Geothermal power plants produce a large volume of brine for power generation. Since these brines are the product of long-term water-rock interactions at elevated temperatures at depth, they contain dissolved chemical components including critical and strategic mineral commodities at various concentrations. Despite the low concentrations for many of these minerals, significant quantities of select minerals could be recovered due to the large volumes of brine utilized by geothermal power plants. Over the years, the U.S. Department of Energy (DOE) Geothermal Technologies Office (GTO) has been funding research activities focusing on characterization of brine resources and development of extraction technologies for the rare earth elements, lithium, and other critical minerals from geothermal brines. The primary goal of the GTO’s efforts is to secure domestic sources for these critical materials as well as provide an additional revenue stream to the geothermal developers and make geothermal energy more competitive against other types of renewable energy.

Our assessment of the US geothermal brines for their mineral contents indicates that several mineral commodities (e.g., Li, Mn, SiO₂, etc.) are present in high enough concentrations and sufficient flow rates to be economically recovered from geothermal brines. In this presentation, we will provide a summary for mineral contents in geothermal brines in the US. Also we will provide a summary of past as well as current mineral extraction status, opportunities, and challenges for the commercial-scale deployment of mineral extraction technologies.

Geothermal brines may contain a plenty of chemical elements in a wider range of concentrations ranging from trace to bulk concentration level. This makes such brines interesting for the winning of metals as well as of bulk chemicals. Main constraints are the high temperatures and pressures that should be maintained during processing, the accompanying gases like Methane and/or Hydrogen Sulfide and the enrichment of naturally occuring radionuclides during processing.

This can make such processes troublesome.

Coming from research in radioactive scales abatement a process and a galvanic high pressure cell were devoloped for electrochemical separation of valuable trace metals like Sb, Tl, Te from geothermal brine and testes over a longer period at our test facility at Neustadt-Glewe, Northern Germany. We also examined the extraction of numerous metals from brine sample from the Großschönebeck geothermal site by means of electrochemical and selective adsorption methods. In Addition based on brines from the Stassfurt geological series the winning of base chemical like hydrochloric acis and sodium hydroxide solutions was also shown to be possible by means of electromembrane processes. The economic potential of such methods will bei evaluated based on experimental data.

In order to increase the economic potential of geothermal power plants in view of environmental protection and sustainability, there are considerations to extract critical raw materials (CRM), such as lithium, from the geothermal fluids. The Upper Rhine Graben (URG) in southern Germany is of particular interest as it represents a hydrothermal fluid reservoir with large CRM potential.

Apart from the sedimentary strata with different reservoir rocks and associated fluids, their Variscan basement is exhumed in the Vosges and the Schwarzwald. Unconformity related hydrothermal vein-type and Mississippi-Valley-Type deposits evolved from paleofluids in the region. Recent fluids precipitate mineralogically and chemically similar scalings in the power plants indicating their potential for CRM extraction from these fluids. These access to all parts of a geological system in the URG area accounts for its consideration as a natural laboratory. Therefore, this study deals generally with metal provenance, reservoir processes, transport and precipitation mechanisms.

One of the hypotheses regarding those processes that lithium is released into the geothermal fluid by hydrothermal alteration of basement feldspars and mica. To corroborate the hypothesis, different reservoir rocks and fluids in various depths are mineralogically and geochemically investigated. The fluids analyzed to this point show different trace element distributions, which are associated with changes in Cl/Br and Rb/Cs ratios and might thus indicate an interaction of the fluids with the reservoir rocks. A comparison of modern fluid chemistry with the geochemistry of altered minerals, will help to link CRM provenance and content in modern fluids with economic potential.

Lithium is one of the critical elements for the realization of electric mobility and energy transition. With a contribution to global Li-production and recycling of less than 1% (2017), Europe depends almost entirely on Li-import. To reduce the dependency, new and unconventional Li resources are explored in the EU. One resource are highly saline brines from geothermal reservoirs of the Upper Rhine Graben (URG), characterized by Li concentrations of up to 200 mg/L. Due to space restrictions, conventional production methods are not suitable and technologies for the direct lithium extraction (DLE), such as Li-Mn oxide sorbents, is needed. Lithium-Mn oxide sorbents have a comparably high Li adsorption capacity and due to ion-sieve properties a high selectivity for Li. Batch experiments with synthetic Li⁺-solutions and natural geothermal brines were conducted to investigate the sorption capacity and kinetics, and the role of competing ions on Li sorption. The batch experiments reveal fast sorption kinetics with an adsorption of >70% of the maximum Li sorption capacity within several minutes. In relation to Li⁺-solutions, Li sorption decreases for geothermal brines due to sorption of competing ions. While alkaline metals show a relatively little influence, Mn and Ba are the major competing ions. We prove successfully that Li-extraction from geothermal brines in the URG by Li-Mn oxide sorbents is technologically feasible at the laboratory scale. Upscaling into a pilot plant integrated into a power plant is in progress.

The energy transition and the associated need for non-energy, mineral raw materials have prompted the German government to expand research and development activities along the entire value chain. It is well known that the highly mineralized thermal waters that circulate during the extraction of geothermal energy have, in some cases, significant enrichments of economically strategic elements such as lithium, rubidium, antimony or magnesium. The extraction of mineral resources from thermal waters is still challenging in terms of process technology, but new sustainable methods are paving the way for economic extraction as an alternative to conventional hard rock mining. Due to the overall high salt concentrations, selective separation of scale-forming minerals in a pretreatment stage is necessary to avoid scalings or membrane fouling in the later process steps.

The focus of this study is on controlling silicate precipitation, which is expected to occur due to temperature changes and proceeding concentration cycles, which are required for raw material and freshwater extraction. The treatment and an associated precipitation process must be cost-effective, integrable into the power plant process, and selective for silica but must not affect the concentration of valuable elements. In a multi-step and interdisciplinary process, a treatment strategy was developed and implemented in a large-scale prototype. In this study, the development of the silica processing strategy from laboratory to prototype design is described. Finally, the construction and implementation of a large-scale prototype with promising field results are presented.

Recently, the growing demand for carbon-free energy has sparked an unprecedented interest in naturally occurring H₂, as it could represent a potential alternative resource to fossil fuels. Throughout the world, and since more than one century, numerous natural H₂-bearing geological fluids have been discovered, but to date, there is neither exploration strategy nor any resource assessment, as practical guidelines for hydrogen targeting are still missing. Here, we lay the foundation of a preliminary exploration guide based on a global ‘source-transport-accumulation’ understanding of H₂-concentrating process and a combination of techniques and data used for both conventional petroleum and mining exploration. Based on different case studies, belonging to contrasted geological settings, we will provide the first elementary bricks to evaluate the sources, migration and trapping of H₂ in the Earth’s crust.

Water radiolysis is a key process for hydrogen (H₂) and abiotic organic molecules generation in the Earth’s crust. The aim of this presentation is to provide some insight into this process from a radiochemist viewpoint. We will transpose the knowledge we gain from water radiolysis in the context of radioactive waste disposal to natural geological settings and draw important conclusions for deep microbial ecosystems development and abiotic organic synthesis. Some examples will be given about: (i) the relationship between H₂ production ant the nature of the emitted particle (α/β/γ) considered for water radiolysis, (ii) the boosted production of H₂ observed when aqueous solutions are in contact with some mineral surfaces such as rutile (TiO₂) and calcite (CaCO₃), (iii) the scavenging role of carbonate anions onto hydroxyl radical and the amplified yield of H₂, (iv) the switch from an inorganic world to an organic one through the carboxylate anions production from carbonate radiolysis.

Radiation chemistry is often overlooked by geologists who consider the process as anecdotic (apart for the thermal budget of Earth) in term of mass balance. However, water radiolysis is a large-scale ubiquist process in the crust and it does not need specific conditions to occur. We will show that at geological time scale, water radiolysis leads to a very diverse, reactive, and fun chemistry able to sustain life and even to create the condition for its emergence.

Temporary underground storage of molecular hydrogen (H₂) in depleted oil and gas reservoirs has recently attracted increasing research interest as it can support chemical industry demands and peak-shaving in the energy supply grid. Experimental parameters related to abiotic chemical reactions, microbial metabolism, and transport mechanisms of molecular hydrogen under elevated pressure conditions in such reservoirs are of potential relevance to these applications but have rarely been studied. As far as abiotic chemical reactions are concerned, since mineral coatings of hematite are a common feature in conventional reservoirs, a thorough understanding of the reactivity of the hematite-H₂ reaction system is of utmost importance. In addition, potential microbial growth in the pore space of reservoirs may affect the preset gas composition as well as petrophysical properties.

In this context, RWTH-Aachen University is coordinating the “H2_ReacT2” project, a follow up cooperation together with the Bundesanstalt für Geologie und Rohstoffe (BGR) and the Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum (GFZ). The overall objective is to gain a comprehensive understanding of relevant abiotic and biotic redox reactions, associated changes of petrophysical properties and molecular mass transfer within potential underground storage formations.

In this session, we will present analytical data of novel experimental approaches to study (1) the kinetics of the H₂-H₂O-hematite reaction system at low temperatures and elevated H₂ pressures, and (2) the effects of microbial metabolism of H₂ and overburden pressure on storage and transport properties of a typical reservoir rock, the Bentheimer sandstone.

Current renewable energies are unsteady resulting in temporary mismatches between demand and supply. The conversion of surplus energy to hydrogen and its storage in geological formations is one option to balance this energy gap. This study evaluates the feasibility of seasonal storage of hydrogen produced from excess wind power electricity in a saline aquifer in Castilla-León region (northern Spain). A 3D multiphase numerical model is performed to test different extraction well configurations during three annual injection-production cycles in a selected underground sandstone formation (Utrillas Fm) in the Duero basin. Results demonstrate that underground hydrogen storage in saline aquifers can be operated with reasonable recovery ratios. A maximum hydrogen recovery ratio of 78%, which represents a global energy efficiency of 30%, has been estimated. Hydrogen upconing emerges as the major risk on saline aquifer storage. However, shallow extraction wells can minimize its effects. Steeply dipping geological structures are key for an efficient hydrogen storage.

Recently, politics and industry has discussed green hydrogen as one of the carbon-zero energy sources of the future. Besides many other countries, Germany formulates clear goals for the energy transition from fossil to hydrogen energy in its "National Hydrogen Strategy". In order to ensure steady supply of hydrogen and to secure national reserves the underground storage of hydrogen (UHS) is increasingly coming into focus. Germany already has extensive experience in storing natural gas to cover supply shortages in the medium term, which follows same geologic principles as for hydrogen. In general, there are two main underground storage options for hydrogen. While in caverns such as salt-caverns operating UHS localities already exist, hydrogen storage facilities in porous media like aquifers or depleted gas reservoirs are still unrealized. In recent studies such as InSpEE and INSPEE-DS, the Federal Institute for Geoscience and Resources (BGR) provided a sound database of potential salt structures and salt horizons that could be used for UHS. This study gives an overview over the research made within all known types of underground hydrogen storage and discusses each their potential in Germany.

Cold and deep subduction is a characteristic feature of modern-style plate tectonics (MSPT) and a prerequisite for the formation of low-temperature/high-pressure (LT/HP) and ultrahigh-pressure (UHP) rocks. Although having strong implications for processes like the movement of materials between surface and mantle, mantle convection, thermal regimes, or the crustal growth rate, the onset of MSPT is poorly understood and controversially debated. One argument for an early onset are local occurrences of Paleoproterozoic retrogressed rocks suggested to have initially formed at LT/HP conditions (e.g., Weller & St-Onge, 2017, Nature Geoscience 10, 305-311). In contrast, a major argument for a late onset is the absence of mineralogical indicators for LT/HP and UHP metamorphism, like glaucophane and coesite, from the pre-Neoproterozoic crystalline rock record (e.g., Stern, 2005, Geology 33, 557-560). A limiting factor for the exploration of LT/HP and UHP rocks through time is the decreasing preservation of crystalline rocks with increasing age. Thus, the sedimentary record represents an important archive that preserves information on ancient continental crust lost due to erosion (e.g., Dhuime et al., 2017, Sedimentary Geology 357, 16-32). Nevertheless, reconstructing metamorphic conditions from a sedimentary perspective is challenging, mainly because we face sand-sized mineral grains that lost their paragenetic context. Here we present a selection of case studies that highlight the applicability of mineral inclusion assemblages in detrital garnet as an excellent petrogenetic indicator. This technique enables to partially reconstruct the paragenetic context and to screen the underexplored sedimentary record for mineralogical evidence supporting the operation of MSPT in deep time.

We present U-Pb, Lu-Hf, and O isotopic data, as well as size-shape data for approximately 3700 detrital zircons from 15 European rivers. In combination with geomorphological information for each river basin (area, drainage length, and hypsometric curves), we evaluate the representativeness and biases affecting such datasets. The new data allow us to demonstrate that the detrital zircon record from major rivers represents all relevant geological events in Europe at the continental scale, with detrital zircon ages ranging from Cenozoic to Archean. Several age peaks can be linked to different orogenic cycles and the formation of supercontinents such as Pangea and the Variscan Orogen, the largest episode of crustal reworking in Europe. These Variscan detrital zircons occur in all rivers, but Permian post-Variscan were only found in the Po (with significant crustal contamination) and Glomma rivers (with radiogenic and mantle-like signatures). Other important age clusters are the Alpine and post-Alpine Cenozoic 25-40 Ma and juvenile 0.2-10 Ma, the Caledonian 400-490 Ma, and the Avalonian-Cadomian 540-650 Ma. Detrital zircons of 930-1170 Ma and 1400-1700 Ma are significant in Scandinavia, as well as ca. 1850 and 2500-2900 Ma in east Europe. Despite the good representation of the different geological events in Europe, this does not occur when analyzing detrital zircon at smaller scales (i.e. the basin scale). The presence, importance, and proportions of peaks are strongly dominated by factors such as fertility, zircon-size-shape, and other geomorphological aspects. Excluding fertility, these factors alone can bias the proportion of peaks by up to 10%.

Detrital heavy mineral compositions are controlled by many factors such as mineral fertility in the source rocks and hydraulic sorting. Quantifying and understanding the resulting bias is crucial especially for the correct interpretation of single-grain analyses such as apatite or zircon geochronology in provenance studies.

In this study, an inter- and intrasample comparison of apatite and zircon concentrations is conducted on modern Alpine fluvial sands from five mono-lithological catchments draining granitoid, ophiolitic, metamorphic and sedimentary sources. The distribution of these minerals was quantified and compared within narrow grain size windows of each sample using point counting in strewn slides, XRF analysis of P₂O₅ and Zr as proxies for apatite and zircon, respectively and modelling based on the size shift. In addition, those results have been compared with other complementary monolitholigical catchments from the Alps.

While in line with published fertility values in the Alps, the apatite and zircon concentrations vary over three orders of magnitude. The intra-sample comparison shows highest zircon and apatite concentrations in the finer grain size fractions (63-250 µm), which is expected from the settling-equivalence principle. Furthermore, the apatite and zircon concentrations derived from point counting correlate well with those estimated from P₂O₅ and Zr concentrations through XRF analysis. However, the XRF analysis also reveals a significant amount of P₂O₅ and Zr contained in the grain sizes smaller than 63 µm. This is especially important, since many single-grain provenance studies do not consider the silt and clay fractions.

In-situ U-Pb-He double-dating of detrital zircon provides information regarding formation and cooling ages of source rocks. Its advantage over conventional dating methods is the unique ability to obtain a high quantity of precise single zircon data with constraints for both low- and high-temperature chronology. In provenance studies the information collected by double-dating can be used to reconstruct more complex tectonic settings and geologic evolution of individual zircons. Here, it is used to distinguish the components and tentative mixing ratios of sediments from multi-source catchments with the aim of assigning them to their respective sources.

The European Alps provide a great natural laboratory to test the capabilities of the method. Considering their well-studied and complex tectonic evolution, i.e. the combination of Proterozoic to Tertiary magmatism and high-grade metamorphism with spatially strongly contrasting Late Mesozoic to Neogene exhumation, none of the conventional chronological tools can draw a nearly as accurate picture.

Detrital zircons from modern river sands taken in the catchments of the Alpine Inn and its tributaries were dated: Ages derived from the Zillertal (dewatering mostly the Tauern window) and the Ötztal (incising the Austroalpine basement nappes) correspond to published data and can explain the complex age distribution of zircons collected near the end of the Alpine Inn. Double-dating is extraordinarily well suited to decipher such in-depth information, especially in complex orogens where different structural units experienced different overprinting of isotopic systems, leading to high spatial contrasts in low- and high-temperature chronological data.

