Bulletin of the Geological Society of Denmark • Volume 58

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Contents Hansen, T. 2010-16-02. Cyrtometopinid trilobites from the upper Volkhov and lower Lynna Formation (lower Darriwilian) of NW Russia Boldreel, L.O., Kuijpers, A., Madsen, E. B., Hass, C., Lindhorst, S., Rasmussen, R., Nielsen, M.G, Bartholdy, J. & Pedersen, J.B.T.; 2010-04-08. Postglacial sedimentary regime around northern Sylt, South-eastern North Sea, based on shallow seismic profiles Weidner, T. & Nielsen, A.T., 2010-04-13. Yuepingia? sp., a ceratopygid trilobite from the upper Cambrian (Furongian) of Scandinavia . Holm, P.M., Pedersen, L.E. & Højsteen, B., 2010–05–17. Geochemistry and petrology of mafic Proterozoic and Permian dykes on Bornholm, Denmark: Four episodes of magmatism on the margin of the Baltic Shield. Hunter, A.W. & Rees, J. 2010-10-24: A new echinoderm faunule from the Lower Jurassic (Pliensbachian) of southern Sweden. Karup-Møller, S., Rose-Hansen, J. & Sørensen, H., 2010-11-10. Eudialyte decomposition minerals with new hitherto undescribed phases from the Ilímaussaq complex, South Greenland. Surlyk, F., Stemmerik, L., Ahlborn, M., Harlou, R., Lauridsen, B.W., Rasmussen, S.L., Schovsbo, N., Sheldon, E. & Thibault, N., 2010-11-11: The cyclic Rørdal Member – a new lithostratigraphic unit of chronostratigraphic and palaeoclimatic importance in the upper Maastrichtian of Denmark . Surlyk, F., Boldreel, L.O., Lykke-Andersen, H. & Stemmerik, L., 2010-11-11: The Skælskør structure in eastern Denmark – wrench-related anticline or primary Late Cretaceous seafloor topography?

Cyrtometopinid trilobites from the upper Volkhov and lower Lynna Formation (lower Darriwilian) of NW Russia

Abstract: Two cyrtometopinid trilobite taxa from the lower Darriwilian of NW Russia are examined. A new species of the genus Krattaspis is described, extending the stratigraphical range of the genus into the lower Darriwilian (Middle Ordovician).

K. paraspinosis n.sp. is the youngest representative of the genus, but is closest to forms assigned to Cyrtometopus and confirms the derivation of Cyrtometopus from Krattaspis. Ontogenetic studies of K. paraspinosis n.sp. and Cyrtometopus clavifrons Angelin, 1854, from the same beds indicates a forward displacement of the eyes with increasing size, which may be contrary to all other known members of the family Cheiruridae.

Key words:  Cyrtometopus clavifrons, Krattaspis paraspinosus n.sp., Cyrtometopinae, NW Russia, lower Darriwilian

Address: , Department of Geography and Geology, Copenhagen University, Øster Voldgade 10, DK-1350 København K, Denmark.

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Postglacial sedimentary regime around northern Sylt, South-eastern North Sea, based on shallow seismic profiles

Abstract: During the past 5 years the coastal zone offshore the northern part of the island of Sylt, has been investigated by sparker seismics and high-resolution subbottom profiling.

The North Sea sector of the area is characterized by northward-directed sediment bypass as a result of strong long-shore (tidal) currents heading towards the Lister Tief. The southern part of Lister Tief is characterized by the presence of a major dune field with up to 8 m high compound dunes with wavelengths up to 350 m indicative of easterly-directed sediment transport (flood dominated).

Further to the northwest, in the outer delta, a dune field suggesting westerly-directed sediment transport is identified. The two dune fields appear to be separated by minor indefinite bed forms. The northern part of the Lister Tief is characterised by the presence of a channel with a depth of 20-30 mbsf (meter below sea level) (30-40 msec TWT (Two Way Traveltime)) and displaying erosion towards the north.

At the western termination of the channel the sediment transport pathway appears to be divided into two directions; one towards the outer delta, and one towards the sediment depocenter SW of Rømø. The Lister Ley is characterized by the presence of minor dunes, indicative of flood-current control, apart from a central zone where ebb-tide is responsible for northward-directed sediment transport.

Sparker seismic and Chirp III data are consistent with processes having been persistent throughout the Holocene. Based on the study a model for the current direction and sedimentation regime is suggested.

