Danmarks Geologiske Undersøgelse Serie A
Danmarks Geologiske Undersøgelse Serie A was published by the Geological Survey of Denmark (Danmarks Geologiske Undersøgelse; DGU) between 1976 and 1995. It consists of 35 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 A is discontinued and is not open for submissions.
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The Hanklit Gaciotectonic Thrust Fault Complex, Mors, Denmark
The Hanklit cliff section is a classical glaciotectonic locality where an excellent cross-section through a thrust fault complex is exposed. The thrust imbrications were thrust from north to the south during a Late Weichselian glacier advance. Three thrust sheets with thickness of more than 50 m are involved in the thrust fault complex. The deposits exposed in the cliff-section comprise ca. 39 m diatomite with ash layers of Paleocene-Eocene age (the Fur Formation), overlain by up to 27 m of Quaternary glacigenic sediments. Common structural features related to compressional thrust fault helts, are recognizable in the glaciotectonic complex, which shows a lateral shortening of more than 40%. Structures created by soft sedimentary deformation due to high water pressure occur in relation to the thrust fault zones. The structural framework is described with the terminology of thin-skinned tectonics and flats, ramps and hanging-wall anticlines are identified in the cliff-section. A balanced cross section has been constructed. Based on this construction the structural model is verified and the glaciotectonic development is interpreted. A geoelectrical investigation has been made to support the construction of the 3-dimensional framework of the thrust complex. This demonstrates that the impressive Hanklit thrust sheet extends for more than 1 km along the strike and is displaced more than 200 m to the south. Superimposed extentional structures, situated above the sole of the Hanklit Thrust Sheet, are interpreted to be related to Tertiary subsidence tectonics.
Palaeozoic tectonic and sedimentary evolution and hyrdrocarbon prospectivity in the Bornholm area
The present distribution of Palaeozoic sediments in the Bornholm area is a consequence of several different tectonic regimes during the Phanerozoic eon. This development may be divided into three main evolutionary phases: A Caledonian to Variscian phase encompassing the Lower Palaeozoic sediments. The sediments are assumed originally to have showed a gradual thickness increase towards the Caledonian Deformation Front located to the south. This pre-rift development may be further subdivided into three sub-phases: A period of slow sedimentation on a relatively stable platform as recorded by the uniformly low thicknesses of the Cambrian to Lower Silurian sediments. A period of foreland-type rapid sedimentation commencing in the Llandoverian to Wenlockian, continuing in the Ludlovian and possibly into the Devonian. The period is characterized by /olding and uplift of the Caledonides to the south causing tectonic loading of the foreland and resultant rapid sedimentation in the foreland basin. A period of gravitational collapse causing minor erosion during the Devonian. The transition to the second major phase in the Phanerozaic structural development, during which the Sorgenfrei-Tornquist zone came into existence, is recorded by regional deposition of Carboniferous sediments. These sediments are, however, mostly removed by tater erosion. A syn-rift phase characterized by sedimentation in graben areas and expanding basins commencing in the Rotliegendes and continuing through the Triassic, Jurassic and Lower Cretaceous. This phase was probably initiated by a Late Carboniferous- Early Permian tensional dominated right-lateral wrench fault system within the Sorgenfrei-Tornquist zone. A Post-rift development phase dominated by Late Cretaceous carbonate sedimentation. During Late Cretaceous and Early Tertiary times the Bornholm area was strongly affected by inversion tectonism caused by compressional strike-slip movements. This resulted in reverse faulting and uplift and erosion of former basinal areas. Understanding the two latter phases is important for understanding the present distribution of the Palaeozoic. A key to understanding the hydrocarbon potential of the area is the maturation of the organic matter in the main potential source, the Ordovician Upper Alum Shale. Maturity was mainly achieved during the Silurian to Late Palaeozoic time, and little further maturation took place later. The Upper Alum Shale is accordingly expected to be overmature in the main part of the study area and mature in the Hano Bay Basin. This reflects the assumed primary uniform thickness of the Lower Palaeozoic, with a general thinning towards the northeast. A Caledonian to Variscian phase encompassing the Lower Palaeozoic sediments. The sediments are assumed originally to have showed a gradual thickness increase towards the Caledonian Deformation Front located to the south. This pre-rift development may be further subdivided into three sub-phases: A period of slow sedimentation on a relatively stable platform as recorded by the uniformly low thicknesses of the Cambrian to Lower Silurian sediments. A period of foreland-type rapid sedimentation commencing in the Llandoverian to Wenlockian, continuing in the Ludlovian and possibly into the Devonian. The period is characterized by /olding and uplift of the Caledonides to the south causing tectonic loading of the foreland and resultant rapid sedimentation in the foreland basin. A period of gravitational collapse causing minor erosion during the Devonian. The transition to the second major phase in the Phanerozaic structural development, during which the Sorgenfrei - Tornquist zane came into existence, is recorded by regional deposition of Carboniferous sediments. These sediments are, however, mostly removed by tater erosion. A syn-rift phase characterized by sedimentation in graben areas and expanding basins commencing in the Rotliegendes and continuing through the Triassic, Jurassic and Lower Cretaceous. This phase was probably initiated by a Late Carboniferous- Early Permian tensional dominated right-lateral wrench fault system within the Sorgenfrei-Tornquist zone. A Post-rift development phase dominated by Late Cretaceous carbonate sedimentation. During Late Cretaceous and Early Tertiary times the Bornholm area was strongly affected by inversion tectonism caused by compressional strike-slip movements. This resulted in reverse faulting and uplift and erosion of former basinal areas. Understanding the two latter phases is important for understanding the present distribution of the Palaeozoic. A key to understanding the hydrocarbon potential of thearea is the maturation of the organic matter in the main potential source, the Ordovician Upper Alum Shale. Maturity was mainly achieved during the Silurian to Late Palaeozoic time, and little further maturation took place later. The Upper Alum Shale is accordingly expected to be overmature in the main part of the study area and mature in the Hano Bay Basin. This reflects the assumed primary uniform thickness of the Lower Palaeozoic, with a general thinning towards the northeast.
