GEUS Bulletin (Geological Survey of Denmark and Greenland)
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Sedimentary facies and architecture of the Holocene to Recent Rømø barrier island in the Danish Wadden Sea
No full textThis paper describes an ongoing multidisciplinary study on the development of the barrier islands in the Danish Wadden Sea (Vadehavet), carried out by the Department of Geography and Geology at the University of Copenhagen and the Geolo gical Survey of Denmark and Greenland (GEUS). Nine sediment cores each c. 25 m long and a total of c. 45 km ground penetrating radar (GPR) profiles have been acquired on the islands of Rømø and Fanø. Geochemical and palaeontological analyses and dating of 150 core samples using optically stimulated luminescence (OSL) are in progress. This multidisciplinary approach has given new insights into the sedimentary architecture and development of the island, and the study is expected to result in a new detailed facies model. Such models are essential for an assessment of the effects of rising sea level associated with global warming. The new facies model can also be used as an analogue for subsurface oil or water reservoirs in similar sedimentary settings. This article presents selected core and GPR data from the Rømø barrier island
A new programme for monitoring the mass loss of the Greenland ice sheet
No full textThe Greenland ice sheet has been losing mass at a dramatic rate in recent years, raising political concern worldwide due to the possible impact on global sea level rise and climate dynamics (Luthcke et al. 2006; Rignot & Kanagaratnam 2006; Velicogna & Wahr 2006; IPCC 2007; Shepherd & Wingham 2007). The Arctic region as a whole is warming up much more rapidly than the globe at large (ACIA 2005) and it is desirable to quantify these changes in order to provide the decision-makers with a firm knowledge base. To cover this need, the Danish Ministry of Climate and Energy has now launched a new Programme for Monitoring of the Greenland Ice Sheet (PROMICE), designed and operated by the Geological Survey of Denmark and Greenland (GEUS) in collaboration with the National Space Institute at the Technical University of Denmark and Asiaq (Greenland Survey). The aim of the programme is to quantify the annual mass loss of the Greenland ice sheet, track changes in the extent of local glaciers and ice caps, and track changes in the position of the ice-sheet margin
Laser ablation analysis of bivalve shells – archives of environmental information
No full textReconstructing past secular environmental variations is an important issue in palaeoclimate research. However, most key variables for palaeoclimate reconstructions cannot be measured directly, and reconstructions are therefore based on proxy data. Here, we demonstrate the potential of bivalve shells as an archive of environmental parameters. The Geological Survey of Denmark and Greenland (GEUS) has developed a fast and reliable method for chemical analyses of shell material by laser ablation - inductively coupled plasma - mass spectrometry (LA-ICP-MS), and here we present some examples of the use of this method. In tropical and subtropical waters, corals can provide century-long archives of past water chemistry with annual resolution. A comparable archive for temperate and Arctic waters would be highly useful in climate research, and therefore it has been examined whether this can be provided by bivalve shells (e.g. Schoene et al. 2005). Long-lived species may provide archives with annual resolution extending over several hundred years, whereas short-lived, fast-growing species can provide archives with a seasonal or in some cases daily resolution over a period of a few years. Most bivalves are sessile, and shells are commonly preserved as fossils. There are, however, a number of challenges related to the use of bivalves as proxy archives: (1) many proxies show species specific behaviour (Seed 1980); (2) only very few proxies are dependent on a single variable (Wefer et al. 1999); and (3) the effects of biology and ontogeny on the uptake of trace elements and stable isotope fractionation in shell carbonate are largely unknown and have to be evaluated empirically. Therefore, any potential proxy must be calibrated individually for each species of interest before it can be used. A large number of chemical analyses are needed to calibrate a proxy. These are commonly obtained by solution ICP-MS, in which sample preparation is time-consuming and labour-intensive. The use of LA-ICP-MS is therefore a considerable advance in bivalve shell proxy research, as it greatly reduces the effort needed for sample preparation. At the same time, the method requires less material for analysis, thus providing better spatial and hence temporal resolution. Proxies based on bivalve shell carbonate can be used in present-day environmental monitoring, and for environmental reconstructions from shells found as fossils. Shells from museum collections and shells found in archaeological middens can give information on historic and prehistoric environmental conditions (e.g. Carrell et al. 1987), and fossil shells can be used as archives of environmental parameters on geological timescales (e.g. Hendry et al. 2001)
Correlation of carbon isotope events in the Danish Upper Cretaceous chalk
