GEUS Bulletin (Geological Survey of Denmark and Greenland)
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Nano-quartz in North Sea Danian chalk
No full textThe main oil reservoir in the Central Graben in the North Sea is chalk of the Maastrichtian Tor Formation, which has high porosity and relatively high permeability. The chalk of the Danian Ekofisk Formation is an additional reservoir, but with highly variable porosity and permeability. Whereas the Tor Formation is almost pure calcite primarily consisting of coccolith debris, the Ekofisk Formation also comprises significant proportions of phyllosilicates (clay minerals) and quartz in addition to coccolith debris. For decades the quartz was assumed to be a normal crystalline α-quartz such as is present in quartz sand, and the clay fraction was assumed to consist predominantly of phyllosilicates. However, Maliva & Dickson (1992) reported the presence of presumably authigenic submicron-size quartz crystals arranged in clusters, and suggested that these clusters were transformed opal-CT lepispheres. Investigations by nano-structural methods (Xray diffraction and atomic force microscopy (AFM)) revealed that the prevailing quartz component in the North Sea chalk comprises α-quartz appearing as nano-size quartz spheres (Jakobsen et al. 2000; Lindgreen et al. 2010). Nano-quartz spheres were first observed in indurated chalk in the Ekofisk Formation in the Ekofisk Field and later in the South Arne Field. Subsequent analyses of the Ekofisk Formation in different chalk fields showed that the content of nano-quartz varies throughout the chalk succession and to some degree reflects the cyclic development of the chalk. The proportion of dispersed nano-quartz in the chalk is highly variable, from 10% to more than 80% in the Lower Danian (Lindgreen et al. 2010). This paper describes the nano-quartz, its formation and structure and presents a model for the formation of flint from nano-quartz in the North Sea Ekofisk chalk
Geology of the Femern Bælt area between Denmark and Germany
No full textGeological and geotechnical investigations in the Femern Bælt area were undertaken from 1995 to 2010 (Rambøll Arup JV 2011) in preparation for the fixed link between Lolland in Denmark and Fehmarn in Germany. As a result, new data have been acquired on the stratigraphy and distribution of the deposits and the major structures and tectonic influence on the layers close to the surface. Previous investigations of Cretaceous–Palaeogene deposits on southern Lolland (Fig. 1) were limited due to lack of outcrops and borehole data. Two deep boreholes and geophysical surveys (1952–1953) revealed: (1) the presence of a salt diapir at Rødbyhavn, (2) upper Maastrichtian chalk 29–143 m below Quaternary deposits and (3) an erosional window in the Palaeogene cover. Boreholes to the east of Rødbyhavn (1992–1994) revealed the sediment distribution on southern Lolland and showed that Cretaceous and Palaeogene deposits are cut by several NW–SE-orientated faults. This paper presents a summary of lithostratigraphic and biostratigraphic investigations and a brief description of the geological development in the area
Rock-cored drumlins on Bornholm, Denmark
No full textThe surface morphology of Denmark is predominantly of glacial origin, created in depositional, deformational and erosional environments. In addition, postglacial marine, freshwater and aeolian processes have formed a variety of landforms. Overviews of the Danish landscape were published as geomorphological maps (Milthers 1948; Schou 1949; Smed 1981), and a new one is currently in preparation. On Bornholm, the morphology differs from the rest of the country because bedrock is present at or near the surface. This paper describes drumlins formed on bedrock on Bornholm, which have not previously been recognised
Cliff collapse at Stevns Klint, south-east Denmark
No full textThe scenic coastal cliff of Stevns Klint is a classical study locality that stretches for 15 km along the east coast of Sjælland and it holds arguably the best exposed Cretaceous−Tertiary boundary in the world (Fig. 1; Damholt & Surlyk 2012). The famous boundary separates the soft Cretaceous chalk from the harder overlying Tertiary bryozoan limestone (Fig. 2), and the difference between the two rock types controls the character of the frequent cliff falls. The relatively soft chalk at the base is eroded by storm waves and is subject to general debris shedding. The overlying bryozoan limestone, with its hardgrounds and flint layers, is more resistant to erosion and is strong enough to form overhanging projections of the coastal cliff that result in large and small recurring collapses
Groundwater protection in Denmark and the role of water supply companies
No full textDenmark has a decentralised water supply structure with about 2500 water supply companies. Until recently, about 150 of these, especially the larger ones, were owned by local authorities; the rest are private, all run on an independent and not-for-profit basis. Recently, a new law, the Water Sector Law (Miljøministeriet 2009), was implemented. Its purpose is to privatise the water supply sector (although, as hitherto, into not-for-profit corporations), and statutory duties are separated from operations in order to make the supply of drinking water to consumers as efficient as possible. An important element of the Water Sector Law is the introduction of a new regulatory body, the Utility Secretariat. The role of this new institution under the Danish Competition and Consumer Authority is to enforce price ceilings on drinking water, based on a selection of benchmark parameters
Anorthosites in Greenland: a possible raw material for aluminium?