Depositional environments of coal and associated siliciclastic sediments in the Lower and Middle Jurassic of Denmark. The Øresund -5, -7, -13, -15 and -18 wells
Five cored wells located in the Fennoscandian Border Zone in the Øresund area, Denmark, encountered Lower or Middle Jurassic coal-bearing strata; the coal seams are Lignite to Sub-bituminous A/High Vol. Bituminous C in rank. A number of shallowing-upward units are recognized in the five wells. Each unit is capped by a coal seam. Correlation of these shallowing-upward units between wells is difficult on the basis of available biostratigraphy and log data. Seven of the coal seams result from establishment of peatforming conditions due to infilling of freshwater lakes, whereas the last two of the coal seams result from peat accumulation on top of restricted brackish lagoon or bay sediments. However, only one of the latter two seams accumulated in an environment influenced by saline water. Hence, the investigated coals represent almost entirely freshwater peat-forming environments. Three main types of environments are defined: 1) Type 1 is a sparsely vegetated open water swamp; it is represented by a limnic facies. The deposit is typically a carbonaceous claystone with a high content of allochthonous organic matter; 2) Type 2 is a densely vegetated rheotrophic, nutrient-rich and anoxic swamp; it is represented by a limnotelmatic to telmatic facies. The coal has a very high content of humified organic matter; 3) Type 3, subdivided into the types 3a and 3b, is the driest environment of the three types. Type 3a is a desiccated ombrotrophic raised bog represented by a terrestrial facies. It is strongly influenced by a fluctuating watertable. The coals contain a high content of inertinite that generally shows a low reflectance. Type 3b is a mesotrophic to ombrotrophic domed bog; the environment alternates between dry oxidizing conditions and wet conditions. It is represented by a telmatic to terrestrial facies. In general, the three types of environments form ecosystems characterized by the groundwater influence, nutrient supply, and vegetation. Successions representing the hydrological evolution towards drier conditions due to vertical peat accretion are recognized in some of the seams. The vegetation was small-statured and consisted of a prominent herbaceous type of flora, shrub-like plants, smaller arboreous plants and, to a lesser extent, larger plants.
Megaspore assemblages from the Jurassic and lowermost Cretaceous of Bornholm, Denmark
There are more than 600 slides containing megaspores in "Helge Gry's collection", housed at the Geological Survey of Denmark in Copenhagen. The majority of the specimens are unnamed, all are from the Danish island of Bornholm in the Baltic Sea, and none has been described hitherto. The stratigraphic distribution of 22 of the taxa was, however, taken into account in a paper by Gry, published in 1969, and 16 of these were illustrated by small line drawings. He considered the lithology, areal extent and depositional history of what were thought at the time to be only Jurassic strata on Bornholm. The youngest part of the succession he discussed, the "Purbeck beds" (Rabekke and Robbedale Formations), are, however, now known to be mainly, if not entirely, of earliest Cretaceous age. In the present paper Gry's megaspore records are brought up to date so that they can be used more effectively along with other microfossils in drawing biostratigraphical and palaeoenvironmental conclusions. All 22 taxa to which he referred are discussed and illustrated, mostly with scanning electron micrographs, and their nomenclature emended where necessary. Descriptions and figures of an additional 15 forms encountered in the collection are included. Three of these arc new species of megaspores and one is a palynomorph of uncertain origin, named Henrisporites bornholmensis, Paxillitriletes kristinae, P. rasmusii and Aneuletes discus respectively. Most, if not all, of the megaspores in Gry's collection are likely to have selagincllalean or isoetalcan affinities. There is no evidence of the presence of heterosporous water ferns. The assemblages differ significantly in composition according to their relative ages, with several forms being of considerable biostratigraphic value. There is, however, still room for greater precision in determining local stratigraphic ranges, and also a need to apply occurrence data to palaeoenvironmental interpretations. This will require carefully documented collecting of new samples.
Deep wells in Denmark 1935-1990. Lithostratigraphic subdivision
The lithostratigraphic data presented here represent the mid-1991 status of the lithostratigraphic database at the Geological Survey of Denmark. The database comprises basic well information such as well location, company, completion date, depths and seismic two-way travel times to top and base of lithostratigraphic units recognized in the wells. Well location maps, a stratigraphic scheme and a list of selected references are included in the present publication. The aim of the presentation is to make these abundant data available to those working with subsurface geology in Denmark and adjacent areas. The key information are depths and seismic two-way travel times to top and base of lithostratigraphic units. The units are primarily recognized by means of petrophysical wireline logs measured in the wells. The boundaries of the units are indicated by significant changes in log pattern and readings as defined in the relevant publications (see reference list). The stratigraphic subdivision of the individual wells has been undertaken over the years by various geologists at the Survey and the level of subdivision thus depends on the data and time available when the subdivision was made. The database is, however, continuously revised as new wells or further work increase our knowledge of the subsurface. The database contains all exploration and appraisal wells drilled on Danish territory. The wells are included irrespective of whether the purpose was exploration for hydrocarbons, geothermal energy, or investigation of possible sites of waste-deposits or gas-storage. However, the wells drilled on the Tostrup salt structure are not included nor are production, observation and injection wells from oil or gas fields since the additional stratigraphic information provided by such wells is generally limited. Wells related to exploration and production of rock salt are not included in the database; most of these were drilled before 1953 and are dealt with in Sorgenfrei & Buch (1964, Table 1, p. 14-17). Further information concerning available logs, reports, and geological samples obtained from the wells, together with information on casings, bit sizes, and test intervals can be found in the Well Data Summary Sheets, vol. 1-16. These can be ordered from the Geological Survey of Denmark. Exploration data in Denmark are in most cases, subject to a 5-year confidentiality period. Therefore, the tables of wells drilled after mid-1986 only show data released by the Danish Energy Agency, such as location, total depth and lithostratigraphic unit at total depth. A few new wells have been released, however, due to relinquished concessions. These wells (Borg-1, Felicia-I, lbenholt-1, Mejrup-1) are presented with full data sets. Furthermore, DONG has permitted release of data from the Stenlille-2, -3, -4, -5, and -6 wells. The authors acknowledge the work of their colleagues who contributed to the database, especially Ole Vejbæk and Jens Jørgen Møller who initiated the data base together with Jens Christian Olsen. Heinke Andersen, Bent Katz, and Uli Heyden are thanked for technical assistance. Jon Ineson (Geological Survey of Denmark) and Olaf Michelsen (University of Arhus) made valuable comments on the manuscript.
