Jörg Bialas

Gas hydrates and deltaic deep-sea fans are main features in continental margin systems, influencing slope stability, fluid migration, and carbon cycling. In the northwestern Black Sea, the Danube Fan remains poorly constrained with respect to subsurface structure, sediment strength, and hydrate dynamics. Here, we present high-resolution multichannel seismic (MCS) and ocean-bottom seismometer (OBS) data to characterise sedimentary structure and fluid-related features. Two integrated OBS–MCS profiles reveal under-consolidated, clay-rich levee deposits interspersed with mass-transport units, chaotic facies, and gas-related anomalies. Derived P- and S-wave velocity models indicate low shear strength and high Vp/Vs-ratios in shallow units, consistent with soft, water-saturated sediments. Deeper layers display compaction-driven velocity increases but remain mechanically weak, rendering the slope prone to failure. Our findings suggest that vertical gas migration is widespread, expressed by seismic chimneys, polarity reversals, and velocity pull-downs, with free gas confined below bottom simulating reflectors and in stratigraphic traps. Hydrates likely occur as sparse, patchy pore-filling accumulations, and the lack of S-wave velocity anomalies suggests they do not act as cementing phases, implying little direct influence on sediment strength or slope stability. The hydrate system appears hydrate-poor, possibly reflecting post-glacial re-equilibration. Overall, lithology, gas migration pathways, and high sedimentation rates emerge as primary controls on hydrate formation and slope instability in the Danube Fan.

Gas hydrates and deltaic deep-sea fans are main features in continental margin systems, influencing slope stability, fluid migration, and carbon cycling. In the northwestern Black Sea, the Danube Fan remains poorly constrained with respect to subsurface structure, sediment strength, and hydrate dynamics. Here, we present high-resolution multichannel seismic (MCS) and ocean-bottom seismometer (OBS) data to characterise sedimentary structure and fluid-related features. Two integrated OBS–MCS profiles reveal underconsolidated, clay-rich levee deposits interspersed with mass-transport units, chaotic facies, and gas-related anomalies. Derived P- and S-wave velocity models indicate low shear strength and high Vp/Vs-ratios in shallow units, consistent with soft, water-saturated sediments. Deeper layers display compaction-driven velocity increases but remain mechanically weak, rendering the slope prone to failure. Our findings suggest that vertical gas migration is widespread, expressed by seismic chimneys, polarity reversals, and velocity pull-downs, with free gas confined below bottom simulating reflectors and in stratigraphic traps. Hydrates likely occur as sparse, patchy pore-filling accumulations, and the lack of S-wave velocity anomalies suggests they do not act as cementing phases, implying little direct influence on sediment strength or slope stability. The hydrate system appears hydrate-poor, possibly reflecting post-glacial re-equilibration. Overall, lithology, gas migration pathways, and high sedimentation rates emerge as primary controls on hydrate formation and slope instability in the Danube Fan.

Gas hydrates and deltaic deep-sea fans are main features in continental margin systems, influencing slope stability, fluid migration, and carbon cycling. In the northwestern Black Sea, the Danube Fan remains poorly constrained with respect to subsurface structure, sediment strength, and hydrate dynamics. Here, we present high-resolution multichannel seismic (MCS) and ocean-bottom seismometer (OBS) data to characterise sedimentary structure and fluid-related features. Two integrated OBS–MCS profiles reveal underconsolidated, clay-rich levee deposits interspersed with mass-transport units, chaotic facies, and gas-related anomalies. Derived P- and S-wave velocity models indicate low shear strength and high Vp/Vs-ratios in shallow units, consistent with soft, water-saturated sediments. Deeper layers display compaction-driven velocity increases but remain mechanically weak, rendering the slope prone to failure. Our findings suggest that vertical gas migration is widespread, expressed by seismic chimneys, polarity reversals, and velocity pull-downs, with free gas confined below bottom simulating reflectors and in stratigraphic traps. Hydrates likely occur as sparse, patchy pore-filling accumulations, and the lack of S-wave velocity anomalies suggests they do not act as cementing phases, implying little direct influence on sediment strength or slope stability. The hydrate system appears hydrate-poor, possibly reflecting post-glacial re-equilibration. Overall, lithology, gas migration pathways, and high sedimentation rates emerge as primary controls on hydrate formation and slope instability in the Danube Fan.

