The superposition of fault networks around the Asse salt structure as a proxy for the regional tectonic evolution – insights from 3D seismic data

The salt-cored Asse-anticline is located in the Subhercynian Basin and was formed during the Late Cretaceous phase of tectonic shortening. The salt anticline contains a former salt mine, in which low- and intermediate-level radioactive waste was disposed during the 1970s. During more than hundred years of mine history and the planning for the retrieval of the radioactive waste in the last 15 years, a large amount of geological and geophysical data were acquired. The interpretation of a 3D seismic data set in combination with new well data recently provided insights into the local structural framework.

We discovered that the Asse salt anticline developed around an intersection of two systems of normal faults formed prior to the Late Cretaceous. The NW-SE trending fault system strikes parallel to the anticline and is located in the vicinity of its crest. Another E-W-trending fault network crosses the eastern part of the anticline and causes an along-strike change of its geometry. Although the exact timing of the faults is unclear, they indicate two separate phases of tectonic extension. During the subsequent phase of tectonic compression, the normal faults in the anticlinal flanks partly became inverted.

The structural trends of the normal faults are also recognized in the intra-salt layers. Here, the dominant trend of the fold axes is NW-SE, which is interrupted by E-W-striking folds in the Eastern part of the salt mine. Thus, we suggest that salt deformation is mostly a relict of the extensional phases and was only partly overprinted by tectonic shortening.