Palynological zonation and palynofacies investigation of the Fjerritslev Formation (Lower Jurassic - basal Middle Jurassic) in the Danish Subbasin
A detailed study of the palynology and palynofacies of the Fjerritslev Formation (Lower Jurassic - basal Middle Jurassic) has resulted in the definition of four spore/pollen zones and four dinoflagellate cyst zones. The spore/pollen zones are the Corollina - Ricciisporites Zone (Late Rhaetian), the Cerebropollenites macroverrucosus Zone (Sinemurian - Pliensbachian), the Spheripollenites - Leptolepidites Zone (Toarcian), and the Perinopollenites elatoides Zone (Middle Jurassic). The dinoflagellate cyst zones are the Rhaetogonyaulax rhaetica Zone (Rhaetian), the Dapcodinium priscum Zone (latest Rhaetian - earliest Sinemurian), the Liasidium variabile Zone (Sinemurian), and the Nannoceratopsis gracilis Zone (Late Pliensbachian - ?Bajocian/Bathonian). These zones, and the Pinuspollenites - Trachysporites Zone Lund 1977 (Hettangian), are proposed for use in the Danish Subbasin. The combined spore/pollen and dinoflagellate cyst zonation has resulted in a detailed biostratigraphical subdivision of the sequences studied. A new combination, Manumia delcourtii (Pocock 1970) nov. comb. et emend., is proposed here, and the species description emended. New photographs of the holotypes of some of the species erected by Nilsson (1958) are included in the plates. The kerogen assemblages recorded from the Fjerritslev Formation, indicate a marine depositional environment, with a high but variable influence of terrestrially-derived organic particles. Stratigraphic variation in the kerogen assemblages generally correlate with the lithostratigraphical subdivision, and support previous environmental interpretations of the Fjerritslev Formation. Indications of strongly reducing conditions in the bottom waters were found in the Stenlille-2 borehole, in samples here referred to the Early Toarcian. The variations in the kerogen assemblages in the sequence investigated from the Gassum-1 borehole are not correlatable with the other boreholes, but seem primarily to reflect a distinct decrease in bioturbation in the Late Sinemurian. The Fjerritslev Formation does not generally represent a potential source rock for oil. Some levels (parts of the F-111 member) show, however, the characteristics of a fair to good source rock. The organic matter is generally immature or only at the earliest stage of maturity.
Well records on the Phanerozoic stratigraphy in the Fennoscandian Border Zone, Denmark. Hans-1, Sæby-1, and Terne 1 wells
The Hans-1, Sæby-1, and Terne-1 wells are located within the Danish part of the Fennoscandian Border Zone and provide significant new data pertaining to the evolution of this important tectonic belt. All three wells encountered Palaeozoic rocks; the Terne-1 well extended into the lower Palaeozoic. Two of the wells are located in the Danish waters of the Kattegat, and thus yield the first deep well data from this part of the border zone. The wells encountered Cambrian to Silurian, Carboniferous to Zechstein and Triassic to Upper Cretaceous successions. The Cambrian to Lower Silurian section is interpreted to represent shelf and shallow marine deposits comparable to those known from Scania and Bornholm. The inferred Upper Silurian section is calculated to be up to 2600 m thick and may represent the fill of a foreland basin in front of the Caledonian 4 deformation front. A hiatus comprising the Devonian to Lower Carboniferous is inferred. A 550 m thick Rotliegende sequence was drilled in the eastern part of the Sorgenfrei-Tornquist Zone; changes in structural dip indicate a syn-depositional faulting. Palaeozoic tectonism is also indicated by Late Carboniferous intrusive and extrusive volcanic rocks. Reworked volcanic rocks characterize the Rotliegende elastic sequence. A thin siliciclastic Zechstein sequence is recognized. The lithology and stratigraphy of the Mesozoic sections are in accordance with well data from the Danish Subbasin. The presence of a Middle Jurassic depocenter within the Sorgenfrei-Tornquist Zone may indicate a tectonically controlled subsidence of the zone. The occurrence of a Late Cretaceous to Early Tertiary inversion tectonism is supported by these new data.
