Contents of 46/1
Erlström, M., Sivhed, U. & Surlyk F.:
A backstepping, fluviatile-paralic-marine succession, Sinemurian, Lower Jurassic, Skåne, southern Sweden
Pedersen, T., Gregersen, S. & the Tor Working Group:
Project Tor: Deep lithospheric variation across the Sorgenfrei-Tornquist Zone, Southern Scandinavia .
Tinn, O. & Meidla, T.:
Ordovician ostracodes from the Komstad Limestone
Madirazza, I.:
The formation of the Voldum salt pillow in the Danish Zechstein basin, Jutland (Denmark)
Bromley, R.G., Ekdale, A.A. & Richter, B.:
New Taenidium (trace fossil) in the Upper Cretaceous chalk of northwestern Europe .
Pulvertaft, T.C.R.:
NOTE, “Paleocene” or “Palaeocene”
Pacaud, L-M. & Schnetler, K.I.:
Revision of the gastropod family Pseudolividae from the Paleocene of West Greenland and Denmark
Riisager, J., Riisager, P. & Perrin, M.:
Palaeodirectional and palaeointensity results of Paleocene and Eocene basalts from West Greenland
Japsen, P. & Bidstrup, T.:
Quantification of late Cenozoic erosion in Denmark based on sonic data and basin modelling
Houmark-Nielsen, M.:
A lithostratigraphy of Weichselian glacial and interglacial deposits in Denmark
Surlyk, F. & Nielsen, J.M.:
The last ammonite?
Contents of Volume 46/2
Skjernaa, L.:
Festskrift i anledning af professor Asger Berthelsens 70 års fødselsdag den 30. april 1998
Pedersen, S.A.S.:
Superimposed deformation in glaciotectonics .
Wahlgren, C.-H. & Stephens, M.B.:
Structural and geochronological evolution of the northeastern part of the Sveconorwegian orogen, south-central Sweden
Hageskov, B. & Mørch, B.:
Adakitic high-Al trondhjemites in the Proterozoic Østfold-Marstrand Belt, W Sweden .
Pedersen, S. & Konnerup-Madsen, J.:
Geology of the Setesdalen area, South Norway: Implications for the Sveconorwegian evolution of South Norway
Skjernaa, L. & Pedersen, S.:
Late Sveconorwegian monzonitic dykes in the Setesdalen area of Central South Norway: Examples of structures in dykes and their indications of accumulated strain
A backstepping, fluviatile-paralic-marine succession, Sinemurian, Lower Jurassic, Skåne, southern Sweden
Erlström, M., Sivhed, U. & Surlyk, F.: A backstepping, fluviatile-paralic-marine succession, Sinemurian, Lower Jurassic, Skåne, southern Sweden. Bulletin of the Geological Society of Denmark, Vol. 46, pp 1–12. Copenhagen, 1999–12–20
https://doi.org/10.37570/bgsd-1999-46-01
Abstract: A temporal exposure of a Lower Sinemurian succession of fluviatile, coastal plain and marine sediments was accessible for study during a short time interval in 1997 at Örby, NW Skåne, Sweden. The succession adds significantly to the knowledge and understanding of the Sinemurian sedimentary evolution of the Fennoscandian Border Zone and the north-eastern margin of the Danish Basin. The top of the section overlaps the base of a section previously exposed at the nearby quarry at Gantofta. The combined evidence from Örby, Gantofta and a few borings shows that Sinemurian sedimentation took place during marked stepwise transgression. This is recorded by backstepping of the depositional environments from braided streams, over lakes and swamps, to estuarine and finally fully marine, offshore conditions. The sedimentary packages of the individual systems are well defined and separated mainly by sharp boundaries representing lacustrine, estuarine and marine flooding and ravinement surfaces. A regional sea-level rise punctuated by a minor fall is suggested to be the main factor controlling Early Jurassic basin evolution of the northeastern margin of the Danish Basin and the Fennoscandian Border Zone.
Keywords:Sedimentology, petrography, biostratigraphy, sequence stratigraphy, Rya Formation, Döshult Member, Skåne, Danish Basin.
