To explore fault-bound hydrothermal systems, knowledge about fluid conduits and the (isotope-) geochemical composition of the geothermal water is necessary. At the hydrothermal vein deposit of the former Schönbrunn fluorspar mine, fluid conduits in the depth between the 293 and the 533 m level were outcropped. Attempts at utilization for deep geothermal energy failed in 1997, because the mine was flooded. The thermal water outflow of the most active fluid conduit, outcropped at the 533 m level was 1 m³ min^-1 and the temperature was 35,7°C. The fluid conduit is controlled by the intersection of a fault bundle of several NNW-SSE and NW-SE striking faults. The horizontal length of the intersection area is about 400 m. A geothermal anomaly exists at the segment of the intersection. The quartz-fluorite bearing mineralization (primary) was redeposited by carbonate-sulfide mineralization with depth.

Research on unpublished water and gas samples (96 and 115 data sets, respectively) from the so called “spa” at the 453 m level of the Schönbrunn mine was carried out by time-series measurements (weekly sampling rate) to investigate 1) composition and origin of the thermal water, 2) reservoir temperature via geothermometry, and 3) potential hydro- and gas-chemical effects of regional swarm seismicity. We revaluated the results and collated them with new findings of the Neumühle thermal water (Prause et al., session 4b) in order to develop deep geothermal energy projects at crystalline rock areas in Western Saxony.

The KTB site near Windischeschenbach is one of the best characterised locations of continental upper crust worldwide. The superdeep boreholes represent a unique in situ underground research laboratory in Europe, allowing research into the sustainable utilisation of the crystalline subsurface for the energy and heat transition.

The GEOREAL experiment aimed at hydraulically stimulating the fractured crystalline metamorphic basement rocks at 4 km depth and to minimise the potential risk of induced seismicity by real-time control of injection parameters. The KTB infrastructure allowed to inject 600 m³ of water into the 4 km deep KTB pilot hole, while the main borehole (only 200 m distant at the surface) was used for seismic monitoring.

Fluid injection took place during 6-15 November 2023 through the stuck GEOREAL packer pressurising the open borehole section at the depth interval of 3.85–4 km. Flow rates were variable (10– 220 l/min). No induced microseismic events were detected. Pressure data, monitored at the well head of the pilot and main borehole, was analysed in conjunction with recordings from a year-long injection experiment into the same formation performed in 2004/5. The hydraulic parameters show similar values as previously obtained. The observations provide more detail on the hydraulic connection at depth between both boreholes. The GEOREAL experiment had to be stopped prematurely due to a leak in the casing cement. Further activities at the KTB deep crustal lab are underway, substantiating the potential of petrothermal research at the KTB deep crustal lab after 30 years of operation.

The E4Geo Project aims to explore fault-bound hydrothermal systems associated with the hidden granite pluton of Eichigt-Schönbrunn in the Vogtland region of SW Saxony, Germany, for potential use as deep geothermal reservoirs. Evidence for enhanced geothermal gradients in this region has existed for several decades, but attempts at utilization for energy production and heating have thus far been limited.

We aim to constrain 1) composition of the thermal water, 2) reservoir temperature, 3) the effects of water-rock interaction, 4) fluid residence times and recharge rates, 5) contributions of radioactive decay to the local heat source, and 6) approximate heat flux. For this purpose, we present new geochemical data from time-series measurements performed on local water samples from regional thermal springs at Neumühle/Vogtland, which are contrasted with samples from the nearby Erzgebirge (Georgsquelle/Wiesenbad, Silbertherme/Warmbad) and Fichtelgebirge (Siebenquell/Weissenstadt) regions.

Geochemical time-series measurements of major cations and anions allow us to estimate reservoir temperatures via geothermometry and to characterize the chemical nature of the thermal waters, including potential scaling effects that may occur during operation of a geothermal plant. Potential hydrochemical effects of rainfall and regional swarm seismicity are likewise examined. Stable isotope analyses (δ¹⁸O and δ²H) of water samples are utilized to decipher the origin of thermal waters and to evaluate potential mixing with meteoric components. Lastly, specific activities of nuclides from the ²³⁸U and ²³²Th decay series are applied with ⁴⁰K in preliminary heat flux estimates and identification of ground water types, while residence times are approximated from ¹⁴C and ³H.

The valley of Geysers, is a multi-habitat environment for microorganisms, ranging from moderate to extreme environmental conditions within short distances. The aim of the present study is to characterize and compare the microbial communities in variable habitats: thermal water pools, outflow transect from a geyser to the Geysernaya river, river bed samples and a recently reactivated geyser in the river buried in landslides in 2007 and 2014. The study combines organic geochemical and geomicrobiological approaches with hydrochemical background data.

The different microbial habitats exhibit a wide range of different cell membrane biomarkers. Hot habitats are dominated by markers for archaea with lower abundances of bacterial biomass, indicating the presence of extremophiles in these habitats. Along the transect from a geyser to the river, the microbial community is dominated by bacteria with specific markers pointing to photosynthetic microbs. The river bed samples show only small amounts of bacterial biomass. A closer look at the taxonomy of the microbial communities of the different locations supports the clear difference between the communities influenced by hot and temperate water. Along the transect, the two sample at the upper end of the outflow (closer to the geyser, 66-84°C water temperature) show many extremophilic archaeal and also bacterial taxa, while the lower samples (around 32-39°C temperature) are characterized by mesophilic bacterial taxa with even some cyanobacteria. Initial result indicates the existence of unknown species within the communities. Overall, the microbial communities show a high spatial variability determined by the thermal conditions of the different life habitats.

Geothermal heat flow (GHF) is essential for evaluating the thermal states and energy balances of the lithosphere, playing a crucial role in geophysics and geothermal energy research. In this study, we initiate our analysis by exploring lateral variations in unknown thermal parameters across Germany. We apply a Bayesian Markov Chain Monte Carlo approach, using established data on surface heat flow, surface temperatures, and the temperatures and thicknesses at the lithosphere-asthenosphere boundary. Our investigation focuses on assessing the lateral variations in crustal and lithospheric mantle thermal conductivities, crustal heat production, and mantle heat flow.

To address the limitations posed by the sparse and uneven distribution of direct borehole data, which consists of only 595 heat flow points, our study integrates a broad spectrum of geophysical and geological datasets. These include gravity, magnetics, seismic data, topography, proximity to faults, and volcanoes, and compositional data within a machine-learning framework. This comprehensive approach not only surpasses traditional Curie depth estimations in accuracy but also robustly tackles the issue of data scarcity.

We employ quantile regression forests to clustering to integrate the datasets in a geothermal heat flow model. This probabilistic, multi-geophysical inversion method leads to a detailed quantification of uncertainties, offering a refined understanding of Germany’s geothermal potential.

Extracting heat from medium-deep hydrothermal reservoirs for municipal heat supply requires adequate reservoir characteristics, suitable extraction techniques, a sufficiently high heat demand and appropriate heat supply infrastructure. Furthermore, the acceptance of local stakeholders and consumers, as well as financial feasibility are crucial factors for the successful implementation of geothermal heat projects.

In the North German Basin (NDB) in particular, there are several deep geothermal projects that have been planned over the years but have never been completed, mostly due to the high exploration and financial risks at the beginning of the project. Some municipalities have already taken the initiative to restart projects.

The aim of this work is to provide technical support for local stakeholders to enable them to initiate and successfully implement hydrothermal projects.