Detrital zircon (DZ) U-Pb geochronology is widely applied in the geosciences to address a very wide range of questions. However, zircon is refractory and discrimination of first- versus multi-cycle origin is challenging which blurs source-to-sink relationships. We performed DZ U-Pb geochronology of modern sediments in fluvial and littoral environments on the Scott Coastal Plain in Western Australia. Principal age modes are at c. 730-500 Ma and c. 1100-880 Ma (Pinjarra Orogen), c. 1240-1120 Ma and c. 1700-1600 Ma (Albany-Fraser-Wilkes Orogen), and c. 2710-2580 Ma (Yilgarn Craton), corresponding to ultimate derivation from local crystalline basement rocks. The DZ U-Pb age spectra show a mismatch to the areal extent of source rocks in the catchment area. Here, we propose the application of a novel approach – source-normalized α-dose – to quantify active time of DZ grains in the sedimentary system and thus identify sedimentary recycling of DZ. This metric compares the α-dose (a measure of metamictization using U and Th content) of DZ and the values of crystals from their source crystalline basement. We show that source-normalized α-dose records the selective removal of labile (high α-dose) grains and is able to discriminate (i) first-cycle and (ii) multi-cycle DZ populations that experienced progressive sedimentary recycling and/or transport. Source-normalized α-dose provides an internal measure to address sedimentary recycling of DZ, i.e., it does not necessitate comparison with other mineral systems. Consequently, this tool aids in the identification of first- and multi-cycle DZ origin and ultimately strengthens source-to-sink correlations improving interpretation of DZ grain histories.

Carbonatites crystallize from mantle-derived carbonate- and volatile-rich melts that exsolve large amounts of fluids during their ascent through and emplacement into the crust. A global review of available fluid inclusion data for carbonatitic systems from variable emplacement depths identified four types of fluid inclusions: (type-I) vapour-poor H₂O-NaCl fluids with <50 wt.% salinity; (type-II) vapour-rich H₂O-NaCl-CO₂ fluids with <5 wt.% salinity; (type-III) multi-component fluids with high salinity without CO₂; and (type-IV) multi-component fluids with high salinity and high CO₂. This global data set indicates initial release of type-I saline brines that may either separate into immiscible type-II and -III fluids (eruption?) or may continuously evolve into type-IV fluids (sealing?). Moreover, fluid inclusions in early magmatic apatite crystallization suggest initial fluid release (type-I) at depths of 12-16 km (brittle-ductile transitions zone), which may be related to a sudden pressure drop initiated by crustal fracturing during rapid, forceful and discontinuous magma ascent.

Our model for the ascent of carbonatitic magmas is adopted from a jackhammer-like process, which explains the apparent absence of shallow carbonatite magma chambers, reflects the observed intrusion geometries, identifies fenitization as a process induced by fluids released during magma ascent and final emplacement, and demonstrates the formation of fluid induced brecciation related to magma ascent. The proposed model of a self-sustaining system is also in agreement with a turbulent ascent and high ascent rates, which allows for the transport of mantle xenoliths through the crust as observed in several cases.

The igneous nature of carbonatites has been controversial for decades until experimental work in the 1960s and 1970s conclusively showed that carbonatite melts can exist in geologically reasonable conditions. The observation of natrocarbonatite eruptions at Ol Doinyo Lengai further confirmed their igneous nature. However, these lines of evidence for igneous carbonatites have been a red herring: many ideas, processes, and terms deriving from silicate magma systems were inaccurately projected into carbonatite systems. Instead, carbonatites should be considered as hybrid metasomatic and magmatic cumulate rocks. The low viscosity and efficient wetting of carbonatite melts makes them behave more like hydrothermal fluids, preventing formation of magma chambers. Their high chemical reactivity and disequilibrium with their host rocks leads to rapid and substantial chemical exchange with their surroundings. Therefore, the chemical composition of their host rocks imparts a first order effect on the mineral assemblage observed in solidified carbonatite rocks. Rare earth elements are typically incompatible during carbonatite melt fractionation. Whether REE mineralisation is observed in Ca, Mg, or Fe-dominated mineral assemblages is strongly dependent on the degree and nature of silicate contamination. In special cases, REE can be highly compatible and mineralisation forms early rather than late. Enigmatic light REE mineralisations in fenite-like assemblages can likewise be explained as an end-member of carbonatite–rock interaction.

Carbonatites host the main REE deposits in the world, with bastnaesite being the main REE-bearing mineral of interest. However, the nature of the enrichment process, magmatic vs hydrothermal, is still debated. This study aims to experimentally determine the behaviour of REE elements during carbonatite crystallisation, and if bastnaesite can be directly crystallised from a carbonate melt.

Crystallisation experiments have been done from 900 to 600°C at 1 kbar on a REE-rich calciocarbonatitic composition. Calcite (Ca,REE)CO₃ is the dominant magmatic mineral, so the residual melt evolves toward natrocarbonatitic compositions as crystallisation proceeds. A small amount of britholite (REE,Ca)₅((Si,P)O₄)₃(OH,F) is observed at high temperatures and is replaced by phlogopite KMg₃(AlSi₃O₁₀)(OH)₂ and apatite (Ca,REE)₅(PO₄)₃(F,OH) at T < 650°C. A small amount of pyrochlore (Ca,Na,REE)₂Nb₂O₆(OH,F) is observed at T < 700°C.

No bastnaesite has been found in any crystallisation experiment. We thus performed a bastnaesite saturation experiment at 600°C. The melt saturated with bastnaesite however contains 20 wt% of REE: such high value implies that magmatic saturation of bastnaesite is unlikely to happen in nature.

F, Cl and water decrease the temperature of calcite saturation, allowing the system to crystallise at lower temperatures. REE are slightly incompatible with calcite, especially at low temperatures. The residual carbonate melt is thus enriched as crystallisation proceeds. Finally, we collected textural and chemical evidence suggesting the presence of a Na,Cl,REE-rich fluid at high temperatures and under hydrous conditions. Such Na,Cl,REE-rich fluids may play a critical role in the remobilisation of REE and the bastnaesite crystallisation during subsolidus reactions.

The Oulad Dlim massif in the southernmost part of Morocco hosts several carbonatite bodies of different ages. The older carbonatite (1.85 Ga) occurs in the eastern Oulad Dlim massif in the Gleibat Lafhouda area and consists of three juxtaposed magnesiocarbonatite outcrops. They are associated with glimmerite, hosted by Archean gneiss, and unusually intruded by massive IOA deposits. The latter contains up to several wt% REE related to numerous monazite-(Ce) inclusions within large apatite crystals. Columbite-(Fe) is the main Nb-mineral and occurs closely associated with Fe-phases, whereas microlite and Ta-rich columbite-(Fe) are mainly associated with coarse-grained apatites hosted by Fe-oxides and silica breccia. Geochemical characteristics and textural relationship suggest that they are genetically linked to the carbonatite and likely formed by late hydrothermal fluids at multiple stages. Small outcrops of nepheline syenite occur at several km from this carbonatite and might be genetically related. The youngest carbonatite (104 Ma) is a soevite and crops out within a ring structure composed of silica breccia and Fe-oxide mineralization at the Twihinat area of the western Oulad Dlim massif without visible associated alkaline rocks. All outcropping rocks at Twihinat show epigentic REE-Nb mineralization, mainly as bastnaesite within the carbonatite and silica breccia and monazite within the Fe-oxides. Pyrochlore senso-stricto occurs within the carbonatite, whereas cerio-pyrochlore is dominant in the silica breccia. The mineralogical and geochemical signatures of all Twihinat rocks suggest ore precipitation from multistage REE-Nb-rich hydrothermal fluids that percolated through the carbonatites and the associated rocks.

Contamination of carbonatite melts is often neglected due to a fast magma ascent and low liquidus temperatures. However, increased silicate mineral formation observed in numerous carbonatite occurrences world-wide requires an external Si introduction. Our study demonstrates that carbonatite dykes penetrating different lithologies of Palabora (South Africa) shows different modes of mineralogical modification. In particular Al and Si-rich lithologies show the most significant effects. Besides silicate mineral formation Si introduction may cause directly and indirectly variations of the REE mineralization at different stages of the carbonatite emplacement. While Si introduction during apatite formation causes an increased REE incorporation into apatite due to the britholite substitution accompanied by an early consumption of REE from the melt, an REE enrichment in the melt and related specific REE mineral formation in late magmatic stages become inhibited. A Ti-rich carbonatite magma additionally experiences the formation of titanite at the expense of ilmenite. Although REE consumption by titanite is less important as for apatite, specific REE consumption can influences REE patterns of subsequent mineralizations. On the other hand, magma wall rock interactions in a carbonatitic systems may furthermore directly influence the type of REE mineralization reflected by discrete REE minerals. In this way contamination can directly control the formation of either allanite, britholite, chevkenite or monazite and hence influences the economic processibility of a REE deposit. Furthermore, the stability of HFSE minerals such as baddeleyite or thorianite can be suppressed by the predominance of their Si-bearing counterparts (e.g., zircon and thorite).

Since 2012 many wind turbines have been installed on the Frankonian Jura and a number of them also in the vicinity of stations of the Gräfenberg array (GRF), consisting of 13 broadband stations within an area of about 50x100 km. It has been shown that these turbines take a significant effect on the noise level at many of the GRF station sites (Stammler & Ceranna, 2016, reference below). The array as a whole suffers from a deterioration of its sensitivity to teleseismic events of more than 0.1 magnitude units at wind speeds above 3.5 m/s (in 10m height). At individual station sites the noise signatures at frequencies above 2 Hz can be attributed to close-by wind turbines observing an approximate power decay law with increasing distance to the recording site. At a frequency of about 1.1 Hz, however, at most stations the strongest influence is visible, but the relation between measured PSD amplitudes and turbine distances does not support a simple decay law when taking into account only the closest wind turbine locations. This suggests that for this frequency turbines at larger distances play a role. This investigation tries to model the propagation of the turbine induced noise and to explain the observed PSD values at the GRF stations. As a result the contributing turbines can be identified as well as average propagation properties for the noise waves determined.

Influence of Wind Turbines on Seismic Records of the Gräfenberg Array, Klaus Stammler and Lars Ceranna, Seism.Res.Lett. (2016) 87(5): 1075-1081, https://doi.org/10.1785/0220160049

Seismologist noticed are worsening of station quality after the installation of wind turbines (WTs) close to seismological stations. Since WTs and seismological stations are installed mostly in areas with low population density, both are looking for solutions to diminish this conflict.

For this, we tested different denoising techniques at affected seismological stations to reduce or to eliminate the disturbing WT signal from the seismological data. Usually, spectral filtering is used to suppress noise in seismic data processing. However, this approach is not effective when noise and signal have overlapping frequency bands which is the case for WT noise. First, we applied a nonlinear thresholding function on our data. This method leads to good results when the event can be already seen in the raw data but it fails when the event is fully covered by noise. As a second method, we used a denoising autoencoder (DAE), which learns a sparse representation from time-frequency coefficients, and maps from there to output masking functions for signal and noise. The DAE is more time consuming in comparison to the nonlinear thresholding function but when the convolutional neural network is trained, using an adequate training dataset, it can also be applied instantly on the raw data. The DAE distinguishes between signal and noise and we are able to correct the seismograms from most of the disturbing noise signals.

Aerodynamic infrasonic signals generated by wind turbines can be detected by highly sensitive micro-barometers showing spectral peaks at the blade passing harmonics, which are above the background noise level. As infrasound is one of the four verification technologies for the compliances with the Comprehensive Nuclear-Test-Ban Treaty (CTBT), decreases in detection capability for dedicated infrasound arrays have to be avoided. Therefore, preventing such decrease is particularly important for the two German infrasound stations IS26 in the Bavarian Forest and IS27 in Antarctica, which are both part of CTBT’s International Monitoring System and have to meet stringent specifications with respect to their infrasonic ambient (natural and anthropogenic) noise levels.

In 2004, micro-pressure variations along a profile starting at a single horizontal-axis wind turbine were measured during a field experiment with mobile micro-barometer stations. As one of the results, a minimum distance to wind turbines for undisturbed recording conditions at infrasound array IS26 was estimated based on numerical modelling, validated with this dataset. Both observations and modelling were in agreement with the literature, where infrasonic signatures of wind turbines are reported at distance ranges up of tens of kilometres. Nevertheless, for broadening the dataset further infrasound measurements at two wind parks with modern large wind turbines have recently been carried out in Lower Saxony and Saxony-Anhalt, respectively. Here various instruments (micro-barometers, microphones, pressure sensors) have been deployed in a comparative manner. We will give an overview of these campaigns, followed by first results of our analysis and interpretation.

Repeated seismic activity can cause progressive failure of rock masses due to material fatigue [1]. To simulate induced seismic loading, an iron ore with alternating quartz- and magnetite-rich layers from the Sydvaranger mine (Finnmark/Norway) was subjected to laboratory uniaxial compressional cyclic loading at low stresses in the range of elastic deformation (about 6 MPa static ±3 MPa dynamic pressure) and frequencies related to induced seismicity (10 – 100 Hz) [2]. Some of the experiments were performed until material failure occurred at up to 2 million cycles. Changes in magnetic behaviour were identified by measurements of magnetic susceptibility from Verwey transition in magnetite (about 120 K) to room temperature after intervals of 150 000 loading cycles. Magnetic domains were analysed with magnetic force microscopy. Deformation-related surface structures on magnetite and quartz were identified by reflected light microscopy and high-resolution scanning electron microscopy and compared to results from Raman spectroscopy.

Dynamic mechanical analysis (DMA) was used for cyclic loading, which is a common method for determination of viscoelastic behaviour, especially of soft materials with pronounced viscoelasticity like polymers. Suitability of DMA for determination of relative changes of viscoelastic parameters during cyclic loading will be discussed under consideration of the relatively high Young’s modulus and almost ideal elastic behaviour of the iron ore under the chosen experimental conditions.

[1] Gischig et al. (2016) Rock Mech Rock Eng, 49, 2457-2478.

[2] https://www.geosig.com (2009), Seismic Signals and Sensors.

Traffic light systems (TLSs) are used in different energy technologies for limiting the strength of induced seismicity. The TLS concept is based on real-time monitoring of induced seismicity in combination with operational mitigation measures that are triggered if the intensity of the seismicity exceeds certain threshold values. We use observations, conceptual and numerical models for investigating efficiency and limitations of TLSs. Most notably, TLS efficiency can be limited by trailing effects caused by post-injection pressure diffusion and stress concentrations at the periphery of previous seismic activity. The latter ‘stress memory’ can be the cause for seismicity occurring a long time after reservoir activities stopped. We speculate that a similar type of stress concentration could have been the nucleus of the M_w=5.5 earthquake at the Pohang geothermal site.

Wind turbines are massive tall buildings which swing considerably above the ground, especially when they are in operation. These oscillations are composed of the eigenmodes of the whole building and the interaction of the passing blades with the tower. The oscillations are transferred into the ground by interaction of the moving foundation with the ground (soil / rock). The radiated wavefield is composed of elastic waves, conformable to seismic waves. Mainly surface waves are excited whose amplitudes decay with distance due to the geometric amplitude decay, the anelastic damping and the wave scattering, depending on the elastic properties of the rock along the propagation path. The related ground shaking is hardly felt by humans, however, sensitive high-tech instruments (electron microprobes, seismometers etc.) can be disturbed even at long distances. Thus, the knowledge about the source and propagation properties is vital to predict ground motion emissions and plan counter measurements. To enhance to development of wind energy as contribution to the exit from nuclear and fossil-fuel energy, expertise is needed to cope with the ground motion emissions of wind turbines.

The potential for the extraordinary island of Iceland to resolve seemingly intransigent problems in Earth Science has long been recognized. Alfred Wegener correctly surmised that his theory of continental drift could be tested there, and the necessary geodetic measurements were started as early as 1938. This, and other geophysical work often produced unexpected results. For example, observations reported before the acceptance of Wegener's hypothesis apparently supported it, while observations reported after its widespread acceptance seemed to contradict it. Iceland has always surprised us. In my presentation I shall report the most recent surprising findings. Long assumed to be one of very few places on Earth where sea-floor spreading can be observed on dry land, this model now requires modification. The convenience of studying oceanic crustal expansion on dry land apparently comes with a price. The crustal extension occurring in Iceland represents not classical seafloor spreading, with or without a mantle plume, but rather the process of continental volcanic margin formation–the process of continental breakup itself. I shall summarize the latest findings of an international group of collaborators of which I am privileged to be a member. I shall outline the rationale for our conclusion that Iceland, far from representing a simple oceanic spreading plate boundary on land, instead comprises magma-blanketed, extended continental crust. This theory is in need of evaluation through the collection of new, independent datasets that can test the predictions of the new model.

One of the most puzzling calcium carbonate minerals is ikaite (CaCO₃ x 6H₂O). Its formation is of particular importance, because anhydrous calcium carbonate minerals occur as pseudomorphs after ikaite. Consequently, ikaite may be an important and frequently forming precursor for more stable carbonate minerals especially in cold environments of Earth (Sánchez-Pastor et al. 2016). Despite the importance of ikaite, its formation conditions are not well constrained and knowledge about its decomposition and transformation is limited. Previous studies showed that cold temperatures and increased alkalinity promote ikaite formation and that dissolved Mg²⁺ and/or phosphate suppress a competing precipitation of calcite and/or vaterite (Purgstaller et al. 2017). However, these studies typically concern homogeneous ikaite formation. Therefore, it is still unknown whether mineral-water interfaces, which are ubiquitous in nature, affect both nucleation and transformation of ikaite.