Addresses:
M. Erlström [mikael [dot] erlstrom [at] sgu [dot] se], U. Sivhed [ulf [dot] sivhed [at] sgu [dot] se], Geological Survey of Sweden, Kiliansgatan 10, SE-223 50 Lund, Sweden. F. Surlyk [finns [at] geo [dot] geol [dot] ku [dot] dk] Geological Institute, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark. 12 October 1998.
Project Tor: Deep lithospheric variation across the Sorgenfrei-Tornquist Zone, Southern Scandinavia
Pedersen, T., Gregersen, S. & the Tor Working Group: Project Tor: Deep lithospheric variation across the Sorgenfrei-Tornquist Zone, Southern Scandinavia. Bulletin of the Geological Society of Denmark, Vol. 46, pp. 13–24. Copenhagen, 1999–12–20.
https://doi.org/10.37570/bgsd-1999-46-02
Abstract: The Tor project makes use of teleseismic tomography across the Sorgenfrei-Tornquist Zone and has now revealed significant variations in the deep lithosphere under northern Germany, Denmark and southern Sweden. Here we present the first interpretations of P-wave traveltime anomalies from the Tor project. The project utilised 120 seismographs placed in a rectangular array, the largest seismic antenna so far used in Europe, for half a year in the period 1996–1997.
The present investigation establishes a 3D crustal/upper mantle model of the P-wave velocity based on existing data. A picture of the crustal influence on the seismic P-wave rays is established by ray tracing through the model. When this is subtracted from that observed by the Tor array, a picture of the influence of the lower lithosphere/asthenosphere system emerges. For several earthquakes it is shown that the observed P-wave traveltime anomalies of nearly 2 seconds can be divided almost equally between known crustal effects and lower lithosphere/asthenosphere differences. The transition appears gradual from most directions but for rays coming from the north-east direction the transition appears sharper. This means that the broad scale deep lithosphere transition is gradual with the sharpest discontinuity plane dipping down steeply in a north-easterly direction from the Sorgenfrei-Tornquist Zone. Based on existing knowledge of the area we conclude that the transition from thin to thick lithosphere occurs within a short distance, and that the lithosphere/asthenosphere boundary dips steeply down from the surface expression of the Sorgenfrei-Tornquist Zone.
Keywords: Tor project, deep lithospheric variation, lithosphere/asthenosphere boundary, Sorgenfrei-Tornquist Zone, 3D crustal model.
Addresses:
Trine Pedersen & Søren Gregersen, Geodynamics Department, Kort & Matrikelstyrelsen, Rentemestervej 8, DK-2400 Copenhagen NV. 20 June 1999.
Ordovician ostracodes from the Komstad Limestone
Tinn, O. & Meidla, T.: Ordovician ostracodes from the Komstad Limestone. Bulletin of the Geological Society of Denmark, Vol. 46, pp. 25–30. Copenhagen, 1999–12–20. https://doi.org/10.37570/bgsd-1999-46-03
Abstract: The results of a pilot study on late Arenigian ostracodes of Bornholm, Denmark,
are reported. The hard thermally altered limestone was disintegrated with sodium hyposulphite, the yielded ostracode material is of satisfactory preservation. The ten identified genera include palaeocopes (Glossomorphites, Aulacopsis, Ctenentoma, Asteusloffia, Euprimites), eridostracans (Conchoprimitia), cytherelliformes (Unisulcopleura) and metacopes (Elliptocyprites, Longiscula, Microcheilinella and “Silenis”). The studied ostracode assemblage shows resemblance to that of the Central Baltoscandian Confacies Belt.
Keywords: Ordovician, Komstad Limestone, ostracodes, Bornholm, Skelbro
Addresses:
Oive Tinn & Tõnu Meidla [ otinn [at] math [dot] ut [dot] ee ; tmeidla [at] math [dot] ut [dot] ee ], Institute of Geology. University of Tartu. Vanemuise 46, Tartu, 51014, Estonia. 29 March 1999.