In a first step, the authors identify aborted geothermal projects in NDB located in geologically well explored regions. Based on related feasibility studies, literature reviews and expert interviews, common constraints and challenges are discussed from geological, technical, social and economic perspectives.

Secondly, a number of selected projects are analysed in more detail. Alternative operating scenarios are developed and the positive impact of new technological developments such as high capacity heat pumps is examined.

Finally, the results will be generalised in order to derive recommendations for interested local stakeholders.

The work is part of the Warm-Up project, funded by the Federal Ministry for Economic Affairs and Climate Action (BMWK).

Geothermie spielt eine entscheidende Rolle für eine klimaneutrale Wärmeversorgung, jedoch sind bisher nur wenige Tiefengeothermie-Projekte in Niedersachsen umgesetzt worden. Das Norddeutsche Becken (NDB) beherbergt potenziell vielversprechende mitteltiefe geothermische Reservoire, insbesondere in den Kalkareniten der Reitbrooker Schichten des oberen Maastrichts. Diese wurden durch zahlreiche Bohrungen der Kohlenwasserstoff-Industrie erkundet und gelegentlich für die Abwasserentsorgung genutzt, was auf eine gute Gesteinsdurchlässigkeit hinweist. Spezifische Untersuchungen zu ihrer geothermischen Eignung fehlen jedoch bisher.

Bohrlochdaten und 3D-Seismik wurden analysiert, um das Reservoir zu kartieren und charakterisieren. Dabei wurden die Bohrungen über zwei mergelige Bereiche korreliert, welche die Arenite in obere und untere Bereiche unterteilen. Es wurde festgestellt, dass sich die Arenite der Reitbrooker Schichten lateral von Nord nach Süd zunehmend mit glaukonitreichem silikatischem Sand vermischen. Die aus Plug-Messungen von Kernproben gemessene Porosität und Permeabilität, kombiniert mit den berechneten Porositäten aus Sonic- und Density-Logs, lassen darauf schließen, dass tendenziell bei stratigraphisch höheren Arenite bessere Reservoirparameter zu erwarten sind. Die Verbreitung und Erhaltung der Arenite unterhalb des Paläozäns stehen im Zusammenhang mit der tektonischen Entwicklung, insbesondere der Inversion des Niedersächsischen Beckens. Große Mächtigkeitsschwankungen im Verbreitungsgebiet werden durch Halokinese verursacht, wobei besonders mächtige Ablagerungen in den Randsenken auftreten, während sie teilweise auf den Salzstöcken fehlen.

Das Zusammenspiel von Tektonik, Halokinese und Sedimentationsdynamik führt zu einem heterogenen Reservoir, das dennoch gut vorhergesagt werden kann. Zur Bewertung des geothermischen Potenzials, zur Kartierung und zur Entwicklung von Erschließungsstrategien sollen noch numerische Simulationen durchgeführt werden.

The geothermal heat anomaly in northern Bavaria was first discovered in the late 1970s and has recently been more precisely localized. An elevated temperature of 57 °C estimated at a depth of 1000 m is estimated to be higher than that based on the normal geothermal gradient. The geothermal gradient is approximately 4.5 °C/100 m with a heat flow density of 110 - 130 mW/m². The location and extent of the geothermal anomaly are constrained by the limited number of deep wells, which has left the cause of the positive heat anomaly in the region enigmatic. In this study, we use geophysical methods and modeling to locate the granitic intrusion in the subsurface as a possible source of the observed high geothermal anomaly.

An important feature of the northern Bavarian subsurface is the presence of granitic intrusions covered by early Carboniferous turbidites and Permian graben and half-graben structures (Rotliegend sandstone), similar to those exposed setting in the western Bohemian Massif. By integrating the geological and geophysical data and modeling, we define the location and geometry of a granitic intrusion and estimate the depth to basement. Our 2D forward models predict the structural and stratigraphic setting satisfying observed geological and geophysical data. Our integrated methodology describes the granitic intrusion, the sedimentary cover, and the regional structural patterns relevant to ongoing deep geothermal exploration. This study contributes to subsurface characterization (e.g. potential reservoir and buried fault zones) and reduces risks associated with exploration and potential future development.

The Bavarian part of the North Alpine Foreland Basin (NAFB) is highly relevant for geothermal exploration, especially amid recent play developments, highlighting the importance of an integrative geological and geophysical approach. Our work focuses on establishing a robust seismostratigraphic framework for the Bavarian NAFB using an unprecedented dataset consisting of digitised (vintage) seismic and well log data.

Based on this unique data set, we interpreted and correlated well logs and identified important seismic reflectors across the NAFB using seismic-to-well ties and synthetic seismograms, refining seismostratigraphic concepts from previous models such as GeoMol [GeoMol Team – Project Report (2015)]. Our study incorporates considerations of different depositional facies, focusing on the continuous traceability of major reflectors throughout the basin. We identified five major Tertiary reflectors that can be consistently tracked across various lithological and facial boundaries and follow major basin-wide unconformities. Especially the main reflectors identified within the complex Egerian successions and their ability to be traced across different lithostratigraphic units (i.e. Lower Freshwater/Brackish/Marine Molasse), serve as an example of how the reflectors are partially independent from stratigraphic boundaries and their varying facies distributions. Instead, the presence of major seismic reflectors in the NAFB is rather determined by basin-wide unconformities, whose distinctive seismic signatures serve as a basis for consistent identification across the basin.

Our work provides a fundamental step towards an integrated seismostratigraphic framework for the Bavarian NAFB, aiming for a coherent approach of seismic interpretation in industry, academia and authorities, thus promoting standardized methodologies for future (geothermal) well development.

The fit for 55 package, which outlines policy measures to deliver the EU Green Deal, calls for a greater than 40 % target for renewable energy sources by 2030 in the Renewable Energy Directive (RED). It also calls for an increased primary (39 %) and final (36 %) energy savings to be achieved by the Energy Efficiency Directive (EED). Accelerating the penetration of cost-effective and energy efficient renewable heating and cooling (RES HC) technologies will be key to the successful achievement of these targets.

Geothermal heat pumps are the most cost-effective and efficient source of renewable heating and cooling on the market. They can meet the heating and cooling needs in residential and non-residential buildings of all sizes with varied energy profiles. Furthermore, they can be applied as individual applications at building scale, or through renewable district heating and cooling systems.

One big challenge at the moment and for future years is decarbonising heating and cooling grids for new builds and in particular for existing buildings. geoENERGIE Konzept presents projects in different stages of development of their wide portfolio. Hereby lies the focus on district heating and cooling grids for new as well as existing buildings, hybrid systems with other renewable sources and underground thermal energy storage.

Scientific drilling is a well-established tool in Earth sciences and related disciplines. For drilling on land, the International Continental Scientific Drilling Program, ICDP is the major player providing implemental funding and technical support. The largest number of ICDP projects aim at drivers of Paleoenvironmental and Paleoclimate evolution with a focus on dramatical and rapid changes. While Quaternary archives such as lacustrine sediments still predominate, more and more Mesozoic to Paleozoic time slices of dramatic System Earth transformations come into the play. Even Precambrian times are on the agenda such as Neoproterozoic Snowball Earth, Early Precambrian oxygenation of the atmosphere, or Early Earth origin and evolution of life.

Another key topic in the ICDP are Geohazards including mainly seismic and volcanic risk and research on landslides or a combination of cascading disastrous events. First approaches in this field of science were often related to the feasibility of drilling in fault zones or active volcanic regions while current ideas focus on monitoring and testing.

