undisturbed recording tasks of a regional seismic array or a single station by a protected area around those endangered stations, it is very important to investigate the behavior of WTs as a seismic source. For that reason, we calculate averaged one-hour long spectra of the power spectral density (PSD) before and after the installation of a new wind farm within the investigated area. These PSD are ordered according to the rotation speed. We observe a clear increase of the PSD level after the WT installation in a frequency range of 0.5 to 10 Hz up to a distance of 5.5 km away from the WT. By analysing seismic borehole data, we also observe a decrease of the PSD of wind dependent signals with depth. The impact of wind-dependent signals is found to be much more pronounced for the shallower station (150 m depth) than for the deeper one (305 m depth). Using short-term profile measurements, we fit a power-law decay proportional to 1/r b to the main WT-induced PSD peaks and differentiate between near-field and far-field effects of ground motions. For low frequencies in the range from 1 to 4 Hz, we determine a b value of 0.78 to 0.85 for the far field, which is consistent with surface waves. The b value increases (up to 1.59) with increasing frequencies (up to 5.5 Hz), which is obviously due to attenuating effects like scattering or anelasticity. These results give a better understanding of the seismic wavefield interactions between wind turbines (or wind farms) with nearby seismic stations, including borehole installations, in a sedimentary setting.

Plant diversity in a water-meadow landscape: the role of irrigation ditches

Species-rich, extensively managed grasslands are among the most threatened ecosystems in Europe. The traditional technique of meadow irrigation, formerly practised in large parts of Europe, may be a viable management option that meets both ecological and economical objectives. While studies on plant diversity of the meadow matrix exist, the role of other landscape components for biodiversity conservation is unknown. We quantify the role of irrigation and drainage ditches compared with field paths, and analysed the local and landscape plant species composition and diversity in a water-meadow landscape. The meadows are located in the river Queich catchment (Upper Rhine valley, Germany). We recorded plant species cover on 18 meadows, adjacent ditches and field paths and analysed alpha, beta and gamma diversity within and among these landscape components. Irrigation and drainage ditches were more species rich than meadows and more heterogeneous in their species composition compared with meadows and paths. Ditches contributed one-third of the landscape’s plant species numbers, habitat for wetland species and refuges for high nature value grassland species. Fertilization of the adjacent meadow had no negative impact on the ditch diversity, while well-maintained ditches were more plant species rich than ditches filled with sediments. Traditional flood meadow irrigation should be taken into account when sustainable grassland management techniques are discussed that meet economical and ecological needs. A major contribution to landscape richness arises from the ditch structures as crucial part of the traditional irrigation technique.

Near-Fault Broadband Ground Motion Simulations Using Empirical Green’s Functions: Application to the Upper Rhine Graben (France–Germany) Case Study

Seismic hazard estimation relies classically on databased ground motion prediction equations (GMPEs) giving the expected motion level as a function of several parameters characterizing the source and the sites of interest. However, records of moderate to large earthquakes at short distances from the faults are still rare. For this reason, it is difficult to obtain a reliable ground motion prediction for such a class of events and distances where also the largest amount of damage is usually observed. A possible strategy to fill this lack of information is to generate synthetic accelerograms based on an accurate modeling of both extended fault rupture and wave propagation process. The development of such modeling strategies is essential for estimating seismic hazard close to faults in moderate seismic activity zones, where data are even scarcer. For that reason, we selected a target site in Upper Rhine Graben (URG), at the French–German border. URG is a region where faults producing micro-seismic activity are very close to the sites of interest (e.g., critical infrastructures like supply lines, nuclear power plants, etc.) needing a careful investigation of seismic hazard. In this work, we demonstrate the feasibility of performing near-fault broadband ground motion numerical simulations in a moderate seismic activity region such as URG and discuss some of the challenges related to such an application. The modeling strategy is to couple the multi-empirical Green’s function technique (multi-EGFt) with a k −2 kinematic source model. One of the advantages of the multi-EGFt is that it does not require a detailed knowledge of the propagation medium since the records of small events are used as the medium transfer function, if, at the target site, records of small earthquakes located on the target fault are available. The selection of suitable events to be used as multi- EGF is detailed and discussed in our specific situation where less number of events are available. We then showed the impact that each source parameter characterizing the k−2 model has on ground motion amplitude. Finally we performed ground motion simulations showing results for different probable earthquake scenarios in the URG. Dependency of ground motions and of their variability are analyzed at different frequencies in respect of rupture velocity, roughness degree of slip distribution (stress drop), and hypocenter location. In near-source conditions, ground motion variability is shown to be mostly governed by the uncertainty on source parameters. In our specific configuration (magnitude, distance), the directivity effect is only observed in a limited frequency range. Rather, broadband ground motions are shown to be sensitive to both average rupture velocity and its possible variability, and to slip roughness. Ending up with a comparison of simulation results and GMPEs, we conclude that source parameters and their variability should be set up carefully to obtain reliable broadband ground motion estimations. In particular, our study shows that slip roughness should be set up in respect of the target stress drop. This entails the need for a better understanding of the physics of earthquake source and its incorporation in the ground motion modeling.

