GEUS Bulletin (Geological Survey of Denmark and Greenland)
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A well-preserved bimodal Archaean volcanic succession in the Tasiusarsuaq terrane, South-West Greenland
No full textDuring the field campaign in the Nuuk region, one of the objectives was to describe Archaean primary geological environments (Hollis et al. 2006). On Nunatak 1390, which is part of the Tasiusarsuaq terrane (Figs 1, 2), a bimodal volcanic succession is preserved and interpreted as former ocean floor. The field investigation included geological mapping and sampling of the volcanic sequence comprising mafic to ultramafic rocks, and associated acid volcanic rocks and granite intrusions
Environmental change in Danish marine waters during the Roman Warm Period inferred from mollusc data
No full textModern geological research into the late and postglacial history of the inner Danish waters (i.e. Kattegat, Bælthavet and Øresund, plus the adjoining fjords and estuaries) began at the turn of the last century. Since then most investigations have focused on the timing of the initial marine inundation of the area, the early to mid-Holocene changes in land–sea configuration and sea level changes during the mid-Holocene Littorina period. Research on the late Holocene marine environment has received less emphasis, undoubtedly due to problems in finding continuous marine sediment records, as sedimentation in large areas of the Danish waters seems to have been characterised by complex spatial and temporal patterns of deposition and non-deposition (e.g. Lykke-Andersen et al. 1993). In an ongoing project we aim to explore the continuous development of Danish coastal environments over the last 9000 years using a variety of proxy data, including molluscs, diatoms, foraminifera, algal pigments, plant macrofossils and physical properties of sediments. The project spans both environmental and cultural history, and addresses the important links between them, as the nature of the coastal environment has exerted major influences on cultural and societal expression and activity from Mesolithic to modern times. This paper presents some of the first results from the project concerning environmental changes in the Roman Warm Period (c. 2000–1600 years B.P.) as shown by changes in molluscan faunas at two coring sites in Horsens Fjord and Tempelkrog in southern Isefjord (Fig. 1)
Colophon, Contents, Introduction
No full textThe Geological Survey of Denmark and Greenland (GEUS) has lived through a period of intense unrest during most of 2006. This was a consequence of the decision by the Danish Government in 2005 to carry out a major reorganisation of the Danish research world. The aim was to improve the quality and competitiveness of Danish universities and research organisations (such as GEUS), by means of a fusion of universities and the merging of independent research institutions with the universities. At the conclusion of this process all but three of the major government research institutions were merged with the universities in Århus and Copenhagen, and the Technical University in Lyngby. For many reasons, one being the special tasks that GEUS is responsible for in Greenland, the Government decided that GEUS should continue as one of these three independent national research institutions
Chalk depth structure maps, Central to Eastern North Sea, Denmark
No full textThe Upper Cretaceous – Danian chalk may be considered to be the economically most important rock type in Denmark. Onshore it constitutes an important groundwater aquifer and it is also quarried for e.g. building materials and paper production. Offshore the chalk reservoirs contain more than 80% of the oil and gas produced in Denmark (Fig. 1). During the last few years efforts have therefore been made to map this important succession in the Danish and adjoining areas (Vejbæk et al. 2003). The stratigraphic interval mapped comprises the Chalk Group of Cenomanian to Danian ages and its stratigraphically equivalent units (Fig. 2). The north-eastern limit of the Chalk Group is determined by Neogene erosion. The limits of the map to the west and south were mainly determined by the amount of available data
Cenozoic evolution of the Vietnamese coastal margin
No full textA series of Cenozoic basins fringes the Vietnamese coastal margin, often characterised by more than 10 km of sedimentary infill (Fig. 1). Greater parts of the margin are still in an early explorational state, although significant petroleum production has taken place in all but the southern Song Hong and the Phu Khanh Basins. This has increased the need for a fundamental understanding of the processes behind the formation of the basins, including analyses of potential source rocks. The basins fringing the Indochina Block provide excellent evidence of the geological evolution of the region, and the basin geometries reflect the collision of India and Eurasia and the late Cenozoic uplift of south Indochina (Rangin et al. 1995a; Fyhn et al. in press). In addition, the basins provide evidence of regional Palaeogene rifting and subsequent Late Palaeogene through Early Neogene sea-floor spreading in the South China Sea. Apart from the regional Cenozoic tectonic record, the basins contain a high-resolution climatic record of South-East Asia due to the high depositional rates, changing depositional styles and large hinterland of the basin (Clift et al. 2004)
Quaternary glaciation history and glaciology of Jakobshavn Isbræ and the Disko Bugt region, West Greenland: a review
No full textThe Disko Bugt region in central West Greenland is characterised by permanent ice streams, of which Jakobshavn Isbræ is by far the most important. The first thorough studies on the glaciology of the region were conducted over 150 years ago by H.J. Rink, who introduced the terms \u27ice streams\u27 and \u27Inland Ice\u27. Rink\u27s work inspired new field work, which has continued to the present, and the long series of observations are unique for an Arctic region.
Cooling during the Cenozoic led to ice-sheet growth in Greenland. A number of interglacial occurrences have been reported from the Disko Bugt region, and during the penultimate glacial stage, the Greenland ice-sheet margin extended to the shelf break. During the last glacial maximum, the ice margin probably extended only to the inner part of the banks on the continental shelf, and large floating glaciers may have been present at this time. During the Younger Dryas cold period, the ice margin may have been located at a marked basalt escarpment west of Disko Bugt.
Disko Bugt was deglaciated rapidly in the early Holocene, around 10 500–10 000 years before present (10.5–10 ka B.P.), but when the ice margin reached the eastern shore of the bay, recession paused, and major moraine systems were formed. With renewed recession, the present ice-margin position was attained around 8–6 ka B.P., and by c. 5 ka B.P. the ice margin was located east of its present position. The subsequent Neoglacial readvance generally reached a maximum during the Little Ice Age, around AD 1850. This was followed by recession that has continued to the present day.