Energy-related scientific drilling projects on e.g., geothermal challenges and other critical resources often acquire funding from national governmental resources. In contrast, fundamental basic research questions are usually developed as bottom-up international academic initiatives. In order to bridge the gap between these two advance lines in geothermal research, ICDP has now established new funding priorities including not only ‘World-Class Science’ and ‘World-Class Sites` but also ‘World-Class Opportunities’.

This contribution will summarize current trends and initiatives in terms scientific objectives and will elucidate funding challenges as well as chances.

To define parameters for future climate change scenarios (IPCC) and their consequences for ecosystems, it is of paramount importance to improve our knowledge of timing, duration, and intensity of past climatic variability and subsequent environmental impact, especially on long geologic time scales and in key regions such as the Tibetan Plateau. Considering that the Tibetan Plateau serves as the source of several major rivers the future hydrological development will clearly have a significant societal impact. Nam Co is one of the largest and deepest lakes on the Tibetan Plateau. Due to this location at the intersection of Monsoon (increased precipitation) and Westerlies (increased evaporation) paleoclimate proxies derived from sediments of Nam Co clearly reflect the spatial and temporal interplay and thus the dominance of one of the two circulation systems.

Seismic data show that the Nam Co basin contains >800 m of well layered undisturbed sediments. Sediment accumulation rates measured on a 10.4 m reference core, seismostratigraphic investigations, and molecular clock analyses suggest an age of the seismically imaged sequence of >1 Mio years. Instead of drilling the entire >800 m sediment sequence in the center of the lake we will use the fact that layers are dipping towards the center of Nam Co producing a higher accumulation rate there. By splicing together multiple cores from three different sites it will be possible to cover the same depositional history found at >800 m in the center, i.e., 1 Ma.

Fossil deep-sea macrobenthos is scarce due to the rarity of onshore deep-sea sediments. Therefore, hypothesized migrations of shallow shelf taxa into the deep-sea after phases of mass extinction or oceanic anoxic events (onshore-offshore pattern) is not constrained by the fossil record. To resolve this conundrum, we investigated 1,475 deep-sea sediment samples (Atlantic, Pacific, Southern oceans; 200 - 4,700 m paleo-water depth). Ca. 41,500 spine fragments from Holasteroida and Spatangoida (Atelostomata) document a continuous occurrence of the groups since 104 Ma (late early Cretaceous). Literature records suggest even an older age (115 Ma). A gradual increase of spine tip morphotypes occurs since the Albian. An abrupt reduction in spine size and morphological inventory following the Cretaceous-Paleogene (K-Pg) Boundary Event is expression of a “Lilliput Effect”, related to nourishment depletion in the deep-sea. The post-event recovery lasted at least 5 Ma. Post-K-Pg Boundary Event assemblages seem to evolve progressively without any morphological breaks towards modern deep-sea assemblages. This observation is interpreted to result from in-situ evolution in the deep-sea and not from onshore-offshore migrations. The calculation of the “atelostomate spine accumulation rate” (ASAR) reveals low pre-Campanian values, possibly related to high remineralization rates of organic matter in the water column in the course of the mid-Cretaceous Thermal Maximum and its aftermath. A Maastrichtian cooling pulse marks the irreversible onset of fluctuating but generally higher atelostomate biomass that persists in the Cenozoic.

Between 5.97-5.33 Ma, kilometre-thick evaporites were deposited in the Mediterranean Basin during the Messinian Salinity Crisis (MSC) under strongly negative hydrological budget. In the light of the IMMAGE initiative to drill the Mediterranean-Atlantic gateway, we present here the reconstructed continental mean annual temperatures (MAT) using branched glycerol dialkyl glycerol tetraether (brGDGT) biomarkers for the MSC Stage 3 (5.55-5.33 Ma) and compare them with continental temperature values obtained from Δ₄₇ clumped isotope geochemistry of paleosol carbonate nodules from few Mediterranean locations. The biomarkers were extracted from outcrops onshore and offshore sites around the Mediterranean Basin. Calculated MATs for the 5.55 to 5.33 Ma interval show values around 16 to 19 ºC for the Malaga, Sicily and Cyprus outcrops. The MAT values for DSDP Leg 13 holes 124, 134 and Leg 42A holes 374 and 376 are lower, around 13 to 16 ºC. Comparing the brGDGT-MAT values with Δ₄₇-MAT values from carbonate nodules, shows high congruence between both approaches. For the northern Mediterranean Δ₄₇-MAT is 24.6 ± 1.6 °C and brGDGT-MAT is 19 ± 4.8 ºC. For Cyprus Δ₄₇-MAT is 20.3 ± 1.7 °C and brGDGT-MAT is 18 ºC ± 4.8 ºC. Given the very different nature of the used paleoproxies, the similarity of the obtained MAT values provides a strong indication of (cross)validity in sampled sections. Additionally, the measured δ¹⁸O for the carbonate nodules used for the Δ₄₇-MAT show high δ¹⁸O of the soil water (~ -5 ±0.7‰) indicating highly evaporative conditions for the two onland Northern Apennines and Cyprus locations.

Shallow weathering patterns and linked hydrostratigraphy in topographic recharge areas are rarely explored even for used groundwater flow systems, as (scientific core) drilling was usually carried out in downstream zones of productive resources. In the Hainich Critical Zone Exploratory (NW Thuringia, Germany), we constructed a well network encompassing the recharge area (hilltop, midslope) in discharge direction (footslope) for long-term monitoring of the links between surface and subsurface biogeosphere (Küsel et al., 2016). In total, ~730 m of rock cores from the limestone-mudstone alternations of the Upper Muschelkalk, including drillings in the thick hillslope aeration zone, were used for the exploration of hydrogeological functions, flow paths and endolithic habitats (Kohlhepp et al. 2017). Based on the core and monitoring data, an advanced conceptual model on multidirectional flow patterns and subsurface ecosystem compartmentalization was developed (Lehmann and Totsche, 2020). Novel and surprising findings revealed unseen patterns in the Upper Muschelkalk flow system: confined weathering phenomena in fissures and pores indicate localized, oxic conditions in sections that were previously encountered elsewhere as anoxic and unweathered. This indicates a higher complexity of flow and transport pathways (e.g., oxygen supply) than commonly expected, despite simple layer-cake geometry of the bedrocks. Besides relief position, it points to a strong influence of fractures on flow in the aeration zone.

References: Kohlhepp et al. (2017): https://doi.org/10.5194/hess-21-6091-2017; Küsel et al. (2016): https://doi.org/10.3389/feart.2016.00032; Lehmann and Totsche (2020): https://doi.org/10.1016/j.jhydrol.2019.124291

Hydrothermal activity is common at active volcanoes. Volcanic gasses rise and form strong acids that lead to fluid-rock interactions affecting a rock’s mineral assemblage by dissolution and remineralization, eventually influencing essential rock parameters like strength and permeability. Despite the far-reaching consequences for the stability of a volcanic edifice, our understanding of extent and variability of hydrothermal alteration is often limited. Within Multi-Marex we aim to better understand the causes and effects of hydrothermal alteration and volcano stability on land and underwater. By close-range remote sensing, we analyze hydrothermal alteration, aiming to describe the morphology (shapes) and optical appearance of hydrothermally active sites over scales and to reveal the general pattern of alteration and its regional variability. We give an overview of optical methods for tracing hydrothermal alteration, compare patterns observed at different systems, and expand our view to the submarine regime. In particular, we compare the alteration pattern at Nisyros, a hydrothermally active volcano in the Aegean Arc with hydrothermal-dominated or magmatic-hydrothermal systems at locations elsewhere. The approaches and the pattern of hydrothermal alterations observed vary, but all systems have in common that there are patterns that can be detected and that indicate variability of gas flux and alteration and therefore zones of contrast considering materials, permeabilities, strength, or other physicochemical properties. Revealing these patterns is beneficial for detailed and focused further investigations and may be particularly useful for monitoring and future risk assessment studies.