Using cryo-mixed batch-reactor experiments (CMBR), we investigate which effects mineral surfaces exert on nucleation of ikaite, its subsequent transformation into more stable carbonates and the product phase selectivity. Besides ex-situ analyses of solution compositions and phase inventories of the reactor, in-situ monitoring of solution pH and Ca²⁺ concentrations gives insights into differences and similarities of ikaite behaviour in experiments with and without added minerals such as quartz and mica. Complementary to CMBR, in-situ flow-through cryo-atomic-force-microscopy (CAFM) can reveal the temporal evolution of the reactions on defined substrates in high spatial resolution. Initial results obtained by a newly developed CAFM will be presented.

The Oman Ophiolite is the largest and best-investigated piece of ancient oceanic lithosphere on our planet. This ophiolite was target of the Oman Drilling Project (OmanDP) within the frame of ICDP (International Continental Scientific Drilling Program) which aimed to establish a comprehensive drilling program in order to understand essential processes related to the geodynamics of mid-ocean ridges, as magmatic formation, cooling/alteration by seawater-derived fluids, and the weathering with focus on the carbonatisation of peridotites.

Over two drilling seasons, the OmanDP has sampled the Samail Ophiolite sequence from crust to basal thrust. The total cumulative drilled length is 5458 m, with 3221 m of which was at 100% recovery. These cores were logged to IODP standards aboard the Japanese drilling vessel Chikyu during two description campaigns in summer 2017 and 2018.

Here we present the main results of the working groups of the Universities Hannover and Kiel, focusing on the magmatic accretion of the Oman paleoridge. During 5 field campaigns these groups established a 5 km long profile through the whole crust of the Oman ophiolite by systematic outcrop sampling, providing the reference frame for the 400 m long OmanDP drill cores.

The profile contains 463 samples from the mantle, through gabbros up to the dike/gabbro transition. Identical samples have been analyzed by several methods (bulk rock geochemistry, mineral analysis, Isotope geochemistry, EBSD analysis). The results allow implication on the accretion of fast-spreading lower oceanic crust as well as on the hydrothermal cooling of the deep crust.

The presentation provides an overview about the project “Mass Movements in Germany (MBiD)” jointly implemented by six State Geological Surveys and the Federal Institute for Geosciences and Natural Resources in the period from 2018 to 2020. The objective pursued in this intervention was to review the practical feasibility of the spatial assessment (modeling) of the landslide susceptibility in Germany both at regional and nationwide level. The chosen approach took into consideration the specific framework conditions with regard to the availability and application of official information to evaluate the spatial probability of this hazard in Germany. Focusing on both rotational and translational landslides as well as on rockfall, fourteen modeling case studies were performed in different natural environments to explore limits and possibilities. The methods applied representing state of the art assessment tools covering bi- and multivariate statistical, heuristic, physical and machine learning methods. The necessary model parameters were mainly deduced from nationwide thematic geoinformation layers that are featured by a high degree of consistency. Based on the case studies, conclusions on the applicability of the methods, the requirements for the recorded mass movement inventory, and the use of the selected parameters and parameter classes and their validity were drawn. The results of the case studies culminated in the development of practical solutions and recommendations (workflows), which include the selection of suitable methods according to requirements and the development of reproducible approaches for modeling the regional landslide susceptibility at different scales.

Exploitation of deep geothermal energy is considered as one of the most efficient renewable energy applications. In this sense, reservoir stimulation is established to extract geothermal energy from EGS (Enhanced Geothermal System) which is highly dependent on its in-situ structural properties: damage/shear zones, faults, fractures, its statistics and characteristics. In more detail, damage zones may behave like a conduit providing preferential pathways for fluid flow in otherwise impermeable rock such as granite or gneiss. To improve the reservoirs’ characteristics frequently hydro-shearing or hydro-fracturing are used. It is imperative to account for the natural heterogeneities of the reservoir particularly with respect to the existing fracture network. In this study, we analyze the pre-stimulation fracture network of the EGS experiments conducted at the Grimsel Test Site, in the Swiss Alps. We use original data acquired at the tunnel wall and in boreholes to constrain a probabilistic 3D model further used for H-M simulations of the enhancement experiments. Fracture analysis include scanline mapping, cluster analysis of the spatial distribution and density plots.

Keywords: geostatistics, fracture analysis, DFN modeling, 3D geological modeling, geothermal energy

Numerical simulations of the governing geophysical processes are crucial for geothermal applications in order to characterize the subsurface. This characterization presents us with major challenges ranging from the correct physical and geometrical characterization to the quantification of uncertainties. Quantifying rock physics uncertainties and performing other probabilistic inverse methods is, even with current state-of-the-art finite element solver and high-performance infrastructures, computationally not feasible for complex basin- and reservoir-scale geothermal applications due to the large spatial, temporal, and parametric domain of the applications. Therefore, a common approach is to construct, for instance, models with a lower degree of resolution. The consequence of this is a significant loss of the information content of the model. Hence, with these models, we fail to improve the characterization of the subsurface, as we will demonstrate in this work. As an alternative, we propose to construct a surrogate model by using the reduced basis method. The reduced basis method constructs low-dimensional models while maintaining the input-output relationship. Hence, we do not restrict our physical domain. In this presentation, we demonstrate how this concept can be used for enabling a combined workflow of global sensitivity analysis and uncertainty quantification to improve our understanding and characterization of the subsurface.

Fracture dimensions largely control rock properties like strength and permeability. Thus, knowing their statistical distributions is of great importance in many applied fields of the geosciences e.g., in geothermics, mineral exploration, and hydrology. They are also of academic interest since the statistical distribution of fracture dimensions (length, height, width) might provide inside in fracture formation mechanisms.

However, in the vast majority of cases this information is derived from observations in 2 dimensions, i.e., instead of a fractures length, not the true length, but a fractures-trace length (FTL) is measured. In conclusion information or even estimates about the length of an individual fracture and about the statistical distribution of fracture lengths of a fracture population are not possible.

We analyze the statistical distributions of FTLs mapped at 3 different scales under the application of different mapping schemes that are commonly used to account for the limitations that are unavoidable, when recording fracture lengths in 2 dimensions.

In our study we test how well powerlaw-, exponential-, Weibull-, lognormal-, and log-logistic distributions fit the FTL data. Our results show that FTLs are lognormal distributed independent of scale and mapping scheme and that the parameters of the lognormal distributions reflect outcrop quality and dimension.

In addition, we provide a comprehensive model that explains the observed lognormal distributions of FTLs. This model is based on random restrictions that control the observable FTLs and includes human error and bias in mapping.

Hydro-mechanical (HM) simulations are essential aspects of geothermal reservoir studies to assess the heat production and the associated-environmental impacts, such as seismicity. HM simulations are numerically expensive (especially for large-scale simulations) since they require a relatively fine mesh to capture the complex interplay between the fluid-flow and geomechanical processes. This aspect makes it difficult to perform detailed studies on uncertainties in HM simulations. In this work, we present a comprehensive review and numerical demonstrations about critical elements in HM simulations for geothermal applications. We then discuss potential surrogate models to reduce the computational cost in performing the simulations, specifically for uncertainty quantification and optimization purposes.

There are four important elements in HM simulations for geothermal applications: the equation of state, the porosity-permeability relationship for both the matrix and fracture, the stress-dependent porosity in the matrix and fracture, and lateral and vertical heterogeneities. We compile the discussion from more than 60 papers and numerically show the significance of these parameters using the MOOSE simulator. The incorporation of these parameters into HM simulations leads to realistic descriptions of geothermal applications. However, accommodating for these complex physics also elevates the computational cost.

We compile surrogate-modeling approaches (dedicated for HM problems) from more than 40 papers. The approaches span from reduced-basis to polynomials chaos expansion methods and machine learning approaches. We found that the combination of reduced-basis methods and machine learning approaches enables to effectively deal with non-linearity in HM simulations, to preserve the physics, and to reduce computational cost for further uncertainty quantification.

The analysis of uncertainties in the description of the subsurface is an important aspect for resource exploration and material storage. Because of the complexity of the subsurface and an often inhomogeneous data situation, models exhibit several aspects of uncertainties. These may be caused by the interpolation of locally sparse data and must be considered when constraining a structural geological model. Further, these interpolations may be subject to errors caused by psychological biases, which need to be identified to avoid error propagation during the model building.

The aim of this study is to develop structural geological models of the Cretaceous units of the Münsterland Basin on the basis of stratigraphic boundaries and orientation measurements derived from maps, boreholes and literature as a framework for future geothermal exploration. In the model construction phase, it is attempted to separate processed input data in a first model setup from additional geological assumptions required to obtain geologically meaningful representations. Potential sources for bias are evaluated during the data processing, and standard deviations of input data points are accounted for during a subsequent uncertainty analysis using probabilistic geomodelling approaches.

The resulting structural models reveal the effects and limitations of purely input data-driven models versus models with additional integrated data and the uncertainties derived from different input data types. The integration of results of the planned seismic investigation in 2021/2022 by the Geological Survey NRW and the results of seismic campaigns acquired in the 1970s and 1980s may help to close these knowledge gaps in future work.

Deep geothermal energy is a key to lower local and global CO2 emissions caused by the burning of fossil fuels. Different initiatives aim at establishing deep geothermal energy production at the Weisweiler coal-fired power plant near the city of Aachen, Germany, in order to replace district heat generated as a side product of coal burning. But how much information do we actually have about or need of the subsurface to carry out such a project?

The conducted investigations will provide a 3D geological and probabilistic subsurface model of the area between Aachen and Weisweiler created with the open-source package GemPy developed at RWTH Aachen University. This model is in contrast to established regional models and more detailed local models.

The geological structures between Aachen and Weisweiler represent a SW-NE striking syncline, the Inde Syncline, embedded in the Aachen fold-and-thrust belt. The syncline is offset by Cenozoic normal faults of the Lower Rhine Embayment. The target layers comprise of karstic Lower Carboniferous Kohlenkalk platforms and Upper/Middle Devonian Massenkalk reef carbonates outcropping along the flanks and down faulted within the Lower Rhine Embayment.

Results show that the Aachen fold-and-thrust belt and the down faulted fault blocks can be modeled integrating the available surface and sparse shallow subsurface data. The probabilistic modeling provides information about uncertainties of the target layers in the subsurface. It can be deduced that a planned exploration well for fall/winter 2021 will reduce uncertainties in the subsurface in the vicinity of the target layers enabling improved economic decisions.

In recent years, the deep geological subsurface gained more and more attention as it offers various reservoirs potentially applicable for different geotechnical use options, e.g. deep geothermal energy, geological storage of CO2 and H2/energy. In this context, knowledge about the occurrence and the controlling processes of fluid-rock reactions in space and time is important to guarantee sustainable long-term reservoir utilization. While fluid-rock reactions occur at pore scale, they can significantly influence both reservoir-scale (transport) processes and regional flow regimes. Based on field observations, exemplary fluid-rock reactions in connection with their wide-ranging effects on geotechnical utilizations will be discussed.

During drilling of the Gotthard Base Tunnel through the Central Alps the exposed fractured rocks and the frequent water inflows provided a deep insight into regional hydrogeological processes in orogenic crystalline basements. Here we report data from the 10 km long central Sedrun section. 211 water samples were collected from frequent inflow points at 900 to 2350 m below the surface. The singular samples and data provide a comprehension of the deep hydrochemical cross-section through the Central Alps. The investigated tunnel section cuts across gneisses and schists of the pre-Alpine basement and across two narrow zones of meta-sediments. Rock temperature varies from 30 °C to 45 °C depending on the thickness of the overburden. The fracture water is of meteoric origin and acquires its composition exclusively by chemical interaction with the surrounding rocks along the flow path.

Water from inflow points in the basement of the Gotthard massif has typically a high pH of about 10 and total dissolved solids in the range of 100 to 300 mg L^-1. Sodium is the prime cation of most waters. Although plentiful in the rocks, calcium, potassium, and magnesium are low to very low in the water. The anions associated with Na are carbonate/bicarbonate, sulfate, fluoride and chloride in widely varying proportions. High fluoride concentrations of up to 15.4 mg L^-1 are characteristic for most waters. As a result of the high pH dissolved silica (SiO₂) reached concentrations of up to 58 mg L^-1 and represents 25 - 30 wt.% of the solutes.

During IODP Expedition 382, two sites were drilled at 53.2°S at the northern edge of the Scotia Sea and three sites at 57.4°–59.4°S in the southern Scotia Sea within the Atlantic sector of the Southern Ocean. Sediments at both locations alternate between dominant terrigenous components during glacials and dominant biogenic components, carbonate at the northerly sites and opal in the southern Scotia Sea, during interglacials. Here we constrain the geochemical environment in interstitial waters using the boron (δ¹¹B), silicon (δ³⁰Si) and ⁸⁷Sr/⁸⁶Sr isotopic composition.

Interstitial water δ¹¹B and δ³⁰Si decrease in the uppermost tens of meters downcore, most likely due to in situ weathering processes preferentially releasing light isotopes to interstitial waters. This process is partly also reflected by strongly increasing alkalinities in this depth interval. While δ³⁰Si at all sites increase already at shallow sediment depth where organic matter degradation is intense, δ¹¹B remain relatively low beyond the lower boundary of elevated dissolved phosphate concentrations at every core site. Below this depth δ¹¹B follow isotopic trends seen in δ³⁰Si towards heavy compositions, presumably because of dominating secondary clay formation.

Interstitial waters obtained as deep as 550 and 670 mbsf from the southern Scotia Sea sites reveal an increasing importance of off-axis hydrothermal fluids within the basement underlying the sediments. This feature is detectable by lowest ⁸⁷Sr/⁸⁶Sr alongside lowest Mg/Sr and strongly decreasing δ¹¹B at the lower end of the cores. Our key aim is to illustrate the dominant diagenetic process at each depth downcore, and how to identify these.

Following a thermal and photogrammetric outcrop mapping campaign undertaken at the Waiwera geothermal reservoir in 2019, a pre-existing 3D hydrogeological model was revised in the present study to assess the impact of the updated structural and lithological interpretation on the existing numerical model calibration. For the latter, well data comprising measured temperature and salinity profiles were employed to reconstruct the reservoir’s natural thermal state and spatial distribution of salinity, supported by numerical simulations of density-driven fluid flow coupled with the transport of heat and sodium chloride. In this context, the previously applied fluid equations of state were extended to consider all relevant parameters as functions of temperature and salinity. Our simulation results demonstrate that the undertaken revisions of the static model and fluid properties substantially improve the agreement between the simulated and observed temperature profiles in the monitoring wells, while the achieved match of the simulation results with early recordings on seawater intrusion emphasizes the general model validity. Ongoing work focusses on applying the newly calibrated numerical model to support the sustainable management of the reservoir and to investigate the reappearance of natural seeps at the Waiwera beach, triggered by a decrease in the past excessive groundwater abstraction.

Hydrate formation from dissolved methane in saline solutions is a hydrochemical process, resulting in the accumulation of gas hydrates in sedimentary strata under the seafloor or overlain by permafrost regions. In the scope of the SUGAR framework, LARS has been established to study gas hydrate formation processes and dissociation strategies under in-situ conditions. In the latest hydrate formation experiments, key parameters have been applied to mimic the local marine environment of the Mallik site, Canada. LARS was equipped with temperature sensors and an electrical resistivity tomography (ERT) array for these tests to monitor the dynamic temperature changes and spatial hydrate distribution. Numerical simulation on the hydrate formation process in LARS has not yet been successfully conducted, so that the equations of state relevant to describe equilibrium hydrate formation from dissolved methane have been implemented into a numerical framework and integrated with the TRANsport Simulation Environment to study and quantify the temporal of CH₄-hydrate formation in our present study. We present our model implementation, its verification against HydrateResSim and the findings of the model calibration and validation against the temperature and ERT data from the corresponding hydrate formation experiment. The simulation results demonstrate that our numerical implementation can reproduce the spatial temperature distribution and hydrate formation processes in LARS. Furthermore, spatial hydrate distribution is in good agreement with that produced by ERT measurements undertaken during experiment. Consequently, our numerical simulation framework can be applied for the design of new experiments and to investigate hydrate formation in representative geological settings.

Central Argentina from the Pampean flat-slab segment to northern Patagonia (27-41°S) represents a classic example of a broken retroarc basin with strong tectonic and climatic control on fluvial sediment transport. In this provenance study, we combine framework petrography and heavy-mineral data to trace multistep dispersal of volcaniclastic detritus first eastwards across central Argentina for up to ~1500 km and next northwards for nearly another 1000 km along the Atlantic coast. Compositional signatures reflect different tectono-stratigraphic levels of the orogen uplifted along strike in response to varying subduction geometry as well as a different character and crystallization condition of arc magmas through time and space.

In the presently dry climate, fluvial discharge is drastically reduced to the point that even the Desaguadero trunk river has become endorheic and orogenic detritus is dumped in the retroarc basin, reworked by winds, and temporarily accumulated in dune fields. At Pleistocene to early Holocene times, instead, much larger amounts of water were released by melting of the Cordilleran ice sheet or during pluvial events. The sediment-laden waters of the Desaguadero and Colorado rivers then rushed from the tract of the Andes with greatest topographic and structural elevation, fostering alluvial fans inland and flowing in much larger valleys than today toward the Atlantic Ocean. Sand and gravel supply to the coast was high enough not only to promote rapid progradation of large deltaic lobes but also to feed a cell of littoral sediment transport extending as far north as the Río de la Plata estuary.

