(From NPD Bulletin no. 5)
updated to follow: Stratigraphic Guide to the Cromer Knoll, Shetland and Chalk Groups of the North Sea and Norwegian Sea. Felix M. Gradstein & Colin C. Waters (editors), Mike Charnock, Dirk Munsterman, Michelle Hollerbach, Harald Brunstad, Øyvind Hammer & Luis Vergara (contributors). Newsletter on Stratigraphy, vol 49/1 pp71-280, 2016
Named after Harald "Hardråde" Sigurdsson, a Norwegian King (A.D. 1046-1066).
The formation consists generally of interbedded limestones and mudstones, except in the Troll area where it is thin and consists of a single limestone bed. The limestones are white or pale, moderately hard to very hard. The mudstones are medium to light grey, often silty and calcareous.
The formation is 291 m thick in the type well (30/11-3) and 10 m in well 31/6-2. It is absent on tilted fault blocks in the Troll area (e.g. well 31/2-9).
The upper boundary is towards the Rogaland Group. When it is towards the Lista Formation it is characterised by an upward increase in gamma-ray intensity and a distinct drop in velocity due to a transition from limestones to mudstones (Figure 36 in Isaksen & Tonstad (1989)). An upper boundary towards the Våle Formation lacks the distinct drop in velocity. This is due to the presence of limestones and a more marly facies in the Våle Formation. An upper boundary towards the Ty Formation is shown by a change to sandstone.
Late Campanian to Maastrichtian.