Airborne electromagnetic measurements as basis for a 3D geological model of an Elsterian incision

摘要

Geophysical surveying served as basis for the construction of a three-dimensional model of the subsurface in an area where deep glacial incisions occur. These incisions of Elsterian age were known from a limited amount of borehole data and it is well-known that they have irregular shapes both in transverse and in longitudinal direction. This makes them difficult to map using traditional methods. To test and improve the research techniques in order to establish the delimitation of these valleys, research institutes from Denmark, Germany and the Netherlands joined forces in the BurVal project. This paper reports on the activities and conclusions of the investigations in Groningen, the Netherlands. The precise geometry and infill of the valleys in the investigated area was not known prior to this research. Airborne electromagnetics, as employed in this survey, shows the variation in resistivity of layers in the upper 70 m of the soil and serves as a basis for finding optimal locations to use additional methods such as seismics, cone-penetration tests and drillings. The seismic data show that a well-defined buried valley is present, which is filled in by three sedimentary units, mostly sandy in nature, topped by a clay layer. Linking borehole data to geophysical properties enables the development of a three dimensional geological model of the buried valley and its direct surroundings. This model governs state-of-the-art information which can be applied in hydrogeological prospecting. This is highly valuable for drinking water extraction and contamination risk assessment.