Copyright (c) 1991 Olaf Michelsen, Lars Henrik Nielsen https://creativecommons.org/licenses/by/4.0
Upper Cretaceous (Cenomanian-Santonian) inoceramid bivalve faunas from the island of Bornholm, Denmark. With a review of the Cenomanian-Santonian lithostratigraphic formations and locality details
The inoceramid bivalve faunas from the Arnager Greensand, Arnager Limestone, and Bavnodde Greensand Formations of the island of Bornholm, Denmark are described. The fauna from the basal part of the Arnager Greensand s. str. is from the Lower Middle Cenomanian and includes Inoceramus crippsi Mantell, /. crippsi hoppenstedtensis Trager, and I. schoendorfi Heinz. The Arnager Limestone at its type locality immediately west of Arnager yielded a diverse fauna, including /. waltersdorfensis cf. hannovrensis Heinz, /. lusatiae Andert, I. cf. rotundatus Fiege, /. striatoconcentricus Gumbel, I. (Heroceramus) cf. hercules Heinz, I. cf. wandereri Andert, I. cf. annulatus Goldfuss, I. cf. renngarteni Bodilevski & Schulgina, and/. (Mytiloides) incertus Jimbo. This fauna is Lower Coniacian. I. cf. lusatiae and /. cf. guerichi Heinz are recorded from the top part of the formation east of Horsemyre Odde, which is Lower Coniacian. /. (Cremnoceramus) schloenbachi Bohm from the upper Lower Coniacian is reported from the Arnager Limestone Formation at Muleby. /. (Volviceramus) koeneni Muller and /. (V.) alievimussensis lvannikov occur in 4 the top part of the Arnager Limestone Formation at Stampe A; this fauna is probably Lower Middle Coniacian. The fauna of the Bavnodde Greensand Formation at the type locality consists of /. (Sphenoceramus) pachti cf. pachti Arkhangelsky and /. (S.) cardissoides Goldfuss which are Lower, but not lowest, Santonian. At Risenholm, the formation yielded I. (S.) subcardissoides Schluter, I. (S.) cardissoides, I. (S. ?) bornholmensis n. sp., /. (S.) sp. ex gr. pachtilcardissoides, and incomplete, poorly preserved inoceramids possibly belonging to the I. (Magadiceramus) subquadratus group; this fauna is basal Santonian. The fauna of the formation at Jydegard comprises I. (S. ?) bornholmensis n. sp. and /. (S.) sp. ex gr. pachti/cardissoides, and the formation here is lowest Santonian and possibly highest Coniacian. The Cenomanian-Santonian lithostratigraphic formations of Bornholm are reviewed and their ages are discussed with regard to various fossil groups, including inoceramid bivalves, ammonites, belemnites, and foraminifera. Locality details are given.
Geochemical investigation of NaCl-KCl-MgCl2-CaCl2-FeCl2 solutions in Zechstein 2 salt, Suldrup Dome, Denmark. Microthermometry on fluid inclusions in halite
Large, irregular fluid inclusions with daughter bischofite, MgCl2 • 6H2O, in recrystallized halite from former brine pockets in grey Zechstein 2 rock salt from the Suldrup dome, Denmark, were studied by means of microthermometry. The test material consists of ca 3 kg cleavage pieces and a piece of core of extremely clean, colourles, limpid halite. Anhydrite and pyrrhotite are present as solid inclusions in trace amounts only. The irregular inclusions studied all contain daughter bischofite at room temperature. Optical, crystallographic, and chemical (melting) methods proved the daughter mineral to be bischofite. The mean dissolving temperature Tmhex = 56.5 ± 0.9°C, 95% confidence limit, of 117 measurements yields, from pertinent phase diagrams, a quantitative composition of the equilibrium solution: 114 mol MgCl2 + 1.2 mol K2Cl2 per 1000 mol H2O, saturated with NaCl (ca. 2 mol Na2Cl2 per 100 mol H2O). Exposed to the atmosphere, the equilibrium solution becomes orange yellowish after some days, thus proving the presence of FeCl2 (5-10 mol/1000 mol H2O). In one inclusion carnallite (KMgCl3 • 6H2O) was observed, the dissolving temperature Tmcar = 81.9°C of which is a minimum trapping temperature. The minimum trapping pressure is calculated at slightly higher than 65 MPa. The viscosity at 80°C is estimated at ca. 4 centipoise. Measurements of the homogenization temperature in fluid phase are meaningless due to the presence of compressed gas, possibly H2S. The following model is proposed concerning the formation of the studied halite: During the end of the diapiric penetration phase in Lower Cretaceous, a metamorphic lye mixed with concentrated sea water in NaCl facies in brine pockets within the grey Zechstein 2 rock salt, causing salting out of the studied halite. The metamorphic lye derived from a metamorphosed carnallitic potash zone. The carnallitic solution was mixed with an infiltrating rinneitic (3KC1 · NaCl · FeCl2) solution. The mixture was squeezed out from the potash zone during the diapiric penetration phase, leaving a trail of disseminated grains and fracture fillings of carnallite all the way up to the former brine pockets. The minerals bischofite and pyrrhotite, Fe1-xS, are reported from Denmark for the first time.
Stratigraphy and sedimentology of the Zechstein carbonates of southern Jylland, Denmark
The Upper Permian Zechstein succession of southern Jylland, Denmark, is composed of a cyclic repetition of carbonate, anhydrite and salt, and includes four main carbonate units: Ca-la, Ca-lb, Ca-2 and Ca-3. The stratigraphy and log-correlation in the southern Jylland area is outlined and compared to other areas. Descriptions of facies and interpretation of depositional models for the four carbonate units are presented. The depositional system comprised a shelf with marginal sabkha evaporites and carbonates; the shelf underwent evolution from a ramp-like to a platform configuration. This evolution is seen as the result of the interplay between evaporite and carbonate sedimentation. Accumulation of sulphate evaporites during Z-1 times produced a sediment body with a platform morphology. Z-2 carbonate deposition further enhanced the platform configuration, with consequent development of a marked zonation of facies according to energy level. Later in Z-2 time the platform - basin system suffered demise as the basinal areas were filled with halite and during the remaining period of basinal history shallow water conditions prevailed throughout the area.