The Delitzsch carbonatite complex, located 25 km NW of Leipzig, constitutes a late Cretaceous ultramafic lamprophyre (UML)-carbonatite occurrence covered by Cenozoic sediments [1,2]. We have analysed UML samples from drillcores for their mineral chemistries by electron-probe microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to better understand their mantle source and magmatic history.

Based on their mineralogy, the rocks can be classified as alnöite, olivine-alnöite, phlogopite-olivine alnöite, and damtjernite [3]. Compositionally, the rocks lie between UMLs and kimberlites with Mg# [= Mg/(Mg+Fe)] ranging from 0.72 to 0.79, and are likely derived from partial melting of carbonated peridotite at pressures of around 5 GPa [4]. Their deep origin is further corroborated by a garnet-peridotite mantle xenolith which equilibrated at 1350 °C and 5.8 GPa.

Olivine is the most common mineral in the studied rocks and exhibits complex zonation. The core compositions show different groups that we attribute to i) mantle xenocrysts (high Mg# and NiO), ii) antecrysts which have crystallized at different levels in the lithosphere (variable Mg# and NiO), and iii) carbonatitic olivines (extremely low NiO). The rims show distinct differentiation trends converging to Mg# of about 0.87 with decreasing NiO contents.

Our results demonstrate the complex magmatic history of the Delitzsch UMLs and provide evidence for a formerly thick lithospheric mantle beneath Central Europe.

[1] Seifert et al. (2000) Lithos 53: 81-100
[2] Krüger et al. (2013) Chem Geol 353: 140-150
[3] Tappe et al. (2005) JPet 46: 1893-1900
[4] Gudfinnsson & Presnall (2005) JPet 8: 1645-1659

Research on hydrothermal alteration investigates the impacts of hot, corrosive fluids circulating within a volcano, which are crucial for comprehending volcanic risks, slope instability, and steam-driven eruptions. Observable phenomena like fumaroles and mineral deposits at the surface offer direct evidence of subterranean hydrothermal systems or volcanic unrest, detectable through remote sensing techniques. In this study, we introduce a novel Hydrothermal Alteration Index (HAI) derived from Ultra Blue, Red, SWIR 1, and SWIR 2 bands of multispectral satellite imagery, facilitated by Google Earth Engine (GEE), to monitor hydrothermal changes. Identifying three primary alteration zones covering a total area of 600,000 m² at Lastarria Volcano, our findings are corroborated by field surveys, affirming the utility of HAI. Through temporal analysis, we pinpoint three distinct events indicating expansion, contraction of alteration zones, and the emergence of new sulfur flows. By aligning spatiotemporal patterns detected by HAI with independent monitoring data, we infer heightened hydrothermal activity. Lastly, we offer fresh insights into the progression of surface hydrothermal phenomena, starting from the summit crater and extending towards the flank region.

North Atlantic rifting during the Palaeocene-Eocene was accompanied by explosive volcanic eruptions. These led to distribution of about 200 ash layers of mainly basaltic composition covering wide areas of NW and Central Europe, also reaching the Tethys realm (Obst et al. 2015).

The ash layers, which are often interbedded in clayish successions, are known from offshore and onshore drillings but also from surface exposures, e.g., cliff sections or clay pits. In part, the pyroclastic material is well preserved in eogenetically carbonate cemented concretions, which occur in northern Germany and Denmark in glacially dislocated rafts of Eocene sediments or as isolated glacial erratic boulders named cement stones (“Zementsteine”).

Petrographic and sedimentological investigations of numerous cemented ashes from several locations in northern Germany (Fehmarn, Klütz Höved, Groß Roge, Grimmen, Wobbanz/Rügen and Greifswalder Oie) allow to distinguish different types of preservation. Single and rarely double ash layers up to 15 cm in thickness may either be preserved undisturbed, intensively bioturbated or reworked. Especially in shallow marine environments, the ashes can partly be eroded by currents or waves, and the basaltic glass particles may be redistributed.

In detail, variations in thickness and grain size as well as varying glass composition and alteration can be used to characterize distinct layers and will help to correlate ashes of the same volcanic event between different occurrences. Furthermore, changes of the sedimentation environment are documented in a NW–SE transect reflecting still water conditions in the central part of the North Sea Basin and near-shore environments at the eastern basin margins.

Volcanic flank instability poses a significant multi-hazard risk, encompassing caldera collapses, landslides, rock avalanches, and potential tsunami generation in active and dormant volcanoes. The mechanical strength and regions of hydrothermal alteration may play a fundamental role in locating and scaling volcano instability. Therefore, investigating hydrothermal alteration, which consequently alters the physicochemical properties of volcanic rocks, is crucial to better understanding the processes that lead to volcanic flank instability and collapse.

Here, we use the southernmost exposure of the Aeolian volcanic archipelago, La Fossa of Vulcano Island (Italy), as our focus site. La Fossa's history of mass wasting, regions of hydrothermal alteration, and episodic fumarole activity make it an ideal natural laboratory for our investigation. Here, we used high-resolution drone remote sensing techniques coupled with in-situ uni-axial compressive strength measurements to identify regions of hydrothermal alteration and assess their associated compressive strength properties. In summary, our results show (1) a heterogeneous distribution of alteration types and intensities, (2) a relationship between increasing alteration intensity and decreasing rock strength, (3) a correlation between regions with the weakest rock strength and the most intensely altered areas, and finally (4) a spatial association of alteration and deep scars resulting from erosion and landslides. Our combined approach allows us to explore the association between rock strength and hydrothermal alteration, enabling us to understand volcanic flank instability better and help us improve future hazard assessment.

Magma contains information on its source and on the processes the magma experienced en route to the surface. This information is, however, locked in the chemical and isotopic composition of minerals and groundmass. Petrologists can help understand volcanic phenomena and geochemical processes. The recent basaltic eruptions on Iceland and in the Canary Islands have now given us the opportunity to study the evolution of individual rift eruptions in extreme detail. Time-resolved sampling of erupted products allows detection of mineralogical and chemical changes on a daily to weekly timescale and gives us the opportunity to correlate this information with seismic data and changes in eruptive style. This allows us to identify rapid changes in magma composition and interpret these changes in respect to magma sources, magma storage, and magma transport.

The recent eruptions at Fagradalsfjall have shown rapid compositional changes in major and trace elements during the eruption, which has been interpreted as reflecting different mantle components that are sampled during a single eruption. Stable isotopes such as oxygen remain virtually unchanged, however, through the 2021 to 2022 events. The 2021 Tajogaite eruption on La Palma also showed rapid changes in lava composition during the first weeks of the eruption. This together with the seismic record indicates that the eruption was initially fed from a crustal reservoir, but later from a deeper upper mantle reservoir. In contrast to Fagradalsfjall, initial magmas show variable oxygen isotope compositions. The implication of these commonalities and differences are discussed in full in this presentation.

