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NORLEX


Mandal Formation

(From NPD Bulletin no. 3)

Tyne Group

Name

From a town on the south coast of Norway. It replaces the Kimmeridge Clay Formation as used by authors in the Central Graben area (e.g. Ofstad, 1983). The name was informally proposed by Hamar et al., (1982).

Well type section

Norwegian well 7/12-3A (BP) from 3514 m to 3552 m, coord N 5706'24.54", E0248'41.56",(Fig. 44).

Well reference sections

Norwegian wells 2/1-2 (BP) from 3300 m to 3316 m, coord N 5657'30.76", E 03 12'32.07", (Fig. 33) and 1/9-3 (Statoil) from 4265 m to 4319 coord N 5624'56.2'', E0254'15.15", (Fig. 43).

Thickness

In the type well 38 m and in the reference wells 16 m and 54 m. The thickness usually varies between 10 m and 70 m and generally thins over structural highs.

Lithology

The formation consists of a dark grey-brown to black, slightly to non-calcareous, carbonaceous claystone becoming fissile in places. It is characterized by a very high level of radioactivity which is a function of organic carbon content. In addition it has an anomalously low velocity, a high resistivity and a low density. It may con-tain thin stringers of limestone/dolomite and, in some areas, sandstone (e.g. 1/9-3).

Boundaries

The contacts of the Mandal Formation with underlying and overlying sediments are easily recognized on logs due to its high gamma ray and resistivity readings and its low velocity and density.

Distribution

The Mandal Formation is found in the Central Graben, and on the margins of the Southern Vestland Arch. The northern limit is the Jasren High.

Occurrences of formation tops in wells
Isopach map FARSUND-MANDAL

Age

Volgian to Ryazanian.

Depositional environment

The formation was deposited in an anaerobic marine environment with high organic productivity and restricted bottom circulation.

Remarks

See Draupne Formation.

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