Interior structure of the Asse salt structure

Knowledge of the saline sequences and the interior structure of the Asse has been increased as a result of an underground core drilling programme. The lithological facies of the evaporite series generally differs from that in the central region of the North German Zechstein Basin. This is evidenced in particular for the later Zechstein 2 by an increase in polyhalite content in the upper part of the 'Hauptsalz', the existence of a very pure overlying rock salt seam and the local sedimentation of the so called 'Tonliniensalz'. In a synclinal bend a locally limited polyhalitic potash seam above the carnallitic Stassfurt seam was found by core drilling. 'Decksteinsalz' and 'Gebaenderter Deckanhydrit' whose presence were hitherto unknown, were also detected. In addition Zechstein 3 is characterized by special lithological facies. Potash seams do not exist in this series. Instead, a significant polyhalite content occurs in the upper part of the early Zechstein 3. At the base of the late Zechstein 3 all eight 'Anhydritmittel' banks were exposed by core drilling. At the northeastern flank of the Asse, the Zechstein 4 is normally overlain by Lower Buntsandstein. At the southwestern flank, on the contrary, the evaporites of the Upper Buntsandstein are joined to those of the Zechstein. The Upper Buntsandstein is dated by lithostratigraphical comparison, sulphour-isotope analysis and palynological associations. (orig.)