Structural evolution and disintegration of oceanic intraplate volcanoes: The Bathymetrists Seamounts and its relation to Sierra Leona Rise (eastern equatorial Atlantic) - Cruise No. M152/2, 03.01. – 12.02.2019, Las Palmas (Spain) – Walvis Bay (Namibia), SEDIS

Summary The Bathymetrists Seamounts (BSM) are located north of the volcanic Sierra Leone Rise in the eastern Atlantic between 6° and 9°N. The three W-E, N-S and NE-SW striking directions of the seamounts indicate a clear structural control for the emplacement of these volcanoes. The origin of the melts, their relationship to the Sierra Leone Rise and the role of the faults in the formation of the melts are unknown as the BSM could be explained by plume related volcanism or decompression melting beneath deep (transform) faults. The SEDIS-cruise M152/2 of RV METEOR strove for a better understanding of the life cycle of submarine volcanoes and their effect on the oceanic lithosphere in the oceanic intraplate setting of the BSM and the relationship to the Sierra Leone Rise. The aims were: 1) to understand the interaction between crustal thickness, tectonics and volcanic phases, 2) to investigate the structural, chronological and petrological evolution of individual seamounts and seamount chains, 3) to review slope failures and resulting mass flow processes. We addressed these objectives by more than 4000 km highresolution reflection seismic and more than 5000 km of parametric echosounder, multi-beam, and gravity and magnetic profiles. Rock samples for ground truthing and geochemical research have been collected during 14 dredge stations. We further determined the concentrations in surface seawater and air and the state of air-sea exchange of a number of nowadays globally banned pesticides, polychlorinated biphenyls, brominated flame retardants, polycyclic aromatic hydrocarbons and their derivatives. Zusammenfassung Die Bathymetrists Seeberge liegen nördlich der Sierra Leone Schwelle, einer vulkanischen Plattform im östlichen Atlantik zwischen 6° und 9° N. Diese submarinen Vulkane gruppieren sich entlang W-E, N-S und NE-SW Trends, was eine strukturelle Kontrolle der Vulkanentstehung indiziert. Die Schmelzentstehung sind unbekannt und können mit PlumeVulkanismus oder Dekompressionsschmelzen unter bisher nicht untersuchten Störungen und tiefen Transformstörungen zusammenhängen. Der Bezug zur Sierra Leone Schwelle ist ebenfalls unbekannt. Im Zuge der SEDIS-Expedition M152/2 mit FS METEOR wurde der Lebenszyklus von Unterwasservulkanen und deren geochemischen Einfluss auf die ozeanische Lithosphäre der Bathymetrists Seeberge untersucht. Anhand der profilhaften geophysikalischer Messungen und Dredge-Proben wollen wir 1) die Wechselwirkung zwischen Krustenmächtigkeit, Tektonik und Vulkanismus verstehen, 2) die strukturelle, chronologische und petrologische Entwicklung von Vulkanen und Vulkanketten untersuchen, und 3) Auslösemechanismen, Transportprozesse und Volumina von Hangrutschungen studieren. Zur Bearbeitung der wissenschaftlichen Fragen sammelten wir mehr als 4000 km mehrkanal-reflexionsseismischer und mehr als 5000 km parametrische Sedimentecholot, Fächerlot, Schwere und Magnetik-Profile. Für die geochemischen Arbeiten sammelten wir an 14 Stationen Gesteinsproben unter Einsatz einer Dredge. Die regelmäßige Beprobung der Luft und des Oberflächenwassers diente der Bestimmung der Konzentration von heute weltweit verbotenen Pestiziden, polychlorierten Biphenylen, bromierten Flammschutzmitteln, polyzyklischen aromatischen Kohlenwasserstoffen und deren Derivaten und um den Austausch zwischen Luft und Meer weiter zu verstehen

Impact of Late Cretaceous inversion and Cenozoic extension on salt structure growth in the Baltic sector of the North German Basin

