This unit was first described by Larsen (1966) as the Børglum Formation. Later it was amended several times, the latest being by Michelsen (1978) who redefined it and reduced it to member status. It has been informally redesignated a formation by Hamar et al. (1982).
In the type area in Jutland, Denmark, the formation is of Kimmeridgian-Volgian age and consists of homogeneous shaly claystones, olive grey to blackish grey, slightly calcareous to non-calcareous, with mica, pyrite, shell fragments and lignite. This description is generally valid also in the eastern and southern parts of the Fiskebank Sub-Basin, as illustrated by the Norwegian well 10/5-1 (Conoco) from 1396 m to 1472.5 m, (Fig. 39). Further to the west a gradual change in lithology can be observed. The amount of carbonaceous material in the upper claystones increases (Norwegian well 9/12-1 (Shell) from 2011 m to 2038 m (Olsen, 1980) resulting in the transition to the Tau Formation in the Fiskebank Sub-Basin and in the Egersund Sub-Basin (see above).
The lower part of the Børglum unit as observed in the eastern areas is probably equivalent to the silty Egersund Formation in the north-west (see above). It is therefore recommended that the Danish nomenclature (the Børglum Member) should be applied in the south-eastern Norwegian Danish Basin and that the revised Norwegian nomenclature as described in this volume should be applied in the north-western area.