Buried tunnel valleys are common features in formerly glaciated areas, and where present, they are very important for the groundwater recharge and flow. Delineation of the structures and modelling of the infill is therefore very important in relation to groundwater mapping. Typically, borehole information is too sparse to enable a detailed delineation of the structures, whereas densely covering airborne electromagnetic data have proven to be very useful for this. In the last decades, the mapping approach has been studied carefully, but the 3D modelling of the valley structures has not been described to the same degree yet. In this study, we create a 3D geological model of an area that is characterised by a complex network of buried valleys mapped with a spatially dense airborne electromagnetic survey. Due to the comprehensive dataset, the modelling requires formulation of an advanced strategy. This contains a number of steps, where the AEM-derived resistivity data are initially interpreted based on the geological background knowledge to identify the buried valleys and build a conceptual geological model. Secondly, the age relationships between the valleys are established from the valley orientations and their internal cross-cut relationships. Thirdly, the deep erosional surfaces are modelled. Subsequently, the interpreted age relationships are utilised to trim the valley floor surfaces, such that younger valleys cut older. Finally, a voxel model is built and populated with lithofacies and stratigraphical units. The model is constructed as a combined layer-based and voxel model in order to map both the overall structures as well as the lithological variations within the 3D model domain. The final model contains 20 buried valleys that show a complex cross-cut setting that indicate the presence of at least eight valley generations. Most of the valley infills show lithological variations, and the final voxel model thus contains 42 different geological units

: This study provides a detailed reconstruction of the formation of a wave-dominated barrier island and assesses the sedimentological and morphological effects of sea-level changes on barrier evolution. Sedimentological and stratigraphic characteristics of the Holocene deposits are resolved by percussion cores and an extensive ground-penetrating-radar survey. A high-resolution chronology of the cored barrier island deposits is constructed by optically stimulated luminescence dating. This approach facilitates a high spatio-temporal resolution of the island’s morphological and depositional evolution. The results show that the barrier island experienced multiple phases of transgressions and regressions during the mid- and late Holocene and that these changes were driven primarily by changes in rates of sea-level rise, sediment supply and the impact of storms. Due to the postglacial sea-level rise, the seaward part of the study area was transgressed by the retreating mainland shoreline, forming a back-barrier basin. At the time of the initial transgression, sea level was rising by more than 4.0 mm yr−1. As sea-level rise decreased to less than 2 mm yr−1 the back-barrier basin rapidly started to fill with sediments before being transgressed by the still retreating open-ocean shoreline. These events were associated with periods of very rapid landward displacement of up to 10 m yr−1 of the mainland shoreline. After stabilization of the barrier island in its most eastward (i.e., landward) location, the open-ocean shoreline prograded about 3 km seaward at a rate of > 3 m yr−1 through the deposition of a 7-m-thick sandy beach and shoreface succession. The progradation occurred despite a sea-level rise of about 1.8 mm yr−1. After the regressive period the barrier island once again became transgressive before shifting back to its current regressive stage. The study shows how comparable rates of sea-level rise can result in very different morphological responses for a single barrier island since sediment supply apparently has varied significantly through time. It also appears that a transgressive situation is reached for this particular barrier island for a sea-level rise higher than about 2 mm yr−1. This gives reason for concern since a number of sea-level change scenarios indicate that such a rate will be reached within a few decades.

We present a large-scale study of the petrophysical relationship of resistivities obtained from densely sampled ground-based and airborne transient electromagnetic surveys and lithological information from boreholes. The overriding aim of this study is to develop a framework for examining the resistivity-lithology relationship in a statistical manner and apply this framework to gain a better description of the large-scale resistivity structures of the subsurface.In Denmark very large and extensive datasets are available through the national geophysical and borehole databases, GERDA and JUPITER respectively. In a 10 by 10km grid, these data are compiled into histograms of resistivity versus lithology. To do this, the geophysical data are interpolated to the position of the boreholes, which allows for a lithological categorization of the interpolated resistivity values, yielding different histograms for a set of desired lithological categories. By applying the proposed algorithm to all available boreholes and airborne and ground-based transient electromagnetic data we build nation-wide maps of the resistivity-lithology relationships in Denmark.The presented Resistivity Atlas reveals varying patterns in the large-scale resistivity-lithology relations, reflecting geological details such as available source material for tills. The resistivity maps also reveal a clear ambiguity in the resistivity values for different lithologies. The Resistivity Atlas is highly useful when geophysical data are to be used for geological or hydrological modeling