Comparison of radon and thoron exhalation and emanation in granites from Central Portugal
1University of Coimbra, LRN-Laboratory of Natural Radioactivity, Department of Earth Sciences, Portugal; 2IATV-Instituto do Ambiente, Tecnologia e Vida, Coimbra, Portugal.; 3University of Coimbra, CITEUC-Center for Earth and Space Research, Department of Earth Sciences, Portugal
Thoron contribution to the inhaled dose is often neglected due to its shorter half-life and lack of strong gamma emissions that hinder its measurement. However, numerous studies report a significant contribution of thoron and/or its progeny to the dose received by the population. In the present work, radon and thoron exhalation rate and emanation coefficient were measured simultaneously with the accumulation method with an AlphaGuard DF2000 monitor in granite samples collected in high background radiation areas located in Central Portugal. The samples were also analyzed by gamma-ray spectrometry using an Ortec NaI(Tl) detector to determine 226Ra and 224Ra assuming secular equilibrium in the respective decay series. The relationship between radon and thoron exhalation rate and emanation coefficient, and the activity concentrations of their parent isotopes, are investigated.
Radon exhalation and emanation are generally higher than thoron’s, however, thoron exhalation rate may exceed the radon exhalation rate in porphyritic granodiorites. Weak correlations are observed between radon and thoron, suggesting they must be estimated independently for the assessment of thoron’s contribution to the dose received by the population. Variations of the radon exhalation rate, radon and thoron emanation coefficient, and the activity concentration of radium (226Ra and 224Ra) are observed linked to the geologic time of emplacement of granitic intrusions during the Variscan orogeny.
Radon and tectonics in an urban area – case study Bad Nauheim (Hesse, Germany)
1Technical University of Darmstadt, Schnittsphanstraße 9, 64287 Darmstadt; 2Hessisches Landesamt für Naturschutz, Umwelt und Geologie (HLNUG), Rheingaustraße 186, 65203 Wiesbaden
Inspired by the new Radiation Protection Act (2013/59/EURATOM), which entered into force at the end of 2018, the city of Bad Nauheim in southern Hesse has been chosen for measurements of soil air radon and CO2. In doing so, the focus is on the variability of concentrations in the area of tectonic features (normal faults), which are hosted in Devonian rocks, overlain by Tertiary and Quaternary unconsolidated sediments (Schäffer & Sass, 2016). Some of the faults, which are trending N-S and W- E respectively, are supposed to be active, enabling the migration of mineralized waters towards the surface.
Within a first measuring campaign, 231 soil air measurements were carried out, following transects that cross tectonic faults perpendicular. Results confirm advective radon anomalies with concentrations of up to 2000 kBq/m³, guided by a positive correlation between radon and CO2. At the same time, this correlation is diminishing with increasing distance to the faults (Möll 2018).
Based on the outcomes a second measuring campaign is on the way, addressing the following questions:
1) Are measured radon and CO2 concentrations reproducible?
2) How much radon is exhalating into buildings located near faults?
Works are focusing on two faults, which are located close to the so called “Sprudelhof” (fountain court), a bath house in the city center, and include both active (Saphymo AlphaGUARD) and passive (Exposimeter) soil air measurements as well as repeated indoor measurements (also active and passive) in the basement of the “Sprudelhof”.
Clay mineral quantification in the Upper Cretaceous Emscher Formation - evaluating a potential hydraulic barrier during mine water rebound in the Ruhr District
1Research Center of Post Mining, Technische Hochschule Georg Agricola University, Germany; 2German Mining Museum, Material Sciences and Research Labs, Bochum, Germany
The sealing potential of geological formations (“cap rocks”) plays an important role in long-term industry projects associated with mine water rebound, carbon sequestration and nuclear waste disposal. It is an important criterion in risk management and monitoring concepts. Clay content and mineralogy were used as screening parameters in order to estimate permeability in the Upper Cretaceous Emscher Formation. The Emscher Formation consists of monotonous grey to greenish alternating clay-, silt- and marlstones with a high amount of micrite. Distribution of clays was quantified on core and cuttings material using combined X-ray diffraction and Rietveld refinement. An important task was to evaluate content and changes in clay mineralogy with respect to expandable clays. The aim is to assess its self-sealing potential. Core sections and cuttings were retrieved from groundwater monitoring wells drilled in the northern part of the Ruhr District. The aim of these wells is to record hydraulic potential in the overburden section during mine water rebound in the Ruhr District. Classical lithological and sedimentological analyses of core section were conducted. Bulk geochemistry included total inorganic and organic carbon measurements. Elemental analyses on selected samples was determined using X-ray fluorescence spectroscopy. Clay mineral identification and quantification was performed on (a) bulk rock, (b) <2µm random powder and (c) <2µm oriented samples. For expandable clays, ethylene glycol and heating to 550°C was applied.