The Ohře/Eger Graben (OEG) marks one of the important spots of the Mesozoic to Cenozoic rift-related volcanic activity in central Europe, and extends over a length of more than 250 km. Here, the volcanic edifices comprise monogenetic maar-diatremes, scoria cones, and lava domes as well as large polygenetic stratovolcanoes. Their composition ranges between melilitite, nephelinite, basanite, and phonolite. It is precisely the northern flank of the OEG, where the timing of eruption has been sporadically dated with outdated methods.

Recent 40Ar/39Ar age analysis has provided new insights, revealing a chronological sequence spanning from 77 to 10 Ma and reshaping our understanding of eruption dynamics in the northern OEG rift structure. The oldest volcanics are melilite-bearing rocks with ages of around 77 to 65 Ma. With eruption ages at 10 Ma, the nephelinitic Landsberg and Buchhübel, as well as the basanitic Ascherhübel of the western Elbe Zone are the youngest volcanoes from the northern rift flank. Volcanoes of the Erzgebirge and Lusatia erupted between 37 and 29 Ma and 35 to 26 Ma, respectively. The age determination of the Vogtland yields younger ages at 30 to 23 Ma.

Melilite-bearing igneous rocks are known to be derived from the partial melting of dolomitic garnet-bearing lherzolite under CO₂-rich conditions at pressures between 27 and 40 kbar. However, there are still unresolved questions regarding their magma evolution. The Vogtland volcanic field is part of the Central European Cenozoic Igneous Province and hosts various olivine melilitite and melilite-bearing olivine-nephelinite diatremes, such as those at Bösenbrunn and Burkhardtsgrün.

The olivine melilitite and melilite-bearing rocks of these two locations are characterized by variable olivine content, often with skeletal or "hopper" morphology. They also contain clinopyroxene, melilite with a typical "pag" structure, magnetite, Cr-spinel, rare nepheline, apatite, zircon, and perovskite. Within some melilitites, the presence of reversely zoned melilite in clinopyroxene-bearing melilitites is probably the consequence of the co-precipitation of melilite with clinopyroxene. As clinopyroxene crystallization initiates, the Al/Mg ratio of the residual melt rises, causing a gradual depletion of åkermanite content from core to rim within the crystallizing melilites. Variations in major and trace elements, along with zoning patterns in coexisting minerals, may be influenced by their affiliation with either Ca-rich or -poor magma series. Trace-element fractionation during differentiation of these parental magmas suggests the existence of two mantle-derived magmas: (i) a melilite-bearing series formed at higher pressures (ca. 35 kbar), which was originally enriched in CO₂, Sr, Nb, and REE (La, Ce, etc) and differentiated at shallower depths, while (ii) a Ca-poor magma began fractionating only at around 17 kbar during magma ascent.

Magneto-mineralogical properties of volcanic rocks can be used to study their emplacement conditions and thus the eruptive behaviour of volcanoes. Two ICDP cores were drilled into the effusive and explosive units of the Bažina Maar, located in the Czech Republic. The drilled volcanic units are up to 160 m thick in total, and consist of lapilli tuff and effusive (sub-)volcanic rocks which are overlain by unconsolidated, highly weathered lapilli and scoria deposits. The units are locally overprinted by apatite-bearing sequences, possibly of hydrothermal origin. We used a KLY-5A Kappabridge to measure the out-of-phase (op) in addition to the traditionally measured in-phase (ip) temperature-dependent magnetic susceptibility and determined Curie-Temperatures (T_c), field depend magnetic susceptibility as well as the anisotropy of magnetic susceptibility (AMS). The most common sources for an op component in igneous rocks are vicous relaxation of superparamagnetic/single domain (titano-)magnetite grains and weak field hysteresis of ferrimagnetic phases like titanomagnetite and pyrrhotite. Ip and op T_cs between 170 – 300°C suggest a Ti-rich titanomagnetite as the main ferrimagnetic phase. Higher T_cs within the explosive products between 450 – 580°C suggest maghemitisation of the juvenile titanomagnetite. The ip AMS component for the effusive volcanic rocks reveals a moderate to steeply inclined magnetic foliation, suggesting an upwards flow as emplacement mechanism. For the lapilli units, the op AMS response is oblique to the ip AMS signal, revealing a magnetic subfabric. Our study demonstrates that the systematic study of ip and op susceptibility can add key information to unravel complex volcanological processes.

The Haukadalur thermal area in southwestern Iceland comprises numerous individual thermal springs, geysers, and hot pots arranged roughly in a north-south orientation. Situated on the eastern slope of a hill, this field is delimited by fissures associated with the Western Volcanic Zone. This study is based on high-resolution unmanned aerial vehicle (UAV) equipped with optical and radiometric infrared cameras to identify over 350 distinct thermal spots across various zones, and puts these in a larger context from geophysical experiments undertaken in the region. Close examination revealed that geysers and hot areas are clusters, but are generally aligning with the presumed tectonic trend in the region. Repeat thermal surveys realized in the past 10 years show systematic and chaotic changes in activity of the geysers. This presentation delves into the structural correlation between the deeper and shallower segments of these geysers, influence of the external effects and water table, and is shedding light on the mechanisms underlying geyser and hot pot activity, with broader implications applicable to thermal fields worldwide.

A swarm of devastating caldera-forming eruptions (>VEI 6) blanketed the Permo-Carboniferous of central Europe with voluminous pyroclastic deposits within a long-lasting period of 50 Myrs. Although of different tectonic setting, the pyroclastic record of this ignimbrite flare-up is similar to the Cenozoic deposits in the western USA, ranging from crystal-poor rhyolitic Snake River-type and compositionally zoned tuffs to crystal-rich monotonous intermediates and rhyolites.

Combined textural and chemical analysis data on whole rock, juvenile fragments (fiamme, glass shards), and mineral phases were acquired to unravel the origin and lithospheric evolution of the magma reservoirs. Two different geochemical suites can be distinguished: (I) a diopside- and (II) a corundum-normative. Examples of the diopside-normative suite are the caldera systems of Wurzen and the Wendland, as well as the vitrophyric Planitz Ignimbrite. Although all pyroclastic deposits show corundum-normative compositions; solely, the magma system of the Flechtingen Ignimbrite crystallizes almandine-garnet in a deep-seated magma chamber. In general, thermobarometric estimations suggest an interplay of hydrous near-solidus granitic systems penetrated by anhydrous SiO₂-rich superheated magmas. These systems can be tracked down to depths of 25 to 40 km (7-12 kbars) and provide insights into the post-Variscan rift-related magmatic activity.

A sudden eruption occurred in December 2022 at Lascar, one of the most popular volcanoes for tourists in Chile. Following the eruption, lava emplacement was observed in summit crater of Lascar. Due to volcanic activity and inaccessibility, we acquired a series of Pleiades tri-stereo satellite images covering this unrest episode. We generated high resolution point clouds and orthomosaics from the satellite images using photogrammetric approaches. We analyze point clouds to quantify morphological and structural details and changes. We found that the crater floor initially uplifted due to lava extrusion and rockfall deposition, and subsequently the crater floor subsided and formed a funnel in the center. To understand the mechanical factors controlling the uplift and subsidence, we designed a novel set of analogue experiments using sand-plaster mixtures to simulate lava extrusion and subsidence from same conduit. We account for topographic effects by running experiments on flat plate and 3D printed mould of the Lascar crater, respectively. We use 2D digital image correlation method to record and visualize displacements during extrusion and subsidence. The results show that extrusion and subsidence occurs along distinct shear faults, which are constrained by conduit diameter and represented as concentric fractures at surface. We develop a conceptual model that lava extrusion is affected by withdrawal from the conduit, forming a funnel-shaped surface depression associated with inward-dipping radial erosion gullies. Thus, combining satellite observations and analogue models help to identify the position and dimension of the underlying conduit, which is essential for understanding future activity of Lascar volcano.

