Inversion tectonics at the northern margin of the North German Basin: Cretaceous to recent reactivation of Triassic normal faults (iTec-NGB)

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Near-surface faults within late Pleistocene, possibly Holocene strata are located in the eastern prolongation of a west-east striking graben across Langeland Island (Danish sector of the Baltic Sea) and correlate with deep-rooted faults within Triassic and Cretaceous strata. These faults are located above a prominent basement horst structure of the Ringkøbing-Fyn High, which marks the northern margin of the North German Basin (NGB). This project strives for investigating the tectonic evolution of the northern NGB margin east of Langeland Island and its relation to the post-Permian to recent evolution of the NGB by means of seismic interpretation. The study area allows investigating the early phases of basin formation dominated by extension and corresponding development of basin margin normal faults during the Triassic, their compressional reactivation as reverse faults during Late Cretaceous and Cenozoic basin inversion, and possible recent tectonic movements as well as post-glacial isostatic adjustments. In 2020, 27 high-resolution multi-channel reflection seismic and parametric echosounder profiles have been collected east of Langeland. To reveal the complex multiphase evolution of the northern NGB margin, these data have to be processed, interpreted and discussed within the tectonic framework. A first data example indicates the reactivation of normal faults, bounding tilted Triassic blocks, as reverse faults that uplifted overlying Cretaceous strata and pierce into overlying Pleistocene units. However, the exact outline of the fault system remains unknown. Incorporating more seismic data into the interpretation will improve the understanding of fault system evolution and reveal its exact outline and connection to deep-seated structures of the Ringkøbing-Fyn High. The quantitative analysis of fault displacement requires seismic depth sections obtained by high-quality velocity models. Migration velocity model building will be achieved by using an innovative processing flow based on a diffraction extraction technique. This technique uses diffraction wavefront attributes to calculate lateral variable velocity information even for short-offset seismic data. Additionally, extracted diffractions will help to identify faults and improve the understanding of the fault system and its geometry. Growth faulting visible in the produced depth sections will allow quantification of active phases of tectonic movement, which will be discussed in the context of the known phases of basin subsidence and inversion from other areas of the NGB and adjacent sub-basins of the Central European Basin System.