The grain-size distribution of sediment particles is an important aspect of the architecture of submarine fans and lobes. It governs depositional sand quality, and reflects distribution of particulate organic carbon and pollutants. Documenting the grain-size distribution of these deep-marine sedimentary bodies can also offer us an insight in the flows that deposited them. Submarine lobes are commonly assumed to linearly fine from an apex, meaning there should be a proportional relation between grain size and distance from the lobe apex. However, not much detailed quantitative work has been done to test this hypothesis. Exposure of a 5 km long dip-section of basin-floor lobes in Clinoform 12, Battfjellet Formation, Spitsbergen, enable the study of basinward grain-size evolution in lobe deposits. Furthermore, the dataset allows testing if there are any documentable grain-size differences between lobe sub-environments.

The results show that fining of lobe deposits occurs predominantly in the most proximal and most distal parts of the lobe, while the intermediate lobe, which is dominated by lobe off-axis deposits, is characterized by a relatively consistent grain-size range. Lobe sub-environments show statistically distinct grain-size distributions from lobe axis to lobe fringe. An explanation for these trends is the interplay of capacity and competence-driven deposition with the grain-size stratification of the flows.

The outcomes of this study help to better understand the proximal to distal evolution of turbidity currents and their depositional patterns. They also provide important insights in reservoir potential of basin-floor fans at lobe scale.

Compositional data on heavy minerals is fundamental in sedimentary provenance analysis. Typically, this data is gathered by optical microscopy and more recently, by mineral chemical analysis (MLA, QEMSCAN) or Raman micro-spectroscopy. In silt-sized sediments optical microscopy is unfeasible. We introduce a systematic and highly efficient approach to assess the heavy mineral composition in fine grain-size fractions (10-30 µm and 30-62 µm) by Raman micro-spectroscopy.

The approach starts with a web-application that creates and visualizes large mosaic images from which arbitrary objects can be selected for training and inference of a region-based convolutional neural network (R-CNN). Here, mineral grains are automatically selected by passing the tiles of a mosaic image of the sample slide into the R-CNN. For each detected grain a polygon is computed from which positional and optical parameters are derived. Using this polygon data, the measurement parameters at the Raman spectrometer are individually set to account for varying Raman scattering intensities and irradiation resistivity. After the compositional data is obtained, Raman spectra are evaluated and further single-grain geochemical methods (ICPMS, EMPA) can be applied to the identified and referenced grains (e.g. U-Pb dating of zircon).

The method was tested on 13 samples from three loess profiles from Germany and Hungary. About 100.000 minerals were analyzed and provenance signals demonstrate clear contrasts between the sections. Being automated, this approach allows for analyzing large sample numbers with higher precision (i.e. counting statistics) on silt-sized materials, thus opening new avenues in sedimentary provenance analysis.

The Zambezi River rises at the center of southern Africa, flows across the low-relief Kalahari Plateau, meets Karoo basalt, plunges into Victoria Falls, follows along Karoo rifts, and pierces through Precambrian basement to eventually deliver its load onto the Mozambican passive margin. The river is subdivided into segments with different geological and geomorphological character, a subdivision fixed by man’s construction of large reservoirs and testified by sharp changes in sediment composition. Pure quartzose sand recycled from Kalahari desert dunes in the uppermost tract is next progressively enriched in basaltic rock fragments and clinopyroxene. Sediment load is renewed first downstream Lake Kariba and next downstream Lake Cahora Bassa, documenting a stepwise decrease in quartz and durable heavy minerals. Composition becomes quartzo-feldspathic in the lower tract, where most sediment is supplied by high-grade basements rejuvenated by the southward propagation of the East African rift. Feldspar abundance in Lower Zambezi sand has no equivalent among big rivers on Earth and far exceeds that in sediments of the northern delta, shelf, and slope, revealing that provenance signals from the upper reaches have ceased to be transmitted across the routing system after closure of the big dams. This high-resolution petrologic study of Zambezi sand allows us to critically reconsider several dogmas, such as the supposed increase of mineralogical “maturity” during long-distance fluvial transport, and forges a key to unlock the rich information stored in sedimentary archives, with the ultimate goal to reconstruct the evolution of African landscapes since the late Mesozoic.

The Blue Nile River Basin contains a thick fluvio-lacustrine sediment succession of Permian to Jurassic age. Its evolution is linked to extensional tectonics during break-up of Pangea in the aftermath of the Carboniferous-Permian glaciation. We collected sandstone samples from several sections in order to study the tectonic evolution and possible impacts of environmental perturbation around the Permian-Triassic boundary. Based on thin-section petrography, bulk-rock geochemistry, heavy mineral spectra, and detrital zircon U-Pb ages we are able to establish a provenance model for the Permian-Triassic basin-fill evolution. The results reveal distinct differences between Lower Permian and Upper Permian to Upper Triassic sediments. The Lower Permian sandstones are rich in feldspar, carbonate cement, and relatively unstable heavy minerals like apatite and garnet. The chemical index of alteration and trace elements suggest little chemical weathering and proximity to the source area. Upper Permian to Upper Triassic sandstones, however, contain a large amount of ultra-stable heavy minerals, and geochemical data point to intense chemical weathering, reworking and/or recycling. In the Lower Permian, detrital zircon U-Pb age spectra are dominated by Pan-African and Tonian ages, whereas Upper Permian and Upper Triassic samples show a higher proportion of old zircons and young zircons (c. 1 Ga and c. <541 Ma) probably from intraplate magmatic rocks. The results show that during the Upper Permian and Triassic, uplift and unroofing was happening accompanied by climate change.

The Gross Brukkaros (Namibia) reflects a broad dome structure showing a crater-shaped depression with numerous peripheral beforsitic carbonatite dykes. These dykes frequently contain an extreme load of basement (Nama-group) xenoliths (> 60 vol.%) including shales, quartzites, granites and gneisses. While xenoliths of exposed country rocks (mainly shales) show an angular habit, a pronounced rounding of xenoliths from other lithologies proves a wide transport and strong abrasion. This consumption of xenolithic material may result in remarkable contamination of the carbonatitic magma. MicroXRF mapping and optical microscopy provides first evidence that the corrosion and alteration of crustal xenoliths is controlled primarily by the xenoliths´ mineralogy and geochemistry. While some xenoliths exhibit distinct zoning reflecting a progressive leaching, others appear to be relatively inert. This proves the Gross Brukkaros of being an ideal natural laboratory to study the influence of crustal contamination in the carbonatitic system, particularly at the subvolcanic-volcanic depth transition. On the other hand, cross-cutting carbonatite dykes generated diatremes almost completely composed of quartz. A closer proximity to the diatreme yields an increase of the Si content in the dykes. In some cases, dykes occur with an extremely high proportion of microscopic xenolith fragments (>95 vol.%) and only subordinate proportions of carbonate. This indicates evaporation of the carbonatite melt during eruption, while the inherent Si remains as a residue along with the xenolith fragments and is precipitated in the diatreme breccia. Combined with C and O isotope systematics, carbonate crystallization is suspected to have proceeded under super-cooled conditions at ~150 °C.

The Chico Sill Complex (Northeast New Mexico) is the result of magmatic episodes from ~37 Ma to 20 Ma and produced a diverse and compositionally discontinuous suite of mostly intrusive silica-saturated and silica-undersaturated rocks. The Chico Phonolite was emplaced ~ 26 to 20 Ma in dikes and large sills. Sills of different composition may be stacked 2 and 3 thick. They bear no chemical affinity to the bulk of other rocks in the complex based on normalized trace element diagrams. Candidates for parent melts are scarce. At least two distinct trends are noted in Zr-La Space. A higher-Zr trend includes dikes and three sills and may represent evolution of a primary phonolite melt. The most-evolved sill (Point of Rocks Mesa) is the last-gasp of phonolite magmatism and likely the companion immiscible silicate for a calciocarbonatite dike 10 km distant.

Calciocarbonatite is a miniscule portion of the complex (outcrop limited to a few hundreds of m²⁾. The carbonate mineral is impure calcite (Mn>Fe>Sr>Mg>>Ba) in matrix goethite. Other minerals present include barite, pyrite, and REE minerals containing Ca and Ca-Ti next to the calcite. Normalized Ba, Th, REE, Y and Sr show 100 times enrichment in the carbonatite. Mineralogy, texture, and O-C isotopes suggest that the original carbonatite melt may have been more sodic and experienced alteration similar to that of lavas at Oldoinyo Lengi. Owing to the distance between outcrops, the separation of the melts (and phonolite evolution) occurred at much greater depth.

Nephelinites are strongly SiO₂-undersaturated volcanic rocks that are often associated with phonolites and carbonatites. In the Gregory Rift in East Africa several major nephelinitic-phonolitic volcanoes occur, with some of them being associated with carbonatitic rocks (e.g., Oldoinyo Lengai, Kerimas, Mosonik, Shombole, Meru), while others lack carbonatites (e.g, Sadiman, Essimingor, Burko). We characterize the magmatic evolution of the Burko volcano and compare our results with published data from spatially associated nephelinite-phonolite±carbonatite associations in the Gregory Rift and elsewhere.

Overall, nephelinites show mineralogical differences, are variably evolved (in terms of X_Mg, LILE and HFSE), and in some cases peralkaline (Na+K/Al >1) nephelinites do occur. Besides nepheline, clinopyroxene and apatite, garnet, magnetite, perovskite and titanite are magmatic phases in most cases. However, magmatic ne-cpx-grt-ttn assemblages can be distinguished from those with ne-cpx-mag-prv. Other phases, such as wollastonite, melilite, combeite, aenigmatite, sodalite and others are restricted to some occurrences and resemble different geochemical flavors of nephelinites, different crystallization conditions, variable differentiation stages and different levels of peralkalinity. Redox- and silica activity-dependent phase equilibria allow for constraining and comparing the magmatic evolution of the different localities by combining textural with mineral chemical data.

In general, high redox conditions above FMQ and peralkalinity seem to favor the formation of carbonatites. However, in several cases that meet these conditions, no carbonatites are exposed and worldwide, carbonatites are often associated with nephelinites that are not peralkaline. We discuss the potential for nephelinites to exsolve carbonate-rich liquids based on a petrological and geochemical comparison of different occurrences.

Foidites and melilitites are strongly SiO₂-undersaturated rocks that form by extremely low degrees of partial melting of the metasomatically overprinted lithospheric mantle. In Central Europe, they occur in volcanic fields, dike swarms or as isolated stocks and diatremes.

Our detailed study on foidites from SW Germany indicates two distinct age groups with marked differences in mineralogy and mineral chemistry: Based on in-situ U‑Pb age data (apatite, perovskite, zircon) a Miocene cohort (~ 9–19 Ma) of predominantly olivine melilitites and melilite-bearing nephelinites can be distinguished from a much older Upper Cretaceous to Lower Eocene group (~ 48–68 Ma) of melilite-free nephelinites and nepheline basanites. This contrasts with previous K-Ar whole-rock and mineral data suggesting continuous magmatism between 90 and 6 Ma.

The older group is characterized by the frequent occurrence of green core pyroxenes, hydroxyapatite, and minor feldspar, whereas the younger group contains melilite, late magmatic fluorapatite, Ba- and F-rich mica and occasionally perovskite, but no feldspar. It crops out in the Freiburger Bucht and the Bonndorf Graben, the Vosges (France), the Odenwald and Kraichgau region, in the Taunus and the Lower Main Plain, whereas the younger group is represented by occurrences in the Hegau, the Urach region and the Central Upper Rhine Graben including the Kaiserstuhl.

As part of the Central European Volcanic Province, the spatial distribution and age of these rocks reflect regional tectonic events, while the petrologic contrasts between the two age groups indicate heterogeneous crystallization conditions and/or magma source variations such as different formation depths.

The Gardiner (E-Greenland) and Kovdor (Russia) alkaline complexes display a similar succession of rock types comprising dunites-pyroxenites, ijolite series rocks, melilitolites and carbonatites. Although similar melanephelinitic parental magmas are suggested for both complexes, they display enrichment in HFSE at strikingly different evolutionary stages: At Kovdor, melilitolites are barren but carbonatites are mineralized with HFSE. In contrast, melilitolites at Gardiner contain ore-grade accumulates of perovskite having wt.%-level contents of Nb, Ta and REE, while associated carbonatites are barren. Previous studies suggested that HFSE-poor carbonatites at Gardiner were formed by liquid immiscibility while Kovdor carbonatites result from fractional crystallization and retained high HFSE contents. These two evolutionary trends were explained by a different CO₂-dependent stability of melilite vs. clinopyroxene+nepheline+calcite during the ijolite stage [1]. However, it is poorly investigated how the HFSE budget is affected by the crystallization of Ti-phases during different stages of the magmatic evolution, which are stabilized depending on magma composition (i.e. aTiO₂, aSiO₂) but also on intensive parameters such as P, T, and fO₂ [2]. Preliminary results suggest that, in contrast to Kovdor, magmas at Gardiner had physiochemical conditions which favoured abundant crystallization of Ti-phases along with co-precipitation of HFSE earlier in the sequence. This is supported by (1) pyroxenites with abundant Ti-magnetite and ilmenite, (2) titanite-rich ijolites and (3) perovskite-rich melilitolites. Possibly, Ti-rich melts reflect a distinct mantle regime beneath E-Greenland, which also produced anomalously Ti-enriched flood basalts ~6-10 Ma before.

[1] Veksler et al. (1998) J.Pet. 39, 2015-2031; [2] Marks et al. (2008) CG 257, 153-172

Halogen (F, Cl and Br), S and δ³⁷Cl variations within grains of Cl-rich minerals sodalite and eudialyte from peralkaline rocks of the Ilímaussaq intrusion were determined using Secondary Ion Mass Spectrometry (SIMS). Samples show either sodalite and eudialyte in direct contact, or sodalite/eudialyte embedded in Cl-free minerals (nepheline, feldspar). Comparing samples allows deciphering potential halogen and S exchange between these minerals during rock cooling.

Results suggest that sodalite (7 wt%) and eudialyte (1.2 wt%) have remarkably constant Cl concentrations. In samples with adjacent sodalite and eudialyte F increases at sodalite boundaries and decreases at eudialyte boundaries. In sodalite not in contact with eudialyte F concentrates at the edges, something obscured by F-rich inclusions. In eudialyte not in contact with sodalite F is constant with no variations at the edges. Br is also constant in eudialyte, but in sodalite its concentration decreases towards the edges. S also is constant in eudialyte, and concentrates significantly at the edges of sodalite, especially strongly if sodalite contacts eudialyte. In hydrothermal eudialyte Cl is low at the edge with higher concentrations away from the edge. Br and S correlate with Cl while little F variation is observed.

δ³⁷Cl in eudialyte is higher than in adjacent sodalite. Within individual grains δ³⁷Cl is higher at the edges than in the centre. Between sodalite grains δ³⁷Cl can vary a few tenths of a permille, while between eudialyte grains, variations can even be higher. In hydrothermal eudialyte δ³⁷Cl increases significantly at the grain boundary with values up to +3.5‰.

Prof. Vening Meinesz opened up the oceans for high precision gravimetric observations. Today, his submarine adventures are an inspiration to my science and education in gravimetric research. We wil follow him along his voyage aboard the K18, along which I will discuss several applications using global gravity field models. The theory of isostasy allows us the use the static gravity field to study GIA processes in Fennoscandia and North America. Also, observed crustal structure from active seismic experiments can be used to correct the gravity field and study the upper mantle. With a regional crustal model of the British Isles and surrounding oceans I was able to study the density variations in the lithospheric mantle underneath the crust. This study revealed a highly varying upper mantle density signature, but compared with seismic tomography large differences were seen. We show that this mismatch can be traced back to regularisation techniques used in seismology. This opened up the the study of mantle convection and its interaction with lithosphere. Seismic-derived mantle anomalies are still highly uncertain but might be improved with future gravity-rate datasets. Preliminary studies show potential in reducing the uncertainty in viscosity structure of the Earth. Finally, with the GOCE mission, a new boost has been given to the use of gravity gradients, I discuss an approach in inverting the full gravity gradient tensor estimating density structure of a subducting plate. By showing this variety of studies, I hope to inspire you to use satellite-derived global gravity fields.

The international networking initiative AlpArray Gravity Research Group (AAGRG) focused on the compiling homogeneous surface-based gravity datasets across the Alps and adjacent areas, on creating digital data sets for Bouguer and Free Air anomalies. In 2016/17 all ten countries around the Alps have agreed to contribute with point or gridded gravity data and data processing techniques to a recompilation of the Alpine gravity field in an area which is limited by 2° to 23° East and 41° to 51° North. For this recompilation, the group rely on existing national data.

The AAGRG decided to present the data set of the recalculated gravity fields on a 2km x 2km and 4km x 4km grid for the public. The densities used are 2670 kg/m3 for landmasses, 1030 kg/m3 for water masses above and -1640 kg/m3 below the ellipsoid. The correction radius was set to the Hayford zone O2 (167 km). The new Bouguer anomaly is compiled according to the most modern standards and reference frames (both location and gravity). Geophysical indirect effect and atmospheric corrections are also considered. In the Western Mediterranem (Ligurian Sea) completely reprocessed ship data of the Service Hydrographique et Océanographique de la Marine/Bureau Gravimétrique International were used. Marginal parts of the map were filled by GGM data.