Experimental interaction of hydrothermal Na-Cl solution with fracture surfaces of geothermal reservoir sandstone of the Upper Rhine Graben

The Upper Rhine Graben (URG) is a Tertiary rift structure in central Europe offering favorable conditions for geothermal energy utilization. Relatively high heat flow combines with sufficiently high permeability of the hydrothermal reservoirs. One of the target stratigraphic levels is the lower Triassic sandstone formation (Buntsandstein), where hot water resources at temperatures up to 250 °C can be utilized. Extensional neotectonics and hydraulic stimulation form new fracture surfaces in the reservoir rocks (enhanced geothermal system, EGS). The exposed fresh rock fracture surface reacts with the highly saline reservoir brines (Na-Cl up to 200 g l−1) with consequences for the permeability of the reservoir.In order to better understand the dynamic evolution of fault systems caused by fluid-rock interaction, we conducted batch-type experiments in a stirred autoclave system and reacted arkosic sandstone with synthetic 2 molal Na-Cl solution at temperatures of 200 °C and 260 °C. After 45–55 days reaction time altered rock samples were compared with the starting material and the geochemical-mineralogical processes were deduced with the help of XRD, SEM methods and EMP measurements. Fluid compositions were examined by ICP-MS, ICP-OES and IC.The arkosic sandstones show a surprisingly high reactivity during the experiments. Quartz grain surfaces show deep dissolution features and all reaction fluids were saturated with respects to quartz. Illite and kaolinite from the primary sandstone cementation completely dissolved from the sample surface. Perfectly euhedral crystals of metastable analcime formed during the experiment as separate crystals on quartz, as groups or clusters and as surface covering mats. The overall net transfer process dissolves quartz + illite + kaolinite ± K-feldspar and precipitates analcime + chlorite ± albite. The process is accompanied by a total volume increase of the solids of 20–30 vol%. K-feldspar dissolution is hampered by albitization rims shielding K-feldspar and efficiently preventing an equilibration of the Na–K exchange with the fluid. The experiments show changes on the rock surface, leading to an increase of the aperture of a single fracture during the early phases of reaction and later to a decrease as the fluid-rock reaction progresses. Alteration of the fracture surface also generates loose fragments and altered minerals. This fine material may efficiently reduce the fracture aperture at narrow points along the fracture.

Apparent Late Quaternary Fault‐Slip Rate Increase in the Southern Lower Rhine Graben, Central Europe

