Mesozoic and Cenozoic basin configurations in the North Sea - From Depositional Systems to Sedimentary Successions on the Norwegian Continental Margin - page 438

upper Miocene CSS-7 sequence (Fig. 9). The upper
boundary of the CSS-8 sequence reveals toplap
truncation in the south-western parts of the
Norwegian-Danish Basin, with onlap from the fol-
lowing sequence CSS-9 (Fig. 2). The Pliocene
sequence is truncated in the Norwegian-Danish
Basin as far south as to the Ringkøbing-Fyn High
and the Stavanger Platform. In the Northern North
Sea, sequence CSS-8 is truncated along the
Øygarden Fault Zone in the east and as far west as
to the Utsira High.
Two main depocentres of Pliocene age are
observed along the axis of the Central Graben
(>300 ms TWT) and in the northern North Sea
(>400 ms TWT; Fig. 14A). In the Central Graben
area the sequence is characterised by SW dipping
clinoforms (Fig. 9), whereas, in the northern North
Sea Basin, sequence CSS-8 is characterised by
westerly dipping clinoforms.
Interpretation: Sequence CSS-8 was probably
deposited during a fall in relative sea-level, which
may have corresponded to the growth of the ice-
sheets across northern Europe and North America
(Buchard, 1978; Haq et al ., 1987) in Mid-Pliocene
time 2.5 Ma (Kiltgord & Schouten, 1986). That
sequence CSS-8 downlaps onto the CSS-7 sequence
in the Central Graben area indicates that this sur-
face is a combined TS/MFS and hence, reflecting a
rapid rise in sea-level. Toplap truncation in the
Norwegian-Danish Basin indicates that the shore-
line of the southern Norwegian landmasses
stretched as far out as to the north-eastern margin of
the Central Graben area in Late Pliocene time. The
W-SW direction of progradation of sequence CSS-8
indicates that in the east and south-east of southern
Norway acted as the source area. The truncation of
the Pliocene sequence in the Norwegian-Danish
Basin as far south as to the Ringkøbing-Fyn High
and the Stavanger Platform appears to coincide
with the maximum extent of the Plio-Pleistocene
glaciers in the Central North Sea area (Fig. 9).

sequence in the Norwegian-Danish Basin (Fig. 2)
and onlaps the CSS-6 sequence at the mid-North
Sea High (Fig. 9). Sequences CSS-9 and CSS-10
are separated by an erosional surface, recorded in
the north-eastern and northern parts of the study
area parallel to the present coast line of southern
Norway. This erosional surface truncates the
underlying Cenozoic succession, as these are
inclined upwards towards north-east and east.
The top of the CSS-10 sequence corresponds with
the present day seabed. In the northern North Sea
area, sequence CSS-9 is seen as a westward pro-
gradational unit (>400 ms TWT), whereas in the
Central Graben area, a more than 300 ms TWT
thick prograding wedge built out towards SW,
onlapping the Mid-North Sea High (Figs 9 and
14B). Also, easterly dipping prograding clino-
forms belonging to sequence CSS-9 are recorded
in the western part of the study area, in the Moray
Firth Basin area.
The CSS-10 sequence infilled the North Sea
Basin in the Central Graben area (>400 ms TWT)
and pinches out northwards across the Utsira
High area and the Patchbank Ridge (Fig. 14C).
The CSS-10 sequence filled the remaining accom-
modation space in the Central Graben area; seismic
reflections, being sub-parallel to the present-day
sea floor (Fig. 9) are in favour of a vertical aggrada-
tion mechanism for the sediment infill succession.
Interpretation: The lowermost boundary is
interpreted as a combined TS/MFS and hence a
non-accretionary TST. The westerly and SW pro-
gradation of sediments belonging to sequence
CSS-9 indicates that the main sediment source
area was located to the east and north-east.
However, erosion of landmasses in the UK is also
indicated from the easterly dipping clinoforms
in the Moray Firth Basin area. The parallel to sub-
parallel nature of the seismic reflections of
sequence CSS-10 in the Norwegian Trench indi-
cates that the sediments were deposited after the
main tilting of the Mesozoic and Cenozoic
successions.

Pleistocene (CSS-9 and CSS-10)

Description: The Pleistocene CSS-9 and CSS-10
sequences are well imaged in the reflection seis-
mic data in the study area. Sequence CSS-9 is
truncated at the Coffee-Soil Fault Complex and
the Sele High in the Central North Sea and at the
Øygarden Fault Complex and the Utsira High in
the northern North Sea.
The lowermost boundary of sequence CSS-9 is
characterised by regional downlap onto the CSS-8

DISCUSSION

The present study reviews basinal configurations
in the North Sea area throughout the Late Mesozoic
and Cenozoic. The two main tectonic phases which
affected the study area, were the Permo-Triassic
and Late Jurassic to earliest Cretaceous rifting (e.g.
Ziegler, 1975, 1989, 1990; Gabrielsen et al ., 1990;