No full textThe famous Swiss-born, Norwegian geologist and geochemist Victor Goldschmidt suggested that anorthosite could be used as a source of aluminium replacing bauxite, and acid leaching of the anorthosite was his innovative idea. Anorthosite is a rock type consisting of more than 90% plagioclase which is an acid-soluble, aluminium-rich silicate mineral occurring in basement rocks of both Norway and Greenland (Fig. 1). Experiments conducted in Norway during the century after Goldschmidt’s initial idea showed that it is technically possible to use anorthosite as a raw material in the production of aluminium metal. Goldschmidt mapped parts of the large anorthosite massifs along Sognefjord in the period 1916–1919. During the Second World War, sampling and core drilling were conducted in Norway, and an anorthosite mine was opened by Norsk Hydro where up to 400 men were employed and some 15 000 tonnes of rock were quarried before sabotage ended the work in 1945. There was renewed interest in anorthosite as an alternative raw material for aluminium in Norway in the years 1976–1982, but experiments conducted in this period did not lead to an economically viable concept. Recent developments at the Institute for Energy Technology in Norway have led to the discovery of a more promising process based on nitric acid that can yield additional products such as Precipitated Calcium Carbonate (PCC) for the paper industry, amorphous silica and ammonium nitrate fertiliser. The process can also be used as a sink for CO2 by taking CO2 from, for example, a power plant and binding it to PCC
Early Holocene sea-level changes in Øresund, southern Scandinavia
No full textThe Baltic Sea and Kattegat are connected via three straits: Storebælt, Lillebælt and Øresund (Fig. 1). Øresund is the shallowest with a threshold around 7 m deep and increasing water depths to the north (Fig. 2). In the early Holocene, global sea-level rise led to reflooding of Øresund. It started in northern Øresund which was transformed into a fjord. However, so far the timing of the transgression has not been well determined, but sediment cores collected north of the threshold, at water depths of 12 to 20 m, and a new series of radiocarbon ages help to constrain this. As the relative sea level continued to rise, the threshold in Øresund was also flooded, and Øresund became a strait. In mid-Holocene time, the relative sea level rose until it was 4–5 m higher than at present, and low-lying areas around Øresund became small fjords. During the late Holocene, the relative sea level fell again. Part of the data set discussed here was presented by Andreasen (2005)
Rock phosphate and lime for small-scale farming in Tanzania, East Africa
No full textPoor soils are a major cause of poverty in sub-Saharan Africa, and thus restoration of soil fertility is a significant challenge for sustainable agriculture. Some of the main resources required, e.g. phosphate and lime, are present in many African countries and can be used by smallholder farmers in a relatively unprocessed form instead of expensive commercial fertilisers. Here we present a small study of the Mbeya region in Tanzania, which locally has both phosphate and lime. Most soils in sub-Saharan Africa are losing nutrients necessary for sustainable agriculture. This is mainly due to intensive farming and the fact that the nutrients are not replaced adequately. Further reasons for nutrient losses are leaching, soil erosion and fixation by iron and aluminium oxides. Vast areas experience moderate to acute phosphorus deficiency (Vanlauwe & Giller 2006). The Mbeya region in south-western Tanzania (Fig. 1) is characterised by intensive smallholder plots along with several local sources of phosphate-bearing rocks and limestone. The former were examined in the 1980s (Chesworth et al.1988, 1989), but have never been utilised (Kalvig et al. 2010)
Shallow geothermal energy in Denmark
No full textThe use of shallow geothermal energy instead of fossil fuels can lead to substantial reductions in CO2 emissions. However, the use of shallow geothermal energy in Denmark is limited compared to, e.g. Sweden and Germany and we still lack know-how and experience with its use in Denmark. In co-operation with research and industry partners, the Geological Survey of Denmark and Greenland is conducting a three-year project GeoEnergy, Tools for ground-source heating and cooling based on closed-loop boreholes (www.geoenergi.org). The objective of the project is to acquire knowledge and develop tools and best practice for the design and installation of shallow geothermal energy systems
Efforts to include geological and geodetic observations in the assessment of earthquake activity in Denmark
No full textAssessment of earthquake hazard is improved if geological and geodetic data are included in addition to seismological data. In earthquake regions like Japan and California, palaeoseismology combines data from geology and seismology, and networks of permanent GPS (global positioning system) stations situated on bedrock supplement the networks of seismographs. A combination of seismographs and GPS stations on ice is also used in current studies of glacial earthquakes in Greenland. In Denmark only broad-scale geodetic coverage is available (Khan et al. 2005) and only a few examples of geological input are found in the literature. However, more thorough geodetic evaluations of deformations are currently made in Nordic co-operation projects and we are looking forward to learn about the results. Also the number of permanent GPS stations in Denmark has recently been increased from 3 to 13. The geological input is limited but may hold some potential, and the aim of this article is to evaluate this. We also discuss new investigations of recent geological movements, both in projects on post-glacial uplift (and accompanying horizontal deformation) of Scandinavia, and more locally of geological indicators of uplift in selected areas. As seismologists, we are interested in a homogeneous evaluation of geological indicators in all of Denmark and its neighbouring areas