GEUS Bulletin (Geological Survey of Denmark and Greenland)
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Zircon record of the igneous and metamorphic history of the Fiskenæsset anorthosite complex in southern West Greenland
No full textThe Fiskenæsset complex in southern West Greenland is part of the North Atlantic craton and is a layered intrusion consisting of gabbro, ultramafic and anorthositic rocks that was deformed during multiple episodes of folding and metamorphism (Myers 1985). We collected late-stage magmatic hornblenditic dykes and adjacent anorthosites and studied these samples integratively with several in situ techniques to determine the igneous and metamorphic history of the Fiskenæsset complex. The work presented here is part of an ongoing joint project between the Greenland Bureau of Minerals and Petroleum and the Geological Survey of Denmark and Greenland (GEUS). Here we report on new radiometric ages and mineral chemistry data from anorthosites from the North Atlantic craton in southern West Greenland (Fig. 1)
Exploration history and place names of northern East Greenland
No full textThe first recorded landing by Europeans on the coast of northern East Greenland (north of 69°N) was that of William Scoresby Jr., a British whaler, in 1822. This volume includes a chronological summary of the pioneer 19th century exploration voyages made by British, Danish, Norwegian, Swedish, French and German expeditions – all of whom reported that the region had previously been occupied by the Inuit or Eskimo; also included are brief outlines of the increasing number of government and privately sponsored expeditions throughout the 20th century, whose objectives included cartography, geology, zoology, botany, trapping and the ascent of the highest mountain summits.
In 1934 the Place Name Committee for Greenland was established, the tasks of which included a review of all place names hitherto recorded on published maps of Greenland, their formal adoption in danicised form, and the approval or rejection of new name proposals. In northern East Greenland, by far the largest numbers of new place names were those proposed by scientists associated with Lauge Koch\u27s geological expeditions that lasted from 1926 until 1958. This volume records the location and origin of more than 3000 officially approved place names as well as about 2650 unapproved names.
The author\u27s interest in the exploration history and place names of northern East Greenland started in 1968, when the Geological Survey of Greenland initiated a major five-year geological mapping programme in the Scoresby Sund region. Systematic compilation of names began about 1970, initially with the names given by William Scoresby Jr., and subsequently broadened in scope to include the names proposed by all expeditions to northern East Greenland. The author has participated in 16 summer mapping expeditions with the Survey to northern East Greenland. Publication of this volume represents the culmination of a lifetime working in the Arctic
Late Cretaceous basin development of the southern Danish Central Graben
No full textThe Danish oil and gas production mainly comes from fields with chalk reservoirs of Late Cretaceous (Maastrichtian) and early Paleocene (Danian) ages located in the southern part of the Danish Central Graben in the North Sea. The area is mature with respect to exploration with most chalk fields located in structural traps known since the 1970s. However, the discovery by Mærsk Oil and Gas A/S of the large nonstructurally and dynamically trapped oil accumulation of the Halfdan Field in 1999 north-west of the Dan Field (e.g. Albrechtsen et al. 2001) triggered renewed exploration interest. This led to acquisition of new high quality 3-D seismic data that considerably enhanced imaging of different depositional features within the Chalk Group. Parallel to the endeavours by the operator to locate additional non-structural traps in porous chalk, the Geological Survey of Denmark and Greenland took advantage of the new data to unravel basin development by combining 3-D seismic interpretation of a large number of seismic markers, well log correlations and 2-D seismic inversion for prediction of the distribution of porous intervals in the Chalk Group. Part of this study is presented by Abramovitz et al. (in press). In the present paper we focus on aspects of the general structural development during the Late Cretaceous as illustrated by semi-regional time-isochore maps. The Chalk Group has been divided into two seismically mappable units (a Cenomanian–Campanian lower Chalk Unit and a Maastrichtian–Danian upper Chalk Unit) separated by a distinct basin-wide unconformity
Borax – an alternative to mercury for gold extraction by small-scale miners: introducing the method in Tanzania
No full textSmall-scale mining is extraction of metals, precious stones, industrial minerals and other commodities using simple technologies. At a worldwide scale, an estimated 100 million people depend on income from small-scale mining (Hinton 2006). In Tanzania, there are more than half a million active small-scale miners, most of whom extract gold from placer and hard-rock deposits. Apart from providing a livelihood for thousands of households, small-scale mining reduces migration from rural to urban areas. However, small-scale mining is associated with a number of negative effects, because mining activities have severe impacts on both the local environment and the miners’ health. Most significantly the widespread use of mercury for gold extraction results in polluted environments and serious health hazards for the miners themselves and for the population in the vicinity of smallscale gold mining settlements (Bose-O’Reilly et al. 2008a, b; 2010; Jønsson et al. 2009)
3-D geological modelling of the Egebjerg area, Denmark, based on hydrogeophysical data