Main aim of the work of the AAGRG is to release a gravity data base which can be used for high-resolution modelling, interdisciplinary studies from local to regional to continental scales, as well as for joint inversion with other datasets.

We present a high-resolution investigation of the Ivrea Geophysical Body (IGB) at intra-crustal scales in the Western Alps. The IGB is a sliver of Adriatic lower lithosphere, located at anomalously shallow depths, and presenting positive gravity and fast seismic anomalies. Despite comprehensive information from previous studies, structural questions persist on the IGB and on its structural relation with the Ivrea-Verbano zone (IVZ), which exposes lower-to-middle crustal composition outcrops at the surface. Therefore, we measured 207 new gravity data points, obtaining a coverage of ca. 1 point every 4-to-9 km² across the IVZ, and we installed 10 broadband seismic stations (IvreaArray) along the linear West-East profile of Val Sesia, operated for 27 months. We compiled a surface rock-density map and used it to define the density-dependent terrain-corrected “Niggli” gravity anomaly to properly model the IGB density structure at depth. We modelled the IGB as a 3D, single density-contrast interface, obtaining 400 ± kg·m^-3 as optimal density contrast and a 20-km wide protruding structure, as shallow as 1 ± 1 km below sea level. The seismic data was then used to constrain the IGB shape along the 2D Val Sesia cross-section by means of a joint inversion of seismic receiver functions and gravity anomaly data. This has confirmed the marked density contrast and shallow segments reaching 1 to 3 km depth below sea level, and provide agreement with the rock’s physical properties (ρ, v_S) and the geological structures observed at the surface. These results are now published (doi:10.1093/gji/ggaa263 and doi:10.3389/feart.2021.671412).

The data sets presented here are used for the preparations of a 3-dimensional modelling of the gravity field in the Western Mediterranean/Ligurian Sea. As part of the AlpArray initiative and the German priority program MB-4D, various compilations of the gravity field are available: Bouguer and Free Air Anomaly, as well as variously calculated residual fields that provide new insight into crustal and lithospheric structures. The anomalies have been processed according to modern standards. The recalculations were part of the research of the international AlpArray Gravity Group. In particular, the residual fields in the area of the Ligurian Sea show hitherto unknown small-scale anomalies after subtraction of long-wave components (satellite gravimetry). The short wavelengths in the gravity field of different magnitudes suggest strong structuring of the lithosphere e.g., offshore Marseille (with an anomaly of about 60 mGal and in the areas between the French-Italian mainland and Corsica-Sardinia (with up to 100 mGal). Furthermore, the new compilations suggest that the crustal underground of this area is not formed by a uniform basin, but by domains of rather different densities. The Italian coastal region between Genoa and Livorno is characterized by a belt of positive anomalies (up to 60 mGal). The subsurface beneath the two islands of Corsica and Sardinia is characterized by strong negative anomalies in the residual field, indicating density deficits beneath. The new findings are supported by applications of Euler deconvolution, gradient methods, directional filters, and curvature calculations considering also the evaluation of GOCE gradients.

The Bohemian Massif represents the largest exposure of rocks deformed during the Variscan orogeny. Western Carpathians form an arc-shaped mountain range related to the Alpine orogeny. In our study, the lithospheric structure of the key tectonic units in the area and their contact zone was analyzed by 2D gravity modelling along the NW-SE oriented CEL09 profile of the CELEBRATION 2000 seismic experiment. New gravity map compiled at the initiative of the AlpArray Gravity Research Group was used. This map is based on a uniform reprocessing of the national terrestrial gravimetric databases of ten countries of the wider Alpine region. The resultant 2D density model based on gravity data was constrainted by results of seismic reflection and refraction method. Applied densities were defined by transformation of the modelled P-wave velocities. A good correlation between the density and seismic models was shown. The resultant 2D density model consisting of five principal layers (sediments, upper crust, lower crust, lower lithosphere and asthenosphere) shows differences between the older, cooler and thicker Bohemian Massif (in average: ~32 km thick crust, and ~120 km thick lithosphere), and the younger, warmer and thinner Carpathian-Pannonian region (~28 km crust, ~95 km lithosphere). The detected contact is delimited by a change in the Moho and the LAB topography, and assumes an overthrusting of the Western Carpathians onto the Bohemian Massif by ~30 km resulting in a neo-transformation of the crust/mantle and related lithosphere after subduction.

The Ligurian Sea in the western Mediterranean Sea is a back arc basin created through the Apennines Calabrian subduction zone between 30 and 15 Ma ago. The inner geological structure of this basin is not well known. To improve the knowledge about the density distribution of the crust and lithosphere, we performed a pre-processing of gravity data prior to 3D-modelling. This work is related to research in the MB-4D priority and AlpArray project.

The satellite gravity gradients from GOCE were directly interpreted and used for filtering of different wavelengths to calculate residual fields, Bouguer and Free-Air anomalies as well as invariants and Euler-Deconvolutions. Furthermore, seismic profiles from several ship-borne surveys as well as OBS measurements of the AlpArray project (LOBSTER, GEOMAR, Kiel) and bathymetry data contributed additional information.

The processed data show an unknown anomaly offshore Marseille and the possibility of several underground structures with different densities. The basin itself is characterized by a mass surplus and positive anomalies with a maximum between Corsica and north-west Italia, while the anomalies underneath Corsica and Sardinia are neutral to negative.

The derived information will be used in the 3D-modelling software IGMAS+ to execute an inversion for the area and create a model of the mass distribution beneath the Ligurian Sea and its margins.

Sicily is a part of the central-Western Mediterranean area and represents a geotectonic boundary between the African and European plates. It is the result of a complex geological process based on a polyphasic evolution of a compressional step beginning with the Oligocene-Miocene clockwise rotation of Corsica-Sardinia simultaneously with the extensional processes of the Tyrrhenian basin. Consequently, the area is constrained by the continuing partial advance of the Sicilian-Maghrebian chain southwards and the Tyrrhenian extensional area towards the internal foreland areas (Hyblean domain). The study focuses on the creation of a 3D lithospheric-scale model of a 300 km x 400 km extended area in the central Mediterranean domain (Lat38°, Lat35°), which is consistent with the available geological and geophysical data, as well as with the observed gravity field. The reconstructed (simplified) geological setting consists of a lithospheric mantle, a crystalline basement (continental and oceanic crust), carbonates, the European margin and the Neogene-quaternary cover including volcanic bodies. The work aims to investigate the geometry of lithosphere integrating tomographic models in order to assess the major density contrasts and the lithospheric thermo-mechanical state. The regional 3D model provides also the boundary conditions for local thermal models to investigate afterwards.

Geoscientific studies in Antarctica are extremely challenging due to the remote location of the continent, its harsh environment and difficult logistics. Additionally, the continental crust is covered by an up to 5 km thick ice sheet, which makes surface based geoscientific studies extremely difficult. Gravity field measurements and gravity based subsurface models are therefore essential in studying the structure, properties and processes of the Antarctic subsurface.

In the last decades a large database of airborne, shipborne and ground based gravity data has been compiled. Recently, all existing and new gravity data were processed to infer an enhanced gravity field solution for Antarctica.

Subsequently, this new gravity field solution can be used for further geophysical studies. We use gravity disturbances to study subglacial topography, sediment thickness and Moho depths to improve respective existing models in Antarctica.

Studying these parameters on a continental scale, we apply 2D Parker-Oldenburg inversion in combination with results from other gravity based studies and further constraining data.

Additionally, we make use of the higher resolution of the new gravity grid (5 km) to study smaller regions in more detail, specifically the Weddell Sea area and Queen Mary Land. Here, we use gravity forward modelling constrained with ice penetrating radar and seismic data to infer geometric structure and densities of the subsurface.

In this contribution we present results of the Parker-Oldenburg Inversion and discuss the underlying parameters. Also, we show the resulting 3D forward models of the Weddell Sea area and Queen Mary Land.

Hydrocarbon seepage is widespread distributed at the southern Gulf of Mexico. During several research cruises in 2003, 2006, and 2015 (SO174, M67/, and M114) we used multidisciplinary approaches, including multi-beam mapping and visual seafloor observations with different underwater vehicles to study the extent and character of complex hydrocarbon seepage in the Bay of Campeche, southern Gulf of Mexico. Our observations showed that seafloor asphalt deposits occur at numerous knolls and ridges in water depths from 1230 to 3150 m. These striking seafloor elevations are formed by diapirs of Jurassic salt deposit associated by hydrocarbon accumulations. The deeper sites like Chapopopte and Mictlan knolls were characterized by asphalt deposits accompanied by extrusion of liquid, and very heavy oil in form of whips or sheets, and in most places by gas emissions, and the presence of gas hydrates (Tsanyao Yang, Mictlan, and Chapopote knolls). Molecular and stable carbon isotopic compositions of gaseous hydrocarbons suggest their primarily thermogenic origin. Relatively fresh solidified asphalt structures were settled by bacterial mats and vestimentiferan tube worms growing through cracks and from under the edges of pavement. The gas hydrates at Tsanyao Yang and Mictlan knolls were covered by a 5-to-10 cm-thick reaction zone composed of authigenic carbonates, detritus, and microbial mats, and were densely colonized by 1–2 m long tube worms, bivalves, snails, and shrimps. The extent of all discovered seepage structure areas indicates that emission of complex hydrocarbons is a widespread, thus important feature of the southern Gulf of Mexico.

Cliffs line many erosional coastlines. Localized failures can cause land loss and hazard, and impact ecosystems and sediment routing. Links between cliff erosion and forcing mechanisms are poorly constrained, due to limitations of classic approaches. Combining multi-seasonal seismic and drone surveys, wave, precipitation and groundwater data we study drivers and triggers of 81 failures along the chalk cliffs on Germany’s largest island, Rügen. We have found that marine processes are negligible in triggering failures but efficient in removing the deposits. Instead, cliff failure has been associated with terrestrial controls on soil moisture and groundwater. During the vegetative season, evapotranspiration impedes groundwater flow into the cliff face. When vegetation is dormant, failure frequency correlates with lunar-mediated precipitation. Failures are triggered by relative air moisture and rain, leading to clustered events during night time. Drier terrestrial conditions prevent smaller failures, which causes beach erosion and ultimately prepares the cliff for sector collapse.

Numerous studies on submarine iron-rich sediments (BIF, ironstones, etc.) focus on environmental changes and ocean chemistry, however, many questions related to underlying hydrothermal processes remain unresolved. As proximal chemical sediments, Lahn-Dill-type iron ores can provide insight into mechanisms of hydrothermal seafloor alteration related metal scavenging, and subsequent Fe-mineral deposition.

Lahn-Dill-type iron ores formed during the Middle/Upper Devonian within the Rhenohercynian back-arc basin associated with intraplate alkali basaltic volcanism. Ores formed on top of volcanogenic successions proximal to centres of volcanic activity. Typically, they occur as hematite-(siderite-)quartz ores reaching up to 60 wt.% Fe. We sampled a 5 m profile within the Fortuna mine in the eastern Rhenish Massif (Lahn syncline, Germany) and conducted a detailed petrographic study and whole rock ICP-MS as well as in-situ LA-ICP-MS geochemical analyses.

Iron is commonly mobile under reducing and acidic conditions. However, geochemistry of Lahn-Dill-type iron ores indicates that hydrothermal fluids may have been able to mobilise HFSE pointing at possible alkaline fluids. This is suggested by positive correlations of Fe with certain HFSE including Zr and HREE. Upon venting into seawater, iron likely precipitated as oxyhydroxides that preferably scavenged Si, W, Mo, Pb and V complexes from seawater by sorption. Subsequent deposition on the seafloor as a Si-Fe-rich gel is indicated by crescent-shaped shrinking cracks. Today, mineral assemblages within ore are characterized by fused hematite mats, hematite dispersed in quartz and/or siderite and microcrystalline quartz that may either be interpreted as diagenetic dissolution-precipitation processes, cyclic changes in primary fluid composition, or potentially both.

Exploration of carbonatite-associated REE-deposits is challenging due to heterogeneous ore distribution and variable and often complex ore mineralogy. The Kieshöhe carbonatite in SW Namibia represents a subvolcanic occurrence hosting dolomite, calcite and ankerite carbonatite dykes, ring dykes and diatremes. Petrography, whole rock geochemistry and microXRF imaging provide insights into the role of silicate xenoliths for the REE mineralization in a subvolcanic environment. Xenolith-rich carbonatites are relatively REE-poor with only minor monazite mineralization, whereas xenolith-free carbonatites show high REE-contents incorporated primarily into REE-F-carbonates. Moreover, the additional presence of barite and pseudomorphic replacement of hexagonal precursor minerals suggest the former presence of burbankite, which might represent the potential REE source. The strong association of REE-minerals, barite and quartz furthermore indicates the simultaneous hydrothermal transport of REE, Ba, S and Si. In particular, Si-saturated hydrothermal fluids promote the potential of sulfate complexes to mobilize REE [1]. Since an enhanced xenolith resorption in xenolith-rich parts of the complex increases the Si content of the hydrothermal fluid and thus the capacity of REE transport, REE precipitation is inhibited in such sections but supported in xenolith-free sections. This demonstrates that xenolith entrainment not only has a strong influence on REE mineralization in synmagmatic stages [2], but may also have strong effects in post-magmatic hydrothermal stages of the carbonatitic system. This observation can potentially be used as a first-order field-based exploration indicator for REE-mineralization in carbonatites.

[1] Cui et al. (2020). Geology, 48(2), 145-148.

[2] Giebel et al. (2019). Journal of Petrology, 60(6), 1163-1194.

Due to the closure of coal mining in the northwestern German coalfields, active mine water drainage becomes technically redundant. As a result, the rising mine water table affects the subsurface stress conditions and may induce heterogeneous ground movements of fault blocks. Petrophysical properties of the Upper Carboniferous (Westphalian A and B) rocks are crucial to understand subsurface behavior during mine water rise. As a part of the interdisciplinary FloodRisk project, we present a petrophysical and petrographical characterization of Westphalian A and B drill cores from the Ruhr area.

Based on fining-upward cycles consisting of basal sandstones (medium-grained, planar laminated) followed by siltstones with intercalated lower (planar/wavy laminated to bioturbated/rooted) mudstones and coal seams at the top, that are locally overlain by clayey deposits, the rock succession was interpreted as fluvio-deltaic facies association. Petrophysical measurements on core plugs indicate that most samples are generally tight (mean permeability: 0.26 mD; mean porosity: 6.4 %) but reservoir properties vary by grain size and facies. Petrographic analyses indicate that sandstone cementation is dominated by ferroan carbonate (mostly siderite and Fe-calcite) and quartz overgrowth in the pore space. Locally, veins are cemented by ferroan calcite or sulfides. Feldspar-rich rock fragments are often replaced by kaolinite, reducing the secondary porosity.

The outcome of this investigation will be integrated into an interdisciplinary model that involves geomechanical, geodetic and geophysical data in order to understand subsurface flow. Furthermore, data can be used to consider the fluid distribution for potential geothermal energy use.

Das natürlich geschlossene System (NGS), das von (Stensen Niels 1669) begründet wurde, ist ein Modell des Komplexes von exakt gemessenen Parametern dualer Gesteinssysteme der Geologie. Die angewandte Messtechnik in den Geowissenschaften deduziert funktionale Zusammenhänge der Proportionalität (h = m) und (h = - m + C). Die Umformung der Funktionen liefert die Invarianten des geologischen Binärsystems (h/m = ±1). Die Funktionen stehen orthogonal aufeinander, sie sind symmetrisch, invers und relational. Reflexive Messwerte (Offhaus 2020) bestimmen die Lagerung der Gesteinssysteme, während die Lote (geologische Profile), im Unterschied zur Lagerung, transitive Eigenschaften aufweisen. Transitive und reflexive Werte liegen in der Geologie partiell übereinander. Die arithmetische Relation (h = - m + C) hat neben der Transitivität die besondere Eigenschaft der Identität von Funktion und Umkehrfunktion durch den Betrag des Anstiegs von (- 1). Inzidenzmatrix und gerichteter Graph (Metz 2010) belegen die Einheit und Verflechtung der Eindeutigkeit dualer Gesteinssysteme in der Geologie. Das NGS hat die Eigenschaften der Symmetrie, der Reflexivität, der Transitivität, es ist nicht antisymmetrisch und nicht asymmetrisch, somit ist es Äquivalenzrelation und Halb- oder Quasiordnung.

Die mathematischen Anwendungen in der Geologie, wie z.B. (Bentz A. 1961); (Eisbacher Gerhard A. 1996), die Verknüpfung von geologischen Prozessen der Tektonik mit der mathematischen Eigenschaft von „Umkehrfunktionen“ zum geologischen Begriff „Inversionstektonik“ (Kley J. 2013) oder die Anwendungen der Session „vorwärts und inverse Modellierung“ von geologischen Daten (Matenko L. u.A. 2020) verifizieren das NGS. Ebenso bestätigt die ausführliche Formenanalyse von Windkantern (R. Schwenecke 2020) die theoretischen Aussagen des NGS mit gemessenen Daten von ca.1000 Windkantern in vollem Umfang, darüber hinaus Verbindungen zur Skaleninvarianz und zur Selbstähnlichkeit.