Two diatreme structures in the Lusatian Mountains (CZ) can be assigned to so-called pre-rift period of volcanism within the Bohemian Massif. This is confirmed by Ar-Ar age determinations on intrusive ultramafic melilithic rocks in the diatremes of Dolní Falknov (≤ 68.34 ± 0.33 Ma) and Stožec (68.80 ± 0.85 Ma). Detailed geological mapping of both volcanic structures enabled to clearly demonstrate typical diatreme breccia only in the Dolní Falknov diatreme. In contrast, mapping of the Stožec volcanic structure 5 km to the northeast only revealed an intense red-brown coloured diamictite deposit. This diamictite also occurs in the top of the Dolní Falknov diatreme fill as separated clods and is interpreted as a collapse breccia. The diamictite as well as the diatreme breccia contain numerous rounded pebbles of different lithologies with diameters of up to 0.5 m. Some of these pebbles probably come from Permian rocks (Rotliegend) and indicate a multi-phase redeposition history. These could be erosion products from the Lausitz Block, which is located 2.5 and 5 km north of the two diatreme structures. The Permian sediments eroded here were later rounded off before being redeposited as terrestrial (red) sediments in the uppermost Upper Cretaceous (Campanian–Maastrichtian). These deposits have only been preserved due to their sheltered position within the pre-rift diatreme structures.

Recent discoveries and studies of maars in the NE Bavaria-Czech Republic border region have significantly expanded our knowledge of Cenozoic volcanism in the western Bohemian Massif. Using geomorphological and geophysical investigations, two new circular geological structures with partly striking geophysical anomalies were discovered: the Bärnau Maar and the Rohrloh Maar. They were explored with two scientific drillings by the Geological Survey at the Bavarian Environment Agency. Both dry maars form shallow depressions from a few hundred to approximately 1000 m in diameter. In the Bärnau Maar, a 150 m thick sedimentary sequence consisting primarily of laminated, organic-rich clayey to silty sediments with numerous diatomite laminae of a lacustrine depositional environment was drilled, with frequent sand beds and soft-sediment deformation structures documenting repeated turbidity flows and slumps. The upper sedimentary sequence comprises soft-sediment deformed lacustrine sediments overlain by gravelly and sandy deposits. The 70 m thick sediment sequence drilled in the Rohrloh Maar similarly consists predominantly of fine-grained lacustrine sediments with intercalated sandy turbidite beds. Both sediment sequences are composed predominantly of quartz-, mica-, and kaolinite-rich sediments, representing the erosion products of neighbouring crystalline rocks; however, elevated smectite contents near both core bases suggest the contribution of juvenile material. The palynological data from the Bärnau Maar and Rohrloh Maar sediments advocate a Lower to Middle Miocene age and Lower Miocene age, respectively. During this time, the climate was predominantly subtropical to temperate, and swamp forests surrounded the maars, whereas mesophytic vegetation was present in the broader region.

Regions with complex topography display a variable degree of deformation during seismic and volcanic events. In the Reykjanes Peninsula rift, both extension and strike-slip motion result from its highly oblique angle with respect to the plate opening, leading to NE- and N-striking structures, including eruptive fissure swarms, tensile fractures, normal faults and strike-slip faults. Structural domains have been explained by factors like tectonomagmatic cycles or proximity to rift axes. However, pre-existing topographic gradients were not previously considered relevant for the resulting fracture network of the area, as suggested by studies at other sites.

Following a period of uplift in the Svartsengi volcanic system, a 2-meter-deep graben formed in November 2023 due to a ~15-km long dike intrusion. In this work, we use high-resolution photogrammetric data from before and after this event to explore how Mount Thorbjorn, situated on the western part of the graben, responded to this deformation event. A Digital Elevation Model (DEM) difference map suggests tilting of the mountain towards the east and reactivation of pre-existing faults. Comparison of orthophotos before and after the event revealed new surface fractures, many corresponding to reactivated buried discontinuities, mainly expressed as normal motion and with fissures showing opening. Statistical analyses were used to test the topographic controls on the resulting faulting pattern, and sandbox analogue experiments helped better understand the process. Preliminary results suggest that the distribution of the fractures is influenced by topography, with denser patterns observed in higher elevation areas, and changes in their strike due to surface adjustments.

Hekla is one of the most active volcanoes in Iceland, with recent eruptions in 1970, 1980-81, 1991, and 2000. The last three eruptions occurred in the early months of the year when the volcano was heavily snow-covered. As a result, tephra and effusive deposits have covered large amounts of snow and ice causing an insulation effect. Using photogrammetric processing and GIS analysis of historical aerial photographs (1945-1982), recent Pléiades satellite tri-stereo images (2022 and 2023), and UAV data acquired during the 2022 and 2023 fieldwork, we found evidence of intense cryospheric processes such as rock glacier emplacement and multiple thermokarst formations. Our results show that the NW flank of Hekla is covered by 6 distinct rock glacier lobes that were recently (after 1982) emplaced atop previously formed rock glaciers identified in 1945-1982 datasets. The total area of the recent rock glaciers is about 2 km². The longest lobe reaches 1.4 km in length and has a 50 m front thickness. The lobe has advanced by 13 m over 1 year (2022-2023). The newly emerged thermokarst sinkholes have been observed in the field in the summit area and on the NE flank. These aspects of Hekla's evolution may play a significant role in the magnitude of hazards in case of future unrest. The emplacement of lava along rock glaciers and permanent snow raises the risk of impending lahars. Volcanic heat can expedite permafrost degradation and the advancement of rock glaciers, culminating in significant landslides.

The DEKORP (Deutsches Kontinentales Reflexionsseismisches Programm) initiative, conducted from 1984 to 1997, was Germany's national reflection seismic program. DEKORP aimed at resolving the deep crustal and upper mantle structure, employing mainly near-vertical incidence seismic surveys that in some cases were complemented by wide-angle seismic studies and accompanied by research projects dedicated to refining and optimizing processing and interpretation methods. The resulting seismic images significantly contributed to the geological interpretation of the crust and upper mantle, e.g., unveiling distinct units of the Central European Variscides in Germany.

We reprocessed several of these DEKORP profiles located within the Federal state of Bavaria and in particular around the German Continental Deep Drillhole (KTB). We employed advanced focusing pre-stack depth imaging techniques in conjunction with newly derived near-surface tomographic velocity models. Our approach yields novel images with improved quality and new structural details in several profile parts. The results provide a comprehensive view of the entire crust and the basis for new geological interpretations and modeling, including a significant enhancement of our understanding of the crustal architecture.

We thank the Bayerisches Landesamt für Geologie for assigning the new processing and providing the seismic data. Particular thanks to J. Großmann and K. Dengler for their support.

The Kraichgau Terrane is a NE-SW elongated high-density body covered by Mesozoic sedimentary rocks and occupies the southwestern parts of the Saxo-Thuringian Zone in the Central European Variscides. Compared to other regions of the Saxo-Thuringian Zone, the Kraichgau Terrane is poorly studied owing to very limited subsurface data. We integrate reprocessed DEKORP-2S seismic reflection profile, filtered Bouguer gravity and total magnetic intensity data and show the regional subsurface litho-structure of the Kraichgau Terrane.

