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Abstract

The NE German Basin has a WNW trending axis and is located in the south-eastern part of the Southern Permian Basin. It contains 1000-2000 m of mobilised Upper Permian Zechstein salt below a Mesozoic-Cenozoic sedimentary sequence of some thousand meters. While the base of salt represents an almost flat and unfaulted surface in the basin area, the present day structural setting of the cover is strongly determined by a variety of salt structures like domes, pillows and diapirs. We analysed salt structure development using a 3D structural model based on seismic and well data. Structural analysis and constraints from reflection seismic and well data suggest, that salt-tectonic deformation varied in time and intensity across the basin. The southern and eastern part of the basin is characterised by numerous salt diapirs piercing their cover layers, while the north-western part of the basin is dominated by salt pillows smaller in amplitude. Salt movement started during Late Triassic in the southern and in the eastern part of the basin whereas the basin centre in the NW was not affected by halokinetic deformation till Late Cretaceous and Cenozoic times. Our results indicate that salt movement during Late Triassic-Early Jurassic was slow and probably triggered by regional extension. This resulted in the formation of the NNE trending Rheinsberg Trough, a structure parallel to the Glueckstadt Graben in the NW German Basin and to the general trend of the North Sea Grabens. In contrast to the Graben structures in the western part of the Southern Permian Basin, no considerable normal faults cut the base Zechstein. Furthermore, evidence of dramatic, short wavelength thickness changes and of normal faulting is sparse in Triassic strata above the salt. Instead, we see a long wavelength thickness increase of Late Triassic Upper Keuper and Lower Jurassic sediments. Nevertheless, salt is almost removed below the Rheinsberg Trough. This indicates, that subsidence of the Rheinsberg Trough was balanced by slow lateral salt extrusion, thus accommodating regional extension without necessity of brittle normal faulting. The phase of slow lateral salt movement was followed by a relatively faster, diapiric phase with widespread removal of salt and salt margin formation in Cretaceous- Early Tertiary times. Furthermore, Late Cretaceous to Early Tertiary inversion structures are present in seismic sections. As the base of salt is almost undeformed below the basin, we can conclude that salt played an important role as a ductile decoupling horizon between its underlying basement and its cover layers due to its viscous rheology.