Das geologische Modell des NGS ist ein mathematisches Objekt, das sich zur Entwicklung einer theoretischen Geologie eignet.

The energy dialog varies by economic status. Western Europe and the United States suggest there is clean and renewable vs dirty and non-renewable energy, and further that clean energy is cheaper than dirty energy. In this narrative, carbon neutral drives the dialog. Some propose to eliminate coal, oil and even natural gas and nuclear altogether, and suggest that solar, wind and batteries can power the world and address climate change. The IEA just released a report on how net zero carbon might be accomplished by 2050. Notwithstanding the assumptions, which require scale and magnitude changes never before seen, the greater underlying assumption is that the emerging and developing world will participate. A different narrative exists in much of the rest of the world, led most profoundly by SE Asia, but also Africa, Latin America, the Middle East and to some degree Russia. Here billions of people seek affordable and reliable energy to lift themselves into economic prosperity. Here the energy transition is best interpreted by examining actions, not rhetoric. Emerging and developing economies have acted to feed their substantial and growing energy appetite with coal and hydro, with natural gas and nuclear growing, and solar and wind getting started but still very small relative to total consumption. Further, although the environmental concerns of the developing world include climate, they are more acutely focused on economic growth, which will then allow them to curb population growth as has been done in the US and Western Europe, and begin to reduce pollution of water, soil, and air. Given this dialog duality, a truly sustainable energy future must eradicate energy poverty while also going nature neutral-- minimizing the impacts of all forms of energy on air, land, water, and the atmosphere.

“Digital sedimentary petrology” models represent the microstructure of clastic rocks in 3D and use forward process models to simulate diagenesis in response to evolving burial conditions. This modeling approach predicts textures and morphologies that can be readily compared with natural samples and laboratory experiments. These models are useful tools for studying diagenetic processes and also are designed to predict rock microstructure in undrilled areas of the subsurface.

Digital petrology models are natural counterparts to “digital rock physics” models that use rock microstructure as input when simulating a broad array of fluid transport and geomechanical properties. Linking these models extends digital rock physics models beyond assessment of rock properties based on scans of physical samples to predicting rock properties in undrilled portions of the subsurface. Applications of this coupled modeling approach includes hydrocarbon and geothermal energy exploration and production, CO₂ sequestration, hydrogen and compressed air storage, wastewater injection, and groundwater studies.

Our work to date on the development of the Cyberstone™ digital sedimentary petrology model involves simulation of sediment deposition, grain rearrangement, mechanical compaction, chemical compaction (pressure solution as well as temperature dependent contact dissolution resulting from chemical corrosion), and growth of various cement types with various morphologies. Although the system was developed for clastic sedimentary rocks, we also have found it to be a useful tool for simulation of the evolution in fluid flow and geomechanical properties of evaporite rubble associated with the collapse of a chamber in a salt dome that is being used for nuclear waste disposal.

Fractures are the predominant flow pathways in low-permeability rocks. Understanding the fluid-rock interactions that occur in rock fractures and their effects on fracture aperture variations is important for assessing the sustainability of reservoir productivity. This study presents two long-term flow-through experiments with fractured pure quartz sandstones to investigate how fluid composition affects fracture changes over time. One sample was continuously flowed through with fluids (DI or Si-rich fluid), while the other sample was subjected to intermittent flow (DI) at certain time intervals. The results show that the hydraulic aperture of the sample with intermittent flow maintains relatively constant, and the pore fluid is enriched with Si that is higher than the corresponding quartz solubility. On the contrary, hydraulic aperture reduces by 50% of its initial value in the case of continuous flow. The pore fluid Si concentrations are far below the quartz solubility. Based on the microstructure variations of contact asperities and the fluid concentration changes, we demonstrate that pressure solution plays a dominant role in rock fracture deformation and permeability changes. The pore fluid composition has a remarkable effect on the permeability decay process. The cumulative Si in the pore fluid without flow would mitigate fracture closure by limiting pressure solution. In contrast, the continuous injection of DI would lead to the continuous mass transfer between the contact asperities and the pore fluid. The permeability evolutions in the two cases are likely governed by the Si precipitation process and the stress-driving dissolution process, respectively.

Clay cements can occur pervasively throughout larger volumes of sandstone, thereby affecting the reservoir properties significantly. They affect irreducible water content and pore surface roughness. Moreover, any induced fluid or heat flow, as a consequence of hydrocarbon and geothermal production or CO2 sequestration, may have unwanted effects because of the clay minerals present. The effects will be dependent on the mineralogy, texture and distribution of the clay minerals. Clay minerals replacing detrital components (feldspars and rock fragments) have limited effect because of their dispersed and isolated occurrence. In this study diagenesis of intragranular clay in siliciclastic sandstones is evaluated, using Rotliegend deposits in the Southern Permian Basin and Lower Triassic Buntsandstein deposits as examples. This study clearly shows that large-scale fluid flow does not play a significant role and that much of the mass involved in diagenesis is retained more or less in situ. In the sandstone proper, clay occurs in various ways: as detrital laminae and beds, as patches related to burrows, and as grain coatings through clay infiltration. In addition, clay occurs as cements rimming grains and replacing detrital feldspars and rock fragments. The apparent detrital clay is partly or largely modified during burial diagenesis and much of the clay is authigenic. Not only the mineralogy is changed but also the location and distribution of the authigenic clays. In conclusion: authigenic clays in reservoir sandstones, including clay rim cement, are genetically associated with and directly linked to infiltrated or bioturbated clay.

The clastic Lower Triassic Buntsandstein Formation in the Upper Rhine Graben of SW Germany and NE France has been identified as an attractive geothermal reservoir due to its fracture density and exceptionally high matrix porosity at depth levels of economic geothermal energy extraction. New petrophysical data from deep exploration wells reveal the existence of ternary porosity systems evolved during a multi-phase subsidence history and diagenesis especially at intra-graben structural highs. Primary elements of these porosity systems are high-permeability faults and fractures which can be utilized as technical fluid conduits connecting geothermal injectors and producers. Second component is the primary matrix porosity, controlled by pure mechanical compaction. Third component is an interconnected system of secondary pores and micropores. Secondary porosity originates from diagenetic dissolution of chemically and mechanically unstable framework grains like feldspars and rock fragments. At depths of about 2.300 m secondary porosity and microporosity can exceed the compaction-controlled primary porosity of around 7 %, causing high total pore volumes of up to 21 %. All matrix pore types are linked to form an interconnected pore network hosting significant connate brine volumes. These brine volumes don´t contribute to technical hydrogeothermal fluid cycling but increase the thermal capacity of the reservoir and favour heat conduction. Although this phenomenon has been described from hydrocarbon pools, their quantitative significance in geothermal reservoirs is still poorly understood. Micro-scale reservoir simulations may help to upgrade geothermal prospects.

Geochemical processes such as mineral dissolution and precipitation alter the microstructure of rocks, and thereby affect their hydraulic and mechanical behaviour. Quantifying and considering these property changes in reservoir simulations substantially supports risk assessments related to geological subsurface utilization.

In our virtual laboratory, 3D pore-scale models of typical reservoir sandstones are applied to determine the effective hydraulic and elastic properties of sandstones. In order to adequately depict characteristic distributions of secondary minerals, the virtual samples are systematically altered, and the resulting changes in geometric, hydraulic, and mechanical rock properties are quantified. Characteristic pore space alterations for a reaction- and a transport-limited precipitation regime are approximated by correlating precipitation with fluid flow velocity magnitudes. A purely surface reaction-limited regime is represented by a uniform modification of the pore space, whereas transport-limited precipitation is characterised by the successive clogging of pore throats and a drastic decrease in permeability. It is demonstrated that the location of mineral growth within the pore space strongly affects the magnitude of permeability reduction. The presented digital pore-scale simulations enable to quantify changes in permeability and stiffness resulting from geochemical processes, and thus are relevant for a wide range of natural and engineered subsurface applications.

The dynamics of subduction zones is linked to the rise and demise of forearc and backarc sedimentary basins in the overriding plate. Subsidence and uplift rates of these distinct basins are controlled by variations in plate convergence and subduction velocities and determined by the rheological and thermal structure of the lithosphere. In this study we conducted a series of high-resolution 2D numerical models of oceanic subduction and subsequent continental collision. The numerical code 2DELVIS involves erosion, sedimentation, and hydration processes. The models show the evolution of wedge-top basins overlying the accretionary wedge and retro-forearc basins in the continental overriding plate, separated by a forearc high. These forearc regions are affected by repeated compression and extension phases. Higher subsidence rates are recorded in the syncline structure of the retro-forearc basin when the slab dip angle is higher and the subduction interface is stronger. This implies the importance of the slab suction force as the main forcing factor creating up to 3-4 km negative residual topographic signals. Extensional back-arc basins are either localized along inherited weak zones at large distance from the forearc region or are initiated just above the hydrated mantle wedge. Back-arc subsidence is primarily governed by crustal and lithospheric thinning controlled by slab roll-back. Our results are compared with the evolution of the Mediterranean and we classify the Western and Eastern Alboran, Paola and Tyrrhenian, Transylvanian and Pannonian Basins to be genetically similar forearc–backarc basins, respectively.

Submarine lobes are high aspect ratio sand-rich deposits that are fed by turbidity currents and debris flows via channels in deep-marine settings. As a major component of submarine fans, they represent 1) an important archive of palaeo-environmental change, 2) sinks for organic carbon and pollutants, and 3) are also of economic interest. Classic models describe lobes as purely depositional tabular sheets that thin and fine from an apex. Over the last decade, outcrop studies, numerical and stochastic modelling, and flume tank experiments have been undertaken to constrain the hierarchy, geometries and stacking patterns of submarine lobe deposits and test these simple models for lobe deposition.

With this talk I want to give an insight into the discoveries made and new understanding gained about lobe deposits, including: 1) The variety of lobe fringe deposits depending on the level of confinement experienced by the lobe: Distinguishing frontal and lateral lobe fringes enables more accurate reconstructions of the geometry, distribution, and orientation of deep-water lobes, whereas the recognition of aggradational lobe fringes enables the reconstruction of subtle intrabasinal relief. 2) Boundary conditions governing lobe dimensions: lobe dimensions, and their relation to their feeder channels, vary with basin-floor angle, and the concentration of sediment within the feeding gravity-current. Discharge rate is also important, controlling when deposition starts. Because these parameters change during evolution of natural deepwater systems, lobes formed at different times will have different geometries.

Permian deposits are found in outcrops and in the subsurface of Central Tunisia. Their sedimentary and stratigraphic characteristics and origin are not fully understood and represents the main focus of this work. Base level changes, location of the palaeo-coastline and stratigraphic architecture and sandstone connectivity of formations are insufficiently known. Answering these questions will impact future hydrocarbon exploration and improve the geological understanding of Tunisia.

Seismic lines and well data of the Jeffara Basin have been re-interpreted and seismic data converted to depth domain. The results indicate a shallow marine rimmed shelf depositional environment, with dimensions of 100 square kilometers and a general east-west orientation. Seventy kilometers to the north of the reconstructed paleoshore line twelve stacked reef complexes up to 3000 meters thick were identified. Literature study of the area indicates a tropical climate. Structurally, it was observed that the Permian is not affected by major normal faults and appears at large scale gently folded. Wells and outcrop investigations provide lithological information, which is composed of limestone and dolomite, with intervals of sand and shale. The thickness gradually increases northwards, reaching 4000 meter maximum.

Using DionisosFlow, 3D stratigraphic models are constructed. They provide a number of equiprobable scenarios of facies distribution through the basin matching the available data. This modelling approach highlighted the impact of base level changes on reef geometry and in the lateral connectivity of clastic deposits. It also indicates depocenters shifting, shoreline evolution and feeder systems position and importance over time.

The distribution of rocks and rock properties is an important part of an overall strategy for reservoir development, placement of new wells and prediction of future production. It also provides a detailed look into the local development of a sedimentary basin. Here we present a case-study from the “Atled Creek” concession, onshore Nigeria. A 3D structural reservoir model of the concession was prepared from available industry seismic data and well logs. Four sandstone reservoirs within the Cenozoic have been identified in the “Atled Creek” and modelled in this study to highlight variations in the reservoir properties. Four available wells were subjected to conventional well log analyses and reservoir units were mapped on the 3D seismic volume. The resulting facies and property logs were upscaled and together with the interpreted seismic horizons and faults formed the input data for facies and property modelling. This resulted in frameworks of 3D facies, petrophysical and fault models. The fault model revealed the dominance of generally W–E trending faults. A major fault trending WNW –ESE (F1) separates the reservoirs into two major blocks with the existing well located in the southern block. Fault assisted anticlinal closure is likely the prominent trapping mechanism revealed by the structural model. The reservoir model classified the reservoirs as moderate to good with total porosity of 23.8 – 34.7% in reservoir unit A, 6.3 – 33.1% in reservoir unit B,3.1 – 42.8% in reservoir unit C and 6.4 – 41.7% in reservoir unit D.

The sedimentary succession of the Helmstedt Lignite Mining District at Schöningen in northern Germany includes the upper Paleocene to lower Eocene Schöningen Formation and the middle Eocene Helmstedt Formation. It covers the entire Paleogene greenhouse phase including the long-term Early Eocene Climatic Optimum (EECO) and short-term events such as the Paleocene-Eocene Thermal Maximum (PETM/ETM1) and its gentle demise almost continuously in an estuarine situation at the southern edge of the proto-North Sea. Due to the interaction between changes in sea level, salt withdrawal in the subsurface and climate-related changes in runoff from the hinterland the area was subject to frequent changes between marine and terrestrial conditions, repeatedly leading to peat formation. A new robust stratigraphic framework for the succession is based on a combination of biostratigraphy, eustatic sea-level changes and carbon isotope data.

The more than 200 m thick succession with 13 up to 15 m thick lignites offers a rare opportunity to study Paleocene–Eocene near-coastal ecosystems and to trace the effects of long- and short-term climate change on the diversity and composition of the plant communities across 10 million years during the Paleogene greenhouse. As far as known, the estuarine succession at Schöningen is worldwide unique with respect to duration and continuity. The aim of an ongoing project is to study the response of the vegetation in this paralic environment to climate change by applying pollen and spores as proxies.

Melt inclusions in zircon (MIZ) directly reflect the physicochemical state of the magma during zircon growth. However, their potential as geothermometers and petrogenetic indicators is still poorly explored. Therefore, we investigated MIZ from well-characterized mafic and felsic rocks of the Bushveld Complex (South Africa) and acquired a novel dataset of major, trace and volatile element contents. Re-homogenized MIZ of all rock types display rhyolitic compositions (65-78 wt% SiO₂) and similar H₂O contents (1.6-4.0 wt%). Liquidus temperatures of MIZ obtained from normative Qz-Ab-Or and rhyolite-MELTS modelling indicate melt entrapment at 930–850°C (at 200 MPa), tailing down to 700°C in some samples. For rutile-bearing mafic cumulates of the lower BC (Marginal and Critical Zone), these temperatures overlap with TiO₂ saturation temperatures of MIZ as well as with Ti-in-zircon of host crystals using aTiO₂=aSiO₂=1.0 [1], in accordance with textural associations of zircon+rutile+quartz. In contrast, MIZ in all rutile-free, magnetite-ilmenite-titanite- and quartz-bearing rocks of the upper BC (Upper Zone ferrogabbros, granitic rocks), display strikingly lower Ti contents, but also higher ƩREE and lower Th/U. Cross-calibration of TiO₂ saturation (MIZ) and Ti-in-zircon thermometers with MIZ liquidus temperatures suggests that zircon crystallized at highly reduced aTiO₂~0.3, significantly below aTiO₂~0.6 previously estimated for rutile-free rocks in the literature, usage of which would underestimate zircon crystallization temperatures by 50-100 °C. In summary, MIZ may inherit chemical signatures of host rocks, are powerful zircon geothermometers and provide constraints for aTiO₂ in Rt-free rocks.

[1] Ferry & Watson (2007) CMP 154, 429–437; [2] Hayden & Watson (2007) EPSL 258, 561-568

Zircons of magmatic rocks can show enormous variations in Th/U ratios (0.2 to 100) and extreme Th/U zoning. We present data from felsic and mafic rocks of the Bushveld Complex in South Africa. Zircon grains in mafic cumulate rocks reveal Th/U ratios up to 70, those in felsic rocks barely exceed 1.0. In mafic rocks zircon mostly occur together with Rt-Bt-Kfs-Qtz in intercumulus domains, and crystallized during final magma cooling between 900 and 700°C, after >75% of fractional crystallization. The resulting zircons reveal very distinct Th/U zoning trends. Group (1) zircons show systematic increase in Th/U from core to rim (from 0.5 to 20), accompanied by a systematic decrease in U content (from >170 to 10 ppm), group (2) zircons the opposite trend, and group (3) zircons nearly no zoning. Modelling result reveal that all three zoning trends can be explained by minor differences in Bt-Rt-Zrc crystallization history. Trend (1) results from Rayleigh-like fractionation due to zircon growth (±Rt), having different partition coefficients for U ≫ Th. Trend (2) results from zircon growth after onset of biotite-in reaction, causing breakdown of previously formed rutile, thereby releasing U≫Th. Trend (3) results from mass balance constrains, causing mutual compensation of fractionation effects. The absence of pronounced Th/U zoning of zircons in felsic Bushveld rocks also results from compensation of zircon fractionation due to coeval crystallization of abundant rock-forming minerals (Opx-Cpx-Hbl-Pl-Kfs-Qtz) at an early stage of fractional crystallization (10-20%), all being highly incompatible for Th and U [1]. [1] Gudelius et al. (2020). Chemical Geology 546, 119647.

