The understanding of the dynamics and scales of glacially induced faulting greatly benefits from an analyis using multiple geophysical datasets. By using a combination of high-resolution 2D seismic reflection data in combination with diffraction imaging, sediment echosounder data and shallow wells, we investigate a fault and graben system offshore Langeland Island in the Baltic Sea, which we term the Langeland Fault System. This approach allows to unravel the spatial character of the Langeland Fault System along an elevated basement block of the Ringkoebing-Fyn High. Our analysis shows the continuation of deep-rooted faults up to the seafloor. Imaging the shallowmost strata reveals Quaternary fault reactivation during glacial or postglacial times. This combination of imaging techniques is rarley realized in the onshore hinterland, thus, representing a unique analysis of Quaternary fault reactivation by combining onshore and offshore data and methods. Seismic data was acquired in September 2020 during a student field exercise cruise onboard R/V Alkor. The survey was organized by the University of Hamburg (Cruise AL545). Seismic data acquisition was carried out using a Mini-GI gun (true GI-mode with a 15 in³ generator and 30 in³ injector volume) and a 48-channel streamer with 4 m group spacing. The data have a dominant frequency of 250 Hz. Signal penetration is up to 1 s two-way travel time (TWT). The seismic processing routine included frequency filtering, amplitude recovery, noise reduction, surface-related multiple attenuation (SRME), Kirchhoff time migration. Innomars SES 2000 parametric sub-bottom profiler, which is hull-mounted on R/V Alkor, was used for the acquistion of the sediment echosounder data (Primary frequencies of about 100 kHz, secondary parametric frequency: 8 kHz). The diffraction imaging is based on separating the dominant reflected wavefield through a coherent summation scheme guided by a dip-based wavefront filter. In a next step, the reflection-only data is subtracted from the input data. The diffraction-only data is then focused using FD migration. By calculating the squared envelope of the focused diffractions, the diffraction energy stacks are obtained. The mapping procedure includes gridding using all available profiles in order to create time-structure maps by minimum curvature spline interpolation. Isochron maps (vertical thickness in two-way time) for the Triassic to Quaternary units were calculated by subtracting the top and bottom horizons of the specific units.
In the Late Cretaceous to Cenozoic, multiple inversion events affected Central Europe's intracontinental sedimentary basins. We investigate the impact of these inversion events on Zechstein salt structures formed prior to inversion based on seismic data located in the Baltic sector of the North German Basin. The study area covers the eastern Glückstadt Graben and the Bays of Kiel and Mecklenburg. We link stratigraphic interpretation to previous studies and nearby wells and present key seismic depth sections and thickness maps at a new level of detail. Prestack depth migrated seismic profiles are part of the BalTec dataset acquired during cruise MSM52 in march 2016 in the Baltic Sea. The seismic equipment consisted of an eight GI‐Gun cluster (45/105 in³) allowing for deep signal penetration with a relatively wide frequency bandwidth with a dominant frequency of 80 Hz. The streamer had an active cable length of 2,700 m with a minimum offset of 33 m. Seismic processing included τ‐p domain prestack predictive deconvolution, surface‐related multiple attenuation (SRME) to attenuate multiples, frequency filtering, amplitude recovery, noise reduction, and prestack depth migration. The time migrated seismic profile was acquired during a student marine excursion of the University of Hamburg in 2019, cruise AL526. A Mini-GI gun (true GI-mode with 15 in³ generator and 30 in³ injector volume) and a 48 channel streamer with 4m group spacing was used. Seismic data processing was analog to the depth sections, except for migration. Here, a poststack kirchhoff time migration was applied. For mapping, we used all available lines in the study and created time-structure maps by minimum curvature spline interpolation with a grid cell size of 300x300 m. By subtracting the top and bottom horizons, we created isochron maps (vertical thickness in two-way time) for the Zechstein, Cenomanian-Turonian, Coniacian-Santonian, Campanian, Maastrichtian-Danian, upper Paleocene, Eocene-Miocene units. We converted the time-isochron maps to vertical thickness in meter by using constant velocities derived from averaging the results of the refraction travel-time tomography.
South Wales is characterised by a rich variety of geologic formations and rocks of different ages and periods, and a large asymmetric syncline, as perhaps its most significant structural geological feature, extending from east to west over a length of approximately 96 km and 30 km from north to south, respectively. This oval-shaped syncline is part of the Variscan orogenic thrust and fold belt in Central Europe and covers some 2,700 km2, with coal-bearing rocks from the Upper Carboniferous (Westphalian Stage) deposited in the central syncline and older rocks outcropping in a peripheral belt around it. The coal-bearing sequence begins with Namurian grits and shales, overlain by the more productive Lower, Middle and Upper Coal Measures. A 3D structural geological model has been implemented for the central part of the South Wales Syncline and its bedrock geology. The oldest rocks in the model domain date back to the Pridoli Series from the uppermost Silurian, the youngest to the Westphalian Stage of the Upper Carboniferous. For model implementation, mainly open access data from the British Geological Survey (BGS) has been used.
The final 3D structural geological model covers the entire Central South Wales Syncline and is 32.8 km wide and 36.6 km long. In total, the 3D model includes 21 fault zones and the elevation depth of ten surfaces: (1) Top Upper Coal Measures Formation; (2) Top Middle Coal Measures Formation; (3) Top Lower Coal Measures Formation; (4) Top Millstone Grit Group; (5) Top Dinantian Rocks; (6) Top Upper Devonian Rocks; (7) Top Lower Devonian Rocks (sandstone dominated); (8) Top Lower Devonian Rocks (mudstone dominated); (9) Top Pridoli Rocks; (10) Top Ludlow Rocks (in parts).