Sulphate rock spread in Lower Saxony 1: 500 000 — viewing area up to 200 m below terrain

The overview map of the sulphate rock spread in Lower Saxony 1: 500 000 shows areas in which sulphate rocks up to 200 m below ground surface 1.) are not to be expected or 2.) are potentially present. The distinction between the two areas is based on the evaluation of comprehensive geoscientific data available at the State Office for Mining, Energy and Geology. In this context, areas without unambiguous information on sulphate proliferation in the corresponding tufic area, as well as areas where sulphate rocks may have already been leached, are categorised as ‘sulfate rocks potentially present’. The map is updated at regular intervals. Near-surface sulphate rocks (gips/anhydrite) pose a threat to drilling as a new connection of water to sulphate-carrying layers may occur during drilling. On the one hand, this water connection can lead to the conversion of anhydrite into plaster with associated volume increase and elevation of terrain, and on the other hand to subrosion. The increase in volume through the anhydrite-gips conversion decreases with increasing overlay. The present map is based on the assumption that at a depth of = 200 m below ground surface there is no longer a fear of volume increase that could lead to surface lifting. For more detailed information on subrosion, please refer to the map of geohazards in Lower Saxony 1: 25 000 — Earthfall and Lowering Areas (IGG25). The map is essentially based on the Geological Map 1: 50 000 (GK50), the Geotectonic Atlas 3D (GTA3D) as well as the drilling data from the Hydrocarbon Database and the Drill Database Lower Saxony. For the preparation of the map, the sulphate-leading stratigraphic units Münder Mergel (Malm), Middle Keuper, Middle Shell Lime, Upper Buntsandstein, Zechstein and Rotlieged were taken into account. As part of the mapping process, the information from these different data sources was combined and compared using further geological data (see “Information on the data”).