Key words: Wadden Sea, postglacial sedimentary regime, Tidal area of Sylt and Rømø, sparker seismic, Chirp III sub-bottom profiling

Address: ^a ., Department of Geography and Geology, University of Copenhagen, Øster Voldgade 10,DK-1350 Copenhagen K, Denmark.
b Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark.
^c Alfred-Wegener Institute for Polar- and Marine Research, Wadden Sea Station Sylt, Hafenstraße 43 D-25992 List.
^d Institute of Geology and Palaeontology, University of Hamburg, Bundesstraße. 55, D-20146 Hamburg, Germany.

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Yuepingia? sp., a ceratopygid trilobite from the upper Cambrian (Furongian) of Scandinavia

Weidner, T. & Nielsen, A.T., 2010-04-13. Yuepingia? sp., a ceratopygid trilobite from the upper Cambrian (Furongian) of Scandinavia. © 2010 by Bulletin of the Geological Society of Denmark, Vol. 58,
pp. 29–33. ISSN 0011–6297. (www.2dgf.dk/publikationer/bulletin)

Abstract: A single pygidium found in an ice-rafted loose boulder of coquinoid bituminous limestone represents an ‘exotic’ trilobite hitherto unknown from the Scandinavian Alum Shale Formation.

The limestone, found on the east coast of Jutland, Denmark, also contains Leptoplastus paucisegmentatus, Parabolina spinulosa and Orusia lenticularis and derives from the upper Cambrian (Furongian) Leptoplastus paucisegmentatus Zone of Västergötland, south-central Sweden. The ‘exotic’ pygidium shows closest resemblance to the ceratopygid Yuepingia glabra, described from Alaska, and is treated as Yuepingia? sp. The Laurentian Y. glabra occurs in the Ptychaspis-Prosaukia Zone which corresponds in age to the Scandinavian Leptoplastus Superzone.

Keywords: Ceratopygid trilobite, Furongian, Alum Shale, Cambrian, Scandinavia.

Addresses: , Ravnholtvej 23, Rårup, DK-7130 Juelsminde, Denmark.
, Geological Museum, University of Copenhagen, Øster Voldgade 5-7, DK-1350 Kbh K, Denmark.

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Geochemistry and petrology of mafic Proterozoic and Permian dykes on Bornholm, Denmark: Four Episodes of magmatism on the margin of the Baltic Shield

Holm, P.M., Pedersen, L.E. & Højsteen, B., 2010–05–17. Geochemistry and petrology of mafic Proterozoic and Permian dykes on Bornholm, Denmark: Four episodes of magmatism on the margin of the Baltic Shield. © 2010 by Bulletin of the Geological Society of Denmark, Vol. 58, pp. 35–65. ISSN 0011–6297. (www.2dgf.dk/publikationer/bulletin).

Abstract: More than 250 dykes cut the mid Proterozoic basement gneisses and granites of Bornholm. Most trend between NNW and NNE, whereas a few trend NE and NW. Field, geochemical and petrological evidence suggest that the dyke intrusions occurred as four distinct events at around 1326 Ma (Kelseaa dyke), 1220 Ma (narrow dykes), 950 Ma (Kaas and Listed dykes), and 300 Ma (NW-trending dykes), respectively.

The largest dyke at Kelseaa (60 m wide) and some related dykes are primitive olivine tholeiites, one of which has N-type MORB geochemical features; all are crustally contaminated. The Kelseaa type magmas were derived at shallow depth from a fluid-enriched, relatively depleted, mantle source,but some have a component derived from mantle with residual garnet. They are suggested to have formed in a back-arc environment.

The more than 200 narrow dykes are olivine tholeiites (some picritic), alkali basalts, trachybasalts, basanites and a few phonotephrites. The magmas evolved by olivine and olivine + clinopyroxene fractionation. They have trace element characteristics which can be described mainly by mixing of two components: one is a typical OIB-magma (La/Nb < 1, Zr/Nb = 4, Sr/Nd = 16) and rather shallowly derived from spinel peridotite; the other is enriched in Sr and has La/Nb = 1.0 - 1.5, Zr/Nb = 9, Sr/Nd = 30 and was derived at greater depth, probably from a pyroxenitic source.

