Bulletin of the Geological Society of Denmark • Volume 52/1

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Dinosaur footprints from the Middle Jurassic Bagå Formation, Bornholm, Denmark

Milàn, J. & Bromley, R.G. 2005–11–15: Dinosaur footprints from the Middle Jurassic Bagå Formation, Bornholm, Denmark. Bulletin of the Geological Society of Denmark, Vol. 52, pp. 7–15.

Abstract: Dinosaur footprints have been found preserved on sandstone blocks discarded from the flooded clay pit Pyritsøen, south of Hasle, Bornholm. The sandstone belongs to the Middle Jurassic Bagå Formation, but the exact horizon is not known. Palynological studies confirm that the sandstone blocks originate from the Bagå Formation. Two specimens were collected, one showing two footprints from a sauropod dinosaur having a foot length of 68 cm, and a small pentadactyl footprint, 26cm long, interpreted as deriving from an armoured dinosaur. These are the first dinosaur footprints recorded from Denmark.

Keywords: Dinosaur footprints, sauropod, Middle Jurassic, Bornholm, Denmark.

Addresses: Jesper Milàn [ ], University of Copenhagen, Geological Institute, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark.
Richard G. Bromley [ ], University of Copenhagen, Geological Institute, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark.

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Palaeomagnetism of Eocene Talerua Member lavas on Hareøen, West Greenland

Schmidt, A.G., Riisager, P., Abrahamsen, N., Riisager, J., Pedersen A. & van der Voo, R. 2005–11–15: Palaeomagnetism of Eocene Talerua Member lavas on Hareøen, West Greenland. Bulletin of the Geological Society of Denmark, Vol. 52, pp. 27–38.

Abstract: The results of a palaeomagnetic sampling carried out along two vertical profiles (altogether 19 lavaflows, 126 samples) covering the entire stratigraphy of the Talerua Member lavas (~39 Myr old) that outcrop on the island Hareøen are presented and represent some of the youngest volcanism in the West Greenland flood volcanic province. Rock magnetic experiments and microprobe analysis demonstrate that the dominant magnetic mineral in all studied lavas is titanomagnetite that has experienced variable amounts of high temperature deuteric oxidation as well as low temperature hydro-thermal oxidation. Based on detailed demagnetization experiments, well-defined palaeomagnetic site-mean directions were isolated from all 19 lavas. The composite profile contains two magnetic polarity zones suggesting a maximum duration of Talerua Member volcanism of ~1.4 Ma. After grouping flows having the same remanent magnetic field direction, 13 individual readings of the palaeomagnetic fields were obtained. The palaeomagnetic pole with coordinates 76.3°N, 201.5°E (A95=7.4°, K=32.7, N=13) is in good accordance with palaeomagnetic poles from other continents rotated back to Greenland using plate kinematic rotation poles.

Keywords: Palaeomagnetism, magnetic polarity, West Greenland, Paleogene, volcanics, North Atlantic igneous province.

Addresses: Anne G. Schmidt, Mærsk Olie og Gas AS, Esplanaden 50, DK-1263 Copenhagen K, Denmark;
Peter Riisager [ ], Geological Museum, Øster Voldgade 5-7, DK-1350 Copenhagen K, Denmark and University of Lund, GeoBiosphere Science Centre, Sölvegatan 12, S-223 62 Lund,Sweden;
Niels Abrahamsen [ ], Department of Earth Sciences, Aarhus University,Finlandsgade 8, DK-8200 Aarhus N, Denmark;
Janna Riisager [ ]
Asger KenPedersen [ ], Geological Museum, Øster Voldgade 5-7, DK-1350 Copenhagen K, Denmark;
Rob van der Voo [ ], Department of Geological Sciences, University of Michigan, Ann Arbor,MI 48109-1063, USA.

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A rock- and palaeomagnetic study ofgeologically recent lavas and 1995 volcanic glass on Fogo (Cape Verde Islands)

Knudsen, M.F., Abrahamsen, N. & Riisager, P. 2005–11–15. A rock- and palaeomagnetic study of geologically recent lavas and 1995 volcanic glass on Fogo (Cape Verde Islands). Bulletin of the Geological Society of Denmark, Vol. 52, pp. 39–52.