The formation of the Voldum salt pillow in the Danish Zechstein basin, Jutland (Denmark)
Madirazza, I: The formation of the Voldum salt pillow in the Danish Zechstein basin, Jutland. Bulletin of the Geological Society of Denmark, Vol. 46, pp. 31–46, Copenhagen, 1999–12–20. https://doi.org/10.37570/bgsd-1999-46-04
Abstract: On the basis of seismic and well data, supported by Bouguer gravity data, the sequence of events leading to the formation of a Zechstein salt pillow – called Voldum – in east central Jutland is discussed (the study area is delimited in Fig. 1). The initial salt movements, activated by faulting in the Triassic, resulted in the formation of a minor salt pillow on the edge of a graben within the Zechstein (Upper Permian) basin. During a renewed faulting (Voldum fault) of the base Zechstein in Late Jurassic and consequent deepening of the graben, a syncline developed above the salt where thick sediments of Late Jurassic age accumulated. In the process large quantities of salt, due to differential loading, withdrew from the graben and moved laterally up-dip across the older fault scarps. Thus a new and larger salt accumulation (Voldum pillow) formed above the southern flank of the graben. A relict Triassic thin, formed during the growth of the first pillow, remains, but no salt accumulation which could account for this thin is present. The Voldum pillow continued to grow during the Cretaceous and the Tertiary, but the speed of growth decreased considerably during post-Late Cretaceous times, although there are still large quantities of, virtually undisturbed, salt present south of the pillow in the part of the basin corresponding to the Silkeborg Gravity High. The graben area apparently underwent a mild inversion at the close of the Cretaceous. The reasons why the Voldum pillow did not develop into a diapir are considered to be a strong and thick overburden which existed at the beginning of the Voldum pillow formation, the deeply buried salt which probably acted as a deterrent to the rupture of the overburden, and the nature of the Voldum fault which, apparently, had an appreciable strike-slip component in dextral sense.
Keywords: Danish Zechstein basin, Voldum fault, Voldum salt pillow, reflection seismic and gravity data, Silkeborg Gravity High.
Addresses:Ivan Madirazza, Department of Earth Sciences, University of Aarhus, Finlandsgade 8, DK-8200 Aarhus N, Denmark, 7 June 1999.
New Taenidium (trace fossil) in the Upper Cretaceous chalk of northwestern Europe
Bromley, R. G., Ekdale, A. A. & Richter, B.: New Taenidium (trace fossil) in the Upper Cretaceous chalk of northwestern Europe. Bulletin of the Geological Society of Denmark, Vol. 46, pp. 47–51. Copenhagen, 1999–12–20. https://doi.org/10.37570/bgsd-1999-46-05
Abstract: A meniscate backfilled trace fossil that is common in Upper Cretaceous chalk of Denmark, Germany and England is described as the new ichnospecies, Taenidium crassum. This ichnotaxon is differentiated from other ichnospecies of the ichnogenus on the basis of the irregular, asymmetrical menisci in the backfill.
Keywords: Taenidium, chalk, flint, Upper Cretaceous, new ichnospecies T. crassum, ichnotaxonomy.
Addresses:K, Denmark. A. A. Ekdale, Department of Geology and Geophysics, University of Utah, Room 719, 135 South 1460 East, Salt Lake City, UT 84112-0111, U.S.A. Bjarni Richter, Orkustofnun (National Energy Authority), Geoscience Department, Grensásvegi, 108 Reykjavik, Iceland. 10 May 1999.
Note: “Paleocene” or “Palaeocene”
Pulvertaft, T.C.R.: Note, Bulletin of the Geological Society of Denmark Vol. 46, p. 52. Copenhagen 1999-12-20.
https://doi.org/10.37570/bgsd-1999-46-17
Abstract: There seems to be some doubt as to which of the spellings “Paleocene” or “Palaeocene” should be used in manuscripts submitted for publication in Europe, while in North America the spelling “Paleocene” is standard. The latter is not surprising, as in North America the prefix paleo- is also used in terms such as Paleozoic, paleomagnetism, etc. In Europe, however, the
prefix derived from the Greek palaios (= ancient, old) is generally spelt “palaeo-”, as for example in palaeontology……………….
Addresses:
T.C.R. Pulvertaft, Geological Survey of Denmark and Greenland (GEUS), Thoravej 8, DK-2400 Copenhagen NV, Denmark. 6 May 1999.
