Bulletin of the Geological Society of Denmark • Vol. 45/2

Abramovitz, T. & Thybo, H.: Pre-Zechstein structures around the MONA LISA deep seismic lines in the southern Horn Graben area. Bulletin of the Geological Society of Denmark, Vol. 45, pp. 99–116. Copenhagen, 1999–01–30.
Seismic reflection data from the Horn Graben area in the southeastern part of the North Sea, off-shore Denmark, have been interpreted to illustrate the upper crustal
structures around the MONA LISA deep seismic lines. The study area comprises the southern Horn Graben area and the eastern part of East North Sea High, where the Caledonian collision suture between Baltica and Eastern Avalonia bends such that the strike direction changes from ESE in the south to NNW in the north. Integrated interpretation of normal-incidence reflection data and wide-angle refraction data reveals substantial occurrences of lower and upper Palaeozoic strata in the area, thickest below the Horn Graben. This may indicate that Horn Graben developed as a graben structure during late Palaeozoic in the former Caledonian foredeep. On the northern and eastern parts of the MONA LISA deep seismic reflection lines 1 and 3, the main E-dipping boundary fault of the southern Horn Graben segment appears to be listric at depth with a sub-horizontal detachment at the top of the reflective lower crust. We have mapped the lateral extent of the lower Permian, volcanic Rotliegend reflector in the study area on the basis of seismic lines from the RTD-81 survey. Dipping reflections observed in the sedimentary strata below the Rotliegend reflector are interpreted as Caledonian structures generated by folding and deformation in Lower Palaeozoic Baltica shelf sediments in the Caledonian foreland basin. A sequence of S- and W-dipping reflections above 4 s twt are interpreted as preserved Caledonian thrusts in the upper crustal frontal part of the SW-dipping Caledonian Deformation Front.
Key words: Horn Graben, seismic reflection and refraction data, MONA LISA, Caledonian structures, Palaeozoic strata, Rotliegend reflector
T. Abramovitz & H. Thybo, Geological Institute, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen, Denmark. 16 April 1997.

Petrographic evidence for hydrocarbon migration in Lower Cambrian sandstones, Bornholm, Denmark

Møller, L. N. & Friis, H.: Petrographic evidence for hydrocarbon migration in Lower Cambrian sandstones, Bornholm, Denmark. Bulletin of the Geological Society of Denmark, Vol. 45, pp. 117–127. Copenhagen, 1999–01–30.
The Lower Cambrian sandstones from Bornholm, and in particular the Hardeberga Sandstone, contain a substance that has been interpreted to be pyrobitumen which causes the dark colour seen at many outcrop localities. The presence of pyrobitumen indicates the former presence of hydrocarbons that migrated through
the sandstones during the Mid Palaeozoic subsidence. In contrast to previous assumptions it is shown that even though the sandstones were extensively compacted,
it had only very little cement, and consequently excellent reservoir qualities at the time of hydrocarbon generation and migration. The only known source rock is the Middle Cambrian Alum Shale that must have been down-faulted relative to the lower Cambrian sandstones at the time of hydrocarbon generation. Quartz cement did not form until deep burial, and similar sandstones at locations outside the onshore Bornholm area that have not been so deeply buried may not have quartz cement and therefore still posses good reservoir properties.
Key words: Hardeberga Sandstone, Nexø Sandstone, pyrobitumen, Lower Cambrian, Bornholm, hydrocarbon migration, compaction, quartz cementation, reservoir properties.
Lars Nicolai Nebel Møller & Henrik Friis, Department of Earth Sciences, University of Aarhus, C. F. Møllers Allé 120, 8000 Århus C, Denmark. April 17, 1998.

Bioerosion: a collection of workshop papers

Richard Bromley
The First International Bioerosion Workshop was held, under the auspices of Geological Institute of the University of Copenhagen, Denmark, at Limensgade Windmill, Aakirkeby, Bornholm in September 1996. The workshop was convened by Richard Bromley and Ulla Asgaard with the object of gathering disparate bioerosionists together under one roof for a week and testing their interest in common ground (Asgaard & Bromley 1997; Bertling 1997). The success of the venture was indicated by the willing response of participants to write papers for collected publication. It was initially the intention to publish these papers as a special issue of Historical Biology. Unfortunately, the journal ran into trouble when it changed editor and copy-setters simultaneously. As late as second proof stage, following prolonged copy-setting problems, Historical Biology decided not to publish the shorter papers in the collection.
The major papers, however, were retained and have now been published. These are: Jacobsen (1998), Freiwald (1998), Freiwald & Wilson (1998), Boerboom et
al. (1998), Walker et al. (1998) and Hallock et al. (1998). The delay in publishing the remaining thirteen shorter papers is much regretted. They have been collected
together here after updating by the authors. Together with the Historical Biology papers, they illustrate a wide variety of bioerosional research. Included are papers on microbial bioerosion, coral reef bioerosion budgets, the work of boring bivalves (in rock and wood), sponges, unidentified organisms, carnivory of foraminifera, hardsubstrate trace fossils, brachiopods as bioerosion substrates and terrestrial bioerosion as well as the use of coastal bioerosion and littoral
notches as indicators of palaeo-shorelines.
The second International Bioerosion Workshop was convened by Debra Krumm at Fort Pierce, Florida in March 1998 and the third is planned for Barcelona in
2000.
R. G. Bromley, Geologisk Institut, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark. 1 December, 1998.

Erratum

In the article by Christensen ‘Belemnitella from the lowermost Maastrichtian of Scania, southern Sweden’ (Bulletin of the Geological Society of Denmark 45(1), pp. 11–21, 1998) Figure 2 on p. 13 was printed incorrectly outwith the author’s control. The correct figure is reproduced below.