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Abstract:
The Central European Basin System is one of the basins where the sedimentary
cover is strongly affected by salt tectonics. The most significant stage of salt
movement occurred during the Triassic. The largest Triassic subsidence occurred in
the different sub-basins surrounding the Ringkoebing-Fyn High such as the Horn
Graben, the Danish Basin and the Glueckstadt Graben. Furthermore, the thickest
Triassic succession is observed in the Glueckstadt Graben where it reaches more than
9000 m. In the present study, the structure and the Permian to recent evolution of the
Glueckstadt Graben are investigated by use of borehole data, seismic lines and 3D
structural modelling.
The evaluation of the diverse deformation patterns of the sedimentary cover and
their relations to salt structures show that the strongest salt movements occurred at the
beginning of the Keuper when the Gluckstadt Graben was affected by extension. The
onlap patterns of the Jurassic sediments onto the top of the Keuper succession indicate
essential changes of the sedimentation style during the Jurassic. Thick Jurassic
sediments are only observed around salt structures and are thinning away from salt
walls or salt stocks. The Upper Cretaceous strata have an approximately constant
thickness and the parallel reflections patterns indicate a quiet tectonic setting with very
minor salt movements in the Late Cretaceous. Renewed salt flow during the
Paleogene-Neogene caused rapid subsidence along the marginal parts of the Central
Triassic Graben in the Westholstein, the Eastholstein and the Hamburger troughs. The
thick Paleogene-Neogene strata within the marginal troughs may also be related to a
regional component of tectonic subsidence in the area, contemporary with rapid
subsidence in the North Sea.
The 3D modelling approach has been used to determine salt distribution at
certain paleo-levels in response to unloading due to sequential removing of the
stratigraphic layers. The modelling approach was also aimed to reconstruct the
original Permian salt distribution immediately after deposition. The initial salt
thickness varies from 1300 m at the flanks of the basin up to 3000 m within the central
part and demonstrates a clear NNE-SSW trend of the basin. The regional trend of the
restored salt distribution points to a westward continuation of the Permian salt basin.
The formation of the deep Central Triassic Graben and the subsequent Jurassic-
Cenozoic marginal troughs was strongly controlled by the development of salt
structures through time. It is shown that the depocentre of sedimentation was moving
away from the central part of the of the original Graben structure towards its margins.
The evaluation of the available data and results of the 3D reverse modelling
demonstrate that a greater amount of subsidence occurred close to the active salt
structures, and may have resulted in gradual depletion of Permian salt. Thus, this study
indicates that the source of such long-term subsidence is derived from gradual
depletion of the Permian salt, which started within the axial part of the basin and
moved towards the basin flanks with time. In this sense, the Glueckstadt Graben was
formed at least partially as a “basin-scale rim syncline” during post-Permian times.
Therefore, the results show that salt withdrawal may have played an important role
during the Meso-Cenozoic evolution and that the effects of salt-driven subsidence
during the Meso-Cenozoic can be considered the main reason for the formation of the
deep Central Triassic Graben and the subsequent Jurassic-Cenozoic marginal troughs.