Revision of the gastropod family Pseudolividae from the Paleocene of West Greenland and Denmark
Pacaud, J.-M. & Schnetler, K. I.: Revision of the gastropod family Pseudolividae from the Paleocene of West Greenland and Denmark. Bulletin of the Geological Society of Denmark, Vol. 46, pp. 53–67. Copenhagen, 1999–12–20. https://doi.org/10.37570/bgsd-1999-46-06
Abstract: The Paleocene deposits on the Nuussuaq peninsula (West Greenland) contain three new species belonging to the family Pseudolividae de Gregorio, 1880. Popenoeum lacunosum sp. nov., Pseudoliva praetermissa sp. nov. and Fusulculus nanapullus sp. nov. are described. The species Fusulculus koeneni (Ravn, 1939) from the Paleocene (Selandian) of Denmark is revised, a lectotype is designated and new figures are published.Pseudoliva (Fusopsis) canalifera Ravn, 1939 is excluded from the Pseudolividae and Fusopsis is considered to be a subjective junior synonym of Suessionia Cossmann, 1889, and therefore reassigned to the family Buccinidae Rafinesque, 1815.
Keywords: Gastropods, Pseudolividae, new species, Paleocene, West Greenland, Denmark.
Addresses:
J.-M. Pacaud, Laboratoire de Paleontologie, Muséum National d’Histoire Naturelle, 8 rue de Buffon, F- 75005 Paris, France. K.I. Schnetler, Fuglebakken 14, Stevnstrup, DK-8870 Langå, Denmark. 12 October 1998.
Palaeodirectional and palaeointensity results of Paleocene and Eocene basalts from West Greenland
Riisager, J., Riisager, P. & Perrin, M.: Palaeodirectional and palaeointensity results of Paleocene and Eocene basalts from West Greenland. Bulletin of the Geological Society of Denmark, Vol. 46, pp. 69–78. Copenhagen, 1999–12–20.
https://doi.org/10.37570/bgsd-1999-46-07
Abstract: Twelve sites (57 drill cores) from two lava series and one dike were sampled for a palaeomagnetic study of the late Paleocene and early Eocene West Greenland flood basalts. Most of the rocks exhibited well-defined one component remanent magnetization with high unblocking temperatures (mostly above 500°C) and high median destructive fields (30–40 mT). All the rocks are reversely magnetized and, when combined with 40Ar/39Ar ages (Storey et al. 1998), a direct correlation with the geomagnetic polarity time scale can be made.
Rock magnetic experiments indicate varying degree of both high temperature (deuteric) and low temperature (hydrothermal) oxidation of primary titanomagnetite. Twenty-three samples with high Curie point (~570°C) were chosen for Thellier palaeointensity experiments. Eleven of them, coming from three different cooling units, yielded reliable palaeointensity estimates. The results are reasonably coherent within sites, and the site-mean virtual dipole moments (VDM) are 1.8, 9.0 and 15.4×1022Am2 . The lowest VDM most probably corresponds to the ~94 ka long C24n.1r subchron, while the two other VDM’s close to present-day and higher than present-day values correspond to chrons C26r and C24r respectively.
Keywords: West Greenland, Palaeomagnetism, Magnetostratigraphy, Palaeointensity, Thellier method, Tertiary
Addresses:
Janna Riisager & Mireille Perrin, Laboratoire de Géophysique et Tectonique, UMR CNRS 5573, Université Montpellier II, Case 060, 34095 Montpellier Cedex 5, France; Peter Riisager [pri [at] dlc [dot] ku [dot] dk], Danish Lithosphere Centre, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark. 8 March 1999.