Determining the tectonic evolution and thermal structure of a tectonic unit that experiences a subduction-related pressure temperature (P-T) loop is challenging. Within a single unit, P-T conditions can vary from top to bottom which can be only revealed by detailed petrological work. We present micropetrological data of the middle section of the Cycladic Blueschist Unit (CBU) in Naxos, Greece, which indicate a different P-T loop than the top of the section.

In the middle section, strong deformation associated with high-T metamorphism erases most of the earlier tectonometamorphic imprints preventing to apply "traditional" geothermobarometry methods. Using Zr-in-rutile and Ti-in-biotite thermometry coupled with quartz-in-garnet elastic barometry and phase equilibrium thermodynamic modeling, we identify a prograde path from ~15.4 kbar to ~19.9 kbar and from ~496 °C to ~572 °C, equilibration during decompression at ~8.3 kbar and ~519 °C followed by near-isobaric heating to ~9.2 kbar and ~550 °C (or even ~584 °C), and a final greenschist-facies equilibration stage at ~3.8 kbar and ~520 °C.

We compare these P-T estimates with published data from the top of the CBU section and find that the bottom half of the CBU on Naxos records higher peak high-pressure (HP) of about 4 kbar than the top, defining the thickness of the CBU to about 15 km in the Eocene. We determine that crustal thickening of up to ~15% occurs in the upper half of the CBU section during exhumation of the HP rocks in an extrusion wedge during convergence.

We present eclogites and garnet pyroxenites from Danmarkshavn (Greenlandic Caledonides). So far, one ultra-high pressure (UHP) location has been described from NE Greenland. There, thermobarometry yielded conditions of 972 ºC/36 kbar (Gilotti and Ravna, 2002).

Eclogites from Danmarkshavn show spectacular exsolution of Qtz from Cpx, which is known from UHP assemblages. The sample most suitable for unraveling precise conditions, however, is a garnet pyroxenite containing abundant Cpx and Opx, some Grt, minor accessory minerals as well as little retrograde Am and Pl. Opx and Cpx preserve high-pressure compositions in cores of large crystals and extremely low Al-content in Opx clearly indicate UHP conditions. A considerable portion of these minerals, however, reequilibrated during exhumation with especially Cpx showing complex retrograde zoning. We infer that Grt grains completely reequilibrated during net-transfer reactions producing Am and Pl.

Precise conditions in such rocks are often achieved by intersection of isopleths, e.g. Al-in-Opx with Grt-Cpx-Mg-Fe thermometry. Both isopleth sets have positive slopes in pressure-temperature space. If exhumation occurs along a trajectory steeper than the thermometer isopleth, equilibration of Mg-Fe-exchange during exhumation leads to possibly dramatic overestimation of peak conditions. In our sample, this yields up to 1000 ºC/>40 kbar. Based on Cpx and Opx core compositions alone, however, we infer considerably lower peak conditions of 800-830 ºC/30-32 kbar.

We find that micro-xrf scans of whole thin sections yield powerful data on mineral zoning, reaction progress and the degree of reequlibration. Such maps allow better defining targets for high-resolution mapping and high-precision microprobe work.

Geological models, as 3-D representations of subsurface structures, can be combined with gravity inversions to obtain geometric representations of geological objects with similar porperty distributions. These models are built on prior assumptions and imperfect information, and they often result from an integration of geological and geophysical data types with varying quality. These aspects result in uncertainties about the predicted subsurface structures and property distributions, which will affect the subsequent decision process.

We discuss approaches to evaluate uncertainties in geological models and to integrate geological and geophysical potential-field information in combined workflows. A first step is the consideration of uncertainties in prior model parameters on the basis of uncertainty propagation (forward uncertainty quantification). When applied to structural geological models with discrete classes, these methods result in a class probability for each point in space, often represented in tessellated grid cells.

A logical extension is the integration of geological forward operators into geophysical inverse frameworks, to enable a full flow of inference for a wider range of relevant parameters. We investigate here specifically the use of probabilistic machine learning tools in combination with geological and geophysical gravity and magnetic modeling. Challenges exist due to the hierarchical nature of the probabilistic models, but modern sampling strategies allow for efficient sampling in these complex settings. We showcase the application with examples combining geological modeling and geophysical potential field measurements in an integrated model for improved decision making.

The inversion of gravity data for crustal thicknesses is a nonunique problem. Therefore, additional independent information (e.g., seismic data) is needed to constrain the inversion process. Despite decades of exploration efforts related to mining and the installation of more seismic stations, knowledge on the deep crustal structure of southern Africa remains limited.

In this contribution we present a crustal thickness model for southern Africa: The initial model is determined by inversion of satellite gravity data. Here, we apply seismically constrained non-linear inversion, based on the modified Bott's method and Tikhonov regularization assuming spherical Earth approximation. The inversion hyper-parameters are determined by Monte-Carlo-Marcov-Chain (MCMC) simulation. The data quality of the (active and passive) seismic constraints is high in general, showing e.g. individual uncertainties per point. The problem is that the constraining data points are irregularly distributed, resulting in large areas without constraints. Therefore, in a next step, we want to validate and improve the modelling result for these unconstrained regions.

We use the initial constraining data set to geostatistically simulate a homogeneous crustal thickness model for the investigation region. For this, we apply a Sequential Gaussian Simulation (SGS) based on Ordinary Kriging that includes the uncertainties of the seismic data and allows to characterize uncertainties of the simulated points. The simulated crustal thickness model is then used to qualitatively validate the inversion result. Additionally, we redo the inversion process with a new constraining data set that combines the preexisting constraining points and the simulated model.

When Western Gondwana broke apart into the South American and African continents ⁓ 120 Ma ago, some of its cratons were broken apart as well. Following the isopycnic hypothesis, their long-term stability and often neutral to positive buoyancy can be explained by the counteracting effects of cooling (density increase) and iron depletion (density decrease). To separate these effects, we created the presented models following an iterative integrated approach using mainly seismic and gravity data. In the first step, seismic models of Depth to the Moho were created to allow correction of the gravity field and calculation of the residual topography. Second, based on mineral physics and S-wave tomography, we assessed temperature variations in the uppermost mantle and subtracted their effects from both residual gravity and topography. Afterwards, a joint inversion enables determination of potential compositional variations. Adapting the initially juvenile mantle composition leads to a change of thermal effects, thus the process was repeated iteratively until convergence. In result, we obtained self-consistent models of temperature, thermal and compositional density variations, and #Mg, a measure of iron depletion. Our results show deep depleted cratonic roots under the Amazonas, São Francisco, Paranapanema (South America), West African, Northern to Central Congo and Zimbabwe Cratons (Africa). Depletion appears to be mostly absent in the Rio de la Plata Craton of South America and its proposed African counterpart, the Southern Congo Craton as well as the Kaapvaal Craton below 100 km depth and the Tanzania and Uganda Cratons.

3D geological modelling in highly complex areas with sparse or ambiguous information is affected be conceptual uncertainty, which can be significantly reduced by the integration of gravity data. However, gravity modelling itself underlies the non-uniqueness problem, indicating that there is more than one model consistent with the observed gravity field. Therefore, cross-validation of gravity models by integration of regional geologic concepts, geometric and kinematic construction and restoration techniques helps solving this problem.

In this regard, we defined an integrated modelling strategy, which starts with extracting a-priori information from geological maps, 2D seismics, borehole and gravity data, which were independently analysed and conservatively interpreted; i.e. non-unique solutions were completely avoided. Subsequently, geologic interpretations were combined with gravity data, which was analysed by use of gradient calculation and 2D-EULER deconvolution. The resulting combined dataset was validated by use of 2D cross-section balancing techniques considering bed-lengths and area consistency. The resulting serial balanced cross-sections served as solid basis for a 3D gravity modelling.

Our integrated workflow was tested for the less-explored eastern part of the Subhercynian Basin (Saxony-Anhalt, Central Germany). We show that the combination of independently ambiguous data holds the potential to generate new insights into the local fault system, the topography of the crystalline basement (transition of the Mid-German Crystalline Rise and Rhenohercynian Zone) and outlines of salt structures as well as the setting of the base Cenozoic. Furthermore, modelling of long wavelength gravity anomalies provides new information on the crustal setting at the margins of the North German Basin.

With this study we revise and improve the three-dimensional lithospheric-scale structural and density model of Germany (3-D-D). Major shortcomings of this model resulted from joining three regional 3-D models that were poorly covered by data at their margins. Merging into a larger model revealed structural inconsistencies in these “marginal” domains. In order to resolve discrepancies between the units in a more consistent way we integrate newly available data from seismic reprocessing, tomography, and use 3-D gravity modelling to improve the fit between the modelled and observed gravity.

The recently initiated reprocessing of the DEKORP seismic profiles, for example, in the region of the Rhine Graben by the federal geological survey of Hesse (Bär et al. in prep.), indicate that previous assumptions on sediment thickness in certain regions, as well crustal structure and Moho depth need to be revised. We integrate this new structural information together with density variations derived from mantle seismic tomography (CSEM Europe, Fichtner et al., 2018; LSP_Eucrust1.0, Lu et al. 2018) and analyse the updated density distribution against the more detailed Bouguer gravity anomaly map of Germany (Skiba, 2011).

The update of the 3-D-D model is important for ongoing research in seismic hazard assessment in that it serves as a basis for thermal and rheological modelling helping to relate observed seismicity with spatial variations in strength. The model provides a data-consistent background for regional studies on sustainable use of geothermal energy and on the suitability of sites for the underground storage of radioactive waste or of CO2.

Tuwaiq Mountain Escarpment in the Central Saudi Arabia exposes the Late Jurassic carbonates, which are one of the world’s most prolific oil-producing strata in the subsurface. The outcrops provide a window of opportunity to study the architecture of these strata that is found usually complex due to heterogeneous lateral and vertical facies. These heterogeneities are sub-seismic in scale, thus, the information from outcrops bridge the gap between seismic and core data. This virtual field trip focuses on the Late Jurassic Hanifa Formation outcrops at Wadi Birk, central Saudi Arabia with an objective to highlight and display interwell scale heterogeneities associated with depositional architecture. The Hanifa Fm is one of the major hydrocarbon reservoirs in the subsurface of Saudi Arabia and is also in many respects analogous to the even more prolific overlying Arab D reservoirs.

The virtual field trip will include a 4x4 km² 3D digital outcrop model (DOM). The VRGS (Virtual Geoscience) platform will be used to run this field trip. The participants will be taken to one of the most spectacular exposures of the Hanifa Formation at Wadi Birk in Central Saudi Arabia. Depositional facies (in outcrop and thin section), 3D Digital Outcrop Models, and geophysical (GPR, Seismic) and petrophysical datasets (Spectral Gamma Ray - SGR) will be discussed. The main learning outcome of this field trip is to show reservoir equivalent facies in the outcrops but also provide clues into the intricacies of the stratal architecture. It will be demonstrated that the layered architecture is actually not so layered (as usually observed and published). Depositional cycles will be defined based on geological, geophysical, and petrophysical datasets (measured sections, core, thin section, and SGR). The mapping of the depositional cycles within the 4x4 km² area at Wadi Birk will aid in demonstrating that vertically and laterally the depocenters (sediment production) were migrating. These depocenters are a product of high sediment production by the buildups (stromatoporoid/coral), and relatively low sediment production or current winnowing in the inter-buildups areas. Further, the variability in the shape and sizes of the stromatoporoid/coral build-ups laterally adds more complexity to the thickness of a depositional cycle and provides clues to environmental dynamics. Uneven topography is healed during the deposition of the next cycle with the areas of higher accommodation availability becoming natural depocenters.

The observations and results will be used as input into high-resolution static reservoir models to address the gap of our understanding in inter-well scale heterogeneities of similar subsurface hydrocarbon reservoirs.

The Wren's Nest National Nature Reserve, situated in the West Midlands, UK, is well known for its exposures of Silurian (Wenlock and Ludlow Series) carbonates. The Wren’s Nest was first recognised as a nature reserve in 1965, and in 2020 it became recognised as part of the part of the Black Country Unesco Geopark. The area has significant geological importance due to the superb preservation of its fossils, with more than 700 macro fossil species identified (including brachiopods, bivalves,corals, crinoids, trilobites, gastropods, cephalopods and bryozoans), and is particularly well known for the trilobite Calymene blumenbachii, locally known as the “Dudley Bug”.

The Wren’s Nest Hill forms a large elongated N-S anticlinal dome structure faulted along is main axis by the Wrens Nest Fault, with the structure forming in the Late Carboniferous as a result of the Variscan Orogeny.

The nature reserve also has an extensive industrial heritage with the limestone being mined since the 1700’s for building stones, lime, fertilizer and during the industrial revolution as a flux for iron smelting, with abundant coal being available locally from the surrounding coal measures. An extensive network of mines and tunnels exists, with Dark Cavern being the largest man-made cavern in the UK. These mines are linked together by a series of underground canals which in turn join the national canal network.

With the underground workings closed off to the public for safety reasons this field tour is constructed using surface data only and attempts to reconstruct as much as possible through information from the archives.

The geodynamics in the Central Alps during the Miocene were majorly characterized by the exhumation of crystalline basement, the so-called external crystalline massifs. Their exhumation had a major impact on the evolution of relief, distribution of drainage networks and sediment-generation. The timing of their first surficial exposure and their total thickness still remains debated. The Swiss Molasse Basin contains ~35 to 13 Ma old clastic deposits that were mostly derived from the immediate hinterland and contain valuable information about its tectonic and climatic evolution.

For this thesis, this sedimentary archive is used to trace the exhumation of the external crystalline massifs. In particular detrital garnet geochemistry is used to investigate 21.8 to 15 Ma old alluvial fan deposits of three different fan systems of the Swiss Molasse Basin. In this context, unusually grossular- and spessartine-rich garnets supplied from greenschist-facies metamorphic granitoid rocks serve as a unique proxy for the sediment supply from the external crystalline massifs. Their first appearance in a 15 Ma old sample in the Napf Fan indicates an at least partial exposure to the surface at that time. These garnets can neither be found in the alluvial fans to the east nor to the west, suggesting a relatively stable N/NW-directed drainage system since Miocene times. Another species of extremely grossular-rich garnets of so far unknown provenance has been found in 16.5-17 Ma sandstone of the Napf Fan, indicating a highly dynamic hinterland evolution during the Miocene, which is contrasting previous findings based on more traditional provenance proxies.

The first step in any provenance study is sampling the sediment of interest, which is subject to many potential sources of error. It is nevertheless commonly assumed that one sample of sediment is enough to provide a somewhat “basin-averaged” compositional signal. Spatial or temporal variability of this signal is often not considered.

In this study, we test the temporal variability of sediment composition in modern fluvial deposits in four German rivers: the Gersprenz, Modau and Mümling in the Odenwald, and the Neckar close to the city of Tübingen. We revisited the same locations 12 times in the course of one year to take a sample. The samples were analyzed for grain size distribution (GSD) and geochemistry via XRF measurement.

The results show that

(1) the four river sediments have overall different GSD, which could be related to their different source lithologies;

(2) there are variabilities in the GSD of samples taken in different months, and these can be correlated with flood events;

(3) the bulk geochemistry changes significantly between months;

(4) within narrow grain size windows (1Φ-steps), the chemical composition varies less than the bulk geochemistry.

We conclude that bulk geochemistry of fluvial sediment varies mostly as a result of varying GSD, and not due to actual provenance changes throughout the year. On the one hand, this is promising for studies that assume fluvial sediment to faithfully reflect a “basin-averaged” provenance signal. On the other hand, it shows that geochemical data should always be interpreted in tandem with GSD.

The paleogeographic position of the Alpine terrane with respect to (peri-) Gondwana during the Paleozoic is still a matter of debate. In this study we use a multi-proxy approach to analyze the provenance of siliciclastic sedimentary rocks from the Carnic Alps and the Northern Greywacke Zone, which include detrital U-Pb zircon dating, petrology and bulk geochemistry. The biostratigraphically well constrained deposits from the Carnic Alps have been used as a reference profile, and these results were compared to samples from the monotonous sediment record of the Northern Greywacke Zone. The stratigraphic interval ranges from the Middle Ordovician to the Silurian.

The petrological and geochemical data indicate a high compositional maturity, which is supported by ZTR-dominated heavy mineral spectra. The results of U-Pb zircon dating (in total 957 concordant ages) show signatures typical for sedimentary rocks from the margin of Northern Gondwana and can be assigned to the East African-Arabian province. Most of the zircons show Pan-African ages, but presence of Meso- to Palaeoproterozoic and few Archean ages point to contributions from central Gondwana. Cambro-Ordovician zircon ages are linked to local volcanism at the northern margin of Gondwana. A stratigraphic trend both in the Carnic Alps and the Greywacke Zone is characterized by an increase of zircons with Tonian ages (900-700 Ma) and a decrease of zircons with Pan-African ages (700-550 Ma).