Log-sequence analysis and environmental aspects of the Lower Jurassic Fjerritslev Formation in the Danish Subbasin
The lithostratigraphic, biostratigraphic, and chronostratigraphic subdivisions of the Lower Jurassic Fjerritslev Formation in the Danish Subbasin are discussed in relation to a log-sequence analysis. The formation is subdivided into three depositional sequences. The upper and lower sequences comprise 15 minor log-sequences, which can be correlated between most well sections. These minor log-sequences are separated by strata boundaries, which by means of biostratigraphic data are shown to be synchronous. The depositional environment is discussed on the basis of previously published data and new organic geochemical data, and in relation to the published sealevel curve. Five major events of eustatic sea-level rises seem to have influenced the benthonic faunas; faunal diversity and density decreased during the sea-level rises, and subsequently increased during the higher sea-level stillstands. The level of oxygen in the bottom waters decreased during the Early Jurassic transgression.
Revision of the Jurassic lithostratigraphy of the Danish Subbasin
The lithology and stratigraphy of the Jurassic sequence in the Danish Subbasin is described from 5 wells situated in the central region of the Danish Subbasin. The chronostratigraphic subdivision of the Lower Jurassic Fjerritslev Formation is discussed and modified in the light of new biostratigraphical and lithostratigraphical data from the five well sections. The Jurassic lithostratigraphic subdivision is amended. The F-Ia, F-lb, F-II, F-III, and F-IV members of the Fjerritslev Formation are redescribed and defined in relation to the reference section in the Hyllebjerg-1 well. The Haldager and Bream Formations are abandoned. The Haldager Sand, Flyvbjerg, Borglum, and Frederikshavn Members are elevated to the rank of formations.
Upper Triassic-Lower Jurassic tidal deposits of the Gassum Formation on Sjælland, Denmark
Three deep wells on the Danish island of Sjælland penetrate the Upper Triassic - Lower Jurassic Gassum Formation. The formation has been the subject of a facies analysis of cored sediments and interpretation of petrophysical logs. The principal part of the work presented is based on data from the Stenlille-1 well. The sediments were deposited in a NW-SE trending, microto mesotidal, prograding coastal zone and the adjacent fluvial hinterland. In the Stenlille-1 well, the coastal progradation is recorded as a thick, coarse-grained sandstone unit deposited within a barrier island complex. This basal part of the formation is overlain by four stacked regressive sequences consisting of finegrained sandstones and mudstones deposited on tidal flats. A thin transgressive sandstone sheet terminates the formation and marks the boundary to marine claystones of the Fjerritslev Formation.
Geology of the Søby-Fasterholt area. Text
A general description of the Quaternary and Neogene of Central Jutland follows after an introductory survey of previous investigations in the area and the general regional geology of the Neogene of Denmark. The Quaternary morphology and especially the solifluction deposits and periglacial structures are described. The Tertiary deltaic browncoal bearing deposits of the S0by-Fasterholt area are described in detail (lithostratigraphy) based upon exposures, wells and the petrography of the browncoal seams. The Miocene marine Hodde Formation and the outcrops of the Gram Formation of the Søby-Fasterholt area are described in general. The Fasterholt Flora especially, but also the Damgaard Flora and the Søby Flora, is discussed in an extended chapter on the biostratigraphy, and the pollen- stratigraphy is compared to the Lower Rhenian region. Finally, The exposures revealing pre-Weichselian disharmonic folding and faulting caused by compression are described and compiled.
Geology of the Søby-Fasterholt area. Atlas
This atlas contains 121 photographic pictures, illustrating the text-volume with field information.
Palynological zonation and stratigraphy of the Jurassic section in the Gassum No. 1-borehole, Denmark
The Jurassic section of the Danish onshore borehole Gassum No. 1 has been investigated palynologically. 126 palynomorph-taxa have been recognized, consisting mainly of microspores and gymnosperm pollen. The palynomorphs are treated morphosystematically. 71 samples were prepared and the relative abundances determined in 32 representative samples. 5 spore- pollen zones, A to E, have been defined based on the stratigraphical ranges and abundances of specific taxa. Correlating with data from Northwest Europe allows the zones to be dated as follows: Zone A: Late Rhaetian, Zone B: Hettangian, Zone C: Early Sinemurian to ?Pliensbachian/foarcian, Zone D: Kimmeridgian/ Early Volgian, Zone E: Middle Volgian. The relative abundances of the main morphological groups of palynomorphs have been calculated and their stratigraphical variations correlated with previously proposed Early Jurassic sea-level changes.
Lower Cretaceous calcareous nannofossil biostratigraphy in the Danish Central Trough
Calcareous nannofossils are described from Lower Cretaceous strata of four borings in the Central Trough of the Danish North Sea sector, and from three Aptian units on Helgoland and at Sarstedt, northern Germany. The assemblages range in age from Upper Hauterivian to Albian-?Cenomanian. Abundances of calcareous nannofossils varied considerably throughout the investigated sequences. They were rock-forming in several Lower Barremian - Aptian sediments, but rare or lacking in many of the Hauterivian and Albian strata. The Middle Barremian - Lower Aptian assemblages were often dominated by nannoconids. Preservation was generally bad in chalk and good in marl deposits. Some finely laminated black sediments yielded extremely well-preserved assemblages. One hundred and sixteen species were recognized. Eighteen species were selected as biostratigraphically particularly useful and their chronostratigraphic ranges are shown and discussed. The ages of the investigated sequences were determined on the basis of the selected nannofossil events. Some distinct sedimentary units in the North Sea could be correlated with time-equivalent formations in eastern England and northern Germany.
