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 well7/12-3A (BP) from 3514 m to 3552 m, coord N 57°06'24.54", E02°48'41.56",(Fig. 44).
Well reference sections
Norwegian wells 2/1-2
(BP) from 3300 m to 3316 m, coord N 56°57'30.76",
E 03° 12'32.07", (Fig. 33) and
1/9-3 (Statoil) from 4265 m to 4319 coord N 56°24'56.2'',
E02°54'15.15", (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.
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.
