Danmarks Geologiske Undersøgelse Serie B
Danmarks Geologiske Undersøgelse Serie B was published by the Geological Survey of Denmark (Danmarks Geologiske Undersøgelse; DGU) between 1977 and 1991. It consists of 16 printed volumes of peer-reviewed monographs and research articles relevant to Danish geology and gesocience. This series replaced Danmarks Geologiske Undersøgelse (I–V). Række. DGU merged with the Geological Survey of Greenland (GGU) in 1995 to form a single organisation, GEUS. The two surveys maintained their own scientific series until these too were merged into one, GEUS Bulletin, in 2003. Danmarks Geologiske Undersøgelse Serie B is discontinued and is not open for submissions.
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Petroleum geology of the Dutch Central North Sea Graben
This contribution presents an extended abstract intended for the proceedings of the symposium: The Jurassic in the Southern Central Graben (Hørsholm, Denmark, June 15-16, 1989). It generally covers the stratigraphic and petroleum geological aspects of the paper entitled: "Late Jurassic" petroleum geology of the Dutch Central North Sea Graben presented by Th. E. Wong, Th. H.M. Van Doorn and B.M. Schroot at the 78th annual meeting of the Geologische Vereinigung (Jiilich, febr. 24-26, 1988). The full text has been published in Geologische Rundschau, 78, 1989, pp. 319-336. The structural and seismic aspects are delt with in detail by B.M. Schroot in the present volume.
Structural development of the Dutch Central Graben
After Heybroek (1975) described the structure of the Dutch Central North Sea Graben and NAM and RGD (1980) published a stratigraphic nomenclature of the Netherlands containing a stratigraphic model for the Jurassic sediments, further work continued, both within the industry and the Geological Survey. Because Herngreen and Wong (1989) set up a revised stratigraphy for the Late Jurassic of the Central Graben and neighbouring areas, it was felt necessary to have a closer look at the structural geology of the Central Graben and to review its hydrocarbon potential. The results of this study have been reported by Wong et al. (1989). This work just about coincided with an increased interest of the industry in the south-eastern extension of the Graben because of the Dutch seventh round of exploration licenses.
Pre-Late Cretaceous structural development of the Danish Central Trough
The structural development of the Danish Central Trough area from the Carboniferous to the Early Cretaceous was studied to test how far back in geological time a graben development can be justified or proved by data.
Diagenetic aspects of Upper Jurassic sandstones in the Danish North Sea sector
Studies of Upper Jurassic sandstone formations, the Heno Formation and the Gert unit, in the Danish North Sea sector have revealed two diverging diagenetic trends, which appear related to sedimentary environments: 1 ) Distal marine sands (lower shoreface to offshore) end up as reservoirs with fair porosities but low permeabilities, 2) Marginal marine sands (beach, barrier-island complex) create reservoirs with fair to high porosities and fair to high permeabilities.
Discussion of Jurassic lithestratigraphy in the Danish, Dutsch, and Norwegian Central Graben Areas
Based on recently published data dealing with the Jurassic lithostratigraphy from the Danish, Dutch, and Norwegian sectors of the Central Graben areas, it seems possible to establish a more consistent and dynamic stratigraphic scheme for these regions. A preliminary proposal of a south-north lithostratigraphic section, from the Dutch to the southern Norwegian sector is discussed. It is suggested to initiate an international cooperation in order to study the common geological features in detail.
Upper Jurassic-Cretaceous stratigraphy of the Vlieland Basin, and adjacent areas, the Netherlands
This contribution presents an extended abstract intended for the proceedings of the symposium: The Jurassic in the southern Central Graben, Hørsholm, (Denmark) June 15-16, 1989. The full text entitled "Tectonostratigraphic development of the Vlieland Basin. The Netherlands" will appear in the Proceedings 1st Conference European Association of Petroleum Geoscientists (Berlin: May 29th - June 2nd, 1989). The Vlieland Basin is located in the northern Netherlands; it covers the NW'ern part of the province of Friesland to the offshore area of the Frisian Island of Vlieland. It is a NW-SE striking structure which is bounded to the W, S and SE by the Texel-IJsselmeer High, and flanked by the Vlieland High, an extension of the Schill Grund High, in the north, and the North Netherlands High in the east. In the Vlieland Basin the major Zuidwal gasfield is located, which recently started production from the Lower Cretaceous Vlieland Sandstone.
