The Harz in Northern Germany is a horst composed of variscan-folded Paleozoic rocks uplifted during the upper Cretaceous. It is surrounded by younger strata. The area of investigation comprises the South Harz Zechstein Belt, about 82 km long and 1 to 5 km wide. The lowermost four Zechstein Cycles (Werra, Stassfurt, Leine, Aller) are exposed of which Aller is found only at a few places. Towards the south, the Zechstein dips below the overlying thick strata of the Buntsandstein (lower Triassic). At the Zechsteinbasis, a marly pelite, the Copper-Shale, was mined for its copper content for centuries in open pits and mines. The overlying clays, carbonates and sulfate rock are quarried intensively today. The originally interspersed salts have been subroded and are now missing along the Zechstein Belt but are mined below the Buntsandstein to the south. The morphology of the Zechstein Belt is characterized by widespread karstification.
Nine published geological maps of the Geological State Surveys, some older than 100 years, and recent large-scale maps, obtained during about 40 diploma theses and many university mapping courses, combined with own field studies were used to construct a new, unified geological map of the Zechstein-Belt. It covers 338 km2 between Förste near Osterode in the west and the location Mooskammer near Morungen in the east, running across three Federal States. The program ArcGIS was used to geo-reference all map details on a scale of 1:10,000. In addition, 150 geological profiles helped to deduce a tectonic model for the South-Harz. Faults are categorized as stratigraphical faults, faults deduced from sinkhole chains, and those that were needed to obtain plausible profile solutions and to connect adjacent profiles. These are based on the hypothesis, that the pre-Zechstein basis continues southwards with a dip of 6 to 15°. Faults turned out to follow the well-known rhenic, variscan, hercynian and eggian tectonic directions found throughout Central Europe. All stayed within a narrow direction margin, only the hercynian faults turn from NW-SE to SW-NE following the southern border of the Harz Paleozoic. The resulting tectonic mosaics and the general tectonic architecture is described.
The Harz is, according to the inversion tectonic (Kley, 2013), the result of three phases of crustal dilatation, compression and renewed extension.
Phase 1 is responsible for the sinking of the North German basin, providing the space for Permian and Mesozoic sediments, many kilometers thick.
Phase 2 caused the hercynian directed, compressional system of step faults and horst-graben sequences, recurring every few hundred meters. These can be interpreted as large-scale compressional flower-structures, associated with the uplifting of the Harz. The compression also causes a few small-scale open anticlines and compressional ridges and led to regional steepening of the dip. A more prominent fault of about 100 m thrust can be followed for about 50 km from Neuhof to Morungen.
Phase 3 is characterized by rhenic and eggian faults, recurring at distances of a few kilometers. Typical graben systems such as the Römerstein-Weißensee, the Bere-Valley and the Thyra-Valley Graben are interpreted as dilatational flower structures.
These fault systems are decisive in interpreting the hydrogeology of the sulfate karst of the South Harz that features a score of creek ponors and river sinking sites and many karstic springs, three of them of very large discharge (Salza-Spring at Förste, Rhume-Spring near Rhumspringe, and Salza-Spring near Nordhausen). | English |