Nachbergbau: Chancen und Herausforderungen
1Institut für Angewandte Geowissenschaften, Strukturgeologie & Tektonik, Karlsruher Institut für Technologie; 2Forschungszentrum Nachbergbau, Technische Hochschule Georg Agricola, Bochum
Bergbau im 21. Jahrhundert bedeutet auch Alt- und Nachbergbau, immer geknüpft an die Bewältigung post-montaner Herausforderungen und die Langzeit- und Zukunftsaufgaben. Hiermit einhergehend sind Fragestellungen zu den damit verbundenen Kosten und der Möglichkeit der Weiterentwicklung im Bereich der Standortintegrität und -überwachung. Zusätzlich ist die gesellschaftliche Akzeptanz (engl. „social license to operate“) von Bergbauprojekten immer ein Thema. Die Forderung der Öffentlichkeit nach mehr Informationen bei der Erkundung, der Erschließung, der Produktion und der Stilllegung eines Bergbaustandortes stellt den Betreiber vor neue, weitere Herausforderungen.
Hier kann ein modernes Geomonitoring, welches Daten aus einer Vielzahl von Messverfahren aus der Luft, an der Oberfläche und untertage, z. B. über Satelliten, Drohnen, Begehungen, in-situ-Sensoren, Bohrlochgeophysik, petrophysikalische und mikroskopische Gesteinscharakterisierungen und Modellrechnungen integriert, helfen. Das Geomonitoring schafft somit ein transparentes, raum- und zeitbezogenes Prozessverständnis und umfasst mikroskopische, makroskopische sowie regionalgeologische Maßstäbe. Zudem kann das Risikomanagement von Bergbauprojekten unterstützt werden.
Slip tendency of faults and pore pressure evolution in the “Wasserprovinz Haus Aden” – Ruhr area
1Karlsruhe Institute of Technology (KIT), Institute of Applied Geosciences, Technical Petrophysics, Germany; 2Piewak & Partner GmbH, Germany; 3Karlsruhe Institute of Technology (KIT), Institut of Applied Geoscience, Structural Geology & Tectonics; 4Ruhr-Universität Bochum, Institut für Geologie, Mineralogie und Geophysik
Mining has required pumping in a wide area of the Ruhr region. In part, this leads to subsidence of more than 10 m. The matrix permeability of the rocks in the underground is rather low. Therefore, fracture fluid flows are assumed to contribute significantly to the groundwater flow. Our study area is the area between Dortmund and Hamm. It includes a number of major faults (in general, one set of faults is NE-SW oriented thrust faults, the other set of faults can be described as NW-SE mainly normal faults) that potentially subdivide the area into compartments with different hydraulic behavior. The dilation tendency is important for migration pathways. We present the dilation tendency based on the contemporary tectonic stress field. Furthermore, the slip tendency is presented for different water levels in comparison to the observed seismicity. The slip tendency shows how changes in effective stress (and thus changes in pore pressure and water level) modify the tendency of a fault to slip (see also other FLOODRisk contributions).
In addition, we use a generic numerical model within the compartment "Haus Aden Shaft 2" to simulate the change in reactivation potential of the bounding faults for water level changes due to activities in a nearby "generic" mine.
Improving field metadata collection using an app
Helmholtz-Zentrum Hereon, Germany
High quality metadata are a pre-requisite for enabling FAIR data products. In Earth and environmental research some metadata, such as the coordinates, need to be recorded directly in field. Other information, e.g. which kinds of samples were collected, may be saved after the campaign at the risk of being erroneous and time intensive.
In order to improve the metadata workflow at Hereon, we established an app for field metadata collection at the Helmholtz Coastal Data Center. The fields that need to be filled in a survey include the coordinates, date and time, the station name, the campaign and sample characteristics. Additional information, such as an image of a sample, can also be attached. The app, Survey123 developed by Esri, is easily customizable and is configured for each individual campaign. A GNSS receiver with up to 0.1m accuracy provides the location to the app.
Advantages of using the field app over previously used paper records are for example the automatic inclusion of GNSS data and a digital record of the metadata. This decreases the chance of manual transcription errors or data loss and allows for direct access of the metadata in the field, e.g. through an online map.
The metadata are transmitted via mobile transfer to our institution’s cloud storage, from where it is quality checked and stored in a database. An automatic registration of IGSNs for the samples is planned at this step. Once the samples are analyzed, the resulting data is connected to the corresponding metadata and published.
Geology across borders - Towards a consistent interpretation of the subsurface in the Central North Sea covering the Dutch, German and Danish offshore areas.
1Bundesanstalt für Geowissenschaften und Rohstoffe, Germany; 2TNO – Geological Survey of the Netherlands, the Netherlands; 3Geological Survey of Denmark and Greenland, Denmark
Geology does not follow national borders and for many areas of application, it is essential to know the characteristics of the subsurface on both sides of the border. In the area of the North Sea, however, consistent interpretation of the subsurface across borders are rare, as most studies carried out here by the Geological Survey Organizations (GSOs) in charge have remained confined to their national territories. As a consequence, the interpretations are often not aligned to each other, and in recent years, it has become more and more obvious by a variety of 3D-modeling projects that there exists in part considerable discrepancies e.g. in depth, distribution and thickness of certain stratigraphic intervals along the borders. Within the framework of the GeoERA research project ”3D Geomodeling for Europe”, the GSOs of the Netherlands, Germany and Denmark addressed these issues and integrated existing national (and regional) geomodels into a harmonized, consistent interpretation of the subsurface in their North Sea offshore border region. The results of the project presented here include: (a) A harmonized cross-border velocity model covering main parts of the Danish, German and Dutch North Sea. (b) A geometrically and stratigraphically consistent geological model of the Central Graben area across the Dutch-German-Danish border. (c) A consistent fault model of a segment of the Coffee Soil Fault. (d) Lithostratigraphic correlation schemes in the area of the Central Graben. The results achieved improve the spatial understanding of the subsurface structures of the project area and serve as a guide for future cross-border studies.