Biostratigraphy of the Jurassic strata in the Dutch Central North Sea Graben
This contribution presents an extended abstract intended for the proceedings of the symposium: The Jurassic in the southern Central Graben, Hørsholm (Denmark) June 15-16, 1989. The full text entitled "Dinoflagellate, sporomorph, and micropaleontological zonation of Callovian to Ryazanian strata in the Central North Sea Graben, The Netherlands" has been published in the proceedings of the 2nd International Symposium on Jurassic Stratigraphy, Lisbon 1989, p. 745-762.
Upper Jurassic dinocyst stratigraphy in the Danish Central Trough
The English dinocyst zonations established by Woollam and Riding (1983) and Riding and Thomas (1988), and the Danish-English zonations of Davey (1979, 1982), are unified for the Danish North Sea area and the subzones of the Endoscrinium luridum Zone are redefined. Two standard sections for the Upper Jurassic are described and correlations to five other wells in the Danish North Sea area are demonstrated.
In June 1989, Dansk Olie- og Gasproduktion A/S (DOPAS) sponsored a well-attended symposium on the Jurassic in the Southern Central Trough held at the DOPAS premises in Hørsholm, Denmark. The background for the symposium was a desire among geologists working in the Dutch, German and Danish sectors of the North Sea to establish a forum to discuss problems of lithostratigraphic correlation across the sector boundaries and eventually arrive at a common nomenclature. A number of lectures were held at the symposium and an informal working group was established to deal with the details of lithostratigraphic correlation. The present publication, sponsored partly by DOPAS and partly by the Geological Survey of Denmark (DGU), contains extended abstracts of the lectures.
Foraminiferal stratigraphy of Quaternary deposits in boring no. 51.12 Anholt, Kattegat
Material from a 229 m deep boring on the island of Anholt in the central part of the Kattegat has been stratigraphically analysed on the basis of its foraminiferal content. Due to the lack of casing in the main part of the bore hole, only very few core samples and some samples from the drilling bit were not contaminated. The results of the foraminiferal analyses have, therefore, to be treated with some reservation. The boring did not penetrate the Quaternary. The bottom 143 m of the boring represents deposits of pre-Eemian, possibly Saalian age. This interval seems to contain three marine interstadials, Anholt 1, 2 and 3, of which the upper interstadial is the warmest. Tills and glaciofluvial sediments are found between the marine sequences. The Eemian is represented by 13 m of marine deposits, which can be correlated with Eemian deposits known from other localities in the Vendsyssel-Kattegat region. They correspond to the Lower Turritella terebra Zone of the Skærumhede Series. The Early Weichselian and the lower part of the Middle Weichselian are missing, while the upper part of the Middle Weichselian, 32 m in all, is represented by marine deposits corresponding to foraminiferal zones known from the Vennebjerg Stadial and the Sandnes lnterstadial in the Vendsyssel-Kattegat region. These Middle Weichselian zones correspond to the upper part of the Portlandia arctica Zone of the Skærumhede Series. The non-marine sequence on top of these deposits is considered to be glacial, belonging to the main Weichselian glacial event. Holocene littoral sands and gravels terminate the Quaternary sequence at Anholt.
Danish Finds of Mammoth (Mammuthus primigenius (Blumenbach)) Stratigraphical position, dating and evidence of Late Pleistocene environment
A catalogue of all known remains of mammoth in Denmark is presented, comprising 125 finds. Half of the mammoth material is molars, which are morphologically referred to Mammuthus primigenius (Blumenbach), a third is tusk, and the rest is bone fragments. 14 specimens of mammoth have been C-14 dated. 13 samples have ages from older than 40 000 to ca 21500 C-14 years B.P., and one sample gave an age of ca 13200 C-14 years B.P. As the skeletal material is redeposited, these dates at the same time give maximum ages of the glacial deposits in which they are found. On the basis of this evidence the glacial development during the Weichselian is reviewed. An ice-free period from before 45000 B.P. to around 20 000 years B.P. is indicated. A mammoth tusk from the Tirstrup sandur on Djursland, dated to 13240 +760/-690 B.P., marks an important stage in the ice retreat in Denmark, and shows that the mammoth re-immigrates after the maximum expansion of the Weichselian ice. Remains of other Late Pleistocene vertebrates are also mentioned. On the basis of floral and faunal remains the environmental changes during the Late Pleistocene are then reconstructed. The ice-free period in the Middle Weichselian was characterized by a steppe biome, which may appropriately be termed the mammoth steppe. This Weichselian environment seems to be incomparable to any environment known today.
