GEUS Bulletin (Geological Survey of Denmark and Greenland)
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Nitrate transport pathways in riparian zones of the Hagens Møllebæk catchment, northern Denmark
No full textThe Water Framework Directive (WFD) of the European Union prescribes “good ecological status” of all waters. In terms of nitrate this means, among other things, to avoid eutrophication and achieve a good ecological balance in surface water systems for the benefit of the groundwater dependent flora and fauna (Hinsby et al. 2012). In Denmark, the nitrate load to estuaries has been nearly halved since the first national action plan was implemented in the mid-1980s, but further abatements are required in many areas to fulfil the WFD. New approaches to regulate nitrate use are needed with measures targeted to the areas where most effect is obtained, and this is recognised at political level. Recent legislation allows farmers to increase nitrate application, but should at the same time introduce new mitigation measures and a more targeted approach to regulation. Therefore the physical system, i.e. the geological framework and topography, of the catchment has to be understood (Winter 1999). Previous studies have shown that in hydrological catchments with high geological variability, sampling of groundwater in riparian zones, the stream water itself and water in the stream bed can help to identify near-stream areas with specific nitrate problems. Detailed studies are, however, not feasible in all catchments, and development of representative typologies to guide an optimal location of mitigation measures in the catchment is thus needed. The present study is a detailed characterisation of nitrate transport and reduction in the groundwater–stream system in the river Hagens Møllebæk catchment for this purpose
Towards a national 3D geological model of Denmark
No full textAs part of its strategy, the Geological Survey of Denmark and Greenland (GEUS) is to develop a national, digital 3D geological model of Denmark that can act as a publicly accessible database representing the current, overall interpretation of the subsurface geology. A national model should be under constant development, focusing on meeting the current demands from society. The constant improvements in computer capacity and software capabilities have led to a growing demand for advanced geological models and 3D maps that meet the current technical standards (Berg et al. 2011). As a consequence, the users expect solutions to still more complicated and sophisticated problems related to the subsurface. GEUS has a long tradition of making 2D maps of subsurface layer boundaries and near-surface geology (Fredericia & Gravesen 2014), but in the change from 2D to 3D and when combining data in new ways, new geological knowledge is gained and new challenges of both technical and organisational character will arise. The purpose of this paper is to present the strategy for the national 3D geological model of Denmark and the planned activities for the years ahead. The paper will also reflect on some of the challenges related to making and maintaining a nationwide 3D model. Initially, the model will only include the Danish onshore areas, with the Danish offshore areas and Greenland to be added later using a similar general setup
Pre-Quaternary rocks and sediments with a high level of radioactivity in Denmark
No full textThe pre-Quaternary sediments and rocks in Denmark generally have a low content of radioactive minerals and elements. Uranium, thorium and radium are built into mineral structures or are, for example, adsorbed on the surface of clay minerals, Fe-minerals or organic material. Radon (222Rn) is a radioactive noble insoluble gas with a half-life of 3.8 days. It belongs to the uranium (238U) decay chain where radon is formed from radium (226Ra). When Rn is formed by radioactive decay from Ra, the emanation process sends part of the radon produced into the pore spaces of rocks and soils. From here, the radon can enter and accumulate in buildings. The source of the radioactive materials in Danish sediments and rocks is primarily from weathered Precambrian crystalline rocks from Norway, Sweden, Finland and the Danish island of Bornholm. Physical and chemical weathering disintegrates these rocks and rivers transport the material into the Danish–Norwegian and Danish–Polish sedimentary basins
Investigations of past climate and sea-ice variability in the fjord area by Station Nord, eastern North Greenland
No full textThe marine record of the Independence–Danmark fjord system extending out to the Wandel Hav in eastern North Greenland (Fig. 1A) is little known due to the almost perennial sea-ice cover, which makes the region inaccessible for research vessels (Nørgaard-Pedersen et al. 2008), and only a few depth measurements have been conducted in the area. In 2015, the Villum Research Station, a new logistic base for scientific investigations, was opened at Station Nord. In contrast to the early exploration of the region, it is now possible to observe and track the seasonal character and changes of ice in the fjord system and the Arctic Ocean through remote sensing by satellite radar systems. Satellite data going back to the early 1980s show that the outer part of the Independence–Danmark fjord system is characterised by perennial sea ice whereas both the southern part of the fjord system and an area 20–30 km west of Station Nord are partly ice free during late summer (Fig. 1B). Hence, marine-orientated field work can be conducted from the sea ice using snow mobiles, and by drilling through the ice to reach the underlying water and sea bottom
Regional climate-model performance in Greenland firn derived from in situ observations
No full textRecent record-warm summers in Greenland (Khan et al. 2015) have started affecting the higher regions of the ice sheet (i.e. the accumulation area), where increased melt has altered the properties of firn (i.e. multi-year snow). At high altitudes, meltwater percolates in the porous snow and firn, where it refreezes. The result is mass conservation, as the refrozen meltwater is essentially stored (Harper et al. 2012). However, in some regions increased meltwater refreezing in shallow firn has created thick ice layers. These ice layers act as a lid, and can inhibit meltwater percolation to greater depths, causing it to run off instead (Machguth et al. 2016). Meltwater at the surface also results in more absorbed sunlight, and hence increased melt in the accumulation area (Charalampidis et al. 2015). These relatively poorly understood processes are important for ice-sheet mass-budget projections
Miocene deposits at Silkeborg, Jylland, and their influence on hydrology
No full textA motorway was constructed in 2010–2016 through the suburbs of the city of Silkeborg (Fig. 1). The Danish Road Directorate wished to climate-proof the motorway against adverse future climate changes. The directorate collaborated with the Geological Survey of Denmark and Greenland (GEUS) to study the hydrological conditions. Studies of historical and projected climate-change-driven variations in groundwater levels in relation to urbanised hydrological fluxes were conducted by Kidmose et al. (2013, 2015). During the construction of the motorway, Miocene and Quaternary deposits were exposed in the slopes of the Gudenå valley and late-glacial glaciofluvial deposits were found in the valley floor. This paper focuses on the Miocene sediments and their influence on the local hydrological conditions.
