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Tarbert formations show overall wedge-shaped
stratal geometry from a very thin condensed sec-
tion in well 34/11-A-6 through a thicker section in
well 34/11-A5-T3, to an even thicker section in
well 34/11-1. Internally, the beds in this package
show a near-tabular appearance in the lower part
with a more pronounced wedge-shaped geometry
up-section. Further eastward, a dramatic reduc-
tion in thickness is observed from well 34/11-1 to
a very condensed sequence in 34/11-A-10. This is
associated with a westward-throwing normal fault
(see the lower cross-section of Fig.  6) located
between the two wells. Well 34/11-A-12 in the
western part of the cross-section, shows another
expanded thickness of the Ness and Tarbert forma-
tions, similar to well 34/11-1. In the wells 34/11-
A-6 and 34/11-A-10, located in the footwalls, the
combined chronostratigraphic and lithostrati-
graphic correlations and log-patterns show stacked
thinly-bedded sandstones and mudstones with
streaks of coal layers. In contrast, this suggests that
these thinly-bedded Ness and Tarbert formations
are condensed versions of the section found in the
other wells (see Fig.  6). The Heather Formation
shows a similar wedge-shaped stratal unit to the
Ness and Tarbert formations in the same wells.
The tabular nature of the Cook, Drake, Rannoch
and Etive formations (Fig. 6) is consistent with a
pre-rift stage. The observed stratal wedge geome-
try of the Ness and Tarbert formations suggests
that this unit represents the early-rift stage,
possibly entering the main-rift stage as the inter-
nal stratal wedge architecture show a gradual
angular variation up-section (Fig. 7; note the simi-
larity to the wedge-shaped Ness-Tarbert unit in
Fig. 4). The complex stratigraphic development of
the Ness and Tarbert formations in the Kvitebjørn
Field can be put into a more regional context, as
this area is located at the footwall crest of the
Kvitebjørn-Gullfaks Permo-Triassic mega-block
(Figs 1 and 4). The westerly dipping faults, indi-
cated in Fig. 7 with the stratal wedge in between,
are antithetic when seen in relation to the deep-
rooted Statfjord Fault (Figs  1 and 4). This com-
plexity may be associated with footwall flexure at
the location of the Kvitebjørn Field.
To explain the limited thickness of the Ness and
Tarbert formations in the two wells in terms of
erosion (or faulted out section) would also imply
erosion in the nearby wells in order to create the
observed stratal wedge shape. Such an interpreta-
tion seems unlikely, as it challenges the log-
signatures and the biostratigraphic timelines. More
importantly, it is contradicted by the wedge-shaped
geometry of individual members of the Ness and
Tarbert formations. Moreover, it seems unlikely that
a scenario of faulted-out section would apply to all
wells with anomalous Ness-Tarbert thicknesses.
Offshore shale (Heather & Drake fms.)
Offshore shale (Heather Fm.)
Beach barrier
Back barrier
Lagoon
Ta rbert Fm.
Bay-head delta
Delta top
Coastal plain
Coastal plain rivers
Coastal plain w/channels
Ness Fm.
Fig. 7. Schematic 3D illustration of the Brent Group on the Kvitebjørn Field. Syn-sedimentary tectonic development,
producing a wedge-shaped geometry for the Ness-Tarbert package across the Kvitebjørn Field contrasts the tabular Rannoch-
Etive formations (below) and is taken to reflect early-stage rifting. The coastline undulations are largely formed by the fault
crests (see Fig. 11).
 
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