No full textContamination of groundwater with pesticides and nitrate has compelled the Danish Government to launch a major hydrogeological mapping programme covering about 40% of the land area of Denmark. Numerous geophysical surveys are currently being carried out in order to acquire the necessary data. These new data are crucial for the 3-D geological models that are used in the planning of future water supply and landuse. Normally, site-specific groundwater protection zones (Thomsen et al. 2004) are based on groundwater modelled catchment areas for each well, but proper 3-D geological models are needed in order to create a valid basis for the groundwater models. Since most of the Danish nearsurface geology is complex, a full geological understanding is required combined with in-depth interpretation of geological and geophysical data. Much research has dealt with geophysical mapping and numerical groundwater modelling, but only limited research has combined these topics for geological modelling. Prior to geophysical mapping, groundwater models were based on simple data extraction from well databases without inclusion of geophysical data. In the following, a concept for detailed 3-D geological modelling with hydrogeophysical data is presented for a specific area
Recent changes in the nutrient status of a soft-water Lobelia lake, Hampen Sø, Denmark
No full textNutrient-poor, low-productive (oligotrophic) soft-water lakes in the Atlantic areas of West and North-West Europe – the so-called Lobelia lakes – are of high conservation value as their low nutrient status favours a particular submerged macrophyte flora with isoetids, which are becoming increasingly rare or threatened due to nutrient enrichment (eutrophication) associated with landuse changes and urbanisation. European Union member states have a duty of care, under the Habitats Directive, to protect the biodiversity of oligotrophic to mesotrophic (moderately productive) standing waters
Silica diagenesis and its effect on porosity of upper Maastrichtian chalk – an example from the Eldfisk Field, the North Sea
No full textDiagenetic precipitation of silicate minerals such as quartz and clay minerals can reduce the permeability and porosity of chalk as they precipitate as cement in pores (e.g. Taylor & Lapré 1987; Maliva & Dickson 1992). However, the precipitation can also result in early lithification and help to preserve porosity during burial. Several studies of diagenesis have been carried out on chalk samples from the North Sea oil fields (e.g. Scholle 1977; Maliva & Dickson 1992; Hancock 1993) but only a few have focused on silica diagenesis (Fabricius & Borre 2007; Fabricius et al. 2007). Silica is not a major constituent of chalk but is abundant in some intervals where it influences the reservoir properties, as seen for example in the Ekofisk Formation and in a few intervals in the underlying Tor Formation in the Eldfisk and Ekofisk fields. This distribution may indicate that the variations are linked to facies and palaeo-oceanography; the silica either representing diagenetically reprecipitated biogenic silica, volcanic ash falls or a high input of detrital minerals (Scholle 1977; Kennedy 1987; Fabricius & Borre 2007). This paper discusses diagenesis of quartz- and kaolinite-rich intervals in the deeply buried upper Maastrichtian chalk of the upper Tor Formation (TA layer) in core 2/7-B-12 A from the Eldfisk Field in the Norwegian sector of the North Sea (Fig. 1). The study was carried out as part of a PhD project at the Geological Survey of Denmark and Greenland and the Department of Geography and Geology, University of Copenhagen (Madsen 2009). The objective of the study was to understand the processes leading to formation and enrichment of quartz and kaolinite and the resulting influence on porosity
Greenland ice sheet monitoring network (GLISN): a seismological approach
No full textThe dynamics of the large outlet glaciers in Greenland is attracting both scientific and political attention due to the possible implications of a rising global sea level. Extensive glaciological and meteorological monitoring programmes have been implemented to quantify and track changes in the ice sheet and local glaciers (Ahlstrøm et al. 2008). The dynamic processes controlling the flow of the outlet glaciers are complex and poorly understood, involving a wealth of parameters such as bed conditions, hydrology and meteorological conditions. It is desirable to obtain as many fundamentally independent data sets as possible to understand and eventually predict the behaviour of the outlet glaciers
An advancing glacier in a recessive ice regime: Berlingske Bræ, North-West Greenland
No full textGreenland is receiving unprecedented international attention, both in scientific and political circles. Characterised by a central ice sheet up to 3.4 km thick (Inland Ice), numerous ice caps and hundreds of outlet glaciers debouching into the surrounding oceans, Greenland supports the second largest ice mass in the world. Analysis of glacier movements, melt rates and ice loss to the sea, provide data with which to assess mass balance changes and thereby predict global sealevel rise. Thus Greenland plays a central role in the current worldwide debate on climate change. Present-day dynamic ice loss is invariably advertised by the fast moving glaciers of western Greenland with their spectacular calf ice production, such as the ice streams around Disko Bugt reviewed by Weidick & Bennike (2007). This tends to overshadow ice stability and expansion seen in the form of stationary and advancing glaciers elsewhere in Greenland (MODIS 2009). While the seawards acceleration of glacier flow and retreat in frontal positions can be readily attributed to a shift in atmospheric and oceanic conditions (global warming), the same explanation can hardly be used for glaciers with contrasting movement histories
Obituary: Knud Ellitsgaard-Rasmussen 23 June 1923 – 1 December 2009
No full textThe former director of Grønlands Geologiske Undersøgelse (GGU; The Geological Survey of Greenland), Knud Ellitsgaard- Rasmussen, died on 1 December 2009, 86 years old. Ellitsgaard was for many years a driving force in the build-up of GGU and became, as a relatively young geologist, its leader in 1956. In 1966 he was formally appointed director and remained in this position until his retirement in 1983