Tryggvason Formation (new) (Tryggvasonformasjonen)
(From NPD Bulletin no. 5)
Shetland Group
Name
Named after Olav Trygvason, a Norwegian king (A.D 995-1000),
Well type section
Norwegian well 25/1-1
from 3790 to 3582 m, coordinates N 59°53'17.40", E 02°04'42.70" (Fig. 33).
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" (Fig. 34). No
cores.
Norwegian well 24/9-1
from 3783 to 3638 m, coordinates N 59°16'09.48", E0P47'31.18" (Fig. 35).
No cores.
Norwegian well 30/11-3
from 3207 to 3162 m, coordinates N 60°02'38.59", E 02°32'15.47" (Fig. 36).
No cores.
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.
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) 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 brownishgrey and argillaceous. The sandstones are clear to light
grey, very fine to fine grained and cemented by calcite.
Basal stratotype
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 (Fig. 33 and 34). This is due to the difference in
carbonate content.
Characteristics of the 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 (Fig. 33). This log change is due to
the lower carbonate content of the Kyrre Formation.
Distribution
The formation is present in the Viking Graben and
northern Tampen Spur area towards the Marulk Basin.
Occurrences of formation tops in wells
Age
Early to Mid Turonian.
Depositional environment
Open marine.
Remarks
The Tryggvason Formation is time-equivalent with the Herring Formation
and the lower part of the Hod Formation in the central
North Sea, and also with the informal "formation C" of Deegan & Scull (1977)
(Fig. 6).
