GEUS Bulletin (Geological Survey of Denmark and Greenland)
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Structures and stratigraphy of Danian limestone, eastern Sjælland, Denmark
No full textWest of København, the top of the pre-Quaternary limestone is found near the terrain surface. There is only a relatively thin cover of Quaternary deposits, which makes the limestone vulnerable to pollution. Region Hovedstaden, being responsible for treating polluted sites, therefore asked GEO and the Geological Survey of Denmark and Greenland to describe the geology and hydraulic characteristics of the limestone formations (Galsgaard et al. 2014). During this work new information and data were collected and a revised geological model established for the area between København and Roskilde (Fig. 1). The model is based on seismic sections, a revised map of the pre-Quaternary surface, biostratigraphy, borehole information and geophysical data. This paper presents the revised geological model
Inversion structures as potential petroleum exploration targets on Nuussuaq and northern Disko, onshore West Greenland
No full textThe onshore Cretaceous–Paleocene Nuussuaq Basin in West Greenland (Fig. 1) has long served as an analogue for offshore petroleum exploration. With the discovery of oil seeps on Disko, Nuussuaq, Ubekendt Ejland and Svartenhuk Halvø in the early 1990s, onshore exploration was also carried out. This eventually resulted in the GRO#3 wildcat exploration well on western Nuussuaq in 1996, which showed several intervals with hydrocarbons (Christiansen et al. 1997). Recent photogrammetric mapping of conspicuous marker horizons within the volcanic sequences of the basin shows that significant compressional structures may have developed in the latest Paleocene on central Nuussuuaq and northern Disko that could be promising potential exploration targets
Greenland, Canadian and Icelandic land-ice albedo grids (2000–2016)
No full textAlbedo, Latin for ‘whiteness’, is a term used to describe the amount of sunlight reflected by the ground. Fresh snow albedo can exceed 85%, making it among the most reflective natural substances. Warm conditions promote snow crystal metamorphosis that, like the presence of liquid water, bring snow albedo down below 65%. With the darkening, caused by the metamorphosis, absorbed solar energy thus increases by roughly a factor of two. Seasonal snow melts over the lower reaches of a glacier leading to the exposure of bare ice with albedo below 55%. Impurities such as dust, black carbon or microbes can bring glacier-ice albedo below 30%, meaning that snow ablation gives way to impurity-rich, bare glacier ice which increases absorbed sunlight by more than a factor of three
Asynchronous ice-sheet development along the central East Greenland margin: a GLANAM project contribution
No full textThe sedimentary record of the glaciated margins of the North Atlantic holds evidence of past ice-sheet activity, and reflects spatial and temporal variations in the ice–ocean–climate interaction as well as the influence of tectonic processes. Furthermore, the record of cross-shelf ice sheets provides a direct link between the continental ice cover and the deep ocean, a relevant issue in the context of climate research
Optimising geological mapping of glacial deposits using high-resolution electromagnetic induction data
No full textThere is a growing demand in modern society for detailed, localised geological maps and 3D models in connection with e.g. planning of major construction works, study of subsurface drainage systems, infiltration of storm water or risk assessment of contaminated waste dumps and pollution plumes. This demand is difficult to meet in Denmark as the surficial glacial deposits that cover most of the country are notoriously very heterogeneous. Standard geological maps are based on regional data collection, and their resolution is far from sufficient to identify structural elements on the 10–20 m scale needed in the above-mentioned applications. Geophysical mapping for geological characterisation of the upper c. 5 m of the subsurface can be carried out using for instance direct-current geoelectrical methods (e.g. Loke et al. 2013), induced polarisation (e.g. Revil et al. 2012) set up with 1–2 m electrode spacing, electromagnetic induction (EMI; e.g. Christiansen et al. 2016; Doolittle & Brevik 2014), ground penetrating radar (GPR; e.g. Neal 2004) or seismic refraction tomography using a multicomponent landstreamer (e.g. Brodic et al. 2015). The resulting geophysical maps show the distribution of the measured parameter, for instance electric resistivity or seismic velocity. To construct geological maps using geophysical methods, the data must be verified and calibrated with geological field observations. GPR imaging of geological structures require laborious interpretation before a geological map can be constructed, and the method is limited to low-loss materials such as sandy sediments (Neal 2004). A new approach, using a combination of shallow, highresolution EMI surveying and traditional spear-auger soil sampling along the same transects, was tested in an area of c. 2 km2 around the contaminated, former landfill site at Pillemark on Samsø (Fig. 1). The resistivity recorded using the EMI method is strongly related to the clay content, and this parameter is therefore well suited for geological mapping. The EMI method is also robust, data acquisition is 5–50 times faster than with other geophysical methods and the processing and inversion scheme is well defined (Christiansen et al. 2016)