The long-term storage of gigaton-scale volumes of CO₂ in basaltic formations is widely discussed as a promising strategy for mitigating anthropogenic CO₂ emissions. Offshore basalt deposits are of particular interest as they are distant to urban areas and other resources. In Europe the Vøring Plateau offshore Norway represents a large igneous province called the North Atlantic Igneous Province (NAIP) formed during the breakup of the North Atlantic approximately 56-58 Ma ago. Our research focuses on the lava flows associated with the seaward-dipping reflectors (Planke et al., 2000).Two sites, previously investigated during ODP and IODP expeditions, on the Vøring Plateau were studied using ocean-bottom seismometers (OBS) and 2D multichannel seismic (MCS) data during cruise MSM140 aboard R/V Maria S. Merian, as part of the multinational PERBAS project. OBS arrays were deployed in a cross-shaped geometry on the seafloor above ODP Site 104–642 and IODP Sites 396–U1571/72. OBS data record both reflected and refracted seismic waves, providing complementary subsurface information to conventional MCS data. In addition, analysis of P-waves and converted S-waves enables detailed velocity modeling and improved characterization of lava flow properties.Preliminary interpretation of the OBS data and forward modeling allows the identification and narrowing down of a subsurface layer package that appears suitable for potential future CO₂ injection.

As part of the PERAS project, basaltic complexes relevant to potential CO₂ storage on the mid-Norwegian margin have been investigated. IODP Sites U1571A and U1572A sample two contrasting volcanic domains: based on seismic interpretations, site U1571A is located on a faulted lava-flow field, whereas site U1572A to the west is located on a younger pitted surface interpreted to reflect the interaction of lava with wet substrate during the original emplacement. These domains also differ in structural deformation, with abundant local NS–oriented normal faults in the eastern flow field, and comparatively minor faulting in the western pitted domain.We present first results of controlled-source electromagnetic (CSEM) experiments acquired during cruise MSM140 (4.9–9.10.2025) across the Vøring Plateau, offshore Norway. To investigate how emplacement style and deformation influence basalt structure, two CSEM experiments were carried out covering the area around sites U1571A and U1572A. A third experiment was measured along a profile line connecting the two sites. In addition, two experiments were carried out around ODP Site 642E to provide a regional reference and to assess regional lateral homogeneity of the basaltic complex.For measurements we used the towed transmitter system CAGEM, which allows for measurements with two horizontal transmitter polarizations. For each of the five experiments, 12 seafloor receivers nodes (OBEMs) were deployed onto the seafloor. This allowed us to collect data in both inline and broadside configurations, improving sensitivity to resistivity anisotropy and 3D structural variability.

Gas hydrates and deltaic deep-sea fans are main features in continental margin systems, influencing slope stability, fluid migration, and carbon cycling. In the northwestern Black Sea, the Danube Fan remains poorly constrained with respect to subsurface structure, sediment strength, and hydrate dynamics. Here, we present high-resolution multichannel seismic (MCS) and ocean-bottom seismometer (OBS) data to characterise sedimentary structure and fluid-related features. Two integrated OBS–MCS profiles reveal underconsolidated, clay-rich levee deposits interspersed with mass-transport units, chaotic facies, and gas-related anomalies. Derived P- and S-wave velocity models indicate low shear strength and high Vp/Vs-ratios in shallow units, consistent with soft, water-saturated sediments. Deeper layers display compaction-driven velocity increases but remain mechanically weak, rendering the slope prone to failure. Our findings suggest that vertical gas migration is widespread, expressed by seismic chimneys, polarity reversals, and velocity pull-downs, with free gas confined below bottom simulating reflectors and in stratigraphic traps. Hydrates likely occur as sparse, patchy pore-filling accumulations, and the lack of S-wave velocity anomalies suggests they do not act as cementing phases, implying little direct influence on sediment strength or slope stability. The hydrate system appears hydrate-poor, possibly reflecting post-glacial re-equilibration. Overall, lithology, gas migration pathways, and high sedimentation rates emerge as primary controls on hydrate formation and slope instability in the Danube Fan.

