Fiskebank Member (revised)
Rogaland Group, Sele Formation
Unit definition
The Fiskebank Member is attributed to the the Intra Sele Formation sandstones in
Subarea SE in Figs. 12 and 13, where it is found in the Norwegian Danish Basin, the
Siri Canyon Area and in the eastern parts of the Central Graben in the Gyda-Ula Area.
Name
The former Fiskebank Formation defined by Deegan and Scull (1977) is hereby
downgraded to the Fiskebank Member. The Fiskebank Member has also been attributed to
the intra Sele Formation sandstones of the siri canyon (Ahmadi et al., 2003).
Although Schiöler et al. (2007) have redefined the Fiskebank Member to the Kolga
Member at the Danish side of the Siri Canyon, we keep the name Fiskebank Member for
the Norwegian side in this area.
Derivatio nominis
Named after the Fiskebank (Fisher bank), offshore southern Norway. Named by Deegan &
Scull (1977).
Type well
Norwegian well
9/11-1:
1483 to 1335m (new definition), coordinates N 57°00'41.40", E 04°00'33.52" (Fig.
117). No cores.
Fig. 117. Well 9/11-1 Composite log Rogaland Group. Stratigraphic position of the
Fiskebank Member is outlined in stratigraphic column to the right.
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Reference wells
Norwegian well
8/9-1 (Fig. 118):
1315 to 1375 mRKB (new definition), coordinates: 57°26'27.28" N, 3°51'03.48" E. No
cores
DK well Siri-3 (Kolga Member seen from seismic to be continous with the Fiskebank
Member Norway), (Fig. 119). Depth 2206.4-2036.1 mRKB. Coordinates N 56°30'34.92",
E 05°03'48.27". Cores: Core 2, 2065-2120 mRKB.
DK Well: Nini-3, 1717.2-1700.4 mRKB. Coodinates: N56°41'31.96", E05°24'12.35"
(Fig. 119). Cores: Core 1, 1684-1765 mRKB.
Fig. 118. Well 8/9-1 Composite log Rogaland Group. Stratigraphic position of the
Fiskebank Member is outlined in stratigraphic column to the right.
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Fig. 119. Well Composite logs wells DK Nini-3 and Siri-3. Position of the
Fiskebank Member is outlined in the stratigraphic column to the left. Modified from
Schiøler et al. (2007) to fit definitions made in the nomenclature for the Norwegian
North Sea (this paper).
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Composition
The Fiskebank Member consists of dark grey to grey brown very fine grained
sandstones, but varies from medium to silt sized and is remarkably clean (<0.1%
detrial clay). It has subrounded grains, is fairly uniform, well sorted, micaceous,
partly micromicaceous, friable, and with calcareous cement in places. There is a high
content of black to dark glauconite pellets (15-25%, Hamberg et al, 2005) that are
found as rounded pellets of the same grain size as quartz grains. Pyritic grains may
also be present. Locally sandstones may be cemented by calcite or chlorite.
In Danish cores the sandstones of the Fiskebank Member (Kolga Member close to the
Norwegian Border) are observed as generally massive, homogenous and with few
structures. Faint deformed lamination and dish and pillar structures are rather
common, and witness post sedimentary water movement in sediments. There are few signs
of primary sedimentary structures in sandstones, although a few examples of faint
cross bedding seem to occur.
Sandstone intrusions are frequently found associated with the upper boundary of
sandstones bodies, often with an abundance of angular and tabular mudstone clasts
(Hamberg et al., 2005).
Wireline log characterization
The Fiskebank Member is often associated with lower gamma ray response than the
surrounding shales of the Sele Formation (and possibly upper
parts of the Lista
Formation). However, it is sometimes difficult to distinguish from the shales by
gamma logs because of the content of radioactive grains of mica and glauconite in the
sandstones. Thus other logs such as neutron, density and resistivity logs are
sometimes more reliable for detecting the sands. Often a coarsening upwards trend can
be inferred from the logs.
Lower boundary (revised)
The lower boundary of the Fiskebank Member is identified by an upwards transition
from the shales of the Sele or the Lista Formation below to the coarser sediments of
the Fiskebank member above.
In the Siri Canyon the log response is characterised by a sharp upwards change from
high gamma-ray readings and low velocity in the shales to low gamma-ray readings and
high velocity in the Fiskebank sandstone. In the north and east the boundary is often
not well defined on the gamma-ray log, and must sometimes be picked by use of sonic
log in combination with other logs such as resistivity and caliper logs to pin point
the shale-sandstone interboundary.
Upper boundary
The Fiskebank Member is usually overlain by the Sele Formation, and the boundary
often marks an abrupt change from sandstones to dark shales. In this case the
boundary is generally seen as an upwards increase in gamma-ray response and a
decrease in velocity.
In some cases the Balder Formation directly overlies the
Fiskebank Member. In these
cases the boundary may be seen as an upwards decrease in gamma-ray response and an
increase in velocity readings.
Thickness
The Member is 82 m in the type well, 60 m in the reference well 8/9-1, 17m in DK Well
Nini-3 and 30 m in Siri-3.
Seismic characterization
In the Siri Canyon area and in the western parts of the Fiskebank member there seems
to be a correlation between thick development of the Sele Formation interval from
seismic and presence of sandstones. From seismic mapping of the Sele Formation
interval, sandstones can be inferred by the observation of elongated thickness
anomalies and from seismic cross sections by the presence of a lenticular to mounded
shape. A seismic line through the Siri Canyon and the Nini Discovery is shown in Fig.
120.
Fig. 120. Seismic line from the axis of the Siri Canyon thorough the Nini discovery.
Presence of the inferred Fiskebank Member is highlighted.
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Age
Latest Paleocene-Earliest Eocene (Late Thanetian-Earliest Ypresian).
Biostratigraphy
Being contained in the Sele Formation, the age of the Fiskebank Member is bounded by
biostratigraphy and age assignments for the Sele Formation. See description for the
Sele Formation in Subchapter 6.1.
Correlation and subdivision
Deposits of the Fiskebank Member occur both above and below the intra Sele Formation
Apectodinum spp. Acme biomarker. Hence, using this criterion the Fiskebank
Member may
be subdivided in a lower unit, Fiskebank S1 and an upper unit, Fiskebank S2.
Geographic distribution
The Fiskebank Member is encountered in the Norwegian - Danish Basin, the eastern parts
of the Central Graben, possibly the Søgne Graben and south eastwards into the Siri
Canyon (Figs. 12, 13 and 102).
Occurrences of member tops in wells
Depositional environment
The coarsening upwards trend seen in the eastern parts of the Fiskebank Member
probably represents shelf to basin margin deposits laid down by a mixture of shallow
marine to turbiditic processes on a prograding slope.
The western and south western parts of the Fiskebank Member was deposited by
gravitational flows in sand-rich basin-floor to toe-of-slope fans systems. The gravity
flows were probably a result of a combination of high density sandy turbidity currents
and sandy debris flow. The high glauconitic content suggests that there was a
significant contribution of shelf sands.
Discoveries with the Fiskebank Member as reservoir
- Siri Field (DK). Part of the reservoir complex. Oil discovery.