Mesozoic and Cenozoic basin configurations in the North Sea - From Depositional Systems to Sedimentary Successions on the Norwegian Continental Margin - page 431

Cenomanian-Danian (sequences K-3-K-6) sion. The recorded increase in thickness of the

Chalk Group towards mainland Norway is in this
respect of particular interest and will be discussed
further below.

Description: The Chalk Group consists of pelagic
chalk and is present in the study area with thick-
nesses up to 500 m to 800 m, as seen in the
Norwegian-Danish Basin (Clausen & Huuse, 1999),
and more than 1500 m in the Central Graben
(Surlyk et al ., 2003). The Chalk Group was
deposited in a quite setting in an epicontinental
sea, although locally affected by ocean bottom
currents (e.g. Esmerode et al ., 2008). Sediments
belonging to the basin configuration 2 are seen
across the whole study area. However, the thick-
ness varies greatly from south to north (Fig. 8).
The data quality is very good across the entire
study area, revealing internal seismic reflectors
belonging to the Chalk Group.
Both the lower and the upper boundaries of the
Chalk Group are marked by high-amplitude reflec-
tions. The internal seismic reflection pattern is
parallel to sub-parallel. At some structural fea-
tures, as in the area of the Utsira High and in the
area at the Øygarden Fault Complex, the Chalk
Group rests on an angular unconformity. An ero-
sional surface is also indicated beneath the Chalk
Group in the Egersund Basin, where the group
rests unconformable on Lower Cretaceous strata
(Fig. 8).
The sediments of the Chalk Group are less
than 100 ms TWT thick in the south-western
parts of the Norwegian-Danish Basin, across the
Ringkøbing-Fyn High and along the Coffee-Soil
Fault Complex. In contrast to this the Chalk Group
thickens gradually towards mainland southern
Norway in the north-eastern parts of the
Norwegian-Danish Basin (>500 ms TWT; Figs 8
and 9). In the Norwegian Channel, where it is pre-
served beneath an erosional unconformity at the
base of the Pleistocene, the Chalk Group thins rap-
idly due to Plio-Pleistocene glacial erosion. The
Chalk Group thins northwards in the northern
North Sea Basin until it becomes absent in parts of
the northern Viking Graben area.
Interpretation: The angular unconformity
recorded beneath the Chalk Group on the Utsira
High and along the Øygarden Fault Zone indicates
subaerial exposure of these structural features in
Early to Middle Cretaceous time. This was fol-
lowed by transgression on top of these SUs and
with deposition of the Chalk Group during ris-
ing sea-level and highstand. The Egersund Basin
was probably infilled during Early Cretaceous
with subsequent exposure and later transgres-

Deposits influenced by rifting and initial
opening of the NE Atlantic: Basin
configuration 3

In the late Palaeocene and Eocene times, deposi-
tion of sequences CSS-1 and CSS-2 corresponded
with uplift and eastward tilting of the East
Shetland Platform and rapid regional subsidence
in the northern North Sea area, which was not
related to faulting (Ziegler, 1990; Milton et al .,
1990; Jordt et al ., 1995, 2000; Faleide et al ., 2002;
Anell et al ., 2011).

Late Palaeocene to earliest Eocene
(sequence CSS-1)

Description: Sequence CSS-1 conformably over-
lies the Upper Cretaceous to lowest Palaeocene
Chalk Group and the upper boundary is equiva-
lent to the top of the Balder Formation. Both
boundaries are characterised by and mapped
along strong amplitude anomalies in the Central
North Sea area, which conformably overlie the
Chalk Group and underlie the Eocene sequence,
respectively (Fig. 9). The data quality of sequence
CSS-1 is poor throughout the study area, although
upper and lower boundaries are easily traced
along the amplitude anomalies. Outside this area,
the identification of seismic reflections inside the
section is hampered by low acoustic impedance
contrast, although the lower and upper seis-
mic reflections are easily mapped along their
amplitude anomalies. One depocentre of sequence
CSS-1, dated to late Palaeocene to early Eocene, is
located in the southern Viking Graben area
(≥700 ms TWT). Sequence CSS-1 in this sub-basin
thins northward along the axis of the Viking
Graben structure. In the northern North Sea,
another depocentre of the same age is documented
offshore Sognefjord and a third is located in the
Ling Depression offshore Hardangerfjord (>300 ms
TWT; Fig. 10A). In the south-eastern parts of the
study area, in the Norwegian-Danish Basin,
sequence CSS-1 reveals one minor depocentre
(>200 ms TWT; Fig. 10A). The CSS-1 sequence,
including the depocentre offshore Sognefjord, is
cut by an erosional unconformity closest to the
Norwegian mainland.