Geochemistry of the Upper Permian Ca-2 Deposits of the Løgumkloster-1 Well, South Denmark
Rock samples of the Upper Permian Ca-2 unit of the Løgumkloster-l well have been subjected to chemical analysis. The Ca-2 interval was undoubtedly originally an aragonite which have undergone several episodes of diagenesis including a dolomitization and a heavy anhydrite mineralization. Two original facies types are recognized, an oolitic shoal facies, and a lagoonal carbonate facies. The samples have been characterized by neutron activation, atomic absorption, Xray diffraction, palaeomagnetism, optical and electron microscopical examination. Samples of the drilling mud has been analyzed as well, and it is found that contamination of the samples included in the present study from the drilling mud is unlikely to have happened. Imprints of both the original facies and the diagenetic events are found in the present work. The Sr and Ba abundances reflect the original facies-bound distribution, which is also reflected in the normalized REE distribution patterns. A low-Sr anhydrite component is clearly distinguishable in several parameter cross plots. Iron, Sc, REE and several other elements are found to be situated in the EDTA-insoluble residue, which has been identified primarily as a muscovite or clay mineral phase. Pyrite is present, although of small relative volume it is thought to be responsible for the occurrence of As, Sb, and possibly Se. A small fraction of the Cr, As, and Sb may originate from the heavy part of the crude oil, the introduction of which was the last process of alteration the rock experienced. A geomagnetically reversed period is encountered in the middle of the Ca-2 interval, and is tentatively identified as one of the Tatarian reversed events.
Diagenesis of the Zechstein Ca-2 carbonate from the Løgumkloster-1 well, Denmark
The carbonate unit Ca-2 found in the Løgumkloster-l well is located on the northern marginal carbonate platform of the North German Zechstein Basin. The ea. 43 m thick sequence includes former oncoidal/algal muds which were deposited in a relatively quiet lagoonal back-barrier environment, and ooidal carbonate sands, deposited in a rather agitated shoal environment. The carbonate sediments of Ca-2 have been subjected to a complex sequence of diagenetic events. However, the present porosity/ permeability, and thus the reservoir quality of the rocks, is primarily linked to four events: two leaching phases, a phase of chemical compaction, and a late anhydritization. The first phase of leaching created mouldic porosity. The last phase of leaching was important as it resulted in a widening of the preexisting pores and fractures and thereby facilitated percolation of sulphate solutions causing the late anhydritization, which considerably reduced the porosity/ permeability of the rock. The present pore geometry of the rock is complex. In the oolitic intervals the intra- and inter-ooidal porosity types are the most widespread. In the oncolitic/algal intervals intra- and inter-oncoidal porosity and vuggy porosity are often combined with intercrystalline porosity. The corresponding Ca-2 rock in the Brøns-l well, situated ca. 20 km northwest of the Løgumkloster- l well, was subjected to the same post-depositional evolution. Comparison with the diagenesis of the upper part of the Ca-la formation in the Aabenraa-1 well and the Ca-1 formation of the Varmes-1 well also shows close similarity in the diagenetic evolution.
Sandy braidplan deposits from the Triassic Skagerrak Formation in the Thisted-2 well, Denmark
Detailed facies analyses have been carried out on the Triassic Skagerrak Formation on core material from the Thisted-2 well, Denmark. Facies patterns in the sediments show affinity to present day river models. The informations are combined into a braidplain model in which the proximal braidplain was composed of featureless Platte-type streams. Deeper South Saskatchewan-type streams represented the intermediate braidplain. The distal braidplain was dominated by ephemeral streams. Towards north and northeast coalescing alluvial fans formed the immediate connection to the source area, the Fennoscandian Shield.
