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NORLEX


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 5736'54.5", E0418'57.7", (Fig. 29).

Well reference section

Norwegian well 18/11-1 (Elf) from 1878 m to 1964 m, coord N 5804'21.3", E 0432'00.1" (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.

Occurrences of formation tops in wells

Age

Callovian.

Depositional environment

The Sandnes Formation was deposited in a coastal/shallow marine environment.

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