Quantification of late Cenozoic erosion in Denmark based on sonic data and basin modelling
Japsen, P. & Bidstrup, T.: Quantification of late Cenozoic erosion in Denmark based on sonic data and basin modelling. Bulletin of the Geological Society of Denmark, Vol. 46, pp. 79–99. Copenhagen, 1999–12–20. https://doi.org/10.37570/bgsd-1999-46-08
Abstract: The amount of section missing because of late Cenozoic erosion is estimated using basin modelling and sonic data from four stratigraphic levels in 68 Danish wells, and is found to be smaller than estimated in previous studies. The missing section increases from zero in the western and southern part of the Danish North Sea to 1000–1200 m towards north-east, on and along the Skagerrak-Kattegat Platform. In a broad intermediate zone, c. 500 m of mainly Paleocene–Miocene sediments are missing where Paleocene sediments subcrop the Quaternary. On the Skagerrak-Kattegat Platform, an additional c. 500 m Upper Cretaceous–Danian Chalk Group were removed where the lower parts of the Chalk are preserved, whereas the missing sediments must have been progressively younger towards south-west where Miocene sediments subcrop the Quaternary. The deep erosion on and along the Skagerrak-Kattegat Platform documents that Neogene uplift and erosion affected the study area prior to glacial erosion during the Quaternary. These results are consistent with Neogene uplift of south Norway as well as of south Sweden centred around the South Swedish Dome that culminates north-east of the Kattegat. There is good correlation between estimates of erosion based on Chalk velocities and on basin modelling. Comparison of different methods indicates that erosion is overestimated when based on sonic data from Lower Jurassic shale in north-eastern Denmark, and this could be due to lithological differences. It is concluded that maximum burial of the Mesozoic succession occurred prior to Neogene erosion throughout the area, and a previous suggestion of deep erosion in the Sorgenfrei-Tornquist Zone during the Late Cretaceous-Paleogene inversion is rejected.
Keywords: North Sea Basin, uplifts, erosion, Neogene, velocity, vitrinite reflectance, basin analysis
Addresses:
Peter Japsen [ pj [at] geus [dot] dk ] & Torben Bidstrup [ tb [at] geus [dot] dk ], Geological Survey of Denmark and Greenland (GEUS), Thoravej 8, DK-2400 Copenhagen NV. 19 April 1999.
A lithostratigraphy of Weichselian glacial and interstadial deposits in Denmark
Houmark-Nielsen, M.: A lithostratigraphy of Weichselian glacial and interstadial deposits in Denmark. Bulletin of the Geological Society of Denmark, Vol. 46, pp. 101–114. Copenhagen, 1999–12–20. https://doi.org/10.37570/bgsd-1999-46-09
Abstract: A lithostratigraphic model of Weichselian tills and inter-till deposits in Denmark is erected. Deposits comprise 1) Till, other diamicts and meltwater sediments deposited during glaciated stadials and 2) Interstadial and stadial fluvial, lacustrine and marine sediments deposited under climatic ameliorations and ice free conditions. Stratigraphic successions are correlated using lithological and palaeoecological evidence and they are linked to the marine sequences in northern Denmark named the Skærumhede series.
Three stadials with one or more glaciation events succeeding Eemian interglacial conditions have been recognized. The oldest, Ristinge stadial, is most likely from the early Middle Weichselian situated between the Odderade and Moershoofd interstadials. It comprises The Ristinge, Ringshøj and Lovns tills of Baltic origin is found in the eastern and central parts of Denmark. The post-Hengelo, Klintholm stadial from the late Middle Weichselian, is represented by the Baltic Klintholm till found in the easternmost part of the country and possibly the Esrum diamicton in the buried Esrum valley belong to this stadial. The post-Sandnes interstadial, Late Weichselian Jylland stadial comprise the Kattegat Till of Norwegian provenance is found in northern Denmark. It is followed by the Mid Danish, Grenå, Fårup, Store Klinthøj, Himmerland tills of middle Swedish origin, and deposited by the ice-stream which reached the Main Stationary Line from northeasterly directions. The East Jylland and North Sjælland tills of respectively Baltic and Swedish provenance overlie the former tills in eastern Denmark. These are succeeded by the Bælthav Till of Baltic origin which is confined to the Danish islands. Late glacial deposits from the Bølling-Allerød oscillation comprises the upper boundary for Weichselian deposits.
The compilation of the stratigraphic model serves the purpose of combining and bringing forward regional and local stratigraphic studies from the past decades and to set up a frame-work for dating the age and duration individual glaciation events and interstadials.
Keywords: Lithostratigraphy, Weichselian, Denmark, relative glaciation chronology.
Addresses:
M. Houmark-Nielsen, Geological Institute, University of Copenhagen, DK-1350 Copenhagen, Denmark. 18 January 1999.
The last ammonite?
