Hydrogeological overview map of Lower Saxony 1: 200 000 — Base of the upper aquifer complex

The map “Base of the upper aquifer complex” illustrates the large-scale distribution and depth (in meters to NN) of the upper supraregionally important aquifer complex. Depending on the information density, the data on the depth position are summarised more or less strongly. If only partially further subdivisions are possible within a colour surface, this depth information appears as colored lines in the surfaces. In this map representation, aquifers are classified as all sands (up to the fine sand area) and gravel whose silt or clay content is less than 5 %. For example, due to the layer description, a very weakly sloppy fine sand is still referred to as a groundwater conductor, while a weakly sloppy fine sand is described as low water conductive. In the loose rock regions of Lower Saxony, two superordinate aquifer complexes are distinguished. The upper aquifer complex consists of sands and gravel of the Pleistocene, as well as sands of the Pliocene and the Uppermiocene. The lower aquifer complex consists of permeable sediments of the sub- to middle-miocene, the so-called lignite sands. The two aquifer complexes are separated by the groundwater inhibitor Oberer Glimmerton, which consists of sloppy-tone sediments of the middle to upper miocene. In the areas where the Upper Glimmerton is missing as a separating intermediate layer (groundwater inhibitor), only one aquifer complex is usually formed — in large-scale terms. This case occurs both in the area of deep cut gutters, as well as in the area of highly elevated salt sticks. In the eastern part of Lower Saxony, the Upper Glimmerton has been demolished extensively. In the map, only one aquifer complex is presented in these areas and is referred to as the upper aquifer complex, although in these areas it is also attributed to the permeable sediments of lignite sands, which otherwise form the lower aquifer complex. The base of the upper aquifer complex is therefore either the upper micaton or, in the absence of it, sub-miocene to oligocene clay and mud. On the map, two areas are distinguished in the color scale: 1. Areas where the aquifer complex is unstructured because either the separation layer micaton is missing or a lower submiocene aquifer is not formed. 2. Areas in which the aquifer complex is divided, i.e. the Upper Glimmerton is widespread and separates an upper floor from a lower floor. It is possible that regionally other low-permeable sediments, such as quaternary basin entones, can assume the function of separating intermediate layers, which then cause a spatially limited division of the aquifer complex into two or more aquifers. On the basis of the available data, however, too little statements can be made about the area-like spread of low permeable quarterly sediments, since they do not have a constant appearance over larger areas like the micaton, but can also be formed very differently over short distances in their facies. Therefore, they cannot be taken into account in this overview map, although they are often of great importance for regional groundwater hydraulics. The thickness of the upper aquifer complex is shown in a separate map.