Sandnes Formation (new)
(From NPD Bulletin no. 3)
Recommended as Member in Norlex
Brent Group
Name
From a town on the south-west coast of Norway. This formation was formerly included in the Haldager Formation (Deegan and Scull, 1977).
Well type section
Norwegian well 9/4-3
(Conoco) from 2490 m to 2507.5 m, coord N 57°36'54.5", E04°18'57.7", (Fig. 29).
Well reference section
Norwegian well 18/11-1
(Elf) from 1878 m to 1964 m, coord N 58°04'21.3", E 04°32'00.1" (Fig. 31).
Thickness
17.5 m in the type well and 86 m in the reference well.
Lithology
In the type well the Sandnes Formation consists of a massive white, very
fine to coarse grained glauconitic sandstone. It is firm to friable, poorly
sorted and slightly silty. In other wells (e.g.
18/11-1)
the formation comprises inter-bedded sandstones and shales. The shales are generally dark grey to brown, micaceous and occasionally carbonaceous.
Boundaries
The base of the Sandnes Formation is usually an unconformable contact with
the non-marine Bryne Formation or older Jurassic or
Triassic rocks. Generally it is defined at the base of the massive and clean
sand, usually well marked on both gamma ray and sonic logs. In the type well
the lower boundary is picked at the top of the first coal bed of the
underlying Bryne Formation. In wells where the Sandnes Formation is more
argillaceous it can be harder to distinguish between the Sandnes and Bryne
Formation on log characteristics alone. In such cases the occurrence of
deltaic/non-marine palynofloras would serve to define this boundary
(e.g. 18/11-1). The upper contact with the overlying silts and shales of
the Boknfjord Group is marked by good gamma ray and sonic log breaks.
Distribution
The Sandnes Formation is developed in the Fiskebank Sub-Basin and in the
Egersund Sub-Basin. It is broadly homotaxial with the
Hugin Formation in the southern Viking Graben and the Flyvbjerg Member
of the Haldager Formation in the Danish Sub-basin.
In the transition between the Southern Vestland Arch and the Fiskebank
Sub-Basin it can be difficult to distinguish between the Ula
Formation and the Sandnes Formation, (see Table 4); In such cases detailed paleontology is required to decide the ages of the sands, and hence their lithostratigraphic relationships.
Age
Callovian.
Depositional environment
The Sandnes Formation was deposited in a coastal/shallow marine environment.