No full textA high resolution carbon isotope (δ13C) profile through the upper Campanian to Maastrichtian chalk was recently completed based on material from the Stevns-1 core from the Stevns peninsula, eastern Denmark. The δ13C variation of marine carbonates essentially reflects global perturbations in the carbon cycle, i.e. the burial fluxes of carbonate carbon versus organic carbon. It is widely observed that the δ13C variation broadly tracks the eustatic sea-level curve, and that δ13C curves can be used for stratigraphic correlation (e.g. Jarvis et al. 2002). In the Stevns-1 core, a total of 29 notable isotope changes have been identified in the upper Cam panian to Maastrichtian succession. In order to evaluate the stratigraphic significance of the isotope changes, the variation in δ13C values of the mid-Maastrichtian chalk from cores in eastern Denmark and the Danish North Sea, and from outcrops at Rørdal, northern Jylland has been examined (Fig. 1). The selected interval is characterised by distinct chalk and marl cycles in the Stevns-1 and Karlslunde-1 cores and in the Rørdal quarry (Fig. 2), whereas a non-cyclic clean chalk is found in the M-10X well from the North Sea. In the Rørdal quarry, the chalk–marl unit spans the upper–lower Maastrichtian boundary in the Boreal brachiopod and belemnite stratigraphies (Surlyk 1984; unpublished data, B. Lauridsen & F. Surlyk). In Stevns-1 and Karlslunde-1 the chalk–marl unit was deposited during the younger part of nannofossil subzone UC20b (Sheldon 2006, in press). This paper presents preliminary results of a high-resolution study of carbon isotopes, carried out by the Geological Survey of Denmark and Greenland (GEUS) in co-operation with partners from the Department of Geography and Geology at the University of Copenhagen. This paper is a product of the Cretaceous Research Centre (CRC) at Geo center Denmark
Mapping of buried tunnel valleys in Denmark: new perspectives for the interpretation of the Quaternary succession
No full textTunnel valleys eroded by subglacial meltwater underneath the Late Weichselian ice sheet are a common feature in the Danish landscape (Ussing 1907; Smed 1998). They occur as undulating elongate depressions with hollows and thresholds and without continuously descending floors. The valleys rise tens of metres before terminating in large outwash fans, primarily along the Main Stationary Line in Jylland, but also along younger ice-margin lines formed shortly after the Last Glacial Maximum. The meltwater was driven by hydrostatic pressure gradients below the glacier towards its margin leading to subglacial erosional features, partly in the form of valleys. The term ‘tunnel valley’ was first used by Madsen (1921), who referred to tunnel-like structures below glaciers that were expected to have carried the meltwater. Worldwide, this term is used for subglacially eroded valleys; however, other terms such as ‘tunnel channel’ and ‘incision’ are also widely used for such valleys. There is general consensus that subglacial meltwater is the primary causative agent that has eroded the tunnel valleys (O’Cofaigh 1996; Huuse & Lykke-Andersen 2000; Jørgensen & Sandersen 2006). The subglacial origin is indicated by: (1) abrupt terminations at former ice margins and the association with the large outwash plains, (2) irregular longitudinal profiles, (3) the occurrence of small channels and eskers in the valleys, and (4) the non-meandering and non-dendritic appearance of the relatively straight-segmented valleys. The exact mode of meltwater erosion remains, however, poorly understood. Valleys are present not only in the landscape; they are also found buried in the subsurface. In Denmark, buried valleys have occasionally been described on the basis of borehole data and early geoelectrical methods (e.g. Sorgenfrei & Berthelsen 1954; Lykke-Andersen 1973; Binzer & Stockmarr 1994). Based on the large amount of newly collected hydrogeophysical data in Denmark, it has recently become possible to define such valleys as tunnel valleys and to acknowledge their wide distribution in the subsurface (Sandersen & Jørgensen 2003; Jørgensen et al. 2005; Jørgensen & Sandersen 2006). Analysis of these data has revealed dense networks of tunnel valleys and has significantly improved our understanding of their distribution, geometry and sedimentary infill. In the following, we review this work and identify new perspectives for the interpretation of the Quaternary succession in Denmark. The work was initiated in 1998 by the former Danish counties (amter), and is currently continued by the Geological Survey of Denmark and Greenland and the ‘miljøcentre’ (environment centres). As part of this project, the buried valleys are continuously being mapped as new data are collected
KenSea – tsunami damage modelling for coastal areas of Kenya
No full textOn 26 December 2004, the eastern part of the Indian Ocean was hit by a tremendous tsunami created by a submarine earthquake of magnitude 9.1 on the Richter scale off the west coast of Sumatra. The tsunami also reached the western part of the Indian Ocean, including the coastal areas of eastern Africa. Along the coast of Kenya (Figs 1, 2) it resulted in a sudden increase in water level comparable to a high tide situation. This rather limited consequence was partly due to the great distance to the epicentre of the earthquake, and partly due to the low tide at the time of the impact. Hence the reefs that fringe two thirds of the coastline reduced the energy of the tsunami waves and protected the coastal areas. During the spring of 2005, staff members from the Geological Survey of Denmark and Greenland (GEUS) carried out field work related to the project KenSea – development of a sensitivity atlas for coastal areas of Kenya (Tychsen 