Tryggvason Formation (new) (Tryggvasonformasjonen)

(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

Shetland Group

Name

Named after Olav Trygvason, a Norwegian king (A.D 995-1000)

Lithology

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.

Thickness

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.

Geographical Distribution

The formation is present in the Viking Graben and northern Tampen Spur area towards the Marulk Basin.

Well type section

Norwegian well 25/1-1 from 3790 to 3582 m, coordinates N 59°53'17.40", E 02°04'42.70" (Figure 33 in Isaksen & Tonstad (1989)). No cores.

Well reference sections

Norwegian well 35/3-2 from 3190 to 2864 m, coordinates N 61°5r05.98", E 03°46'28.22" (Figure 34 in Isaksen & Tonstad (1989)). No cores.
Norwegian well 24/9-1 from 3783 to 3638 m, coordinates N 59°16'09.48", E0P47'31.18" (Figure 35 in Isaksen & Tonstad (1989)). No cores.
Norwegian well 30/11-3 from 3207 to 3162 m, coordinates N 60°02'38.59", E 02°32'15.47" (Figure 36 in Isaksen & Tonstad (1989)). No cores.

Upper and lower boundaries

Upper Boundary

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.

Lower Boundary

The lower boundary is defined by a decrease in gamma-ray intensity and an increase in velocity from the Blodøks Formation into the Tryggvason Formation (Figures 33 and 34 in Isaksen & Tonstad (1989)). This is due to the difference in carbonate content.

Age

Early to middle Turonian.

Correlation

The Tryggvason Formation is time-equivalent with the Herring Formation in the Central North Sea and the Macbeth Formation in the Northern North Sea, and also with the informal "formation C" of Deegan & Scull (1977) (Figure 6 in Isaksen & Tonstad (1989)).

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Depositional environment

Open marine.