Construction of a 3D-Structural Model of the Ohm-Graben zone in West-Thuringia, Germany

The Ohm-Graben zone in West-Thuringia, Germany, is located 20 km south of the Harz Mountains and 30 km east of the Leine Graben region. It stretches over 30 km from N to S and comprises multiple smaller graben structures, all striking NNE-SSW with a width of about 1 km. During the 20th century, its ground has been excessively explored for potassium salt mining. For that reason, it presents a good target for structural analysis of the Mesozoic sediments and – if possible – the Palaeozoic basement units. 30 km to the west at Göttingen, these basement rocks are the target of a geothermal exploration by the Universität Göttingen and the MEET project (Multidisciplinary and multi-context demonstration of EGS exploration and Exploitation Techniques and potentials), which provides the motivation for this project.

Therefore, a structural 3D model has been created, using the software ‘MOVE’ by Midland Valley. The source data is made up of old geological maps, especially by Karl von Seebach (1872) and Curt Dietz (1923), survey reports, especially by Helmut Knape (1957) and Hans Kästner (1997), and borehole data from the potassium exploration.

The result shows a most likely continuous graben system dominated by extension and strike-slip movement. The ages of the structures are not known precisely, but episodic movement at least from the lower Cretaceous to the Pleistocene is certain. The faults form negative flower structures, which converge in the level of the Zechstein salinar horizons in around 500 to 700 m depth below surface. The indications for strike-slip movement imply nearly vertical continuations of the faults into the Palaeozoic basement, but no drilling could verify this theory up to now. Salinar tectonics seems to compensate the extension movement only, but does not represent a major influencing factor like in the similar striking Leine valley graben to the west.