Contents
Kalkreuth, W., Andreasen, C., Petersen, H.I. & Stemmerik, L., 2012-02-24.
The petrology and provenance of coal artifacts from Thule settlements in north-eastern Greenland
Rasmussen, J.A. & Surlyk, F. 2012-03-20.
Rare finds of the coiled cephalopod Discoceras from the Upper Ordovician of Bornholm, Denmark
Waight, T.E., Frei, D. & Storey, M. 2012-06-15.
Geochronological constraints on granitic magmatism, deformation, cooling and uplift on Bornholm, Denmark
Lauridsen, B.W., Bjerager, M. & Surlyk, F. 2012-10-02.
The middle Danian Faxe Formation – new lithostratigraphic unit and a rare taphonomic window into the Danian of Denmark
Madsen, T. M. & Piotrowski, J. A. 2012-12-05.
Genesis of the glaciotectonic thrust-fault complex at Halk Hoved, southern Denmark.
The petrology and provenance of coal artifacts from Thule settlements in north-eastern Greenland
Kalkreuth, W., Andreasen, C., Petersen, H.I. & Stemmerik, L., The petrology and provenance of coal artifacts from Thule settlements in north-eastern Greenland
©2012 by Bulletin of the Geological Society of Denmark, Vol. 60, pp. 1–13.
ISSN 0011–6297. (www.2dgf.dk/publikationer/bulletin).
https://doi.org/10.37570/bgsd-2012-60-01
Abstract: Coal petrographic techniques have been used to trace the origin of coal used to produce artifacts by the Thule people in north-eastern Greenland. The coal artifacts were collected from the north-east coast settlements between 76°55’–80°18’N and date back to the 15th century A.D.
The petrographic data suggest that they have a common source, the Middle Jurassic coals outcropping south of 75°15′ in north-eastern Greenland. It is thus evident that the Thule people used local material rather than bringing the coal from the known “mines” in Arctic Canada. It also implies that contemporaneous Thule people groups along the east coast of Greenland were in contact and traded.
Keywords: Coal artifacts, coal petrology, Thule Culture, north-eastern Greenland
Addresses:
Wolfgang Kalkreuth, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil.
Claus Andreasen, Greenland National Museum and Archives, P.O. Box 145, DK-3900 Nuuk, Greenland.
Henrik I. Petersen , Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark.
Lars Stemmerik, Natural History Museum of Denmark, Øster Voldgade 5-7, DK-1350 Copenhagen K, Denmark.
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Rare finds of the coiled cephalopod Discoceras from the Upper Ordovician of Bornholm, Denmark
Rasmussen, J.A. & Surlyk, F. 2012-03-20.Rare finds of the coiled cephalopod Discoceras from the Upper Ordovician of Bornholm, Denmark
©2012 by Bulletin of the Geological Society of Denmark, Vol. 60 pp. 15-22.
ISSN 2245-7070. (www.2dgf.dk/publikationer/bulletin).
https://doi.org/10.37570/bgsd-2012-60-02
Abstract: Coiled nautiloid cephalopods of the genus Discoceras are locally common in the Middle and Upper Ordovician of Baltica, for example in the Oslo Graben, but are exceedingly rare in contemporaneous strata from the Danish island of Bornholm.
The two new species of Discoceras described here, D. costatum n. sp. and D. vasegaardense n. sp., occur in shales of the Upper Ordovician Lindegård Formation. The nautiloids are preserved as external molds in laminated siliciclastic mudstones.
The very rare occurrence of cephalopods, combined with the apparently endemic nature of the Discoceras fauna, may be explained by the location of Bornholm distally on the Baltoscandian shelf combined with the influence of relatively cold ocean currents from the adjacent Rheic Ocean.
Keywords: Nautiloid cephalopod, Discoceras, Lindegård Formation, Upper Ordovician, Bornholm, Denmark.
Addresses:
Jan Audun Rasmussen, Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5–7, DK-1350 Copenhagen K, Denmark.