2006; Tychsen et al. 2006). Local fishermen and authorities often asked what would have been the effect if the tsunami had hit the coastal area during a high tide, and to answer the question GEUS and the Kenya Marine and Fisheries Research Institute (KMFRI) initiated a tsunami damage projection project. The aim was to provide an important tool for contingency planning by national and local authorities in the implementation of a national early warning strategy. The tsunami damage projection project used the database of coastal resources – KenSeaBase – that was developed during the KenSea project. The topographical maps of Kenya at a scale of 1:50 000 have 20 m contour lines, which is insufficient for the tsunami run-up simulation modelling undertaken by the new tsunami project. Therefore new sets of aerial photographs were obtained, and new photogrammetric maps with contour lines with an equidistance of 1 m were drawn for a 6–8 km broad coastal zone. The tsunami modelling is based on the assumption that the height of a future tsunami wave would be comparable with the one that reached the coastal area of Kenya in December 2004. Based on the regional geology of the Indian Ocean, it appears that the epicentre for a possible future earthquake that could lead to a new tsunami would most likely be situated in the eastern part of the ocean. Furthermore, based on a seismological assessment it has been estimated that the largest tsunami that can be expected to reach eastern Africa would have a 50% larger amplitude than the 2004 tsunami. It was therefore decided to carry out the simulation modelling with a tsunami wave similar to that of the 2004 event, but with the wave reaching the coast at the highest astronomical tide (scenario 1) and a worst case with a 50% larger amplitude (scenario 2: Fig. 3). The 2004 tsunami documented that the coastal belt of mangrove swamps provided some protection to the coastline by reducing the energy of the tsunami. Hence we included in this study a scenario 3 (Fig. 4), in which the mangrove areas along the coastline were removed. Maps for the three scenarios have been produced and show the areas that would be flooded, the degree of flooding, and the distribution of buildings such as schools and hospitals in the flooded areas. In addition, the force and velocity of the wave were calculated (COWI 2006)
Colophon, contents and introduction
No full textThis Review of Survey activities presents a selection of 22 papers reflecting the wide spectrum of activities of the Geological Survey of Denmark and Greenland, from the microscopic to the plate-tectonic level.The Survey\u27s activities in Denmark are illustrated by 13 articles. Five of them deal with petroleum-related topics and two others with groundwater-related topics. Four others describe raw material activities and environmental change, one paper presents a new Base Quaternary map of Denmark and one paper describes the deep structure below Denmark.Activities in Greenland are covered by five papers. Three of these address mineral and petroleum exploration, one concerns monitoring of the Greenland ice sheet and one focuses on historic investigations of Hans Ø, a small island in Nares Strait between Greenland and Canada.International projects and two new geoscientific methods: The survey also carries out many projects outside Denmark, Greenland and the Faroe Islands. This bulletin includes descriptions of a coastal protection project in Kenya and a multinational project dealing with the implementation of the European Union\u27s Water Framework Directive. Finally, two examples of new developments in instrumental geoscience are presented
Evaluation of the quality, thermal maturity and distribution of potential source rocks in the Danish part of the Norwegian–Danish Basin
No full textThe quality, thermal maturity and distribution of potential source rocks within the Palaeozoic–Mesozoic succession of the Danish part of the Norwegian-Danish Basin have been evaluated on the basis of screening data from over 4000 samples from the pre-Upper Cretaceous succession in 33 wells. The Lower Palaeozoic in the basin is overmature and the Upper Cretaceous – Cenozoic strata have no petroleum generation potential, but the Toarcian marine shales of the Lower Jurassic Fjerritslev Formation (F-III, F-IV members) and the uppermost Jurassic – lowermost Cretaceous shales of the Frederikshavn Formation may qualify as potential source rocks in parts of the basin. Neither of these potential source rocks has a basinwide distribution; the present occurrence of the Lower Jurassic shales was primarily determined by regional early Middle Jurassic uplift and erosion. The generation potential of these source rocks is highly variable. The F-III and F-IV members show significant lateral changes in generation capacity, the best-developed source rocks occurring in the basin centre. The combined F-III and F-IV members in the Haldager-1, Kvols-1 and Rønde-1 wells contain \u27net source-rock\u27 thicknesses (cumulative thickness of intervals with Hydrogen Index (HI)> 200 mg HC/g TOC) of 40 m, 83 m, and 92 m, respectively, displaying average HI values of 294, 369 and 404 mg HC/g TOC. The Mors-1 well contains 123 m of \u27net source rock\u27 with an average HI of 221 mg HC/g TOC. Parts of the Frederikshavn Formation possess a petroleum generation potential in the Hyllebjerg-1, Skagen-2, Voldum-1 and Terne-1 wells, the latter well containing a c. 160 m thick highly oil-prone interval with an average HI of 478 mg HC/g TOC and maximum HI values> 500 mg HC/g TOC.
