Svarte Formation (new) (Svarteformasjonen)
(From NPD Bulletin no. 5)
Shetland Group
Name
Named after Halvdan Svarte, King of Ringerike, Norway about A.D. 850.
Well type section
Norwegian well 25/1-1
from 3995 to 3807 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 3447 to 3207 m, coordinates N 61°5r05.98", E 03°46'28.22" (Fig. 34). No
cores.
Norwegian well 24/9-1
from 3992 to 3804 m, coordinates N 59°16'09.48", E 01°47'31.18" (Fig. 35). No
cores.
Thickness
In the Viking Graben, the formation is 188 m thick in the type well 25/1-1,
240 m in well 35/3-2 and 188 m in well 24/9-1.
Lithology
The formation generally consists of mudstones interbedded with limestones.
Sandstones occur in the Agat area. The content of limestones relative to
mudstones is generally lower in the northern than in the southern part of
the Viking Graben. The mudstones are medium to light grey, often calcareous,
occasionally micaceous, glauconitic and pyritic. The limestones are mainly
white to medium grey, argillaceous or sandy. The sandstones are clear to
light grey and often cemented by calcite.
Basal stratotype
The lower boundary shows a general upward decrease in gamma-ray intensity
and an increase in velocity from the Cromer Knoll
Group into the Svarte Formation (Fig. 34). This is due to a higher content
of carbonate in the Svarte Formation.
Characteristics of the upper boundary
The upper boundary is generally easily located, and is characterised by an
increase in gamma-ray intensity and a distinct decrease in velocity from
the Svarte Formation up into the Blodøks Formation
(Fig. 33). This is caused by a lower carbonate content in the Blodøks
Formation.
Distribution
The formation is present in the Viking Graben and north of the Tampen Spur
towards the Marulk Basin. It is, however, lacking on structural highs such
as the Lomre Terrace (e.g. Norwegian wells 35/8-1 and 35/8-2), (Nybakken
and Backstrøm, in press).
Occurrences of formation tops in wells
Age
Cenomanian.
Depositional environment
Open marine.
Remarks
The Svarte Formation is time-equivalent with the Hidra
Formation in the central North Sea and with the informal "formation A" of
Deegan & Scull (1977) (Fig. 6).