In regions of low strain, long earthquake recurrence intervals (104–106 yrs) and erosive processes limit preservation of Quaternary markers suitable for distinguishing whether faults slip at uniform or secularly varying rates. The Lower Rhine graben in the border region of Germany, The Netherlands, and Belgium provides a unique opportunity to explore Quaternary slip‐rate variations in a region of low strain using the basal (2.29±0.29 Ma) and surface (700±80 ka) contacts of the regionally extensive main terrace (“Hauptterrasse”), deposited by the Rhine and Maas Rivers. These surfaces are vertically offset 3–140 m and 0–68 m, respectively, across individual fault strands within a distributed network of northwest‐trending, slow‐slipping ( 80% of the sites record an apparent increase in slip rate for the more recent interval from 700 ka to present, which corresponds to a period of increased uplift of the nearby Rhenish Massif and regional volcanism. However, the apparent increase in slip rate could result, in part, from erosion of the footwall surface below the main terrace, leading to an apparent displacement that is smaller than the total vertical offset since the start of the Quaternary. Prior work focused on characterization of these faults as seismic sources in the Lower Rhine graben has preferentially relied on the average fault‐slip rate constrained using the base of the main terrace. We suggest that average fault‐slip rates calculated using the ∼700 ka main terrace surface are subjected to fewer uncertainties and sample a time interval that is more relevant for seismic‐hazard analysis. [Electronic Supplement:][1] Table of main terrace surface and basal contact offset measurements, figure describing an unrealistic faulting scenario, and a KML file with the fault‐trace mapping spanning the Lower Rhine graben. [1]: http://www.bssaonline.org/lookup/suppl/doi:10.1785/0120160197/-/DC1

The Cultural Project: Formal Chronological Modelling of the Early and Middle Neolithic Sequence in Lower Alsace

Starting from questions about the nature of cultural diversity, this paper examines the pace and tempo of change and the relative importance of continuity and discontinuity. To unravel the cultural project of the past, we apply chronological modelling of radiocarbon dates within a Bayesian statistical framework, to interrogate the Neolithic cultural sequence in Lower Alsace, in the upper Rhine valley, in broad terms from the later sixth to the end of the fifth millennium cal BC. Detailed formal estimates are provided for the long succession of cultural groups, from the early Neolithic Linear Pottery culture (LBK) to the Bischheim Occidental du Rhin Supérieur (BORS) groups at the end of the Middle Neolithic, using seriation and typology of pottery as the starting point in modelling. The rate of ceramic change, as well as frequent shifts in the nature, location and density of settlements, are documented in detail, down to lifetime and generational timescales. This reveals a Neolithic world in Lower Alsace busy with comings and goings, tinkerings and adjustments, and relocations and realignments. A significant hiatus is identified between the end of the LBK and the start of the Hinkelstein group, in the early part of the fifth millennium cal BC. On the basis of modelling of existing dates for other parts of the Rhineland, this appears to be a wider phenomenon, and possible explanations are discussed; full reoccupation of the landscape is only seen in the Grossgartach phase. Radical shifts are also proposed at the end of the Middle Neolithic.

Active Structures in Central Upper Rhine Graben, SW Germany: New Data from Landau Area using Electromagnetic Radiation (EMR) Technique and Cerescope

Two conjugate sets of active faults oriented NNE-SSW and NNW-SSE have been detected at Landau area in SW Germany. These faults follow the old trends of the rift-related structures predominating in the Upper Rhine Graben (URG), which originated during Late Eocene-Miocene time. Linear and horizontal measurements were performed by using the Cerescope device and interpreted, applying the Electromagnetic Radiation (EMR) Technique. Linear EMRprofiles were helpful for mapping active faults, while the main horizontal stress (σH, N to NNE) was easily identified with EMR-horizontal measurements. Reactivation of rift-related structures of the Upper Rhine Graben at Landau area produces a new system of active shallow fractures following old trends, and has been detected through the present study by Cerescope applying the EMR-Technique. The present results imply that the Enhanced Geothermal System (EGS) to the south of Landau has a great impact on reactivation of the pre-existing rift-related faults by mechanical hydro-fracturing occurring within the reservoir rocks underneath the area.

Hydrothermal characterization of wells GRT-1 and GRT-2 in Rittershoffen, France: Implications on the understanding of natural flow systems in the rhine graben