Finn Surlyk, Department of Geography and Geology, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark.
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Geochronological constraints on granitic magmatism, deformation, cooling and uplift on Bornholm, Denmark
Waight, T.E., Frei, D. & Storey, M. 2012. Geochronological constraints on granitic magmatism, deformation, cooling and uplift on Bornholm, Denmark
©2012 by Bulletin of the Geological Society of Denmark, Vol. 60, pp.23-46.
ISSN 0011–6297 . (www.2dgf.dk/publikationer/bulletin).
https://doi.org/10.37570/bgsd-2012-60-03
Abstract: U-Pb ages on zircon from 11 samples of granitoid and gneiss from the Danish island of Bornholm have been obtained using laser ablation – inductively coupled plasma mass spectrometry. These ages indicate that the felsic basement rocks were generated over a restricted period in the Mesoproterozoic at 1455 ± 10 Ma.
No evidence has been found for the presence of 1.8 Ga basement gneisses as observed to the north in southern Sweden and as inferred in previous studies. No distinction in age can be made between relatively undeformed granitic lithologies and gneissic lithologies within the errors of the technique. This indicates that granitic magmatism, deformation and metamorphism all occurred within a relatively restricted and contemporaneous period.
The granitic magmatism on Bornholm can thus be correlated to similar events at the same time in southern Sweden, Lithuania, and elsewhere in Baltica, and is therefore part of a larger magmatic event affecting the region. Argon and Rb-Sr ages on various minerals from a single sample of the Rønne Granite provide constraints on the cooling and uplift history of the basement in the region. Using recently published closure temperatures for each isotopic system a cooling curve is generated that illustrates a period of rapid cooling immediately after and/or during crystallisation.
This likely represents the period of emplacement, crystallisation, and deformation of the felsic basement. The modelled rate of post-emplacement cooling is highly dependent on the choice of closure temperature for Ar isotopes in biotite. Use of recently published values of around 450˚C defines a prolonged period of slower cooling (c. 4˚C per million years) over nearly 100 million years down to c. 300˚C and the closure temperature of Sr isotopes in biotite.
Use of older and lower closure temperatures defines curves that are more consistent with theoretical models. The low closure temperature of Sr isotopes in biotite explains much of the wide variation in previous age determinations using various techniques on Bornholm. There is no evidence in the geochronological data for disturbance during later tectonic events in the region.
Keywords: Bornholm, geochronology, zircon, granitoid, gneiss, Danolopolian, Rb-Sr, 40Ar-39Ar.
Addresses:
Tod Waight, Department of Geography and Geology, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark.
Dirk Frei, Geological Survey of Denmark and Greenland (GEUS), Øster Voldgade 10, DK-1350 Copenhagen K, Denmark; presently at Department of Earth Sciences, Corner Ryneveld and Merriman Streets, Stellenbosch, Private Bag X1, Matieland, 7602, South Africa.
Michael Storey, QUADLAB, Department of Environmental, Social and Spatial Change, Roskilde University, Universitetsvej 1, DK-4000 Roskilde, Denmark.
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Download zircon data:
Supplementary data file 1 – xls-file (164,71 Kb)
The middle Danian Faxe Formation – new lithostratigraphic unit and a rare taphonomic window into the Danian of Denmark
Lauridsen, B.W., Bjerager, M. & Surlyk, F. 2012. The middle Danian Faxe Formation – new lithostratigraphic unit and a rare taphonomic window into the Danian of Denmark
©2012 by Bulletin of the Geological Society of Denmark, Vol. 60, pp. 47-60.
ISSN 0011–6297. (www.2dgf.dk/publikationer/bulletin).
https://doi.org/10.37570/bgsd-2012-60-04
Abstract: The new middle Danian Faxe Formation is defined on the basis of the succession exposed in the large Faxe quarry in eastern Denmark. The formation is defined as a distinct mappable ithostratigraphic unit of interfingering coral and bryozoan limestone passing laterally into bryozoan limestones of the Stevns Klint Formation.
