Mesozoic and Cenozoic basin configurations in the North Sea - From Depositional Systems to Sedimentary Successions on the Norwegian Continental Margin - page 429

as sub-sequence J-2.1 and is characterised by a
prograding pattern with dip-direction of the clino-
forms towards W-SW (Fig. 6D). The clinoforms are
downlapping onto the sub-sequence J-2.1 with a
parallel oblique geometry. The maximum height
of the clinoforms is approximately 400 ms TWT
and they dip between 3 o and 4 o .
The J-2 sequence, as seen in the Egersund Basin,
onlaps a structure at the Lista Fault Blocks in the
east, which is also associated with an erosional
surface in the Upper Jurassic (Fig. 7).
Interpretation: The downlap surfaces within
both sub-sequences are interpreted as maximum
flooding surface (MFS) based on their downlap
patterns, both in the Åsta Graben-Stord Basin and
in the Egersund Basin. In the Egersund Basin, sub-
sequences J-2.1 and J-2.2 are divided by the upper
sequence unconformity of sub-sequence J-2.1. The
sediments of sub-sequence J-2 were sourced from
the east, into the northern Horda Platform area,
indicating a continued depositional history from
the sub-sequence J-1. The W-SW progradation of
sub-sequence J-2.1 in the Åsta Graben-Stord Basin
may reflect a source area to the E-NE. The sub-
sequence J-2.2 in the Egersund Basin was depos-
ited to the south-west of sub-sequence J-2.1, which
is taken to indicate that the shoreline was displaced
farther into the basin during deposition of sub-
sequence J-2.2. The source area may have been the
Lista Fault Blocks, based on the erosional surface,
which is correlated to the Jurassic sequence J-2
(Fig. 7). The water depths appear to have been
approximately the same during deposition of sub-
sequences J-2.1 and J-2.2 in the Egersund Basin, as
shown by the clinoform heights, although expo-
sure of the shorefaces is indicated by the upper
sequence boundaries of both sub-sequences. The
oblique geometry of the prograding systems belong-
ing to sequence J-2 is typical for coarse-grained sys-
tems (Mitchum et al ., 1977; Veeken, 2007).

The lower bounding surface of sub-sequence
K-2.1 corresponds with the upper SU of sequence
J-2 in the Egersund Basin, whereas the upper
bounding surface is characterised by onlap from
younger Lower Cretaceous strata. A downlap sur-
face is recorded internally in sub-sequence K-2.1
(Fig. 6E). The sub-sequence K-2.1 has a maximum
thickness of 400 ms (TWT) (Fig. 6E) and it pinches
out towards the Utsira High in the west and against
Sele High and the southern boundary of the
Egersund Basin in the south-west and south,
respectively. Below the downlap surface, sub-
sequence K-2.1 consists of parallel, sub-horizontal
seismic reflectors whereas SW dipping clinoforms
are seen above the downlap surface (Fig. 6E). The
clinoforms included in sub-sequence K-2.1 have a
sigmoidal geometry. The height of the clinoforms
is approximately 250 ms TWT.
Interpretation: The sigmoidal geometry of the
prograding clinoforms indicates that sub-sequence
K-2.1 consists mainly of fine-grained material
(e.g. Bullimore et al ., 2005). The prograding K-2.1
probably represents shelf deposits, based on the
clinoform heights. This is in accordance with
Wood & Barton (1983) and White & Latin (1993)
who state that the Lower Cretaceous succession in
the Norwegian-Danish Basin is characterised by a
package of sediments characterised by horizontal
reflections representing inner shelf deposits. The
pinching out of K-2.1 towards the Utsira High,
the Sele High and the southern boundary of
the Egersund Basin indicates that in the Early
Cretaceous the Egersund Basin was separated
from the Viking Graben in the west by the Utsira
High and the Sele High, like it was in the Late
Jurassic. The sediment transport may have been
through the Hardangerfjord, similar as for sub-
sequence J-2.1 in the Stord Basin-Åsta Graben
(Fig. 5B).

Sequences of the late post-rift stage:
Basin configuration 2 Aptian-Albian (sub-sequence K-2.1)

Description: In the study area, one prograding
sub-sequence (K-2.1), which is incorporated in
the K-2 sequence of Gabrielsen et al . (2001;
Aptian to Albian age), is recorded in the area west
of the Stavanger Platform and the Lista Fault
Blocks. The data quality of the Cretaceous succes-
sion is good, although seismic mapping is chal-
lenged by low contrasts in acoustic impedances.
However, mapping the sub-sequence K-2.1 was
unproblematic.

Basin configuration 2 includes the Late Cretaceous
to Danian Chalk Group. At the time of deposition,
most of the structures which acted as local source
areas during basin configuration 1 had been eroded
to base level and subsequently transgressed. This
gave rise to a continuous basin that extended
across the entire study area (e.g. Gabrielsen et al .,
2001; Kyrkjebø et al ., 2001; Surlyk et al ., 2003),
which is the most prominent feature of basin
configuration 2.