The seismic reflections show a stratified crust with high amplitude, continuous and subhorizontal middle and lower crust in the SE and NW separated by a central zone of medium to low amplitude and transparent area hosting several oppositely dipping high amplitude reflections. This central zone (CZ) is approximately 80 km wide along the DEKORP-2S profile, exhibits a high density anomaly and shows two distinct linear features on the vertical derivatives of the magnetic intensity data. Further NE along the DEKORP-3MVE profile, the CZ is approximately 20 km wide, is denser than surrounding areas, and exhibits a single linear feature on the vertical derivative of the magnetic data. This linear feature is correlated with exposed Early Paleozoic magmatic rocks known as the Vesser units.

In addition to the magnetic and gravity signature of the Vesser units, the tilt and vertical derivatives of the Bouguer gravity anomaly show several NE-SW linear structures in the central and southeastern parts of the Kraichgau Terrane. These linear structures are interpreted as the folded and overthrusted Saxo-Thuringian units during the Variscan tectonics.

We are in the process of making a tectonometamorphic map of the Erzgebirge and present our preliminary state of this work. We follow the scheme of previous studies and distinguish four major allochthonous units in the Erzgebirge: Basal Gneiss Unit, Gneiss-Eclogite Unit, Mica schist-Eclogite Unit, and Phyllite Unit.

In the course of this project we would like to address the following open questions:

1. Where are tectonic boundaries between these units? Which subunits can be distinguished?

2. Do high-pressure/ultrahigh-pressure (HP/UHP) conditions form different clusters? If so, what is the extent of these clusters and is the current scheme of two HP and one UHP cluster accurate?

3. Are high-pressure rocks solitary occurrences in a matrix with different pressure-temperature evolutions or did the units share a common evolution? If units behaved coherently – how do the HP clusters fit into this picture and where are the associated tectonic boundaries?

4. Does the main foliation in the HP units reflect exhumation from eclogite-facies conditions, exhumation from mid-crustal levels or even something else?

5. What explains the overall distribution of metamorphism in the Erzgebirge? While high-pressure and Barrovian conditions seem to fade out towards higher structural levels in the west, the eastern border of the Erzgebirge towards the Elbe Zone is metamorphically abrupt, represents a major structural jump and shows similarities to an extensional detachment fault.

The Elbtalschiefergebirge - the tectonic border between the Lusatian Massiv and the Erzgebirge – is limited by two large regional faults, the West Lusatian fault and the Mid Saxonian fault. In Saxony, both NW-SE striking faults are running mostly parallel. So, a generally cogenetic evolution of both structures was assumed until now.

The paleozoic units of the Elbtalschiefergebirge itself are limited very often also by faults. However, deep drillings are missing until now.

During the still running project „Railway tunnel Dresden-Prague“ several geological units and faults are exposed by numerous drillings up to 400 m depth.

The new results show, that the West Lusatian fault as thrust zone and the Mid Saxonian fault as shear zone are not comparable as well in time as in genesis. The thickness of the Mid Saxonian fault is proved by drillings of at least 900 m. On the other hand, the fault volume of the West Lusatian fault includes only several meter. This is untypical for such a regional fault zone, but the main movement seems to have taken place about 300 m south of the recently mapped fault position.

Instead this, the faults in the Elbtalschiefergebirge are thrusts with considerable displacement.

The drillings of the ongoing project will just be investigate by several research groups of different institutions. Numerous new drillings in special areas are planned in the next years.

In the Saxothuringian Zone a unique assemblage of high to ultra-high pressure and ultra-high temperature metamorphic units is associated to medium-to-low pressure and temperature rocks. The units were studied in a campaign with garnet and monazite petrochronology of gneisses, micaschists and phyllites, and monazite dating in granites. P-T path segments of garnet crystallisation were reconstructed by geothermobarometry and interpreted in terms of monazite stability field, EPMA-Th-U-Pb monazite ages, and garnet Y+HREE zonations (Schulz and Krause 2024). One can recognise (1) Cambrian plutonism (512-503 Ma) with contact metamorphism in the Münchberg Massif. Subordinate monazite populations may indicate a (2) widespread but weak Silurian (444-418 Ma) thermal event. A (3) Devonian (389-360 Ma) high pressure metamorphism prevails in the Münchberg and Frankenberg Massifs. In the ultra-high pressure and high pressure units of the Erzgebirge the predominant (4) Carboniferous (336-327 Ma) monazites crystallised at the decompression paths. In the Saxonian Granulite Massif, prograde-retrograde P-T paths of cordierite-garnet gneisses can be related to monazite ages from 339 to 317 Ma. A (5) local hydrothermal overprint at 313-302 Ma coincides partly with post-tectonic (345-307 Ma) granite intrusions. Such diverse monazite age pattern and P-T-time paths characterise the tectono-metamorphic evolution of each crustal segment involved in the Variscan Orogeny.

Schulz, B., Krause, J. (2024): Electron probe petrochronology of monazite and garnet bearing metamorphic rocks in the Saxothuringian allochthonous domains (Erzgebirge, Granulite and Münchberg Massifs). Geol. Soc. Spec. Publ., 537:249-284. https://doi.org/10.1144/SP537-2022-195.

The TUNB project, conducted from 2014 to 2021, marks an important step in the geological 3D modelling of the North German Basin. Through the collaboration of the State Geological Surveys of the participating federal states and the Federal Institute for Geosciences and Natural Resources, a comprehensive 3D model was created, comprising 13 geological horizons and important structural elements such as faults and salt structures. The model finds application, for example, as a basis for further investigations and planning in the subsurface, ranging from CO2 storage to the final disposal of radioactive materials.

The follow-up project, 'TUNB Velo 2.0,' extends this work by evolving the geological 3D structural model towards a parameterized volume model, with 'seismic velocity' as the key parameter. This enhancement allows the precise conversion of seismic data from the time domain to the depth domain, thereby correcting the apparent geometry of geological structures distorted by velocity variations. This allows for a more realistic spatial representation of the geological subsurface and paves the way for the creation of more accurate and detailed future 3D geological models in this region.

TUNB Velo 2.0 marks a significant step forward in the geological exploration of the North German Basin and is a vital tool for enhancing the precision and resolution of future geological 3D models. In our presentation, we will introduce the project and its history, summarize ongoing work, discuss key challenges, and highlight the expected benefits for future projects.

A harmonized regional 3D depth model of the subsurface for the North German Basin from Cenozoic to the base of Zechstein was developed from 2014 to 2020 in the framework of the TUNB project. In a next step, this model will be parametrized with a focus on seismic velocities (and optionally other parameters).

The seismic database in the former Eastern and Western parts of Germany differs due to different historical conditions (e.g. concepts of exploration and interpretation, availability of seismic equipment and computing power).

In the eastern part of the North German Basin (Federal States of Mecklenburg-Western Pomerania, Brandenburg, Saxony-Anhalt) most of the velocity data were acquired in 2D-seismic surveys from the 1960s to the 1980s that focused on deep Permian reservoirs. Strata and structure of the Mesozoic were also documented, but were usually not an exploration target. Besides processing velocities and in a minor extent sonic logs comprehensive data from check-shots and vertical seismic profiles were documented for several hundreds of wells. Based on these heterogeneous data, interpretations concepts and velocity models were developed from the 1960s to the 1980s on local scales for detailed seismic surveys and on regional scales for Northeastern Germany.