Ostracoda of the Holsteinian Interglacial in Jutland, Denmark
Ostracoda are described from several marine Holsteinian deposits in Jutland, Denmark. The faunas are extremely uniform all over Jutland. Very little difference is seen between them and the faunas present in Late Elsterian deposits of the same area. They are largely boreal in aspect but contain a few species from warmer realms. With the exception of Callistocythere sp and Semicytherura sp, all the species are extant, though Carinocythereis whitei and Pterygocythereis coronata do not live in Danish inshore waters today. The environment at all the investigated localities was one of open, shallow waters (10-30 m depth) and normal marine salinities. No shallower water facies have as yet been identified. The Holsteinian ostracod faunas of Denmark are analogous to those recorded in North Germany, and show similarities to those reported from Mid-Pleistocene deposits in Great Britain.
Foraminifera in Late Elsterian-Holsteinian deposits of the Tornskov area in South Jutland, Denmark
Foraminiferal faunas from marine Late Elsterian and Holsteinian deposits in the Tornskov borehole have been investigated. The faunal succession is correlated with the pollen zones of the same boring, and the assemblages are compared with Late Elsterian and Holsteinian faunas described from adjacent areas. Arctic foraminiferal faunas at the base of the marine sequence at Tornskov indicate that a marine transgression occurred prior to the establishment of full interglacial conditions, i.e. in the Late Elsterian. Marine sedimentation continued during much of the Holsteinian Interglacial. The assemblages here indicate boreal, mainly sublittoral conditions and relatively open access to the North Sea. Evidence for withdrawal of the Holsteinian sea from the area is not recorded in the faunas at Tornskov, the uppermost part of the marine sequence having probably been removed by subsequent glacial erosion. The general trend for corresponding deposits over the whole area of SW Denmark and N. Germany is that the regression took place before any indication of climatic deterioration is seen in either the fauna or the flora.
Bibliography of Moraine Deposits in Denmark 1875-1974
The literature on Quaternary glacigene deposits in Denmark is extensive, and it may easily involve a great deal of work to unearth the relevant material on a smaller region of Denmark or on a specific subject. It is therefore my hope that this bibliography will prove helpful to students in finding this type of literature and that it may serve as a guide to students interested in the history/ development of geology, helping them to understand the background for our present interpretation of the genesis and extension of the Quaternary glacial deposits in this country. The bibliography was originally planned as part of a Nordic project. Thus the subject index was prepared in cooperation with colleagues from the other Nordic countries. Unfortunately, so many practical difficulties arose that the joint publication was abandoned. I wish to take this opportunity of thanking my colleagues for an inspiring collaboration, which due to external reasons did not lead to the result hoped for. Thanks to Jon Eirfksson (Iceland), Sylvi Haldorsen (Norway), Hans G. Johansson (Sweden) and Marjatta Pcrttunen (Finland). To professor A. Dreimanis (Canada) I express my gratitude for many stimulating discussions concerning the subject index.
The present chapter contains a review of the potential reservoir rocks drilled in the Danish Central Graben. The source data for this descriptive summary originates primarily from wells drilled to explore chalk reservoirs. The main part of possible chalk reservoirs has been evaluated only by using wire line logs, since few cores have been cut and very few tests performed. Therefore, further investigations are necessary to evaluate and describe these possible reservoir rocks properly. In this chapter, each zone in which shows have been recorded, and each porosity zone, is described. This is done with reference to the formations/log-units given earlier in the paper. The characteristics relevant to reservoir evaluation, such as the extension, thickness, depth, porosity, and permeability, are described. The characterizing terms (good, fair, etc.) used for reservoir parameters in sandstone reservoirs cannot be applied automatically to chalk reservoirs. The descriptions are accompanied by maps showing the known occurrences.
The formation of hydrocarbon traps is the result of local depositional and deformational history. The trap formation is governed by three main parameters: the geometry of the reservoir body, the sedimentary sealing history and the tectonic history. In the present chapter is discussed the distribution of potential hydrocarbon traps in different areas, each characterized by a structural style (figs. 47, 48). After a short definition of basic trap types, various areas of the Danish Central Graben, each of which is characterized by a certain structural style, are listed and described with emphasis on the distribution of potential hydrocarbon traps.