The relative sea-level history shows a rapid sea-level fall in the early Holocene, and a slow rise in the late Holocene. This development mainly reflects a direct isostatic response to the ice-margin history.
Jakobshavn Isbræ is the main outlet from the Greenland ice sheet. It drains c. 6.5% of the present Inland Ice, and produces c. 35–50 km3 of icebergs per year, corresponding to more than 10% of the total output of icebergs from the Inland Ice. The velocity of the central part of the ice stream at the front has been around 7 km/year since records began, but has nearly doubled in recent years. Other calf-ice producing glacier outlets in Disko Bugt produce c. 18 km3 per year. The large calf-ice production of Jakobshavn Isbræ may have been initiated at about 8 ka B.P. when the glacier front receded from the iceberg bank (Isfjeldsbanken) near Ilulissat. Ice streams in inner and outer Egedesminde Dyb may have been active during the early Holocene and during the last glacial maximum
Are Carboniferous coals from the Danish North Sea oil-prone?
No full textThe Central Graben in the North Sea is a mature petroleum province with Upper Jurassic – lowermost Cretaceous marine shale of the Kimmeridge Clay Formation and equivalents as the principal source rock, and Upper Cretaceous chalk as the main reservoirs. However, increasing oil prices and developments in drilling technologies have made deeper plays depending on older source rocks increasingly attractive. In recent years exploration activities have therefore also been directed towards deeper clastic plays where Palaeozoic deposits may act as petroleum source rocks. Carboniferous coaly sections are the most obvious source rock candidates. The gas fields of the major gas province in the southern North Sea and North-West Europe are sourced from the thick Upper Carboniferous Coal Measures, which contain hundreds of coal seams (Drozdzewski 1993; Lokhorst 1998; Gautier 2003). North of the gas province Upper Carboni-ferous coal-bearing strata occur onshore in northern England and in Scotland, but offshore in the North Sea area they have been removed by erosion. However, Lower Carboniferous strata are present offshore and have been drilled in the Witch Ground Graben and in the north-eastern part of the Forth Approaches Basin (Fig. 1A), where most of the Lower Carboniferous sediments are assigned to the sandstone/shale-dominated Tayport Formation and to the coal-bearing Firth Coal Formation (Bruce & Stemmerik 2003). Highly oil-prone Lower Carboniferous lacustrine oil shales occur onshore in the Midland Valley, Scotland, but they have only been drilled by a single well off shore and seem not to be regionally distributed (Parnell 1988). In the southern part of the Norwegian and UK Central Graben and in the Danish Central Graben a total of only nine wells have encountered Lower Carboniferous strata, and while they may have a widespread occurrence (Fig. 1B; Bruce & Stemmerik 2003) their distribution is poorly constrained in this area. The nearly 6000 m deep Svane-1/1A well (Fig. 1B) in the Tail End Graben encountered gas and condensate at depths of 5400–5900 m, which based on carbon isotope values may have a Carboniferous source (Ohm et al. 2006). In the light of this the source rock potential of the Lower Carboniferous coals in the Gert-2 well (Fig. 1C) has recently been assessed (Petersen & Nytoft 2007)
Petroleum systems and structures offshore central West Greenland: implications for hydrocarbon prospectivity
No full textA detailed geophysical mapping project has been carried out by the Geological Survey of Denmark and Greenland (GEUS) in the offshore region south-west and west of Disko and Nuussuaq, central West Greenland as part of the preparations for the Disko West Licensing Round in 2006 (Fig. 1). The main purpose of the study was to evaluate the prospectivity of this almost 100 000 km2 large region, and to increase knowledge of basin evolution and the structural development. Results of the work, including a new structural elements map of the region and highlights of particular interest for hydrocarbon exploration of this area, are summarised below. Evidence of live petroleum systems has been recognised in the onshore areas since the beginning of the 1990s when seeps of five different oil types were demonstrated (Bojesen-Koefoed et al. 1999). Oil seeps suggesting widely distributed marine source rocks of Mesozoic age are particularly promising for the exploration potential (Bojesen-Koefoed et al. 2004, 2007). Furthermore, possible DHIs (Direct Hydro carbon Indicators) such as gas-clouds, pock marks, bright spots and flat events have been interpreted in the offshore region (Skaarup et al. 2000; Gregersen & Bidstrup in press). The evaluation of the region (Fig. 1) is based on all public and proprietary seismic data together with public domainmagnetic and gravity data. The seismic data (a total of c. 28 000 line km) are tied to the two existing offshore exploration wells in the region (Hellefisk-1 and Ikermiut-1). The study also incorporates information on sediments and volcanic rocks from onshore Disko and Nuussuaq (Fig. 2). Ten seismic horizons ranging from ‘mid-Cretaceous’ to ‘Base Quaternary’ (Fig. 2) have been interpreted regionally. Large correlation distances to wells, varying data quality and a thick cover of basalt in the north-eastern part of the region, add uncertainty in the regional interpretation, especially for the deeper horizons such as the ‘mid-Cretaceous’ equivalent to Santonian sandstone interval drilled in Qulleq-1 far south. Based on the seismic interpretation (Fig. 3) structural elements maps, horizon-depth maps and isopach maps have been produced; these maps, together with general stratigraphic knowledge on potential reservoirs, seals and source rocks (Fig. 2), provide important information for discussions of critical play elements including kitchens and structures.The existence of many large structures combined with the evidence of live petroleum systems has spurred the recent major interest for hydrocarbon exploration in the region