Geochemical investigation of Potassium-Magnesium Chloride mineralization of Zechstein 2 salt, Mors Dome, Denmark
Solid-rich inclusions at 20°C of the Na-K-Mg-Cl-H2O system, found in euhedral quartz from the top of Zechstein 2 salt in the Mors dome, Denmark, were objects of microthermometrical investigation. The quartz crystals, all of the long prismatic, slender type, average length of 750 μm, are genetically closely connected to the intercalated clay in the deck halite Na2r. The inclusions are faceted negative crystals, crystallographically orientated with the host quartz. Carnallite (KMgCl3 ·6H2O) is the main daughter mineral, followed by tetrahydrate (MgCl2-4H2O) and minor sylvite (KCl). Halite (NaCl) is found as grains in suspension in the trapped solutions. The trapped solutions represent melts of carnallite or tetrahydrate saturated with NaCl. The concentrations range from 167 mol MgCl2 + 83 mol K2Cl2 +3 mol Na2Cl2 per 1000 mol H2O to 250 mol MgCl2 + 5 mol K2Cl2 + 0 mol Na2Cl2 per 1000 mol H2O, corresponding to salinities from 52 to 62 weight%. Melting temperatures measured, 170-185°C, and estimated pressures, 80-110 MPa, are minimum trapping values. In a few cases highly irregular, "dry" grains of carnallite, containing dissolved high-pressure gas, were observed to have been trapped. In this study it is shown that the melting temperature of carnallite in a closed space, where evaporation is prevented, depends on the prevailing pressure. It is also shown that high-pressure gas is dissolved in trapped grains of carnallite or halite, but not in the solutions. Finally, the results lead to the proposal of a model, related to time and space, of the metamorphism of an original carnallitic potash bed and subsequent K-Mg-Cl mineralization of the deck halite. The original paragenesis kieserite-halite-carnallite, sedimented in the deeper parts of the basin, was altered to the present kieseritic hard salt by means of progressive geothermal metamorphism from Upper Triassic to Lower Cretaceous. The hanging wall of the potash bed, the deck halite, was mineralized by the metamorphic solutions, squeezed out from the potash bed, possibly during the diapiric penetration phase in Upper Jurassic - Lower Cretaceous.
Diagenesis of the Gassum Formation Rhaetian-Lower Jurassic, Danish Subbasin
The Upper Triassic-Lower Jurassic Gassum Formation is a shallow marine or deltaic sandstone body with intercalated mudstones. The sandstones are primarily arkoses and subarkoses, but the composition is strongly influenced by diagenesis. Depths of burial vary between ea. 550 m and 3350 m, and the diagenetic modifications are strongly dependent on depth. The diagenetic pattern is also related to primary lithology. At shallow depth of burial, the most important diagenetic changes are compaction, calcite cementation, formation of kaolinite, and dissolution of feldspar. In deeply buried parts of the formation, the most important diagenetic changes are reduction of primary and secondary porosity by strong cementation by quartz, albitization of partly dissolved feldspar and ankerite cementation. In chlorite-cemented parts, quartz cementation was inhibited, and here pressure solution occurred in deep parts of the formation. The porosity in these deeply buried samples may be reduced to secondary intragranular porosity in partly dissolved feldspar and intercrystalline porosity in clay mineral cements. Other diagenetic minerals are siderite, pyrite, anhydrite, potassium feldspar and illite. The diagenesis evolved through the eodiagenesis and the immature and semimature stages of mesodiagenesis, whereas mature stages have not been reached.
Lower Cretaceous dinoflagellate biostratigraphy in the Danish Central Trough
This study deals with Lower Cretaceous biostratigraphy based on dinoflagellates in the Central Trough (Danish North Sea sector). The stratigraphical distribution in Northwestern Europe of the species used in the analysis is evaluated on the basis of the literature, and a dinoflagellate range chart for the Lower Cretaceous of Northwestern Europe is presented. Two wells, Adda-1 and 1-1, containing a complete marine Lower Cretaceous sequence, are biostratigraphically analysed, primarily on the basis of ditch cutting samples. All six Lower Cretaceous stages are identified and their probable positions in the wells are indicated. Additional sections which cover minor parts of the Lower Cretaceous are analysed in the wells M-8, V-1, E-1 and Adda-2 (mainly based on cores and sidewall cores). The ammonite Simbirskites (Craspedodiscus) cf. gottschei, indicating the Hauterivian gottschei Zone, is described from the Adda-2 well. The lithostratigraphical and seismic stratigraphical units of the Central Trough are dated within the framework of dinoflagellate and ammonite stratigraphy. The dinoflagellate species are systematically documented in photographic plates with remarks concerning their identification where necessary. udy deals with Lower Cretaceous biostratigraphy based on dinoflagellates in the Central Trough (Danish North Sea sector). The stratigraphical distribution in Northwestern Europe of the species used in the analysis is evaluated on the basis of the literature, and a dinoflagellate range chart for the Lower Cretaceous of Northwestern Europe is presented. Two wells, Adda-1 and 1-1, containing a complete marine Lower Cretaceous sequence, are biostratigraphically analysed, primarily on the basis of ditch cutting samples. All six Lower Cretaceous stages are identified and their probable positions in the wells are indicated. Additional sections which cover minor parts of the Lower Cretaceous are analysed in the wells M-8, V-1, E-1 and Adda-2 (mainly based on cores and sidewall cores). The ammonite Simbirskites ( Craspedodiscus) cf. gottschei, indicating the Hauterivian gottschei Zone, is described from the Adda-2 well. The lithostratigraphical and seismic stratigraphical units of the Central Trough are dated within the framework of dinoflagellate and ammonite stratigraphy. The dinoflagellate species are systematically documented in photographic plates with remarks concerning their identification where necessary.