Seismic Interpretation of a deltaic-fluviatil system within the Bückeberg-Formation (Berriasian, Lower Cretaceous, Lower Saxony Basin)
Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), Germany
As part of the geothermal project GeneSys, the Federal Institute for Geosciences and Natural Resources, drilled the Groß Buchholz Gt1 geothermal well. At a depth of approx. 1,100 - 1,330m several sandstone layers of the Lower Cretaceous (predominantly Bückeberg Fm/Wealden) are present. Additionally to the borehole data, two seismic surveys covering the surrounding area (BGR 01-2001, 01-2006) were generated. For potential geothermal usage of these sandstone layers, their regional distribution within the larger Hanover area is one of the main questions. During the Early Cretaceaous the Lower Saxony Basin was bordered by the Pompeckj Swelll to the north, by the Rhenish Massif and Hildesheim Peninsula to the south, the Flechtingen High to the east and the East Netherlands Triassic Platform to the west. These large areas isolated the Lower Saxony Basin mainly from the sea at that time. The study area is located northeast of Hanover at the former basin margin, which is dominated by siliciclastic units (Bückeberg Fm, Wealden). Although there is some literature on the origin of these units, a detailed depositional model explaining their genesis is lacking. Therefore, we analyzed two 2D seismic sections in terms of seismic facies. First results pointing to a prograding deltaic - fluviatil system. These findings give new insights into the deposition of the so-called Wealden in the area of Hanover as well as in a regional context.
Geobiotropy on Early Earth and in the Rocky Universe
University of Strasbourg, France, France
It is currently proposed that life existed 3.5-3.8 Ga ago. However, the origin of the microorganisms is not yet explained. This presentation shows an anoxic path of formation of ferric minerals together with production of H2, when ferrous rocks interact with water at 300°-350°C, 10-25 MPa, 700-600 kg/m3, and at very alkaline pH, 11-14. The released H2 can interact with the dissolved CO2 and lead to CO that is known to be the preferred simple molecule for prebiotic chemistry reactions. Fluid inclusions that form during the hydrolysis can thus contain H2, CO, H2O. When N2 is present, this assemblage of molecules is known in the laboratory to lead to organic molecules of life. Therefore, from the rocks may form the molecules that are required for the emergence of life, process that I represented in 2016, by the concept of geobiotropy.
This conclusion arises from the analysis of the redox potential E of the electrochemical system Fe-high subcritical water, in the high pH range. The induced precise values of T, P, density, pH, can be applied to the anoxic geological world, such as Early Earth and Enceladus, the icy satellite of Saturn.
A Raman observation of a sample from the 3.4 Ga Buck Reef Chert, Barberton Greenstone Belt, South Africa, shows quartz, siderite, hematite and the peak of water inside a 1 μm fluid inclusion in quartz. Other lines are under study.
The theoretical predictions on anoxic ferrous iron oxidation will be tested with laboratory experiments that are currently under preparation.
Episodic mantle overturn in a non-plate tectonic mantle
Aarhus University, Denmark
Using ultra-high-resolution, 2D-thermomechanical modeling, we explore the evolution of the mantle of a terrestrial planet with a stagnant lid like Venus or the early Earth. Without plate tectonics, the mantle will heat over time from the decay of radiogenic isotopes. The convecting upper mantle will undergo partial melting and thicken a basaltic crust. When the crust reaches a critical thickness, the base of it transforms into eclogite. As eclogite is considerably denser than the underlying mantle it will ultimately delaminate. While ringwoodite in the peridotitic ambient mantle turns into perovskite and periclase at around 24 GPa and becomes about 10% denser, the similar phase reaction for garnet into perovskite in the basaltic crust occurs deeper, at around 27 GPa. The delaminated crust therefore accumulates in the 24-27 GPa range, where it has an intermediate density of the material above and below, and therefore suppresses convection across. Over time, this causes a significant temperature offset, as the upper mantle can continuously vent radiogenic heat, while the lower mantle cannot. Eventually, the crust-rich layer is pushed beyond 27 GPa and becomes denser than the underlying lower mantle. This triggers a run-away global mantle overturn. Superheated lower mantle streams upwards into the melting zone, increasing magmatic production by orders of magnitude for ≈50 Myr. After overturn, the mantle is highly heterogeneous with preserved domains of primitive mantle in a fooliated mélange of depleted mantle and basaltic crust.