Surlyk, F. & Nielsen, J. M.: The last ammonite? Bulletin of the Geological Society of Denmark, Vol. 46, pp. 115–119. Copenhagen, 1999–12–20. https://doi.org/10.37570/bgsd-1999-46-10
Abstract: A fragment of red-brown flint with imprints of two ammonite aptychi has been found loose on the beach of the Boesdal quarry on Stevns Klint. The quarry exposes only Lower Danian bryozoan limestone. The nearest occurrence of Maastrichtian strata is 400 m to the west in Skeldervig bay, north of Korsnæb, where 50 cm of chalk with small dark-grey and black flint nodules are exposed below the basal Danian Fish Clay over a stretch of 15 m. Maastrichtian chalk is normally dark-grey to black and has a thin white rind. Danian flint is much more variable in colour and degree of silicification, and red-brown varieties are common. The two aptychi clearly belong to the same ammonite individual and cannot have been redeposited from the crests of the top-Maastrichtian mounded bryozoan chalk. Finds of the ammonite Hoploscaphites constrictus and Baculites sp. have been reported in the literature from the lowermost Danian Cerithium Limestone. They are normally considered reworked, but their age should possibly be re-evaluated in the light of the new find. It is thus very likely that two ammonite genera survived the mass extinction at the K-T boundary and lived on as rare elements in the earliest Tertiary fauna.
Keywords: K-T boundary, extinction, aptychus, ammonite, Danian, Stevns Klint, Denmark.
Addresses:
Finn Surlyk [ finns [at] geo [dot] geol [dot] ku [dot] dk ] & Jesper Milan Nielsen, Geological Institute, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark. 22 March, 1999.
Festskrift i anledning af professor Asger Berthelsens 70 års fødselsdag den 30. april 1998
Skjernaa, L.: Festskrift i anledning af professor Asger Berthelsens 70 års fødselsdag den 30. april 1998. Bulletin of the Geological Society of Denmark, Vol. 46, pp. 121–123. Copenhagen.
https://doi.org/10.37570/bgsd-1999-46-18
Abstract: This volume is in honour of Professor Asger Berthelsen on the occasion of his 70th birthday. Asger Berthelsen has made important contributions within the areas of basement geology, tectonics, structural geology, Quaternary geology, salt tectonics and deep seismic interpretations. He is an outstanding writer and illustrator.
Addresses:
L. Skjernaa [ lilians [at] geo [dot] geol [dot] ku [dot] dk ] Geological Institute, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark. 7. January 2000.
Superimposed deformation in glaciotectonics
Pedersen, S.A.S.: Superimposed deformation in glaciotectonics. Bulletin of the Geological Society of Denmark. Vol. 46, pp. 125–144, Copenhagen. https://doi.org/10.37570/bgsd-1999-46-11
Abstract: The identification of glaciotectonic structures is an exclusive field for the structural geologist. The structures comprise a series of different types and regimes. The sequential development of the glaciotectonic structures reflects superimposed subglacial and proglacial deformation processes. The glaciotectonic structures may involve earlier formed structures thus superimposed by the glaciotectonics, or the glaciotectonic structures may eventually be overprinted by neotectonic deformations. Four different superimposed settings may be distinguished: 1) glaciotectonic deformation superimposed on pre-Quaternary tectonics, 2) glaciotectonic deformation superimposed on earlier formed glaciotectonic structures (superimposed deformation involving two or more glaciodynamic events), 3) glaciotectonic deformations superimposed sequentially in the same glaciotectonic unit (two or more glaciotectonic phases in the same glaciodynamic event), and finally 4) neotectonic deformation superimposed on glaciotectonic structures. Examples of type 1 are taken from the deformed Palaeogene diatomites with ash layers at Hanklit, Mors, and Hestegården, Fur. Dokumentation of glaciotectonic deformation superimposed on halokinetic structures is demonstrated from Erslev, Mors, and further examplified by structures occurring at Junget on the north side of the Batum salt diapir in Salling. Type 2 is examplified by glaciotectonic structures in the Skarrehage mo-clay pit on Mors. An example of Elsterian glaciotectonics superimposed by Saalian glaciotectonics is recorded from the hilly island Møborg, central part of western Jylland. The classic glaciotectonic site Møns Klint is described as a combination of an imbricate fan and an antiformal stack formed by the Young Baltic ice advance in the Late Weichselian superimposed by a regressional re-advance from the east. Type 3 is exemplified by the glaciotectonic complex at Feggeklit. Type 4 is described from the island of Fur where glaciotectonic structures are cut by neotectonic faults roughly parallel to the main E-W trend of Limfjorden.