Gas hydrates and deltaic deep-sea fans are main features in continental margin systems, influencing slope stability, fluid migration, and carbon cycling. In the northwestern Black Sea, the Danube Fan remains poorly constrained with respect to subsurface structure, sediment strength, and hydrate dynamics. Here, we present high-resolution multichannel seismic (MCS) and ocean-bottom seismometer (OBS) data to characterise sedimentary structure and fluid-related features. Two integrated OBS–MCS profiles reveal underconsolidated, clay-rich levee deposits interspersed with mass-transport units, chaotic facies, and gas-related anomalies. Derived P- and S-wave velocity models indicate low shear strength and high Vp/Vs-ratios in shallow units, consistent with soft, water-saturated sediments. Deeper layers display compaction-driven velocity increases but remain mechanically weak, rendering the slope prone to failure. Our findings suggest that vertical gas migration is widespread, expressed by seismic chimneys, polarity reversals, and velocity pull-downs, with free gas confined below bottom simulating reflectors and in stratigraphic traps. Hydrates likely occur as sparse, patchy pore-filling accumulations, and the lack of S-wave velocity anomalies suggests they do not act as cementing phases, implying little direct influence on sediment strength or slope stability. The hydrate system appears hydrate-poor, possibly reflecting post-glacial re-equilibration. Overall, lithology, gas migration pathways, and high sedimentation rates emerge as primary controls on hydrate formation and slope instability in the Danube Fan.

Gas hydrates are relevant to global carbon cycling, climate change and ocean acidification. In particular, hydrates play an important role in sub-seafloor fluid migration because they reduce the porosity and permeability of sediments. Gas hydrates, and their associated underlying free gas zones, have also been linked to sediment failure and submarine mass transports. The active Hikurangi Margin hosts New Zealand’s largest gas hydrate province, with concentrated accumulations generally focused below accretionary thrust ridges.Recently acquired high-resolution Ocean-Bottom-Seismometer (OBS) data at the southern Hikurangi Margin images highly reflective layers beneath the accretionary Honeycomb Ridge. This ridge is of particular interest as it is thought to host a concentrated gas hydrate system. Unlike previous surveys, we have the advantage of being able to record converted shear waves that help us identify the nature of the highly reflective layers in the gas hydrate stability zone. In March 2023, we deployed 20 OBS from R/V Tangaroa with a USBL-wired system to position each OBS with 100 m spacing along an existing 2D seismic profile. A 150 in3 GI-gun was fired at a shot rate of 7 s, to ensure for excellent lateral and vertical resolution. This setup allows us to present an updated high-resolution seismic velocity model and inversion of Honeycomb Ridge, and partially Glendhu Ridge.OBS data were processed in Seismic Unix and Vista 2023. In Vista 2023, the data were flattened, filtered with Ormsby bandpass, FK-filter and a threshold median noise attenuation and reduction (THOR) filter. Reflection and refraction phases were picked with PASTEUP and used for forward modeling with MODELING (RAYINVR). The detailed P-wave forward model served as input for the 2D tomography inversion (TOMO2D). The tomography for 8 iterations results in a χ2 of 2.1 and RMS-fit of 30 ms.The P-wave tomography confirms a low velocity zone below the BSR in both ridges. Higher velocities are resolved in the landward limbs of the ridges compared to seaward limbs in agreement with previous findings. The areas of higher velocities correspond to high-reflectivity layers in the seismic data. We suggest that the anomalously high-reflectivity layers above the BSR in the ridge represent concentrated gas hydrate accumulations, fed by underlying free gas via stratigraphic pathways that enable fluid migration into the system. We also aim to test whether positive and negative polarity reflections within the regional gas hydrate stability zone are due to simultaneous presence of gas hydrates and free gas, respectively. Supplementary analysis of S-waves will allow us to test our hypothesis that free gas is injected into the hydrate stability zone and remains, at least partially, in the gaseous phase. Our detailed study contributes to a better understanding of how gas hydrate systems and fluid migration pathways evolve at active margins.