The Late Cretaceous to Cenozoic is known for its multiple inversion events, which affected Central Europe's intracontinental sedimentary basins. Based on a 2D seismic profile network imaging the basin fill without gaps from the base Zechstein to the seafloor, we investigate the nature and impact of these inversion events on Zechstein salt structures in the Baltic sector of the North German Basin. These insights improve the understanding of salt structure evolution in the region and are of interest for any type of subsurface usage. We link stratigraphic interpretation to previous studies and nearby wells and present key seismic depth sections and thickness maps with a new stratigraphic subdivision for the Upper Cretaceous and Cenozoic covering the eastern Glückstadt Graben and the Bays of Kiel and Mecklenburg. Time‐depth conversion is based on velocity information derived from refraction travel‐time tomography. Our results show that minor salt movement in the eastern Glückstadt Graben and in the Bay of Mecklenburg started contemporaneous with Late Cretaceous inversion in the Coniacian‐Santonian. Minor salt movement continued until the end of the Late Cretaceous. Overlying upper Paleocene and lower Eocene deposits show constant thickness without indications for salt movement suggesting a phase of tectonic quiescence from the late Paleocene to middle Eocene. In the late Eocene to Oligocene, major salt movement recommenced in the eastern Glückstadt Graben. In the Bays of Kiel and Mecklenburg, late Neogene uplift removed much of the Eocene‐Miocene succession. Preserved deposits indicate major post‐middle Eocene salt movement, which likely occurred coeval with the revived activity in the Glückstadt Graben. Cenozoic salt structure growth critically exceeded salt flow during Late Cretaceous inversion. Cenozoic salt movement could have been triggered by Alpine/Pyrenean‐controlled thin‐skinned compression, but is more likely controlled by thin‐skinned extension, possibly related to the beginning development of the European Cenozoic Rift System.In the Baltic sector of the North German Basin, minor salt movement started comremporaneous with Late Cretaceous inversion in the Coniacian‐Santonian and lasted until the end of the Late Cretaceous. A late Paleocene to middle Eocene phase of tectonic quiescense was followed by recommencing major salt movement in the Glückstadt Graben in the Late Eocene‐Oligocene. This Cenozoic phase of salt structure growth critically exceeded salt flow during the Late Cretaceous inversion and is likely controlled by thin‐skinned extension, possibly related to the beginning development of the European Cenozoic Rift System.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/50110000165

Prestack depth migrated, multichannel seismic data, thickness maps and time-structure maps of the Baltic Sea sector of North German Basin

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

The Paleozoic Hydrocarbon System in the Gotland Basin (Central Baltic Sea) Leaks

AbstractThe Baltic Basin is known for its numerous Paleozoic hydrocarbon reservoirs. There is published evidence that hydrocarbons are leaking from the seafloor, however, little is known about the hydrocarbon migration pathways from Paleozoic source and reservoir rocks toward the seafloor and their escape structures. To investigate these processes, we utilize a new set of multibeam, parametric sediment sub‐bottom profiler and 2D seismic reflection data. The integrated analysis of seismic profiles, diffraction imaging and bathymetric maps allow to identify a hydrocarbon migration system within Silurian and Devonian strata that consists of layer parallel and updip migration beneath sealing layers, migration across seals along faults, and seafloor escape structures in form of elongated depressions. The general migration trend is directed updip, from the Paleozoic reservoirs below the southeastern Baltic Sea toward the Gotland Depression in the northwest. The locations of the hydrocarbon escape structures at the seafloor and their elongated shape are mainly controlled by the regional geological setting of outcropping Paleozoic layers. In addition, iceberg scouring may have facilitated hydrocarbon migration through the Quaternary deposits. The description of this hydrocarbon migration system fills the gap between the known reservoirs and the observed hydrocarbon accumulations and seepages. With regard to potential Carbon Capture and Storage projects, the identification of this hydrocarbon migration system is of great importance, as potential storage sites may be leaking.Plain Language Summary: The Baltic Basin including the Baltic Sea is well known for its hydrocarbon reservoirs with ongoing oil production since the 1940s. While there is some published evidence that hydrocarbons are leaking from the seafloor, little is known about the pathways from the reservoirs toward theses leakages. In this study, we use three imaging techniques for the seafloor, the uppermost sediments and the first few kilometers of the subsurface to image the hydrocarbon migration pathways and their escape structures. We find that hydrocarbons are migrating along dipped geological layers from the reservoirs in the southeast toward the Gotland Deep in the northwest. Additionally, we also observe that hydrocarbons are penetrating through these geological layers at locations of pre‐existing small‐scale fractures. The locations, at which the hydrocarbons escape from the seafloor, are mainly controlled by the regional tectonic setting. In addition, iceberg scouring may have had an influence on the exact escape locations. With our findings in this study, we fill the gap between the known reservoirs and the observed seepages and can contribute to questions regarding the potential storage of CO2 in the Baltic Basin.Key Points: Numerous elongated fluid escape depressions are observed at the eastern margin of the Gotland Deep, central Baltic Sea First evidence for fluid migration pathways from Paleozoic toward Quaternary strata in the region Locations of fluid escape is controlled by the regional tectonic setting Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659https://doi.org/10.1594/PANGAEA.957436https://doi.org/10.1594/PANGAEA.956740https://doi.org/10.1594/PANGAEA.95742

Multibeam bathymetry processed data (Kongsberg EM710 working area dataset) of RV METEOR during cruise M177, Gotland Basin, Baltic Sea