Little has been published on source rocks of Paleozoic and Mesozoic ages in the North Sea. Gas in many fields of the southern North Sea is known to originate from Late Carboniferous Coal Measures, (Eames 1975). In the East Midlands area of England, the oil in Carboniferous reservoirs is believed to originate from Carboniferous rocks (Bernard & Cooper 1981). Several papers published on the oil fields in the southern and northern North Sea suggest a Late Jurassic source rock (see review by Weismann 1979 and Bernard & Cooper 1981). Also Early and Middle Jurassic shales are suggested as possible source rocks in parts of the North Sea (Fuller 1975, Oudin 1976). Published data on source rock conditions in the Danish sector is limited to Weismann (1979).
Borehole temperatures have been studied to evaluate the natural temperature field of the geological formations (fig. 37). Formation temperature and time are main factors affecting maturation of source rocks and should, therefore, be compared with maturation measurements. Furthermore, temperature gradients through sedimentary sequences provide information about relationships between their heat conductivities, and this can be used to extrapolate temperatures measured in wells to the surrounding rock masses.
During the Quaternary and Tertiary a regional subsidence took place resulting in a large depositional basin, the axis of which coincides with the central part of the present North Sea. Thick Tertiary and Quaternary series were deposited, consisting mainly of clays with an increasing amount of sand upwards. The upper part of the series is particularly uninfluenced by deeply seated structures or by major tectonic activities (fig. 36).
At the termination of the Early Cretaceous period, the sea transgressed large earlier land areas. The transgression, the reduced relief of the continents, the generally diminished tectonic activity, the climatic change, and the enormous production of calcareous nannoplankton in the oceans profoundly changed the gross facies pattern in the North Sea region. The elastic sedimentation was replaced during Late Cretaceous time by offshore relatively deep water carbonate sedimentation. This resulted in the deposition of a chalk sequence reaching a thickness of 1-2 km in the Danish Subbasin and the North Sea area.
The Early Cretaceous sea primarily covered the same basinal regions as the Late Jurassic sea but, late in the Early Cretaceous the sea also covered Late Jurassic land masses. During Early Cretaceous time the topography of the North Sea region became gradually buried. The following major transgression comprises the transition Early/Late Cretaceous. At the Jurassic/ Cretaceous transition, the Late Cimmerian unconformity is a significant feature (fig. 24), known from large parts of the North Sea region. The subsequent transgression and sedimentation of marine clay (the Valhall Formation), and marine sand (the LC-1 Unit), started late in Late Jurassic. Therefore, the formations described in the present chapter also comprise sediments of Late Jurassic age. Thicknesses of the Lower Cretaceous sediments are given in fig. 15.
During Early Jurassic time, deposition continued in the basinal areas occupied by Triassic sedimentation. The Danish Central Graben subsided strongly and more than 4000 m of sediments were deposited during Jurassic time (fig. 14). North of the area the thickness seems less than 2000 m and, in the Norwegian-Danish Basin, approximately 1200 m. The rhythm of sedimentation corresponds closely to what is known from adjacent areas in the Northwest European sedimentary region. During the Early Jurassic, relatively uniform marine claystone series, the Fjerritslev Formation, were deposited all over the North Sea region, including the main part of the highs. Large areas were uplifted and eroded during the Mid Cimmerian phase (fig. 23), accompanied by a general eustatic lowering of the sea level. During the Middle Jurassic period, deltaic or fluvial conditions prevailed in the main part of the North Sea, and coal-bearing sand bodies, the J-2 Unit, were deposited. During the Late Jurassic a general subsidence took place, but more restricted areas were transgressed by the sea than in the Early Jurassic. Thick marine claystone series (the J-3 and J-4 Units) were deposited in the main part of the basin. Near marginal highs, only minor sand bodies (the W-1 Unit) were laid down. The Late Jurassic is a period of main subsidence for the Central Graben. Figs. 21 and 23 show the distribution of Jurassic sediments.
Deposition during the Triassic continued in the basinal areas developed during the Permian, but in Early Triassic the highs were also gradually covered by sediments. The pattern of sedimentation in the two mega-basins is analogous to that of the Rotliegendes, i.e. with a pronounced, more coarse-grained elastic infill in the northern basin (fig. 20). The Triassic represents a regressive period in the North Sea area, with dominant continental sedimentation of sandstone, shale, and evaporites in red bed facies. Strong subsidence is recorded in the center of the Danish Subbasin with more than 5000 m Triassic sediments, and in the Horn Graben with approximately 3000 m. In the Danish Central Graben the Triassic has not yet been mapped, but thicknesses of about 2000 m or more are expected locally.