At Silkeborg the Gudenå valley is c. 35 m deep (Fig. 1). The surrounding terrain is a till plain. In the slope of the valley, glaciofluvial sand is found below the till. Miocene deposits are found below the glaciofluvial sand. The floor of the Gudenå valley is covered by c. 15 m thick glaciofluvial deposits, which rest on Miocene deposits. In borehole no. DGU 87.907 49 m of Miocene deposits belonging to the Vejle Fjord Formation are recorded, consisting primarily of marine clay with minor occurrences of sandy deposits. About 12 km south of Silkeborg lower Miocene deposits are seen in outcrops and boreholes (Fig. 2). Here the fluvial Addit Member of the Billund Formation (Rasmussen et al. 2010) is separated from the underlying marine Vejle Fjord Formation by a sharp erosional contact (Rasmussen 2014)
Types of formation water and produced water in Danish oil- and gasfields: implications for enhanced oil recovery by injection of ‘smart’ water
No full textInjection of chemically tuned, ‘smart’ water in oil reservoirs may increase both oil recovery rates and the total recovery (e.g. Morrow & Buckley 2011; Austad 2013; Zeinijahromi et al. 2015). This kind of water management has gained increased importance in the Danish North Sea reservoirs due to decreasing sweep efficiency in maturing oilfields. Knowledge about the compatibility of the injected water with local formation waters is, however, a prerequisite for successful implementation. Here, we present a regional overview of formation waters from oil reservoirs in the Danish North Sea, which comprise three main types of formation brine, and one type of modified seawater related to extensive water flooding. The water types show a distinct geographical distribution, which reflects original connate waters that are modified by saline brine being either depleted or enriched in SO42–.
 
Palaeovalleys at the basal unconformity of the Palaeoproterozoic Karrat Group, West Greenland
No full textIn the Rinkian belt of West Greenland, reworked Archaean gneisses are overlain by supracrustal successions of the Palaeoproterozoic Karrat Group, defined by Henderson & Pulvertaft (1967) as comprising two formations: the Qeqertarssuaq Formation and the Nûkavsak Formation. The group was later extended to include the Mârmorilik Formation (Henderson & Pulvertaft 1987) originally considered to be of Archaean age (Henderson & Pulvertaft 1967) but later shown to be Palaeoproterozoic, resting with a depositional unconformity on Archaean gneiss (Garde 1978). Henderson & Pulvertaft (1987) suggested that the carbonatedominated Mârmorilik Formation in the south was laterally equivalent to the siliciclastic-dominated Qeqertarssuaq Formation in the north, the two subbasins being separated by a basement topographic high
The Greenland Mineral Resources Portal – another step forward
No full textIn April 2015, the Geological Survey of Denmark and Greenland (GEUS) together with the Ministry of Mineral Resources in Greenland (MMR) made further progress in the development of web-based facilities to present and disseminate geoscientific information and data. This was presented in a new version of the Greenland Mineral Resources Portal. The portal now provides the users with access to a wealth of geological, geophysical and geochemical data – mostly free of charge (Fig. 1). The primary goal of the portal is to facilitate data searches for exploration companies, but the benefits from the easy access to geoscience data are also open to academic researchers. It is the plan to add several new functionalities to the portal in 2016, and interested users are invited to visit the portal at www. greenmin.gl on a regular basis to follow progress
A WebGIS portal for exploration of deep geothermal energy based on geological and geophysical data
No full textThe Danish subsurface contains deep geothermal resources which may contribute for hundreds of years to the mixed Danish energy supply (Mathiesen et al. 2009). At present only a limited fraction of these resources are utilised in three existing geothermal power plants in Thisted, Margretheholm and Sønderborg (Fig. 1) where warm formation water is pumped to the surface from a production well and, after heat extraction, returned to the subsurface in injection wells (Fig. 2). Deep geothermal energy has the advantage of being a sustainable and environmentally friendly energy source which is furthermore independent of climate and seasonal variations, in contrast to wind and solar energy. The implementation of deep geothermal energy for district heating replacing conventional energy sources, especially coal and oil, may thus lead to a considerable reduction in the emission of greenhouse gases. There are therefore good reasons to include geothermal energy as a central component in Denmark’s future supply of energy for district heating. Furthermore, heat-demanding industries may consider the possibility to integrate geothermal energy and energy storage in their production process. In order to facilitate the use of geothermal energy, a broad majority in the Danish parliament has granted financial support for initiatives within the geothermal field (Energy policy agreement of March 22, 2012). The present paper deals with one of the outcomes of this agreement, namely a WebGIS portal with an overview of existing and interpreted geological and geophysical data. This will be relevant for all stakeholders in the exploration of deep geothermal resources in the Danish subsurface. The portal focuses on geothermal reservoirs within the 800–3000 m depth interval and provides an overview of the amount and quality of existing geodata, the geological composition of the subsurface, and interpreted thematic products such as geological maps of potential geothermal reservoirs. A comprehensive map from the portal showing onshore and nearoffshore locations where the geological conditions are potentially suitable for extraction of deep geothermal energy in Denmark is shown in Fig. 1. Many of the thematic maps are outcomes of the project The geothermal energy potential in Denmark – reservoir properties, temperature distribution and models for utilization under the programme Sustainable Energy and Environment funded by the Danish Agency for Science, Technology and Innovation