(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 Olav Trygvason, a Norwegian king (A.D 995-1000)
The Tryggvason Formation consists generally of mudstones with interbedded limestones. Interbedded sandstones are common in the Agat area. The content of limestones relative to mudstones is generally lower in the northern part of the Viking Graben (from blocks 30/2 and 30/3 northwards) than in the southern part. At the transition between the Viking Graben and the Horda Platform (e.g. block 30/11; Fig. 36 of Isaksen&Tonstad, 1989) the formation consists of limestone.The mudstones are light to dark grey, often calcareous, occasionally micaceous, glauconitic and pyritic. The limestones are white to light grey or brownish grey and argillaceous. The sandstones are clear to light grey, very fine- to fine-grained and cemented by calcite.
In the Viking Graben, the formation is 208 m thick in the type well 25/5-1, 326 m in well 35/3-2 and 145 m in well 24/9-1. It is 45 m thick in well 30/11-3 on the western margin of the Horda Platform.
The upper boundary shows an increase in gamma-ray intensity and a decrease in velocity from the Tryggvason Formation upwards into the Kyrre Formation (Figure 33 in Isaksen & Tonstad (1989)). This log change is due to the lower carbonate content of the Kyrre Formation.
Early to middle Turonian.