Keywords: Glaciotectonics, superimposed deformation, structural geology, Quaternary geology.
Addresses:
S.A. Schack Pedersen [ sasp [at] geus [dot] dk. ], Geological Survey of Denmark and Greenland, Thoravej 8, DK 2400 København NV. 18 January 1999.
Crustal structure and tectonic evolution of the Tornquist Fan region as revealed by geophysical methods
Thybo, H.: Crustal structure and tectonic evolution of the Tornquist Fan region as revealed by geophysical methods. Bulletin of the Geological Society of Denmark, Vol. 46, pp. 145–160. Copenhagen. https://doi.org/10.37570/bgsd-1999-46-12
Abstract: Crustal structure derived primarily from geophysical investigations reveals features that may be related to the complex tectonic evolution of the Tornquist Fan region. This northwestwards widening splay of Late Carboniferous – Early Permian fault zones in the Danish region emanates from the Teisseyre-Tornquist Zone in northern Poland. Seismic reflections and velocity anomalies image collisional fault zones that formed during the Proterozoic and Palaeozoic amalgamation of the crust. Re-equilibration of Moho appears to have taken place before late Palaeozoic rifting and magmatism initiated the main phase of basin formation that continued into the Mesozoic. The resulting, strong Moho topography, with variation between depths of 26 and 48 km, has been practically “frozen in” since then, although the late Cretaceous – early Cenozoic inversion tectonics may have formed a crustal keel underneath part of the Sorgenfrei-Tornquist Zone which cuts across the Proterozoic crust of the Tornquist Fan region.
Keywords: Crust, Mantle, Geophysics, Seismic velocity, Tornquist Fan
Addresses:
Hans Thybo, Geological Institute, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark. 3 May 1999.
Structural and geochronological evolution of the northeastern part of the Sveconorwegian orogen, south-central Sweden
Wahlgren, C.-H. & Stephens, M.B.: Structural and geochronological evolution of the northeastern part of the Sveconorwegian orogen, south-central Sweden. Extended Abstract, Bulletin of the Geological Society of Denmark Vol. 46, pp. 161–163. Copenhagen 2000–02–10.
https://doi.org/10.37570/bgsd-1999-46-13
Abstract: An important tectonic model for the Sveconorwegian orogen north and northeast of Lake Vänern, south-central Sweden, was presented by Berthelsen (1980). Both the Mylonite Zone and the frontal area of the Sveconorwegian orogen were interpreted to be related to large-scale compressional tectonics. Earlier thrusting to the west was inferred to be followed by later thrust movement to the east.
Addresses:
Carl-Henric Wahlgren [ carl-henric [dot] wahlgren [at] sgu [dot] se ] & Michael B. Stephens, Geological Survey of Sweden, Box 670, SE-751 28 Uppsala, Sweden. 24 February 1999.
Adakitic high-Al trondhjemites in the Proterozoic Østfold-Marstrand Belt, W Sweden
Hageskov, B & Mørch, B.: Adakitic high-Al trondhjemites in the Proterozoic Østfold-Marstrand Belt, W Sweden. Bulletin of the Geological Society of Denmark, Vol. 46, pp. 165–179. Copenhagen. https://doi.org/10.37570/bgsd-1999-46-14
Abstract: This paper investigates the first identified intrusives in SE Norway–W Sweden with the specific signature of adakitic arc magmas, which in recent settings are preferably explained as partial melts extracted from subducted oceanic crust. The studied adakitic high–Al trondhjemites occur as sheets in the Koster archipelago, W Sweden, where they form the oldest recognized granitoids in the metasupracrustals of the Stora Le–Marstrand formation. The trondhjemites were intruded during a short ca. 1.59–1.58 Ga interlude between the early and the main orogenic events of the Gothian orogeny (1.6–1.56 Ga, Åhäll et al. 1998). This interlude is otherwise characterized by ‘ordinary’ calcalkaline magmatism which on Koster is predated by the trondhjemites.
