Southern North Sea Project Borehole BH 89/1: a technical report

The EEC 'Southern North Sea Project - Quaternary Geology' was carried out between 1989 and 1991. The project included geologists from the Geological Surveys of five countries : the Netherlands, Great-Britain, Germany, Denmark and Belgium. The major goal of the project was to study and to reconstruct the development of the Southern North Sea Basin during the Quaternary .To this end 9 boreholes were drilled in the Southern North Sea. These were complemented by a seismic survey, connecting most of the boreholes. A complete report is given here of the different investigations which were carried out on the Belgian core, BH 89/1, situated in the north-eastern part of the Belgian Continental Shelf. The investigations include the geographical and geological setting of the Belgian borehole, the lithological and sedimentological analysis of the core and the determination of the heavy minerals, of the isothermal remanent magnetization of the magnetic minerals and of the clay mineral composition. Furthermore different samples were analysed for their dinoflagellate and foraminiferal content. The age of organic fragments found in a sample was determined using C14-dating. The sequences in the borehole were related to seismo-stratigraphic units identified on available seismic lines from this part of the Belgian Sector. On the basis of the obtained data, the following conclusions could be drawn. The Tertiary deposits belong to the Lower Eocene (Gent Formation, leper Group ). They were deposited in a shallow marine environment. These deposits are covered by Quaternary sediments which fill a valley-like depression scoured in Tertiary deposits. The lower Quaternary sequence consists of probably reworked marine sands, deposited by a fluvial or fluvio-periglacial system during the Weichselian. This sequence is related to or might belong to the Kreftenheye Formation. The upper Quaternary sequence has a Holocene age and consists of the active seabed sediments. This sequence corresponds with the Bligh Bank Formation