Mesozoic and Cenozoic basin configurations in the North Sea - From Depositional Systems to Sedimentary Successions on the Norwegian Continental Margin - page 434

Early Oligocene (sequence CSS-3) and Late
Oligocene (sequence CSS-4)

The lower boundary of sequence CSS-3 is char-
acterised by an amplitude anomaly across exten-
sive parts of the study area. Also, in the eastern
parts of the Norwegian-Danish Basin sequence
CSS-3 is downlapping an erosional unconform-
ity terminating the underlying CSS-2 sequence
(Fig. 2 F and G). Termination of sequence CSS-2
is also seen at the Patchbank Ridge, offshore
Hardangerfjord (Fig. 12). The boundary separating
sequences CSS-3 and CSS-4 is characterised by an
amplitude anomaly in most of the northern North
Sea and the Central Graben area. In the eastern
North Sea, sequence CSS-4 onlaps the sequence
boundary on top of sequence CSS-3. The upper
boundary of sequence CSS-4 is characterised by
toplap truncation (Fig. 2).
Easterly dipping clinoforms are observed within
the CSS-3 sequence in the Viking Graben area. In
the Norwegian-Danish Basin, sequence CSS-3
downlaps onto sequence CSS-2, with clinoforms

Description: The Early Oligocene sequence CSS-3
corresponds to the units 4.1, 4.2 and lower parts
of 4.3 of Michelsen & Danielsen (1996). The Late
Oligocene CSS-4 sequence is equivalent to the
upper part of unit 4.3 and the unit 4.4 of the same
authors (Fig. 4). Sequence CSS-3 is observed to
have accumulated across the entire study area,
although with enhanced thickness in two sepa-
rate depocentres, one located in the Viking
Graben area (>300 ms TWT) and the other in the
eastern Norwegian-Danish Basin (>500 ms TWT;
Fig. 11A). The Late Oligocene sequence CSS-4 is
also present throughout the entire study area.
Similar to sequence CSS-3, sequence CSS-4 dis-
plays two main depocentres, one in the Viking
Graben area (>400 ms TWT) and one in the east-
ern Norwegian-Danish Basin (>600 ms TWT;
Fig. 11B).

(A) (B)

N

N

ESP ESP ESP ESP

ESP ESP ESP ESP V V V V V V V V V VG V V V V V V V V V V V V V G

H

P

H H H H H H H H H H

H

S S S S S S S S S S

S S B S

S

Å Å

Å Å Å Å Å Å Å ÅG

PBR PBR PBR P P P P PB

PBR PBR PBR PB B PB P BR P B B PB

E E

E E E E E E E EB

FF Z

FF Z

L L F L B L L L LFB

LFB LFB LFB LFB LFB LFB LFB LFB L B L

NDB NDB NDB NDB NDB NDB NDB NDB ND B

ND B N N N D B

C C C

C C C C C C C C C C

100km 100 km

RF F RFH

RF F F F F F F FH

0 ° 4 ° 8 ° 0 ° 4 ° 8 °

Legend

Source areas
Sediment transportation
Base CSS-3 truncation

> 200 ms TWT > 400 ms TWT > 600 ms TWT

> 300 ms TWT > 500 ms TWT > 700 ms TWT

> 100 ms TWT

Fig. 11. Time-thickness maps of the Oligocene sequences CSS-3 (A) and CSS-4 (B).