Sotra Member (New)

updated to follow: Stratigraphic Guide to the Rogaland Group, Norwegian North Sea. Harald Brunstad, Felix M. Gradstein, Jan Erik Lie, Øyvind Hammer, Dirk Munsterman,  Gabi Ogg, and Michelle Hollerbach. Newsletter on Stratigraphy, vol 46/2 pp137-286, 2013.

Rogaland Group, Lista Formation

Unit definition

The Sotra Member is attributed to the intra Lista Formation sandstones in subarea NW in Figs. 1.

Fig 1: Location map of the Members of the Lista Formation.



The Sotra Member is defined for the first time in this study. This member status is attributed to sandstones of intra Lista Formation with an eastern provenance in the Sogn Graben and the Stord Basin.

Derivatio nominis

The Sotra Member is named after one of the largest islands in Hordaland.

Type well

Norwegian well 35/8-3 (New, Fig. 91). Depth 1665-1709 mRKB. Coordinates N 61°21'05.35", E 03°32'02.63". No cores.

Fig. 91. Well 35/8-3 Composite log Rogaland Group. Stratigraphic position of the Sotra Member is outlined in stratigraphic column to the right.

Reference wells

Norwegian well 35/3-1 (New, Fig. 92). Depth 1392-1422 m RKB, major body of Member. Several thinner sandstone beds in interval 1422-1540 m RKB. Coordinates N 61°50'41.89", E 03°43'41.36".

Norwegian well 35/11-3S. Depth 1905-1997 mRKB. Coordinates N 61°10'59.27", E 03°20'18.47". Core 1.

Fig. 92. Well 35/3-1 Composite log Rogaland Group. Stratigraphic position of the Sotra Member is outlined in stratigraphic column to the right.


The Sotra Member consists of clear to white, sometimes grey quartzitic sandstones. Grain size is fine to very coarse, but predominantly medium and sorting poor to moderate, with angular to subrounded grains. The sandstones have traces of pyrite, glauconite and mica, and are occasionally calcite cemented. There are few cores taken from the Sotra Member, and thus there is limited information about variability in facies. A core photo example from Norwegian well 35/11-3 S is shown in Fig. 93.

Fig. 93. Example of massive, clean, structureless sandstones of the Sotra Member 35/11-3. Photo from NPD Fact Pages at

Wireline log characterization

Wire line log response of the Sotra Member is blocky to serrated, representing thick clean sandstones and series of thinner sandstone layers in alternation with mudstones. Sometimes zones of high velocity sonic readings and high values on density logs are seen, which seem to correspond to zones of calcite cementation in the sandstones.

In some cases content of glauconite in the sands increases their natural radioactivity and thereby makes it difficult to assess the sand amount and the distinction between the Sotra Member and the Lista Formation from gamma logs. In these cases their identification must rely on other logs such as density, neutron and resistivity logs.

Upper boundary

The Lista Formation usually overlies the Sotra Member, and the boundary is usually characterised by higher gamma-ray readings and lower velocity upwards into the Lista Formation.

Lower boundary

The Sotra Member overlies the Lista and sometimes the Våle Formation, and the boundary is characterised by lower gamma readings and increased velocity upwards from the Lista and Våle Formation below.



The Sotra Member is often seen as scattered stringers of m scale and up to some tens of meters. Thickness of the Sotra Member is 44 m in Type well 35/8-3, 92 m of blocky sand in reference well 35/11-1 and 132 m of blocky sand in 31/2-19 S.

Seismic characterization

To the east in the distribution area the sandstones belonging to the Sotra Member typically occur in westwards dipping layers in westwards thinning wedges (prograding slope) of the Rogaland Group on the Måløy Terrace and the Horda Platform, partly stretching into the Sogn Graben. In some cases a blocky log response corresponds to mounded geometries, especially in the lower part of the wedge.

West of the wedge, in what is believed to represent a basin floor setting, channels and lobe like geometries sometimes stand out as thickness increase of the Lista Formation, and can be interpreted as the presence of sands belonging to the Sotra Member. Fig. 94 shows a seismic section through Norwegian well 35/11-1, with the Sotra Member shown.

Fig. 94. Seismic Cross section through southern parts of Quadrant 35 and well 35/11-1. Inferred presence of Sotra Member is outlined.


Late Middle to Late Paleocene (Late Selandian to Early Thanetian)

Biostratigraphy and age

Being contained in the Lista Formation, the age of the Sotra Member is bounded by that of the Lista Formation. The Lista Formation belongs in the foraminiferal Zone NSR2A - 2B, A. ruthvenmurray - R. pauperum (Gradstein & Bдckstrцm, 1996), and the dinocyst Zones D3b - D4 in Luterbacher et al. (2004). The age is Late Selandian through Thanetian, late Middle through Late Paleocene. See also description for the Lista Formation.

Correlation and subdivision

The Sotra Member is divided into three units: Sotra L1, Sotra L2 and Sotra L3, corresponding to Lista L1, L2 and L3 (see Lista Formation).

Geographic distribution

The Sotra Member is present from the area south of 62°N, stretching south to the Horda Platform, and westwards into the Sogn Graben (Figs. 1 and 72). It is not known whether the Sotra Member is stretching further southwards into the Sogn Graben due to lack of wells in that area.

Depositional environment

In eastern areas the Sotra Member was deposited as gravity flow sands in a prograding slope setting sometimes in submarine slope fans. Further west in the Sogn Graben they were deposited in a basin floor setting (Fig. 72).

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