Both sources were probably recycled material in a mantle plume. A few of these dykes are much more enriched in incompatible elements and were derived from garnet peridotite by a small degree of partial melting. The Kaas and Listed dykes (20-40 m) and related dykes are evolved trachybasalts to basaltic trachyandesites. They are most likely related to the Blekinge Dalarne Dolerite Group. The few NW-trending dykes are quartz tholeiites, which were generated by large degrees of rather shallow melting of an enriched mantle source more enriched than the source of the older Bornholm dykes. The source of the NW-trending dykes was probably a very hot mantle plume.

Keywords: Bornholm, dykes, Baltic Shield, petrology, geochemistry.

Address: , Department of Geography and Geology, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen K.

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A new echinoderm faunule from the Lower Jurassic (Pliensbachian)of southern Sweden

Hunter, A.W. & Rees, J. 2010-10-24. A new echinoderm faunule from the Lower Jurassic (Pliensbachian)of southern Sweden. © 2010 by Bulletin of the Geological Society of Denmark, Vol. 58, pp. 66–73.
ISSN 0011–6297. (www.2dgf.dk/publikationer/bulletin)

Abstract: In Sweden, Jurassic echinoderms are extremely rare. This present study documents an Early Jurassic echinoderm assemblage collected from a temporary exposure near Helsingborg in Skåne, southern Sweden, which includes a previously undescribed species of isocrinid crinoid, Isocrinus ranae sp.nov., and an acrosaleniid echinoid.

The Swedish specimens demonstrate that even limited echinoderm material from small exposures can be assigned to a high systematic level and provide data of considerable significance to the evolution of the group as a whole.

Keywords: crinoids, echinoids, taphonomy, palaeoecology, Lower Jurassic, Skåne, Sweden.

Addresses: , Department of Earth and Planetary Science, University of Tokyo,Hongo, Tokyo, 113-0033, Japan. & Department of Palaeontology, Natural History Museum, Cromwell Road, London SW7 5BD United Kingdom.
Jan Rees, Department of Biology, Karlstad University, SE-651 88 Karlstad, Sweden.

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Eudialyte decomposition minerals with new hitherto undescribed phases from the Ilímaussaq complex, South Greenland

S. Karup-Møller, J. Rose-Hansen & H. Sørensen. 2010-11-10. Eudialyte decomposition minerals with new hitherto undescribed phases from the Ilímaussaq complex, South Greenland. © 2010 by Bulletin of the Geological Society of Denmark, Vol. 58, pp. 75–88.
ISSN 0011–6297. (www.2dgf.dk/publikationer/bulletin)

Abstract: Eudialyte is a distinctive mineral in the agpaitic group of peralkaline nepheline syenites. The paper describes the alteration of eudialyte from the Ilímaussaq complex, South Greenland, which is the type locality for eudialyte, as well as for agpaitic rocks. 

Two types of alteration are distinguished: alteration of eudialyte to catapleiite is widespread in the complex, whereas alteration to zircon only occurs in strongly altered rocks. additionally, the fol-lowing minerals have been identified in the altered eudialyte: aegirine, K-feldspar, albite, analcime, fluorite, monazite, apatite, allanite, Y-fergusonite, Ce-fergusonite, fersmite, nacareniobsite-(Ce), uranothorianite, neptunite and grossularite. Some unidentified Nb and/or REE minerals have been distinguished.

The different styles of alteration can be explained by different late- and post magmatic conditions at different settings in the complex. Alteration to zircon is caused by fluids of external origin or by fluids expelled from intersecting lujavrite and pegmatite dykes. Alteration to catapleiite is caused by late-magmatic interstitial fluids.

The alteration has resulted in distinct fractionation of some elements; Zr is, for instance, located only in zircon and catapleiite, Nb and REE in separate minerals.

Keywords: Ilímaussaq complex, South Greenland eudialyte decomposition products, marginal peg-matite, kakortokites, unidentified Nb- and REE-minerals.

Addresses: , Department of Environmental Engineering. Technical University of Denmark, Lyngby, Denmark;
J. Rose-Hansen  and H. Sørensen, Department of Geography and Geology, University of Copenhagen, Denmark.