The Baltic Basin is known for its numerous Paleozoic hydrocarbon reservoirs. There is published evidence that hydrocarbons are leaking from the seafloor, however, little is known about the hydrocarbon migration pathways from Paleozoic source and reservoir rocks towards the seafloor and the escape structures. To investigate the processes related to fluid escape at the seafloor, we utilized a bathymetric map from the eastern margin of the Gotland Deep. The data was acquired during the 2021 M177 Meteor expedition led by the University of Hamburg. Data acquisition was carried out using the hull-mounted SIMRAD EM710 multibeam swath sounder system, which operates in a frequency range between 70 and 100 kHz. The data was calibrated with the water velocity by using two sound velocity measurements. Data processing included manual removal of data errors and gridding with a grid size of 5 x 5 m. Due to bad weather during the acquisition and the resulting ship movements, some errors and artifacts (e.g. periodic wobbling) remained in the data even after intensive processing. The grids are available in UTM coordinates (UTM zone 34N)

2D multichannel seismic reflection processed data (GI Gun working area dataset) of RV METEOR during cruise M177, Gotland Basin, Baltic Sea

The Baltic Basin is known for its numerous Paleozoic hydrocarbon reservoirs. There is published evidence that hydrocarbons are leaking from the seafloor, however, little is known about the hydrocarbon migration pathways from Paleozoic source and reservoir rocks towards the seafloor and the escape structures. To investigate the processes involving the fluid migration pathways, we utilized 2D seismic reflection data from the eastern margin of the Gotland Deep. The data was acquired during the 2021 M177 Meteor expedition led by the University of Hamburg. Data acquisition was carried out using two GI guns (true GI-mode with 45 in3 generator and 105 in3 injector volume) and a 144-channel digital streamer with a channel spacing of 6.25 m and an active length of 600 m. Due to technical difficulties, only 72 channels - distributed over the whole streamer length – could be used for processing. Seismic data processing was divided into pre-processing, multiple attenuation and post-stack processing. Pre-processing consisted of geometry-setup (UTM zone 33N), filtering, despiking and spherical gaining. For multiple attenuation, we applied a predictive deconvolution in the τ-p domain, surface related multiple attenuation (SRME) and an f-k filtering attenuation scheme based on move-out differences between primary and multiple reflections. In between these steps we performed several iterations of manual velocity analysis. The post-stack processing included time migration, white noise suppression (4D-DEC), time-variant filtering and RMS scaling. The dominant frequency of the data is about 100 Hz and the vertical resolution of the final seismic images calculated with a velocity of 2000 m/s is about 5 m. The data is stored in SEGY-format with CMP No in header bytes 21-24, CMP x-coordinates in byte header 181-184 and CMP y-coordinates in byte header 185-188

Sediment echosounder processed data (Atlas Parasound P70 working area dataset) of RV METEOR during cruise M177, Gotland Basin, Baltic Sea

The Baltic Basin is known for its numerous Paleozoic hydrocarbon reservoirs. There is published evidence that hydrocarbons are leaking from the seafloor, however, little is known about the hydrocarbon migration pathways from Paleozoic source and reservoir rocks towards the seafloor and the escape structures. To investigate the processes involving fluid migration in shallow depths and seafloor fluid escape, we utilized sub-bottom profiler data from the eastern margin of the Gotland Deep. The data was acquired during the 2021 M177 Meteor expedition led by the University of Hamburg. Data acquisition was carried out using the hull-mounted transducer of the PARASOUND system that emits a 4 kHz signal penetrating the first several tens of meters below the seafloor. The data was digitized and stored in SEG-Y format (FFID in byte header 9-12, shot x-coordinate in byte header 73-76 and shot y-coordinate in byte header 77-80). Processing included geometry setup (UTM zone 33N) and bandpass filtering

The Paleozoic Hydrocarbon System in the Gotland Basin (Central Baltic Sea) Leaks

Abstract The Baltic Basin is known for its numerous Paleozoic hydrocarbon reservoirs. There is published evidence that hydrocarbons are leaking from the seafloor, however, little is known about the hydrocarbon migration pathways from Paleozoic source and reservoir rocks toward the seafloor and their escape structures. To investigate these processes, we utilize a new set of multibeam, parametric sediment sub‐bottom profiler and 2D seismic reflection data. The integrated analysis of seismic profiles, diffraction imaging and bathymetric maps allow to identify a hydrocarbon migration system within Silurian and Devonian strata that consists of layer parallel and updip migration beneath sealing layers, migration across seals along faults, and seafloor escape structures in form of elongated depressions. The general migration trend is directed updip, from the Paleozoic reservoirs below the southeastern Baltic Sea toward the Gotland Depression in the northwest. The locations of the hydrocarbon escape structures at the seafloor and their elongated shape are mainly controlled by the regional geological setting of outcropping Paleozoic layers. In addition, iceberg scouring may have facilitated hydrocarbon migration through the Quaternary deposits. The description of this hydrocarbon migration system fills the gap between the known reservoirs and the observed hydrocarbon accumulations and seepages. With regard to potential Carbon Capture and Storage projects, the identification of this hydrocarbon migration system is of great importance, as potential storage sites may be leaking

Studierendenbericht Seepraktikum Geophysik 2022 (UHH) Cruise No. AL582

04.10.2022 - 15.10.2022 Kiel (Germany) - Kiel (Germany) Seepraktikum 22-UH