Channel development in the chalk of the Tor Formation, North Sea: evidence of bottom current activity - From Depositional Systems to Sedimentary Successions on the Norwegian Continental Margin - page 557

2/4 2/5

To r

S.E. To r

Ekofisk

A

A

B

C

D

E

Eldfisk

B

F

2/7 2/8

Salt-dome/wall structure

Inversion structure

C

D

E

Legend
Interpreted limits of the channel-like structure

Top Ekofisk Formation

Top Tor Formation

Top Magne Formation 2km

F

Fig. 5. Series of seismic sections across the channel developed parallel to the northern slope of the Lindesnes Ridge.
The inset map shows the location of the seismic lines and the funnel-shaped, plan-view geometry of the palaeochannel
extending towards the south-east (Fig. 4).

to black interval in Figs 5, 6 and 7) and an upper
unit characterised by negative amplitude (orange
to red interval in Figs 5, 6 and 7). The upper unit
was penetrated both by wells 2/8-15 and 2/4-12,
whereas the lower unit was partially penetrated
by well 2/8-15 (Figs 6 and 7).
In the western segment, the channel has a well-
defined perimeter and fairly parallel margins
(Fig. 4). Close to the Ekofisk Field, the channel's
northern margin is slightly irregular, probably
because of the local alteration of seismic response
by fluids and faults. In seismic cross-sections, the
western segment of the channel fill has a tabular
geometry with a uniform thickness of 100 m to
150 m and width of 1 km to 2 km. The channel-fill
internal reflections have moderate to weak ampli-
tudes (Fig. 5, Sections A and B). The channel base
is irregular and incised into the surrounding

seismic facies of parallel reflections. The channel-
fill top correspond to the boundary between the
Tor and Ekofisk formations and coincides on
seismic data with a zero phase crossing at the base
of a strong positive amplitude reflection correlating
to the high gamma ray interval of the Ekofisk
dense zone (Figs 5, 6 and 7). In Block 2/4,
the Tor-Ekofisk boundary is somewhat irregular
and the channel margins appear to be well defined
and relatively steep (Fig. 5, Sections A and B). The
transition from the western to the central segment
of the channel is near seismic Section C (Fig. 5) on
the eastern flank of the Ekofisk Field.
The channel's central segment is characterised
by a sudden expansion of its northern margin
towards the NE in the four-corners area of blocks
2/4, 2/5, 2/7 and 2/8 (Fig. 4), resulting in channel
widening from 2 km in its western segment to