The typical adakitic signature suggests that the trondhjemitic magma was extracted from a MORB (Mid Ocean Ridge Basalt) like source, and that a hornblende eclogite restite was left in the region of melting. The restite composition indicates melt extraction at PT conditions in the range of 18–25 kb/800°C to 13-15 kb/950–1050°C. These requirement can only be met by subduction of warm (young or shear heated) oceanic crust beneath a crust including early Gothian metamorphosed and deformed Stora Le–Marstrand formation or by melting of metabasaltic material at a deep crustal level. The latter is a less likely possibility and demands that the Stora Le–Marstrand formation at the time of melt extraction was part of a > 45 km thick crust.
Keywords: Adakites, high–Al trondhjemites, Mesoproterozoic, Gothian Complex, tectonics.
Addresses:
Bjørn Hageskov [ BjornH [at] Geo [dot] Geol [dot] KU [dot] DK ] and Bente Mørch, Geologisk Institut, Københavns Universitet, Østervoldgade 10, 1350 Copenhagen K, Denmark. 25 June 1999.
Geology of the Setesdalen area, South Norway: Implications for the Sveconorwegian evolution of South Norway
Pedersen, S. & Konnerup-Madsen, J.: Geology of the Setesdalen area, South Norway: Implications for the Sveconorwegian evolution of South Norway. Bulletin of the Geological Society of Denmark, Vol. 46, pp. 181–201, Copenhagen. https://doi.org/10.37570/bgsd-1999-46-15
Abstract: Crust forming processes in the Setesdalen area in the central part of southern Norway are dominated by the development of pre-Sveconorwegian supracrustal rocks (immature clastic sediments and bimodal volcanics) with an assumed depositional age of 1150–1100 Ma and by the emplacement of scattered infracrustal granitoids. The supracrustal rocks were deposited on a partly older than 1300 Ma gneissic basement including rocks which may have suffered one or more pre-Sveconorwegian orogeneses. During the Sveconorwegian orogeny, with the main upper greenschist to middle amphibolite facies high-temperature metamorphism and deformational phases in the period 1060–970 Ma, igneous activity comprising K-rich rocks high in elements such as P, Ti, La, Sr, Zr, and LREE and Ba was dominant. Significantly younger than this activity is the development of many REE pegmatites which are so characteristic for the region. The Precambrian geological activity terminated (at about 830 Ma?) with the development of E-W trending tholeiitic dolerites.
Keywords: Geochronology, granites, metagabbros, Norway, Precambrian, REE pegmatites, Sveconorwegian orogeny
Addresses:
Svend Pedersen & Jens Konnerup-Madsen, Geologisk Institut, Copenhagen University, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark. 22 June 1999.
Late Sveconorwegian monzonitic dykes in the Setesdalen area of Central South Norway: Examples of structures in dykes and their indications of accumulated strain
Skjernaa, L. & Pedersen, S.: Late Sveconorwegian monzonitic dykes in the Setesdalen area of Central South Norway: Examples of structures in dykes and their indications of accumulated strain. Bulletin of the Geological Society of Denmark. Vol. 46, pp. 203–223.
Copenhagen. https://doi.org/10.37570/bgsd-1999-46-16
Abstract: In the Setesdalen area, Central South Norway, a large number of monzonitic dykes and other minor bodies were intruded during the late stages of emplacement of Sveconorwegian magmatic complexes. Some of the dykes define cone sheet and bell-jar sheet systems. The dykes possess internal linear and planar fabrics, which are not seen in any of the host rocks. Also, cross-cutting granitic veins within the dykes are deformed and may show ptygmatic folds, whereas in the host rocks these same veins appear undeformed. The internal strain in the dykes was determined from vein deformation to be mainly simple shear with or without a volume reduction. The strain preferentially accumulated in the ductile monzonite dykes while the more rigid host rock blocks were passively displaced. In some cases, an additional minor component of flattening affected both the dykes and their host rocks.
Keywords: Foliated dykes, monzonite dykes, strain analysis, ptygmatic folds, cone sheets, bell-jar sheets, ring intrusion, central intrusion, Setesdalen, Sveconorwegian.
Addresses:
L. Skjernaa [ lilians [at] geo [dot] geol [dot] ku [dot] dk ] & S. Pedersen [svendp [at] geo [dot] geol [dot] ku [dot] dk] Geological Institute, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark. 8 March 1999.