In North-West Europe two mega-basins began their development during Late Carboniferous to Early Permian: The South Permian Basin stretching from eastern England into Poland , and the North Permian Basin reaching from Scotland into Denmark. These two basins were separated by the Mid North Sea High and the Ringkøbing-Fyn High which came into existence early in Permian. The initial phase of subsidence was accompanied by extensive subaerial volcanism. This was followed by a period of oxidation and erosion under desert conditions and deposition of red beds and sabkha sediments in the two Permian basins (fig. 19). These rocks are included in the Rotliegendes Group as originally established by Werner (1786). Continuous subsidence and transgression of the sea, but with a restricted connection to the ocean, lead to the formation of the evaporites of the Zechstein Group.
Data on Pre-Permian rocks are reported only from the P-1 well, which was bottomed in Caledonian basement. The geology of this formation in the western part of the Danish sector is, therefore, poorly known. According to the age determinations performed and reviewed by Frost et al. (1981), the North GermanPolish Caledonides extend under most of the North Sea and join the Scottish-Norwegian Caledonides, whereas most of the Ringkøbing-Fyn High is underlain by Precambrian basement.
The Central Graben is a broad, complex trough with a long history of differential subsidence. It was probably initiated in the Permian and was controlled by major rifting during the Mesozoic. To the south in the Dutch sector the trough is divided into two parts. From here it passes northwards and divides the southern North Sea Basin into the Anglo-Dutch Basin and the Northwest German Basin. It also separates the Mid North Sea High from the Ringkøbing-Fyn High. These highs form broad, east-west trending, relative stable ridges. The further continuation of the Central Graben is to the northwest, towards the centre of the North Sea, where it passes into the Viking Graben and the Moray Firth Basin at about 58° N. Where the Central Graben divides the two major highs, there is an elongate central narrow horst, the Dogger High, which is the southernmost of a row of mid-Graben highs. Both sides of the Graben are clearly defined by normal rotational faults that were intermittently active from Triassic to Early Cretaceous times.
Lithostratigraphy and sedimentary evolution of the Triassic, Jurassic and Lower Cretaceous of Bornholm, Denmark
A new lithostratigraphic subdivision of the Triassic to Lower Cretaceous sequence of Bornholm is presented including 2 new groups, 3 new formations and 10 new members. The Late Ladinian-Carnian variegated clay, sand and conglomerates of arid flood-plain origin with thin marine intercalations are tentatively referred to the Kagerod Formation. The Jurassic sediments are placed in the Bornholm Group (new) comprising a lower Hettangian-Sinemurian Rønne Formation (new) which contains a succession of lacustrine clay, fluviatile sand and coal, and tidal flat and marsh heteroliths and sand. The overlying Lower Pliensbachian Hasle Formation (new) includes shallow marine fossiliferous sandstone, while the Bajocian-Bathonian Baga Formation (new) is characterized by fluviatile fining-upwards sand-clay-coal sequences and resedimented conglomerates. This is followed by the Lower Cretaceous Nyker Group (new), comprising a basal Rabekke Formation (Lower Berriasian, possibly extending down into the Tithonian and up into the Upper Berriasian) which contains fluviatile coarse, sometimes ferruginous sand and sandy clay, and swamp and lagoonal dark grey clay. This is overlain by the Robbedale Formation (Upper? Berriasian) which comprises tidal flat, beach and lagoonal fine-grained sand and clay and rather coarse-grained barrier beach and shelf sand. Then follows the Jydegard Formation (uppermost Berriasian - Valanginian) comprising back-barrier and washover fan sand, and lagoonal clay, clay-ironstone and silt with thin sands. The Triassic-Lower Cretaceous sequence thus reflects deposition in a variety of coastal environments, and while eustatic sea-level changes seem to have controlled the main facies evolution, the local depositional environments and breaks in sedimentation seem to reflect the interplay between eustacy and synsedimentary tectonic phases.