Mesozoic and Cenozoic basin configurations in the North Sea - From Depositional Systems to Sedimentary Successions on the Norwegian Continental Margin - page 428

Interpretation: The lower bounding surface is
interpreted as a combined sequence unconformity
(SU) and maximum flooding surface (MFS), based
on the erosional surface and downlap pattern
from sequence J-1. The oblique shape of the clino-
forms indicates that the sediments were deposited
in a high-energy environment, with mainly coarse-
grained material trapped in the clinothems (e.g.
Mitchum et al ., 1977). This is in agreement
with observations by Gibbons et al ., (1993) and
Goldsmith (2000), who concluded that the Upper
Jurassic succession in the northern Horda Platform
area consists of shoreface to proximal shelf sand-
stones interbedded with lagoonal to marine
embayment facies. The SW direction of prograda-
tion indicates the existence of a source area to the
north-east. The accommodation space created
during the syn-rift stage was completely infilled,
as indicated by the truncation of the topsets
(Fig. 6B).

sequence boundary is characterised by toplap
truncation, as seen in the Åsta Graben area (Figs 2
and 6C). A high and continuous seismic reflector
is recorded internally in sequence J-2.1, which
also acts as a downlap surface in the Åsta Graben
area (Fig. 6C). Similar boundary conditions are
recorded for sub-sequences J-2.1 and J-2.2 in the
Egersund Basin (Figs 2 and 6D). In the Åsta
Graben-Stord Basin, the maximum thickness of
sequence J-2 is 300 ms TWT and the sub-sequence
pinches out towards the Utsira High in the west.
In the Egersund Basin, sequence J-2 reveal thick-
nesses up to 500 ms TWT (Fig. 5A). Outside these
basinal areas, sequence J-2 has a maximum thick-
ness of less than 100 ms TWT (Fig. 5A). Both sub-
sequences J-2.1 and J-2.2 in the Egersund Basin
pinch out towards the west and south-west. On
the Utsira High and the Jæren High they are absent
or have an accumulated thickness below that of
the seismic resolution.
In the Åsta Graben-Stord Basin, sub-sequence
J-2.1 displays westerly to SW dipping clinoforms
(Fig. 6C) which have a tangential, oblique geome-
try. The height range of the clinoforms is 150 ms
TWT to 350 ms TWT.
In the Egersund Basin, the sub-sequence J-2.1
represents a W-SW prograding system, which
incorporates W-SW dipping clinoforms (Fig. 6D).
Here, sub-sequence J-2.1 is characterised by
truncation below the offlap break of the topset
(Fig. 7). The maximum height of the clinoforms
is approximately 250 ms TWT and their dip
is approximately 4 o . They have a parallel oblique
geometry (Fig. 6D).
The J-2.2 sub-sequence, which is only recorded in
the Egersund Basin, shares the same characteristics

Volgian (sequence J-2)

Description: For sequence J-2, three independent
prograding systems have been mapped in the study
area, namely in the Åsta Graben-Stord Basin area
(J-2.1) and in the Egersund Basin (J-2.1 and J-2.2)
(Fig. 5A). The top of the J-2.1 sub-sequence is
equivalent to the top Sauda Formation, whereas
the top of J-2.2 sub-sequence is equivalent to the
top Flekkefjord Formation (Fig. 4). The data quality
of both sub-sequences is excellent (Figs 6C and D).
In the Åsta Graben-Stord Basin, the bottom
bounding surface of sub-sequence J-2.1 is charac-
terised by onlap against the prograding J-1
sequences offshore Sognefjord, whereas the upper

WNW ESE

0.0

-0.5

20 km

Fig. 7. Correlation of sequence J-2 in the Egersund Basin and the erosional surface on the Lista Fault Blocks. The section
is flattened on the top J-2.2 sub-sequence. Note the truncation on the Lista Fault Blocks and onlap patterns alongside the
structure.