STRUCTURAL BALANCING OF THE LOWER SAXONY BASIN AND THE SOUTHERN BORDER OF THE NORTHWEST GERMAN BASIN

We have determined the amount of Late Cretaceous shortening in the Lower Saxony Basin (LSB) and along its southern border from geologic cross sections which are part of the Geotectonic Atlas of Northwest Germany (Baldschuhn et al. 2001). Several balancing techniques were used for cross section construction, but the focus was on line (bed) length balancing. In the LSB most of the NNE to NE contraction during the Late Cretaceous is accommodated by inversion of Upper Jurassic to Lower Cretaceous grabens. In the case of the Osning fault zone, it has resulted in the partial inversion of Triassic to Jurassic structures and creation of a basement flexure. The deformation of the LSB comprises both thick-skinned and thin-skinned structural styles. The activation of detachment horizons in salt formations of the Zechstein and Upper Buntsandstein decoupled the deformation at different levels and had a major influence on the structural geometries in the suprasalt Mesozoic strata. The structural inversion of often deeply eroded graben structures with no or small fault offsets in the subsalt strata, the thin-skinned deformation and the complex halotectonic evolution of the LSB are the greatest obstacles to the construction of self-consistent, balanced structural cross-sections. By comparing the spatial distribution and amounts of contraction along a grid of balanced cross sections in map view, the limitations of structurally balancing single cross-sections in complex settings like the LSB become apparent and it is easier to build a balanced model which fits the regional amount and distribution of deformation. The results of the present structural balancing study indicate maximum shortening of 14-18 km in NE-SW direction along a transect through the LSB from the Münsterland basin to the Pompeckj block in the north of the LSB during the Late Cretaceous compression event.

Baldschuhn, R., et al. (2001). Geotektonischer Atlas von Nordwestdeutschland und dem deutschen Nordsee-Sektor - Strukturen, Strukturentwicklung, Paläogeographie. Geologisches Jahrbuch, A 153: 3-95.