Jurassic - Lower Cretaceous of the Danish Central Trough; - depositional environments, tectonism, and reservoirs
A revised model for the Jurassic - Early Cretaceous basin development in the Danish Central Trough is described on the basis of new studies of the bio- and lithostratigraphy and sedimentological and seismic data. The trough has been subdivided into a number of areas, each characterized by specific structural evolution. Middle Jurassic fluvio-deltaic and coastal sands follow the mid Cimmerian unconformity and probably cover large parts of the trough. Right-lateral movements, initiated during the Late Jurassic along WNWESE trending faults, caused fault controlled basin subsidence. The Jurassic and early Early Cretaceous sedimentation were dominated and characterized by clay. More than 4000 m of clay were deposited. Organic carbon rich clays were deposited from the Kimmeridgian until the Late Ryazanian, when deposition of organic carbon poor sediments under oxygenated conditions commenced. During the Late Jurassic transgression coastal sands were deposited along tectonically quiet basin margins. Sands deposited from density currents accumulated along tectonically active margins at the Jurassic-Cretaceous transition. More centrally in the basins, more distal turbidite deposits of Late Jurassic age may be present. Early Cretaceous basin expansion caused by elevation of the sea-level led to decreasing siliciclastic deposition rates and hence to more calcareous sediment types. Contemporaneously basin subsidence decreased. At mid Hauterivian time the importance of differential subsidence governed by left-lateral transtensional wrenching along NNW-SSE trending faults decreased. This change was accompanied by a mild inversion controlled by NNW-SSE directed right-lateral transpression, heralding regional subsidence. Following this inversion chalk was deposited in almost the entire trough area. Later, during the Barremian and Aptian anoxia in the basin caused deposition of marls rich in organic carbon, followed by marls deposited under oxygenated conditions during the Albian transgression. The distribution and character of possible reservoir bodies are discussed.
The diagenesis of the Lower Triassic Bunter Sandstone Formation, Onshore Denmark
The Lower Triassic Bunter Sandstone Formation is a continental redbed sequence deposited under arid to semi-arid conditions in a low-energy, fluviatile-aeolian sabhka environment. The sediments display many diagenetic features in common with modern and ancient redbeds deposited under similar conditions, but local influences on the diagenetic assemblage by factors such as provenance, structural setting and depositional environment can be ascertained. With burial depths of only 1000-2000 meters, effects of compaction are limited, high intergranular porosities remain, and no clear depth-related patterns are noted. The diagenetic assemblage consists of quartz and feldspar overgrowths, Fe-Ti oxides, carbonates (calcite and dolomite), analcime, authigenic clays, anhydrite and halite. The distribution of authigenic minerals is controlled by sedimentary facies, with greater amounts of poikilotopic anhydrite and halite in sandstones and more abundant dolomite and analcime in claystones and heterolithic sands. In addition, the replacement of ferromagnesian minerals by mixed-layer clays results in the greater abundance of these clays in sandstones relative to claystones. A well-preserved eogenetic assemblage consisting of albite and quartz overgrowths, analcime, dolomite, calcite, gypsum and clays is indicative of highly evaporative conditions and may reflect higher sodium concentrations in the depositional brines associated with the more basinal, low-energy parts of the depositional environment. Such concentrated brines strongly influenced the diagenetic pathways. In contrast, anhydrite and halite are the product of mesogenetic reactions in association with late stage Zechstein brines which invaded the more permeable sands during halokinesis. The strength and character of the depositional brine is an early control on subsequent diagenetic evolution. Within the specific geochemical regime of a given lithofacies, selective reactions occur which characterize particular microenvironments. These reactions impart an early eogenetic imprint upon later diagenetic events.
Palynology of the Middle Jurassic Lower Graben Sand Formation of the U-1 well, Danish Central Trough
Twentyone sidewall core samples from the lower 56 metres of the Lower Graben Sand Formation in the U-1 well are described with respect to their kerogen content and microflora in order to gain a better understanding of the depositional environment and the age relations. Based on e.g. the inconsistent dinoflagellate cyst occurrences, marginal marine conditions are concluded. The dinoflagellate cysts Pareodinia prolongata, Acanthaulax senta, Scriniodinium crystallinum, Energlynia acollaris, Wanaea thysanota and Hystrichogonyaulax cladophora and the recovered palynomorph assemblage in general permit an age determination as follows: 21 m Callovian undifferentiated, 7.9 m latest Middle Callovian - earliest Late Callovian, 6.1 m latest Late Callovian and 21 m latest Late Callovian? - earliest Early Oxfordian.
Seismic structural mapping of the Middle and Upper Jurassic in the Danish Central Trough
The Middle and Upper Jurassic of the Danish Central Trough have been studied by the use of seismic structural mapping. The area studied is divided into the following structural elements which are the Ringkøbing-Fyn High, the Mid North Sea High, the Mads High (new name), the Inge High (new name), the Mandal High, the Tail End Graben, the Arne-Elin Graben (new name), the Feda Graben, the Gertrud Graben (new name), the Salt Dome Province, the Sogne Basin, the Pout Plateau (new name), the Heno Plateau (new name), the Outer Rough Basin, the Grensen Nose, and the Gert Ridge (new name). These structural elements are described individually. The structural framework is demonstrated to be dominated by north-south trending normal faults and northwest-southeast trending right-lateral strike-slip faults. The most active rifting phases in the Mesozoic period took place during the Middle and Late Jurassic. The tectonic activity ceased during the Late Jurassic in the southern part of the Danish Central Trough, while in the northern part the activity continued into the Early Cretaceous. During the Late Cretaceous and Early Tertiary the faults were reactivated by inversion caused by transpression related to the formation of the Alpine Fold Belt.
Jurassic - Lower Cretaceous lithostratigraphic nomenclature for the Danish Central Trough
The Jurassic and Lower Cretaceous sequences have been subdivided into lithostratigraphic units. The subdivision is primarily based on interpretation of petrophysical logs like gamma ray, sonic, neutron and density logs. The lithology descriptions are based on evaluation of logs and descriptions of cuttings samples, in a few intervals supplemented by sedimentological characteristics interpreted from core samples. Biostratigraphic analyses as well as seismic interpretations have been used for correlation from well to well and for description of the sediment bodies. As far as possible the lithostratigraphic units established in the adjacent regions have been extended into the Danish region. In the Jurassic sequence the following new formations are established: Lola Formation, Heno Formation, and Poul Formation. Furthermore, a hot unit is separated from the Farsund Formation. The Lower Cretaceous Valhall Formation is slightly emended, as the new Tuxen Formation and Sola Formation are separated from it. The lowest part of the Valhall Formation is defined as the Leek Member. Finally, the Vyl Formation is established as a formation marginal to the basin.
