GEUS Bulletin (Geological Survey of Denmark and Greenland)
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Observationally constrained reconstruction of 19th to mid-20th century sea-ice extent off eastern Greenland
No full textArctic sea ice has a significant impact on the global radiation budget, oceanic and atmospheric circulation and the stability of the Greenland ice sheet (Vaughan et al. 2013). Prior to the era of aircraft and satellite, information on sea-ice extent relied on observations from ships and people living at the coast. This information is a valuable contribution to better understand the history of sea ice. However, the information exists in a range of formats, e.g., sea-ice extent before the late 1800s is typically reported in the literature as an annual index from a single geographical point or as hand-drawn maps. This makes it difficult to assess and compare data across time and space. The combination of digitised historical maps and single-point data makes the information more accessible and provides a record that can help understand the dynamics and processes of the climate and its interactions with the cryosphere (Chapman & Walsh 1993). In this study, maps of sea-ice extent by Koch (1945) were digitised. We use these maps in combination with sea-ice charts from the Danish Meteorological Institute (DMI) and Koch’s sea-ice index from 1820 to 1939, to map estimated sea-ice extent between Iceland and Greenland going back to 1821. This information has not been included in even the most recent databases of Arctic sea ice (Walsh et al. 2015, 2017). Furthermore, we extract time series of sea-ice extent at a number of locations and investigate the relationship between them. Our observation area is along eastern Greenland, between the southern tip of Greenland at 59°46´N northwards to 77°21´N
Analytical procedures for 3D mapping at the Photogeological Laboratory of the Geological Survey of Denmark and Greenland
No full textPhotogrammetry is a classical remote sensing technique dating back to the 19th century that allows geologists to make three-dimensional observations in two-dimensional images using human stereopsis. Pioneering work in the 1980s and 1990s (Dueholm 1992) combined the use of vertical (nadirlooking) aerial photographs with oblique stereo images from handheld small-frame cameras into so-called multi-model photogrammetry. This was a huge technological step forward that made it possible to map, in three dimensions, steep terrain that would otherwise be inaccessible or poorly resolved in conventional nadir-looking imagery. The development was fundamental to the mapping and investigation of e.g. the Nuussuaq basin (Pedersen et al. 2006). Digital photogrammetry, the all-digital version of multi-model photogrammetry, is nowadays an efficient and powerful geological tool that is used by the Photogeological Laboratory at the Geological Survey of Denmark and Greenland (GEUS) to address geological problems in a range of projects from 3D mapping to image-based surface reconstruction and orthophoto production. Here we present an updated description (complementary to Dueholm 1992) of the analytical procedures in the typical digital workflow used in current 3D mapping projects at GEUS
Arctic geopolitics and the beginning of earthquake monitoring in Denmark and Greenland
No full textWhere there scientific or political reasons behind Denmark’s decision to establish its first seismological stations for earthquake monitoring? In a nation where earthquakes are few and of small magnitude, it is remarkable that since 1927 the Geological Survey of Denmark and Greenland (GEUS), and its predecessors back to the Danish Geodetic Institute have recorded seismological events from permanent stations in Denmark and Greenland and shared data through international data centres
Lithostratigraphy, geology and geochemistry of the volcanic rocks of the Vaigat Formation on Disko and Nuussuaq, Paleocene of West Greenland
No full textThe Paleocene volcanic rocks in the Nuussuaq Basin on Disko and Nuussuaq comprise the Vaigat Formation (c. 62–61 Ma) and the Maligât Formation (c. 60 Ma). The Vaigat Formation in this area is 0–1600 m thick and is dominated by olivine-rich picrites. The formation was deposited during three volcanic episodes and is divided into 10 formally defined members and about 20 informal units. The first episode gave rise to the Anaanaa Member. The second episode gave rise to the Naujánguit Member, which is intercalated with the minor, crustally contaminated Nuusap Qaqqarsua, Nuuk Killeq, Asuk, Tunoqqu and Kûgánguaq members and the uncontaminated Qordlortorssuaq Member. The third episode gave rise to the Ordlingassoq Member and the minor alkaline Manîtdlat Member. Contemporaneous sediments deposited during the first two episodes are the marine Eqalulik Formation, and during the third episode the nonmarine Atanikerluk Formation. During the second episode, the polarity of the geomagnetic field changed from normal (Chron C27n) via a transition zone to reversed (C26r).
The deposits of the first volcanic episode are situated on western Nuussuaq. During the second and third episodes, the volcanism gradually spread eastwards and southwards so that the Vaigat Formation now forms a domed structure, thickest in the north, thinning out on northern Disko and reaching eastwards to the high gneiss country on central Nuussuaq. The earliest eruptions took place on the sea floor and quickly built up a subaerial lava plateau. All three episodes gave rise to complicated facies changes between subaqueous and subaerial eruption products caused by the eastmoving volcanism, subsidence, volcanic aggradation and blockage of the sea connection against the elevated eastern gneiss country. Eruption sites are widespread for all three volcanic episodes. Within certain time periods, a number of contemporaneous high-level magma reservoirs developed within sediments of the Nuussuaq Group, and the crustally contaminated members formed in these reservoirs by reaction between Mg-rich magmas and sediments.