The Baunekule facies is recognized in the upper part of the coral mound complex of the Faxe Formation, where it forms isolated lensoidal bodies in the flanks of some of the coral mounds. It is characterised by a high diversity invertebrate fauna with both calcite and originally aragonite-shelled benthic invertebrates set in weakly consolidated coral-dominated floatstone to rudstone.
The diagenesis of the Baunekule facies is of special significance because a high proportion of the originally aragonite-shelled fauna is preserved by recrystallization to calcite during early burial diagenesis. More than 80% of the species from the Baunekule facies are unknown from other parts of the Faxe Formation.
The carbonate mud matrix is only slightly consolidated and the invertebrate fossils are accordingly easy to prepare in contrast to the fossils from the lithified parts of the Faxe Formation, which are commonly only preserved as moulds or casts. The facies therefore presents an exceptional taphonomic window into a cold-water coral mound fauna, giving an unusually complete picture of the diversity and density of the shelly invertebrate fauna.
Keywords: Faxe Formation, Baunekule facies, Danian, Denmark, coral limestone, fossil invertebrates, taphonomy.
Addresses:
Bodil Wesenberg Lauridsen, Finn Surlyk , Department of Geography and Geology, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark.
Morten Bjerager , Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark.
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Genesis of the glaciotectonic thrust-fault complex at Halk Hoved, southern Denmark.
Madsen, T. M. & Piotrowski, J. A. 2012. Genesis of the glaciotectonic thrust-fault complex at Halk Hoved, southern Denmark.
©2012 by Bulletin of the Geological Society of Denmark, Vol. 60, pp. 61-80.
ISSN 0011–6297 . (www.2dgf.dk/publikationer/bulletin).
https://doi.org/10.37570/bgsd-2012-60-05
Abstract: The coastal cliff of Halk Hoved, southern Jutland, Denmark, is a major glaciotectonic complex formed by proglacial deformation of the North-East (NE) advance from the Scandinavian Ice Sheet in Late Weichselian. We describe and interpret the pre-, syn- and post-tectonic sedimentary successions and macro-scale architecture of this complex.
Initially, the Lillebælt Till Formation (unit 1) and the overlying glaciofluvial sediments (unit 2) were deposited during the Warthe glaciation in Late Saalian. During the NE advance towards the Main Stationary Line (MSL) in Late Weichselian, these sediments were pushed along a décollement surface whereby a thrust-fault complex was formed. In a cross section the complex extends for more than 900 m and consists of eighteen c. 15–20 m thick thrust sheets stacked by piggyback thrusting. Accumulated displacement amounts to at least 235 m along thrust faults dipping at 30–40° towards N-NE, resulting in at least 24% glaciotectonic shortening of the complex.
Deformation was presumably facilitated by elevated pore-water pressure in the Lillebælt Till Formation. As the compressive stress exceeded the shear strength of the weakened till, failure occurred, and a décollement horizon formed along the lithological boundary between the Lillebælt Till Formation and the underlying aquifer. During deformation, piggyback basins formed wherein sediments of hyperconcentrated flow (unit 3) and glaciolacustrine diamicton (unit 4) were deposited.
The whole thrust-fault complex and the intervening sediments were truncated subglacially as the NE advance finally overrode the complex. Following the retreat of the NE advance, a succession of glaciofluvial sediments (unit 5) and finally the East Jylland Till Formation (unit 6) were deposited during the advance of the Young Baltic Ice Sheet. The Halk Hoved thrust-fault complex is a prominent example of glaciotectonism at the southern fringe of the Scandinavian Ice Sheet.
Keywords: Glaciotectoctonic, thrust-fault complex, pore-water pressure, lithostratigraphy.
Addresses:
Tillie M. Madsen, Rambøll Danmark A/S, Olof Palmes Allé 22, DK-8200 Aarhus N, Denmark. Jan A. Piotrowski , Department of Geoscience, Aarhus University, Høegh-Guldbergs Gade 2, DK-8000 Aarhus C, Denmark.