The main goal of the ongoing project is to develop workflows to revitalize the historical data with modern methods and possibilities of 3D modelling to derive cross-country-wide harmonized and seamless 3D-velocity fields. These velocity models allow large-scale depth-time- and time-depth-conversions of geological 3D models and support upcoming seismic processing and reprocessing campaigns.

The TUNB model provides a 3D model for the North German Basin consisting of 13 lithostratigraphic units from Zechstein to Tertiary and numerous salt domes and fault systems. The aim of the project TUNB Velo 2.0 is to assign reasonable seismic velocities to the lithostratigraphic units. The resulting velocity model enables to convert information on a regional scale from time to depth domain and vice versa. Therefore, a 3D volume model is created from the 3D structural model and then parameterised with seismic velocities.

For Schleswig Holstein and Lower Saxony, Jaritz (1991) published a regional velocity study within the Tectonic Atlas (GTA) project that serves as the database for velocity modelling. The authors derived the velocities mainly from Vertical Seismic Profiling measurements as well as considerations of the regional geology. Their model covers 11 layers from Zechstein to Tertiary. For every sediment layer, maps display its surface velocity. The velocities can be calculated in depth using the surface velocities, an individual gradient for every layer and the dedicated depth.

Both Federal States use Aspen SKUA for region-wise velocity modelling. Close to the border, we harmonized the velocities to enable the creation of a consistent, trans-border model.

In this talk, we will provide insights in the processing of the database, the modelling methods in Aspen SKUA and show the resulting velocity distribution.

References:

Jaritz W., Best G., Hildebrand G., Jürgens U. (1991) Regionale Analyse der seismischen Geschwindigkeiten in Nordwestdeutschland. Geol Jahrb 45:23–57

Reliable geological models of the North Sea are essential for a robust assessment of subsurface potentials in this vital European economic region. While commercial and scientific surveys have effectively explored the upper 2 to 4 km, there is currently no well data reaching the base of the locally more than 10 km deep rift structures such as the Central and Horn Graben. This leads to considerable uncertainties in the regional seismic velocity model and thus in the depth-conversion of reflection seismic profiles. Our objective is to reduce these uncertainties in the German North Sea by integrating the abundant gravity data, offering additional constraints on both the geometry and petrophysical properties of deep basins. We present the results of 2D gravity forward modelling, which combines existing regional and global crustal models with the most recent structural model of the Paleozoic to Cenozoic sedimentary sequences. Density information is thereby derived from well logs, seismic tomography studies, and further literature implications. The calculated free-air gravity anomalies are then compared with the measured gravity field to assess the quality of the used crustal and sedimentary models. The insights gained will subsequently inform a more intricate inverse 3D modeling, resulting in a quantitative description of the geological uncertainties.

The new Dresden - Prague railway line is a Saxon vision. Since 2014, the Geological Survey of Saxony has been developing the geological 3D model on the basis of archive data and geophysical investigations.

In cooperation with the TU Bergakademie Freiberg (TU BAF) and the Czech geological survey, a cross-border model was built that illustrates the complex geological structures in the underground of the route corridor. As part of an INTERREG project, the model was presented to the public in a walk-through 3D room at the TU BAF.

When the planning task was assigned to Deutsche Bahn, the geological 3D model proved its worth as a basis for the first steps of exploration planning, regional planning and preliminary planning in combination with GIS.

The model will be updated as knowledge is gained during the explorations.

It is a real pilot project for successful cooperation between authorities, research institutions and the railway companies in using graphic datamangement and 3D-modeling.

In the German national annex of Eurocode 8 (EC8) "Design of structures for earthquake resistance", the influence of local ground conditions on earthquake impact has to be taken into account. Generally, the shallow structure is classified as a combination of one of three geological subsurface classes and one of three subsoil classes in the national annex. For the determination of the subsoil class, the rock mass down to a depth of 30 meters is considered. For the determination of the geological subsurface class, the structure below 30 m depth down to several hundred meters is considered.

As part of the recent update of the national annex of EC8, the map of geological subsurface classes, which is a part of the code, was revised. For the new map, the methods of geological 3D modelling were used for the first time. Based on data from the geological 3D models of the federal states Baden-Württemberg, Bavaria, Hesse, North Rhine-Westphalia, Rhineland-Palatinate, Saxony, Saxony-Anhalt, and Thuringia, the thicknesses of Quaternary and Tertiary sediments were determined first. Based on these thicknesses, the geological subsurface classes "R" (rock), "T" (shallow sediment basins), and "S" (deep sediment basins of more than 100 m thickness) were assigned. The geological subsurface classes were presented on a grid with a cell size of 1 km x 1 km. Compared to the previous assignation of geological subsurface classes, in which geological structures of less than 20 km extension or diameter could not be considered, a significantly higher spatial resolution was achieved.

Semi-automatically generated maps highlight the variability of the stratigraphic thickness of the Helvetic Kieselkalk. This geological unit is exposed in different Helvetic nappes over more than 300 km along the Swiss Alps and it is commonly extracted to produce hard rock aggregates for the national road and railway infrastructure. The deposition of this unit onto the European (Helvetic) continental margin during the Early Cretaceous coincided with normal faulting, which lead to strong lateral thickness variations.

The Python and MATLAB approach used to create the thickness maps was developed as part of a Switzerland-wide mineral resource mapping project and has been applied to the geological vector dataset GeoCover. The approach is designed to rapidly generate large-scale map overviews of the stratigraphic thickness, for which the construction of 3D models would be very time consuming.

Our results highlight an increase in thickness along the Alps from 100 m in the west to 1000 m in the east. The depositional thickness was certainly modified by the subsequent burial, folding, and faulting during the formation of the Helvetic nappes. Two discrete thickness jumps indicate the presence of three sedimentary basins in east-west direction with a half-graben-like geometry. These thickness jumps coincide with present-day nappe boundaries and suggests that the inherited basin geometry influenced the nappe formation.

The large-scale thickness maps and the improved undestanding of the paleogeography and tectonic evolution are used to rapidly identify mineral occurrences with favourable geometry. These can, when sufficiently investigated, be considered in land use or resource safeguarding plans.

Structural geologic modeling and subsurface process simulation are important tools in geoscience. Various software solutions—ranging from manual to semi-automated—are available in this field. These include proprietary and open-source software, often covering specific components of a larger workflow. Consequently, comprehensive workflows typically combine different software solutions and custom-built tools to address specific scenarios.

However, these workflows frequently require substantial manual adjustments and are tailored to particular applications, making reuse challenging without significant modifications by skilled professionals. In addition, it is not always possible to access all parts of a workflow, reducing transparency and the flexibility to modify components.

To address this issue, within the project WBGeo, supported by BMBF through the programme “Geoforschung für Nachhaltigkeit (GEO:N), Digitale Geosysteme: Virtuelle Methoden und digitale Werkzeuge für geowissenschaftliche Anwendungen”, we aim to develop a workbench for digital geosystems. This workbench enables the creation of complete workflows by integrating three core components: structural geologic modeling, numeric process simulation, and visualization as well as the interfaces between these components. A visual scripting environment using an underlying domain-specific language provides intuitive access for users with limited technical expertise. At the same time, the flexible modular structure ensures that experienced users have full access to the underlying code, allowing them to customize existing or add new components as needed.
This structure increases reproducibility, transparency, accessibility and comparability of workflows, as a multitude of components are available in a single framework.