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The cyclic Rørdal Member – a new lithostratigraphic unit of chronostratigraphic and palaeoclimatic importance in the upper Maastrichtian of Denmark

Surlyk, F., Stemmerik, L., Ahlborn, M., Harlou, R., Lauridsen, B.W., Rasmussen, S.L., Schovsbo, N., Sheldon, E. & Thibault, N. 2010-11-11. The cyclic Rørdal Member – a new lithostratigraphic unit of chronostratigraphic and palaeoclimatic importance in the upper Maastrichtian of Denmark. © 2010 by Bulletin of the Geological Society of Denmark, Vol. 58, pp. 89–98.
ISSN 0011–6297. (www.2dgf.dk/publikationer/bulletin)

Abstract: The Maastrichtian chalk of the Danish Basin has been referred to the Tor Formation of the North Sea, but this may not be tenable because this formation in its type area shows a much higher degree of redeposition than the Maastrichtian chalk of the Danish Basin. The onshore succession has not been lithostratigraphically subdivided due to its rather monotonous nature and the widely scattered outcrops.

An exception is the uppermost Maastrichtian exposed at Stevns Klint which is been referred to the Sigerslev Member, comprising rather benthos-poor, deep-water pure chalk, and the overlying mound-bedded, bryozoan-rich chalk which is placed in the Højerup Member. In addition, a thin marly chalk bed, the Kjølby Gaard Marl Member, containing Tethyan planktonic foraminifers is known from localities in northern Jylland and from water wells around Køge, eastern Sjælland.

The new Rørdal Member is a cyclic chalk-marl unit, about 10 m thick, sandwiched between pure white chalks. It is well exposed in the large Rørdal quarry in Aalborg, and is recognised in boreholes south of Aalborg and in the Stevns-1 and Karlslunde-1 boreholes south of Copenhagen. Coccolith and brachiopod data show that it belongs to the UC20b-cBP nannofossil zone of the North Sea scheme for the Upper Cretaceous Boreal province, and the semiglobularis-humboldt iibrachiopod zone, both indicating the lower upper Maastrichtian.

Isotope data show that it represents a distinct early late Maastrichtian cooling event. The member thus has a basinwide distribution and is an important isochronous marker.

Keywords: Lithostratigraphy, cyclicity, chalk, marl, Rørdal Member, Maastrichtian, Denmark.

Addresses: , Lars Stemmerik, Morten Ahlborn, Rikke Harlou, Bodil W. Lauridsen, Nicolas Thibault, Department of Geography and Geology, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark.
Susanne L. Rasmussen, Niels Schovsbo, Emma Sheldon, Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark.

 
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The Skælskør structure in eastern Denmark – wrench-related anticline or primary Late Cretaceous seafloor topography?

Surlyk, F., Boldreel, L.O., Lykke-Andersen, H. & Stemmerik, L. 2010-11-11. The Skælskør structure in eastern Denmark – wrench-related anticline or primary Late Cretaceous seafloor topography? © 2010 by Bulletin of the Geological Society of Denmark, Vol. 58, pp. 99–109.
ISSN 0011–6297. (www.2dgf.dk/publikationer/bulletin)

Abstract: Sorgenfrei (1951) identified a number of NW–SE oriented highs in the Upper Cretaceous – Danian Chalk Group in eastern Denmark, including the Skælskør structure and interpreted them as anticlinal folds formed by wrenching along what today is known as the Ringkøbing-Fyn High.

Recent reflection seismic studies of the Chalk Group in Øresund and Kattegat have shown that similar highs actually represent topographic highs on the Late Cretaceous – Danian seafloor formed by strong contourparallel bottom currents. Reflection seismic data collected over the Skælskør structure in order to test the hypothesis of Sorgenfrei show that the Base Chalk reflection is relatively flat with only very minor changes in inclination and cut by only a few minor faults.

The structure is situated along the northern margin of a high with roots in a narrow basement block, projecting towards the northwest from the Ringkøbing Fyn High into the Danish Basin. The elevated position is maintained due to reduced subsidence as compared with the Danish Basin north of the high. The hypothesis of wrench tectonics as origin can be refuted.

The seismic data show that the upper part of the Chalk Group is characterised by irregular mounded reflections, interpreted as representing contourite drifts, mounds and channels formed by strong, mainly late Maastrichtian bottom currents. The Skælskør structure of Sorgenfrei is thus in reality a Late Cretaceous topographic seafloor high formed by a combination of differential subsidence complemented by topographic features on the seafloor created by bottom currents in the late Maastrichtian.

Keywords: Skælskør structure, Chalk Group, wrenching, seafloor topography, bottom currents.

Addresses: , Lars Ole Boldreel, Lars Stemmerik, Department of Geography and Geology, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark.
Holger Lykke-Andersen, Geological Institute, University of Aarhus, Høegh-Guldbergs Gade 2, bygning 1670, DK-8000 Aarhus C.
 
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