We interpret the shift in detrital zircon ages by enhanced sediment input from the center of Gondwana mainland and reduced input by detritus from Cadomian crust of Northern Gondwana.

Evolutionary stages, from late Eocene to Miocene, of Pindos foreland, mark the transition from Pindos oceanic basin, in the east, to Gavrovo carbonate platform sedimentation in the west. Pindos Thrust as a crustal-scale structural element resulted in the formation of the Pindos foreland. Current research, which is based on detailed field campaign and on cross-sections, correlates and interprets the tectonic evolution of the area. The study area is part of the external Hellenides and belongs to the eastern Pindos foreland (SE Aitoloakarnania region). Pindos foreland consists of a syn-orogenic sedimentary succession with thick clastic deposits where compressional deformation acted synchronously to sedimentation. The activation of NNW elongated Gavrovo and Ionian Thrusts modified and controlled the syn-orogenic evolution of the area. In particular, the study area is characterized by the formation of fault-related fold structures of Gavrovo Thrust, such as the Varasova and Klokova anticlines and the Vassiliki syncline. Westwards propagating thrusting deformation has been partitioned by dextral strike-slip faults like Evinos Fault. This dextral strike-slip fault acts as a pathway to Evinos River flow. Finally, the syn- to late-orogenic evolution of the area is modified by normal faulting, forming the current geotectonic framework of the area.

Acknowledgments

This work was funded by the H.F.R.I. (Hellenic Foundation for Research and Innovation) and GSRI (General Secretarial for Research and Innovation) through the research project "Global climate and sea-level changes across the Latest Eocene-Early Oligocene, as reflected in the sedimentary record of Pindos foreland and Thrace basin, Greece, 80591".

Turbidites are the main reservoir rocks in many sedimentary basins. Through well log profiles and using stratigraphy of high-resolution sequences, 6 stratigraphic surfaces of 3 and 4 order were interpreted. These surfaces were defined trough facies association (cores) and petrofacies (thin sections). Each surface has an electrical signature and a seismic amplitude. Correlating wells and mapping the seismic lines, the 2D and 3D stratigraphic surfaces are then obtained. With Schlumberger's Petrel a seismic and stratigraphic verification points were defined. Then the 3D structural model was built by the faults and zones of the top and bottom layers. For this area, a Grid with 50X50m cell size (horizontal limit) was defined. Following this, the pillar gridding and the layering are generated. For facies modeling, a facies profile was obtained in the stratigraphic sections trough the correlation between logs and rock. A good log and seismic signature can separate the reservoirs (sandstones), from the source rock (shale) and carbonates. Histograms are necessary to define the accuracy and representativeness of the model, defining the vertical modeling limit. To complete the model, it is necessary after the study with histograms, the scale up of the model and if necessary, insert a trend (a paleocurrent for example). The most representative interpolation method for this model was SIS Modeling (Sequential Indicator Simulation). The result was considered satisfactory and correlated with the profiles of existing wells, indicating a methodology to be used constantly by the industry. This serves the O&G sector, geothermal energy and groundwater exploration.

Apatite is a pivotal mineral in carbonate rocks, because it can incorporate all of the major magmatic volatile species (H, P, F, S, Cl), as well as REE and HFSE into its structure. To quantify the effects of fractional crystallization of apatite crystals on the (H, P, F, S, Cl) volatiles and metal budget in the residue melt, the partition coefficients of a broad range of elements (F, Cl, S, REE, HFSE, Co, Ni, Sr, Mo, Ba, W, Pb, Th and U) between apatite and carbonatite melts were determined at 800 °C and 200 MPa using internally heated pressure vessels. The experimental results show that the partition coefficients of Sr, Y and REE (D) are in the range 2-10, and the partition coefficients of Sc, Mn, Fe, Co, Ni, Mo, W, U and HFSE are <<1. The effects of volatiles and oxygen fugacity on the partition coefficients are insignificant. This study defines the apatite-melt partition coefficients for the halogens: D_F= 0.68-1.76; D_Cl=0.10-0.19; and D_S= 0.016-0.05. The P₂O₅ solubility in carbonatite melt decreases from 6.8 to 1.4 wt% in ‘dry’ carbonate to volatile (H₂O, F, Cl and S)-bearing carbonate. The results suggest that apatite is preferred to be saturated in hydrous carbonate, and thus cumulated apatite sequester more REE from the residue melts. Finally, we will show that the experimentally determined partition coefficients make apatite a potential indicator for the volatile and trace element abundances in carbonatite magmas.

There is a large amount of downhole logging data gathered for scientific and commercial purposes, but studies applying time series analysis and cyclostratigraphy are not abundant. Especially the fast availability of logging data makes it valuable, also for decisions on which cores to investigate first. Here, we summarize the specific properties of downhole logging data most relevant for time series analysis and cyclostratigraphy. As for data from core- or outcrop analysis, it is important to be aware of both the potential and also possible issues of data. For logging data challenges, include changing borehole diameter, influences of drilling fluids and the fact that logged data may be a composite record. This contribution tries to give a concise summary of chances and possible challenges.

The late early to early middle Eocene (~48 Ma) maar lake sediments of the famous Messel fossil-pit, located near Darmstadt, SW Germany, represent a prime archive for climate dynamics operating during the geologically most recent greenhouse period of the Earth. In this study, we investigate the potential of geochemical data obtained via high-resolution XRF core scanning to decipher hydrologic variability from the Messel sediments. Such data have the potential to yield insight into the paleoenvironmental and paleoclimatic evolution of Messel in unprecedented temporal resolution. As such, they may provide further help towards understanding potential climatic impact on evolutionary patterns as revealed by the fossil record. Our preliminary results from the research drill core of 2001 show a robust correlation with available data on the vegetation from the pollen and spore record and hence hint at the great potential of using XRF core scanning as a tool to decipher wet-dry variability during the early and middle Eocene on orbital to interannual time scales.

Lithium is an important compound in several industrial applications and is mostly found in lithium ion batteries (LIBs), ceramics and glass. Lithium deposits are hosted in pegmatites, sedimentary rocks and brines (i.e., salt lakes, salars, oilfield brines, and geothermal brines) comprising 25 - 26 %, 8 % and 59 - 66% of the world’s Li resources, respectively. Geothermal brines in the Upper Rhine Graben, Germany, with Li concentrations of up to 200 mg/L and resources of 2.7 Mt Li₂CO₃ represent potentially economically mineable Li deposits. The scope of our project is to extract Li from these high saline (i.e., TDS ~100 - 200 g/L) geothermal brines by sorption using natural and synthetic zeolite and clay minerals. These high saline brines are slightly acidic in pH and characterized by high concentrations of major cations (e.g., Na⁺ up to 60 g/L, K⁺ up to 4 g/L, Ca²⁺ up to 11 g/L and Mg²⁺ up to 1.9 g/L) and anions (e.g., Cl^- up to 120 g/L and SO₄^2- up to 1.5 g/L). Synthetic zeolite 13X and natural clinoptilolite-mordenite-montmorillonite mixtures have been used for preliminary sorption experiments. We performed batch sorption experiments with synthetic Li-solutions and variable concentrations and temperatures between 25 – 60 °C. Furthermore, we studied the effect of competing ions (e.g., Na⁺) on Li-sorption. Thereby, we investigate the different materials for sorption capacity and kinetics, chemical stability, structural effects of Li incorporation and their applicability to geothermal brines.

Geoscientific studies in Antarctica are extremely challenging due to the remote location of the continent, its harsh environment and difficult logistics. Additionally, the continental crust is covered by an up to 5 km thick ice sheet, which makes surface based geoscientific studies extremely difficult. Gravity field measurements and gravity based subsurface models are therefore essential in studying the structure, properties and processes of the Antarctic subsurface.

In the last decades a large database of airborne, shipborne and ground based gravity data has been compiled. Recently, all existing and new gravity data were processed to infer an enhanced gravity field solution for Antarctica.

Subsequently, this new gravity field solution can be used for further geophysical studies. We use gravity disturbances to study subglacial topography, sediment thickness and Moho depths to improve respective existing models in Antarctica.

Studying these parameters on a continental scale, we apply 2D Parker-Oldenburg inversion in combination with results from other gravity based studies and further constraining data.

Additionally, we make use of the higher resolution of the new gravity grid (5 km) to study smaller regions in more detail, specifically the Weddell Sea area and Queen Mary Land. Here, we use gravity forward modelling constrained with ice penetrating radar and seismic data to infer geometric structure and densities of the subsurface.

In this contribution we present results of the Parker-Oldenburg Inversion and discuss the underlying parameters. Also, we show the resulting 3D forward models of the Weddell Sea area and Queen Mary Land.

Sicily is a part of the central-Western Mediterranean area and represents a geotectonic boundary between the African and European plates. It is the result of a complex geological process based on a polyphasic evolution of a compressional step beginning with the Oligocene-Miocene clockwise rotation of Corsica-Sardinia simultaneously with the extensional processes of the Tyrrhenian basin. Consequently, the area is constrained by the continuing partial advance of the Sicilian-Maghrebian chain southwards and the Tyrrhenian extensional area towards the internal foreland areas (Hyblean domain). The study focuses on the creation of a 3D lithospheric-scale model of a 300 km x 400 km extended area in the central Mediterranean domain (Lat38°, Lat35°), which is consistent with the available geological and geophysical data, as well as with the observed gravity field. The reconstructed (simplified) geological setting consists of a lithospheric mantle, a crystalline basement (continental and oceanic crust), carbonates, the European margin and the Neogene-quaternary cover including volcanic bodies. The work aims to investigate the geometry of lithosphere integrating tomographic models in order to assess the major density contrasts and the lithospheric thermo-mechanical state. The regional 3D model provides also the boundary conditions for local thermal models to investigate afterwards.

The Ligurian Sea in the western Mediterranean Sea is a back arc basin created through the Apennines Calabrian subduction zone between 30 and 15 Ma ago. The inner geological structure of this basin is not well known. To improve the knowledge about the density distribution of the crust and lithosphere, we performed a pre-processing of gravity data prior to 3D-modelling. This work is related to research in the MB-4D priority and AlpArray project.

The satellite gravity gradients from GOCE were directly interpreted and used for filtering of different wavelengths to calculate residual fields, Bouguer and Free-Air anomalies as well as invariants and Euler-Deconvolutions. Furthermore, seismic profiles from several ship-borne surveys as well as OBS measurements of the AlpArray project (LOBSTER, GEOMAR, Kiel) and bathymetry data contributed additional information.

The processed data show an unknown anomaly offshore Marseille and the possibility of several underground structures with different densities. The basin itself is characterized by a mass surplus and positive anomalies with a maximum between Corsica and north-west Italia, while the anomalies underneath Corsica and Sardinia are neutral to negative.

The derived information will be used in the 3D-modelling software IGMAS+ to execute an inversion for the area and create a model of the mass distribution beneath the Ligurian Sea and its margins.

The Bohemian Massif represents the largest exposure of rocks deformed during the Variscan orogeny. Western Carpathians form an arc-shaped mountain range related to the Alpine orogeny. In our study, the lithospheric structure of the key tectonic units in the area and their contact zone was analyzed by 2D gravity modelling along the NW-SE oriented CEL09 profile of the CELEBRATION 2000 seismic experiment. New gravity map compiled at the initiative of the AlpArray Gravity Research Group was used. This map is based on a uniform reprocessing of the national terrestrial gravimetric databases of ten countries of the wider Alpine region. The resultant 2D density model based on gravity data was constrainted by results of seismic reflection and refraction method. Applied densities were defined by transformation of the modelled P-wave velocities. A good correlation between the density and seismic models was shown. The resultant 2D density model consisting of five principal layers (sediments, upper crust, lower crust, lower lithosphere and asthenosphere) shows differences between the older, cooler and thicker Bohemian Massif (in average: ~32 km thick crust, and ~120 km thick lithosphere), and the younger, warmer and thinner Carpathian-Pannonian region (~28 km crust, ~95 km lithosphere). The detected contact is delimited by a change in the Moho and the LAB topography, and assumes an overthrusting of the Western Carpathians onto the Bohemian Massif by ~30 km resulting in a neo-transformation of the crust/mantle and related lithosphere after subduction.

Underground storage of hydrogen could be an alternative way to store large amounts of energy. However, microbial consumption of H₂ is still a major uncertainty factor. Since microbial life is widespread in the crust of the earth an underground storage site needs to be seen as a habitat for microorganisms. Microbial activity at the H₂ storage site might affect the stored H₂ as well as the integrity of the storage site itself.
There is great need for more information about microbial H₂ transformation activity at conditions relevant for underground H₂ storage i.e. elevated pressure, high temperature and about potential geochemical interactions with surrounding fluid and rock material.
In this study, different fluids from potential subsurface storage sites representing storage in salt caverns or porous rock reservoirs were investigated. While some fluids were inactive, long lasting hydrogen consumption was observed by a porous rock reservoir fluid. Microbial H₂ oxidation tolerated high pressure as well as pressure and temperature fluctuations reflecting cycles of H₂ storage. In this fluid microbial H₂ consumption was shown to be sulfate dependent and led to the formation of sulfide. Furthermore, an increase of sulfate reducing bacteria during microbial H₂ consumption was identified by high-throughput sequencing of 16S rDNA. These results indicated the oxidation of H₂ by sulfat reducing bacteria to be the presumed process in this porous rock reservoir fluid. Due to the heterogeneity of the investigated fluids, microbial H₂ oxidation activity at different H₂ underground storage sites cannot be generalized but requires site specific investigations.

The save and effective storage of hydrogen in geological formations is an important part towards the implementation of renewable energy use. Due to fluctuating power supply from wind or solar plants, it is envisaged to use excess energy for electrolytical hydrogen production and the subsequent temporary storage in geological formations, as buffer for energy at “high-demand-low-production-times”.

The preferred geological storage formations are either salt deposits or porous sandstones with a gas-tight caprock. To date, these formations are generally confirmed to be appropriate for natural gas storage. However, the deviant physical properties of hydrogen, in terms of density, viscosity and hence mobility, require a reassessment of migration characteristics in these rocks.

For this purpose, an experimental set-up was designed, constructed and tested to quantify hydrogen migration rates in rocks. It comprises two gas chambers, separated by a through flange, containing the epoxy-embedded sample section with an exposed area of 7 cm². The retentate chamber is filled with a gas mixture of 2 Vol% hydrogen in synthetic air at 0.1 MPa. The permeate chamber contains air and includes an amperometric hydrogen sensor. Since there is no pressure gradient, the driving force for hydrogen movement is solely the concentration gradient between both sides of the rock sample. The hydrogen break-through and transport rates are monitored. In initial tests, core pieces of various length of sandstone and salt at dry and wet conditions are employed. The results approve the functional capability of the set-up and allow for a first-approach characterisation of hydrogen gas transport.

Hydrogen is a prospective energy carrier whose storage in extensive volumes is still an unsolved problem. One approach is underground hydrogen storage, in which geological formations such as salt caverns or depleted natural gas and oil reservoirs are used to hold large amounts of gas under pressure. However, in those formations minerals can react with the hydrogen stored and therefore deplete or contaminate the gas recovered.

In our previous project we have shown that various minerals (e.g. pyrite, smectite, hematite) reacted with hydrogen under storage conditions (~120°C, <100 bar). Especially the Fe³⁺/Fe²⁺ switch in a reaction in which hematite is reduced to magnetite forming water (3 Fe₂O₃ + H₂ → 2 Fe₃O₄ + H₂O) was found to be active. Mechanistic data of that reduction is abundantly available at high temperatures (>500°C). However, studies at storage conditions (45-120°C) are rare up to this point. Especially the influence of pressure is unclear.

The work presented aims to understand the processes by which hematite is reduced under those conditions. For that purpose, we built a system in which we measure the decreasing hydrogen concentration periodically. Is consists of a heated pressure vessel on whose outlet a 10-port-valve flushes a gas-sample to a mass spectrometer. The resulting H₂-peaks in the MS-spectra are quantified using Ne as internal standard. This way we are able to obtain time-resolved data on the consumption of H₂ as well as formation of H₂O by hematite. Additionally we quantify the hematite to magnetite ratio using XRD after the experiment.

NASA's Mars Science Laboratory mission, with its Curiosity rover, has been exploring Gale crater since 2012 with the goal of assessing its potential to support life. The mission has compiled compelling evidence that the crater basin accumulated sediment transported by marginal rivers into lakes that likely persisted for millions of years in the early Hesperian. Fluids simultaneously circulated in the subsurface and likely existed through the dry phases of lake bed exposure and eolian deposition creating a continuously habitable deep biosphere environment that persisted of millions to even hundreds of millions of years, conceivably even into early Amazonian time. Geochemical and mineralogical assessments indicate that ancient environmental conditions would have been suitable for sustaining life, if it ever were present. A diversity of organic molecules has been preserved, though degraded, with evidence for more complex precursors. In situ studies of modern wind-driven sediment transport and multiple large and active aeolian deposits have led to advances in physical theory of boundary conditions and bedform development. Despite 9 years of exploration, rover systems and science instruments remain healthy and capable of performing all key scientific objectives.