Three-dimensional mapping of Quaternary sediments improved by airborne electromagnetics in the case of the Quakenbruck Basin, Northern Germany

The increasing demand on using the subsurface raises the call for a better understanding of the depositional architecture. In this study, we demonstrate how 3D subsurface models can be improved by airborne electromagnetic data. The study area is located in the Pleistocene Quakenbruck Basin in Northern Germany. This overdeepened basin is fronted by a push moraine ridge and filled with Middle Pleistocene (Saalian) to Holocene sediments known from a limited amount of borehole data. In 2009, this area was target of an aeroelectromagnetic survey with the SkyTEM system. For the interpretation of SkyTEM resistivity data, a relation between grain size and resistivity was derived using resistivity borehole logs from the larger study area. The analysis of the data showed a positive correlation as resistivity increases with increasing grain size and permeability. Each stratigraphic layer was then modelled with the commercial software GOCAD (R) based on the geological and geophysical information as each sediment layer is characterised by a specific resistivity in the SkyTEM data. Our results demonstrate that by integrating airborne electromagnetic data into geological 3D models, the distribution of stratigraphic units can be modelled with higher lateral resolution due to higher data density. The resistivity-grain size relation can be applied to other study areas with comparable geological conditions. Saline groundwater can clearly be identified and distinguished from non-saline regions in the Quakenbruck Basin by low resistivities.