Seismic stratigraphy and tectonic evolution of the Lower Cretaceous in the Danish Central Trough
The Lower Cretaceous sequence of the Danish Central Trough has been studied by the use of seismic stratigraphic analysis. The sequence has been subdivided into 6 seismic stratigraphic units named LCA, LCB, LCC, LCD, LCE and LCF. The studied area includes the Feda Graben, the Gertrud Graben (new name), the Tail End Graben, the Arne-Elin Graben (new name) and the Salt Dome Province, whereas the Grensen Nose and the Outer Rough Basin are not included. These basins are separated by the Inge High, the Mads High, the Gert Ridge (new name), the Manda! High, the Heno Plateau (new name) and the Pollerne Ridge (new name). The fault controlled subsidence of the Lower Cretaceous basins is claimed to have been governed by left lateral transtensional wrenching. This wrenching gradually ceased and gave way to regional subsidence with intermittent events of inversion resulting from right lateral transpressive wrenching in the Late Cretaceous and Early Tertiary. The first weak inversion is shown to have occurred in the Late Hauterivian. Sedimentation was influenced by a general gradual relative rise in sea-level starting with a low in the Volgian - Early Ryazanian times coeval with the deposition of the Farsund Formation and culminating in the Late Cretaceous. At the beginning of the Early Cretaceous gravity flow became an important depositional mechanism and resulted in preferred deposition in topographical lows, which were generated by simple tensional block-faulting or by wrench-induced, rapid local subsidence. As tectonic activity decreased and the elastic source areas became more remote and worn down, depocentres became less pronounced, especially with the last unit of the Lower Cretaceous.
Petrography of the quartz sand deposits of the Lower Cretaceous of Bornholm, Denmark
The quartz sand of the Lower Cretaceous Robbedale Formation and lowermost part of the Jydegard Formation in the Arnager-Sose fault block of Bornholm has been investigated with respect to mineralogy, grain-size, grain rounding and grain shape. Analyses of both light and heavy minerals have been carried out for 18 samples from different localities and facies. The purpose of the investigation was to try to recognize the possible types of source rocks and provenance areas. The Precambrian basement rocks of Bornholm are not the main sources of the sand, especially not the heavy minerals, but parts of the sand may have originated from the basement. The Palaeozoic sandstones and siltstones have delivered only a small amount of material. Parts of the older Mesozoic sediments of the Bornholm Group and Homandshald Member may have been redeposited in the Lower Cretaceous as they contain the same kinds of heavy minerals as the Robbedale and Jydegard Formations, although in differing amounts. It seems very possible, however, that most of the Mesozoic sediments of Bornholm have had a source area outside Bornholm, and this source area has been nearly the same during the whole span of time. The Fenno-Scandian Shield seems to be the most obvious provenance area, but eastern and southern areas are possibilities too. It is concluded that most of the Lower Cretaceous sands are first deposition cycle sediments of both local and distant origin combined with minor amounts of polycyclic sediments of mainly local origin.
Middle Jurassic deltaic and coastal deposits in the Lulu-1 well of the Danish Central Trough
Four cores from the Middle Jurassic Bryne Formation of the Lulu-I well in the northernmost part of the Danish Central Trough have been investigated. The cores were slabbed and a detailed description and facies analysis carried out. The cored sequence is very heterogeneous and includes beds of sand-, silt-, claystone, and coal. Seven facies are defined and the sequence is interpreted as sediments of a deltaic interdistributary bay and associated environments overlain by sediments of a coastal environment.
Seismic Stratigraphy and Tectonics of Sedimentary Basins around Bornholm Southern Baltic
Identification of structural elements in the offshore area around Bornholm has been possible with the use of reflection seismic data. The area straddles the Fennoscandian Borderzone, extending into the Danish Polish Trough. Major structural depressions are the Rønne Graben, the Arnager Graben (new name), the Christiansø Half-graben and the Hano Bay Basin. Structural highs are the Christiansø High, the Hammervand High, the Bornholm Gat Uplift, The Dueodde High (new name), the Southern Bornholm High (new name) and Bornholm High. The Palaeozoic sediments show rapidly increasing thicknesses to the south towards the Caledonian deformation front, and to the east towards the Peribaltic Syneclise. The present distribution of thick Palaeozoic sediments is however primarily a result of Late Palaeozoic–Early Mesozoic erosion. Occurences of Triassic, Jurassic and Lower Cretaceous sediments are primarily restricted to graben areas. These were generated in a Late Carboniferous-Early Permian tension dominated right-lateral wrench fault system parallel to the Tornquist line. The Mesozoic sediments of the above-mentioned ages were deposited in expanding basins interrupted by tectonic activity, which resulted in renewed restriction of sediments to graben areas accompanied by erosion on structural highs. Late Jurassic and Late Early Cretaceous tectonic events are identified. The most spectacular tectonic event is of an Early Tertiary age. The Rønne Graben and the Arnager Graben were subjected to compression in a right lateral fault system during this phase, and were subsequently uplifted and erosion occurred accompanied by reverse faulting and minor folding.
Dinoflagellate stratigraphy of the uppermost Danien to Ypresian in the Viborg 1 borehole, central Jylland, Denmark
Dinoflagellate cysts in the uppermost Danian to Lower Eocene section in the cored Viborg 1 borehole are described. The stratigraphical distribution of the dinoflagellates is shown; eight informal dinoflagellate zones are suggested. The dinoflagellate assemblages in sediments from various Danish localities are correlated with the Viborg 1 cores. A correlation with assemblages from other European Paleocene-Lower Eocene deposits is proposed. Two new species are described, and two new combinations are proposed.