The source-rock evaluation suggests that a Mesozoic petroleum system is the most likely in the study area. Two primary plays are possible: (1) the Upper Triassic – lowermost Jurassic Gassum play, and (2) the Middle Jurassic Haldager Sand play. Potential trap structures are widely distributed in the basin, most commonly associated with the flanks of salt diapirs. The plays rely on charge from the Lower Jurassic (Toarcian) or uppermost Jurassic – lowermost Cretaceous shales. Both plays have been tested with negative results, however, and failure is typically attributed to insufficient maturation (burial depth) of the source rocks. This maturation question has been investigated by analysis of vitrinite reflectance data from the study area, corrected for post-Early Cretaceous uplift. A likely depth to the top of the oil window (vitrinite reflectance = 0.6%Ro) is c. 3050–3100 m based on regional coalification curves. The Frederikshavn Formation had not been buried to this depth prior to post-Early Cretaceous exhumation, and the potential source rocks of the formation are thermally immature in terms of hydrocarbon generation. The potential source rocks of the Fjerritslev Formation are generally immature to very early mature. Mature source rocks in the Danish part of the Norwegian–Danish Basin are thus dependent on local, deeper burial to reach the required thermal maturity for oil generation. Such potential kitchen areas with mature Fjerritslev Formation source rocks may occur in the central part of the study area (central–northern Jylland), and a few places offshore. These inferred petroleum kitchens are areally restricted, mainly associated with salt structures and local grabens (such as the Fjerritslev Trough and the Himmerland Graben)
Geology of outer Horns Rev, Danish North Sea
No full textIn 2006, Dong Energy initiated the development of the Horns Rev II offshore wind farm in the North Sea (Fig. 1). In order to evaluate and map the characteristics of the surface features of the sea bed and to characterise the subsurface in the wind farm area, the Geological Survey of Denmark and Greenland (GEUS) conducted a geophysical survey of the area. The survey utilised a variety of instruments: sparker, side-scan sonar, marine caesium magnetometer and a multibeam echo-sounder. In addition, information on the subsurface sediments was obtained by cone penetration tests (CPT) and by drilling to 30–50 m below the sea bottom. Geological correlation of the CPT results with the other survey results was extremely complicated but was required in order to understand the architecture of the ice marginal glaciotectonic complex. Information on the geology is crucial for evaluation of the geotechnical problems of the region
Hans Ø, celebrated island of Nares Strait between Greenland and Canada: from dog-sledge to satellite mapping
No full textHans Ø – or Tartupaluk to the indigenous population of North-West Greenland – is a small steeply sided island in Nares Strait at c. 80°50´N. Charted in 1871 and named after Greenlander Hans Hendrik, it is one of five limestone islands forming an integral part of the Greenland Silurian succession. Rising less than 170 m above normally ice-infested waters, the 1.25 km2 island is physiographically far overshadowed by nearby Franklin Ø (Fig. 1). The island’s notoriety results from its placing more or less equidistant between the coasts of Kennedy Channel on the political boundary between Greenland and Canada. For 40 years the rocky patch has been the subject of a dispute be tween the Danish/Greenland and Canadian governments regarding sovereignty rights, an issue that remains unresolved. However, there is mutual understanding between Canada and Denmark that “since the question of sovereignty over the island has not yet been solved no action should be taken by either side which might prejudge the settlement of the issue” (Brückner 1984). Formally, this remains the position today