Seismic and sub-seismic deformation on different scales in the NW German Basin

(TYPE=abstract)The evolution of sedimentary basins is often strongly affected by deformation. Large-scale, subsurface deformation is typically identified by the interpretation of seismic data and evaluated by palinspastic reconstructions. However, sub-seismic small-scale deformation and the thereby generated fractures play an important role: they may accommodate a significant proportion of the total strain during basin evolution, lateral variation may cause compartmentalised deposits and reservoirs, and fracture networks may act as conduits for diagenetic fluids. These aspects depend primarily on the magnitude of deformation, the strain accumulation in space and time, and the processes that control both during basin evolution under varying kinematic constraints. However, methodology limitations result in information gaps between large crustal-scale 2D seismic lines, high-resolution upper-crustal-scale 3D seismic data, and very small-scale 1D bore-hole data. To bridge these gaps in size and dimension between the different methods, and to correlate the deformation over large scale ranges, it is necessary to get the most out of the data with respect to the method’s resolution, and to simulate the processes which are responsible for the next lower-scale deformation by appropriate modelling approaches. For this purpose we analysed the orientation, distribution, and evolution of tectonic structures by using the following methods: analysis of 3D seismic data, analysis of well data, 3D kinematic modelling (retro-deformation), and analogue modelling. A high-resolution 3D seismic data set with corresponding well data, located within the NW German Basin, was interpreted in detail. Large-scale deformation was analysed in terms of sedimentation, salt diaprism, as well as orientation, distribution, displacement, kinematic and timing of faulting. Processes like strain partitioning, as well as coupling/decoupling due to salt have been recognised, and several deformation phases from Carboniferous to Tertiary have been documented for the study area, and compared with the superimposed Central European Basin System. On a smaller scale, 3D fault-surfaces have been studied. Displacement measurements and fault-attributes (dip, azimuth, curvature) helped not only to analyse the kinematics of these faults and the principal stress direction during Permian extension, but also to investigate fault-growth and linkage over time and over several scales down to the limits of seismic resolution. A scale below, 3D kinematic retro-deformation of the fault’s hanging wall volume helped to reveal information about orientation and density of sub-seismic strain during a special deformation period. Comparison of these medium-scale modelling results with large-scale seismic data and very small-scale well data allowed the quantification of sub-seismic strain, and to bridge the information gap between these scales, in the here investigated working area. A final analysis integrating the timing of deformation over a broad scale range has been carried out with scaled physical sandbox models. A cohesive mixture of sand and gypsum was used for the observation of fault-growth processes, such as initiation and propagation of fractures, fault-segment-linkage, and the alternation of activity between different faults through time. All here presented investigations from several scale ranges show a similar result: deformation is expressed as large heterogeneity in orientation, density, and timing of faults and fractures, and can have a similar pattern over a large scale range. However, this heterogeneity underlies different spatiotemporal causes dependent on processes relevant on the actual scale, and therefore complicates and questions a correlation.