Buried tunnel valleys in Denmark and their impact on the geological architecture of the subsurface
No full textBuried valleys are elongate erosional structures in the Danish subsurface now partly or completely filled and covered with younger sediments. The majority was formed by meltwater underneath ice sheets. The number of buried-valley structures in Denmark is large, and because the valley-infill in many areas hosts significant groundwater resources, knowledge of them and their formation is important. This was the starting point of the buried-valley mapping project, which was initiated in the late 1990s and continued until the end of 2015 (Sandersen & Jørgensen 2016). This project became part of the National Groundwater Mapping Programme which was set up with the purpose of mapping the groundwater resources within areas of specific groundwater interest (Thomsen et al. 2004). The areas of specific groundwater interest encompass existing catchment areas and cover around 40% of the country. Within these areas, high-density electromagnetic surveys have typically been performed together with exploration drilling and supplementary geophysical measurements. The mapping of the buried valleys has been based on these newly collected data as well as existing data in the national databases. In some instances, it has also been possible to map buried valleys in less data-dense areas outside the surveyed areas, mainly on the basis of borehole data
Karst sinkhole mapping using GIS and digital terrain models
No full textDanish glacial landscape elements such as basal till plains, hummocky moraine areas and outwash plains contain a variety of small and large depressions. They were probably formed in glacial, late-glacial or Holocene time and may represent dead-ice holes or degraded pingos, or sinkholes formed by interaction between pre-Quaternary chalk or limestone bedrock and the thin glacial co ver. The aim of this study is to map terrain depressions that might potentially be karst sinkholes by analysing digital terrain models in the geographic information system (GIS). The incentive to apply the technique for mapping of sinkholes came from an accidental acquaintance with a farmer, Jens Kirk, whose farmland is located near Thisted. Jens Kirk told us that the front end of his tractor had suddenly sunk into the ground during routine farming work, and this incident was our inspiration to start the project described here
Potential hydrocarbon reservoirs of Albian–Paleocene age in the Nuussuaq Basin, West Greenland
No full textThe onshore Nuussuaq Basin in West Greenland is important for hydrocarbon exploration since many of the key petroleum systems components are well exposed and accessible for study. The basin has thus long served as an analogue for offshore exploration. The discovery of oil seeps on Disko, Nuussuaq, Ubekendt Ejland, and Svartenhuk Halvø (Fig. 1) in the early 1990s resulted in exploration onshore as well. In several wells, oil stains were observed in both the siliciclastic sandstone and in the volcanic series. An important aspect of any petroleum system is a high quality reservoir rock. The aim of this paper is to review petrophysical aspects of the reservoir potential of key stratigraphic intervals within the Nuussuaq and West Greenland Basalt groups. Reservoir parameters and porosity–permeability trends for potential siliciclastic and volcanic reservoirs within the relevant formations of the Nuussuaq Basin are discussed below
New programme for climate monitoring at Camp Century, Greenland
No full textCamp Century was a military base constructed by the US Army Corps of Engineers (USACE) in 1959 in the nearsurface layers of the Greenland ice sheet at 77.13°N and 61.03°W and 1910 metres above sea level (Clark 1965). The c. 55 ha base housed between 85 and 200 soldiers and was continuously occupied until 1964 (Fig.1). Camp Century primarily served as an experimental facility for the USACE to test ice-sheet construction concepts. Recent Danish scholarship has documented the political and military history of Camp Century in substantial detail (Petersen 2007; Nielsen & Nielsen 2016). To summarise, Project Iceworm, the US Army ambition to deploy offensive missiles within the ice sheet, was never realised. After three years of seasonal operation, Camp Century was finally abandoned with minimal decommissioning in 1967. The Government of Denmark has now established a GEUS-led programme for long-term climate monitoring, as well as one-time waste mapping, at Camp Century. Here, we briefly review the historical scientific activities at Camp Century and introduce the future goals of the Camp Century Climate Monitoring Programme. Finally, we discuss the challenges and outlook of climate monitoring and waste mapping at the former military site