Abstract: Fogo is the only island in the Cape Verde archipelago with accounts of historical volcanic activity. Here we present palaeomagnetic data from seven geologically recent lava flows on Fogo, including one glassy, volcanic flow from the eruption in 1995. Almost all samples behaved well during alternating-field (AF) and thermal demagnetisation, and the characteristic remanent magnetisations (ChRMs) were generally easily isolated. The dominant magnetic mineral in all flow units, including the glassy flow, is titanomagnetite with a varying titanium content. The non-glassy flow units alldisplay pseudo-single-domain (PSD) behaviour, whereas the hysteresis parameters for the glassy flow unit tend to plot in a region associated with mixtures of superparamagnetic (SP) and single-domain (SD) grains. Despite historical accounts of the eruptive activity on Fogo it was impossible toobtain unique correlations between the historical flow flelds and the non-glassy flow units presented in this study. One of six non-glassy flow units yields a direction consistent with existing approximative reference curves for the historical secular variation on Fogo. Consequently, we suspect that some of the non-glassy flow units have been subjected to post-cooling block rotation. The glassy flow from 1995 proved to be a reasonable recorder of the geomagnetic fleld, yielding a direction (dec = 353.8° and inc = 12.9°), quite similar to the International Geomagnetic Reference Field(1995) for this site location (dec = 346.8° and inc = 14.4°).

Keywords: Fogo, Cape Verde Islands, rock magnetism, hysteresis, palaeosecular variation, volcanicglass.

Addresses: Mads Faurschou Knudsen [ ], Department of Earth Sciences, University of Aarhus,Finlandsgade 6–8, DK-8200 Aarhus N., Denmark, present address: Department of Earth Sciences, Univer-sity of Oxford, Parks Road, Oxford OX1 3PR, United Kingdom;
Niels Abrahamsen [ ],Department of Earth Sciences, University of Aarhus, Finlandsgade 6–8, DK-8200 Aarhus N., Denmark,
Peter Riisager [ ], Geological Museum, University of Copenhagen, Øster Voldgade5–7, DK-1350 Copenhagen K., Denmark, present address: GeoBiosphere Science Centre, Quaternary Sciences, University of Lund, Sölvegatan 12, S-223 62 Lund, Sweden.

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Jørgensen, F., Sandersen, P.B.E., Auken, E., Lykke-Andersen, H. & Sørensen, K. 2005–11–15. Contributions to the geological mapping of Mors, Denmark – A study based on a large-scale TEM survey. Bulletin of the Geological Society of Denmark, Vol. 52, pp. 53–75.

Abstract: Recent improvements of the transient electromagnetic (TEM) method provide unprecedented capabilities of imaging geological features in the uppermost few hundred metres of the subsurface. This is documented with an example from the island of Mors, Northern Jutland, Denmark, where 2655 TEM soundings have been acquired as a part of Viborg County’s hydrogeological investigation programme. Horizontal aspects of the interpreted TEM soundings are presented in thematic maps revealing variations of resistivities in specified depth intervals and depths to the resistivity basement, i.e. the deepest recorded low-resistive layer. Vertical aspects are displayed in cross-sections.The dense coverage of TEM soundings, combined with borehole logs, allows the precise delineation of major geological features. These comprise the Mors salt diapir, intricate systems of buried Quaternary valleys and several glaciotectonic complexes, all contributing to a complicated geological framework for the island. The layers above the salt diapir, which have been subject to severe erosion, are distinctly imaged in the thematic maps, even though they are frequently dissected by buried valleys. At least four generations of buried valleys can be identified on the basis of their preferred orientations; these were mainly formed during early glaciations. Large parts of the island were glaciotectonically deformed during the Late Weichselian subsequent to valley formation, and it is suggested that the presence of deep valleys may have affected the process of glaciotectonic deformation.

Keywords: Transient electromagnetic; TEM; hydrogeophysics; salt diapirs; buried valleys; glaciotectonic deformation; subglacial; Quaternary; Pleistocene; Mors; Denmark.

Addresses: Flemming Jørgensen [ ], Vejle Amt, Damhaven 12, DK-7100 Vejle, Denmark.
Peter B.E. Sandersen [ ], Watertech a/s, Søndergade 53, DK-8000 Aarhus C, Denmark.
Esben Auken[ ], Hydrogeophysics Group, Department of Earth Sciences, University of Aarhus,DK-8200 Aarhus N, Denmark.
Holger Lykke-Andersen [ ], Department of Earth Sciences,University of Aarhus, DK-8200 Aarhus N, Denmark.
Kurt Sørensen [ ], Hydrogeophysics Group, Department of Earth Sciences, University of Aarhus, DK-8200 Aarhus N, Denmark.

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