An extended description of the implementation of the deep geothermal wells GRT-1 and GRT-2 respectively drilled in 2012 and 2014 in the framework of the ECOGI project is given. These wells located in Rittershoffen (France) offer a unique opportunity to gather high quality datasets on a deep geothermal system in the Upper Rhine Graben at the transition between the Buntsandstein sandstone and the Palaeozoic granite basement. We present the extensive logging and well testing program that was applied and focus on hydraulic and thermal characterization of the targeted deep reservoir. Well architectures of GRT-1 and GRT-2 are described. Temperature logs in both wells are discussed in details. In particular, temperature in the production well GRT-2 is shown to reach 177°C at 3196m MD at thermal equilibrium. Production tests of both wells, reservoir development strategy applied in well GRT-1 and circulation test realised between wells are analysed. Productivity and injectivity indexes of GRT-1 and GRT-2 are estimated: Post-stimulation injectivity of GRT-1 and productivity of GRT-2 are respectively estimated to 2.5l/s/bar and 3.5l/s/bar. Hydraulic properties of the reservoir are inferred from production tests. Implications for the characterization of the large scale natural hydro-thermal system are discussed.

Seismic slip on the west flank of the Upper Rhine Graben (France–Germany): evidence from tectonic morphology and cataclastic deformation bands

Abstract The Upper Rhine Graben (URG) is a seismically active tectonic structure in intraplate Europe. Large and moderate earthquakes have occurred along the URG in the past but no coseismic surface faulting has been reported so far. We investigated active faulting along the western edge of the northern URG and identified the 25 km-long linear Riedseltz–Landau normal fault scarp as a major tectonic structure affecting late Pleistocene and Holocene deposits. The fault zone is exposed in the Riedseltz quarry where it affects Pliocene sand and gravels and overlying late Pleistocene (Wurm) units. These units have not been buried deeper than a few tens of metres and yet the fault zone contains cataclastic deformation textures. Cataclasis is demonstrated by spalling and transgranular fractures in quartz grains concentrated in deformation bands with reduced grain size. The observed microstructures suggest multiple phases of deformation with cataclasis followed by emplacement of a prominent Fe-oxide matrix into deformation bands, and later emplacement of a clay-rick matrix into fractures. Previous geological and geophysical studies along the fault show late Pleistocene (Wurm) loess deposits ( c. 24–10 ka before present) and early Holocene sand–silty deposits with individual or cumulative 1.5 and 0.7 m surface slip, respectively. Field observations and previous results from shallow geophysics provide a minimum 0.15 mm a −1 time-averaged slip rate. The Riedseltz fault parameters integrated in a dislocation model suggest a minimum Mw 6.6 earthquake as a plausible scenario in the northern URG. The observations of cataclasis in shallowly buried sediments coupled with observations of the late Quaternary fault scarp call for palaeoseismic studies that may document the occurrence of a larger earthquake on the western edge of URG. Surface faulting of young, shallowly buried sediments associated with cataclasis provides new evidence for assessing the occurrence of large earthquakes and seismic hazard assessment in the northern URG.

Analysis and simulation of the water and energy balance of intense agriculture in the Upper Rhine valley, south-west Germany

The Upper Rhine valley (SW Germany) belongs to one of the agriculturally most intense used regions in Germany. Climatic favourable conditions with mild winters, early springs and warm autumns lead to long vegetation periods and high agricultural productivity. One limiting factor is the water supply because of a negative annual climatic water balance, which has been increasing by −10 mm per decade in the last 50 years to −150 mm at present. Thus irrigation measures become more and more important for agricultural production in this region. Aim of this study was to measure and simulate water and energy fluxes on farm level in respect to the effects of irrigation measures in a region where farm sizes are small and diversity of land use high. In future these results will be used to conduct studies of energy and water fluxes on spatial scale (e.g. water catchments). The dynamics of the water and energy balance was observed with micrometeorological measurements using the eddy covariance methodology. Our investigation area had a size of about 6.5 ha and was cultivated with spring barley (Hordeum vulgare L.). Continuous measurements of all components of the water and energy balance as well as the vegetation specific-parameters, such as LAI, crop height and phenological macrostages, were conducted during the growing season which lasted from the beginning of April to 16 July 2014 (95 days). Additional irrigation was applied three times in this period by using a mobile sprinkler irrigation system. The observed dynamics were simulated with the physically based hydrological model TRAIN, which uses the Penman–Monteith approach for evapotranspiration simulation. Model efficiency was evaluated with Nash–Sutcliffe coefficient (NS). The TRAIN model was performing the simulations well with an r 2 = 0.72 with an slope of 1 and a NS = 0.77.