The uncontaminated rocks in the Vaigat Formation are picrites with 12–31 wt% MgO and subordinate basalts with 7–12 wt% MgO. The crustally contaminated rocks range from silicic picrites with 12–16 wt% MgO (Nuusap Qaqqarsua Member) to native-iron-bearing magnesian andesites with 6–10 wt% MgO and up to 62 wt% SiO2 (Asuk Member). The Asuk Member includes unique, strongly reduced rock types with native iron, graphite and sulfide. The contaminated units have individually distinct compositions, indicating individually different contamination events. The alkaline Manîtdlat Member contains an enriched lithospheric component.
Present-day seeps of migrated oil are widespread in the oldest part of the volcanic succession on western Nuussuaq. Some of the contaminated magmas in the Asuk and Kûgánguaq members have fractionated sulfides with Cu and Ni and have been explored for nickel and platinum-group elements. 
Towards a geothermal exploration well in the Gassum Formation in Copenhagen
No full textGeothermal resources in the deep subsurface in many parts of Denmark have the potential to form a central component in the future Danish energy supply for district heating. Geothermal energy is sustainable and environmentally friendly and independent of climatic and seasonal variations, in contrast to solar and wind energy. Furthermore, geothermal plants may be integrated with other green energy supplies. The sandstone reservoirs from which the warm geothermal water is extracted may also act as temporary storage for excess heat e.g. from industrial production processes or from solar-heated water in summer periods when the demand for heating is low
Prospectivity mapping for orogenic gold in South-East Greenland
No full textNumerous studies have proven that conceptual targeting based on integration of various geo-datasets can aid exploration companies to identify exploration targets (e.g. Joly et al. 2013). This is particularly true in remote, underexplored areas that are commonly just covered by airborne geophysics and remote sensing and mapped geologically only on a regional scale. Such regions are ‘exploration greenfields’ and may possess undiscovered economic deposits
Pre-drilling geothermal assessment of porosity and permeability of the Bunter Sandstone Formation, onshore Denmark
No full textDenmark constitutes a low-enthalpy geothermal area. Current geothermal production takes place from two sandstone-rich formations: the Bunter Sandstone and Gassum Formations. These formations form major potential geothermal reservoirs, but information about the permeability of the potential sandstone reservoirs is difficult to obtain. This may be explained by deposition in a variety of environments under different climatic conditions, and by variable diagenetic overprint (Olivarius et al. 2015). Thus, the sandstone characteristics and properties are diverse, and in areas where wells are scarce, the assessment of the extent and reservoir properties of sandstone layers is associated with much uncertainty. In order to reduce exploration risk it is therefore essential to develop a robust method for prediction of porosity and permeability prior to drilling
Generation and origin of natural gas in Lower Palaeozoic shales from southern Sweden
No full textThe Lower Palaeozoic succession in Scandinavia includes several excellent marine source rocks notably the Alum Shale, the Dicellograptus shale and the Rastrites Shale that have been targets for shale gas exploration since 2008. We here report on samples of these source rocks from cored shallow scientific wells in southern Sweden. The samples contain both free and sorbed hydrocarbon gases with concentrations significantly above the background gas level. The gases consist of a mixture of thermogenic and bacterially derived gas. The latter likely derives from both carbonate reduction and methyl fermentation processes. The presence of both thermogenic and biogenic gas in the Lower Palaeozoic shales is in agreement with results from past and present exploration activities; thermogenic gas is a target in deeply buried, gas-mature shales in southernmost Sweden, Denmark and northern Poland, whereas biogenic gas is a target in shallow, immature-marginally mature shales in south central Sweden. We here document that biogenic gas signatures are present also in gas-mature shallow buried shales in Skåne in southernmost Sweden
The rescue of seismic field data from exploration activities in the Danish North Sea
No full textIn 2009, the Danish Energy Agency informed the Geological Survey of Denmark and Greenland (GEUS) that a new legal act (Lov om fordring/Forældelsesloven) would become effective in 2011. The new act introduced a limitation period of three years on the government’s right to request data from licensees’ oil and gas activities in Denmark (www.retsinformation.dk 2007), and it became the catalyst for a major change in the standard procedure for licensees’ submission of seismic data related to exploration activities to GEUS. A consequence of the new legal act was that the Danish authorities would have to request data from the licensee (following the Consolidated Act of the Use of the Subsoil) from the licensee no later than three years after their generation or publication; otherwise the authorities would have no legal right to the data. It was emphasised by the Danish Energy Agency that GEUS would have to submit all requests for outstanding data to the licensees no later than 1 January 2011
An integrated public information system for geology, groundwater and drinking water in Denmark
No full textDenmark has a long tradition for having central geological databases, including a systematic collection and storage of geological and hydrological information from all surficial boreholes which was initiated in 1926. Since the mid-1970s such data have been stored digitally. A large variety of users access a central Danish, geological database: the public, for information about their local drinking water quality, environmental employees in municipalities, regions and the state for using, entering and updating data as well as consultants and drilling companies working for public administration and local water works