Unravelling the nature of deep-marine sandstones through the linkage of seismic geomorphologies to sedimentary facies; the Hermod Fan, Norwegian North Sea - From Depositional Systems to Sedimentary Successions on the Norwegian Continental Margin - page 653

Background shales
of the Sele Fm
Hermod Mbr
sand fairways
Area with mounded
geometries
Substratum faults
(near Base Te rtiary)
Well correlation
panel shown in Fig.4

Fig.6a

II ʹ

25/3-1

25/2-7

C1N

Fig.3

C1

C1S

STORD
BASIN

C2

C2N

25/2-14
25/2-6
25/5-1

Fig.13 & Fig.7

C3

C2S II

26/4-2

FRØY

Fig.6b

C4N

25/5-2

25/6-3

C4

Fig.14

C4S

N

UTSIRA HIGH

0 5 km

Fig. 5. Gross seismic geomorphologies of the outer Hermod fan (Fig. 1) with location of the well section in Fig. 4 and maps
shown in other figures. The four main feeder channels are labelled C1 to C4 and their branches are labelled N for North and
S for South. The green polygon indicates an area over the Jurassic Frøy Field where primary depositional patterns have not
been recognised due to severe post-depositional sediment remobilisation.

(avulsion angles) are variable but in most cases
less than 55°. Channel orientations of the main
feeder channels are mainly towards east or south-
east, but individual channels are locally devi-
ated towards the north-west.
The main channels branch into narrower chan-
nels in a down-stream direction. Branching
appears to be the most common, recurring process
that elongates the fan and avulsion seems to be a
less frequent process that initiates new branching
clusters (Fig. 6a).
Some systematic differences between the north-
ern and southern channels and their branches
may be inferred. The most striking dissimilarities
are firstly that the avulsion angles are lowest in
the southernmost channel and highest in the
northernmost channel and secondly that the
northernmost channels make sharp turns near
substratum faults and have sections that follow
the two dominant fault orientations mapped in
the underlying strata (i.e. north-west to south-east
and south-west to north-east).

The link between channel and fault orientations
suggests that the flows encountered a basin with
subtle steps controlled by substratum faults. The
avulsions had a tendency to direct flows in a more
northerly direction at such steps, particularly in the
northern part of the study area. It appears that
the structural control on sand fairway orientations
is strongest in the north-east (C1N). an exception is
the distal part of C4N which is also structurally
guided and turns towards the north in the out-
board Stord Basin. The C1 channel in the north
and the C4 channel in the south can be considered
as end members with respect to run-out lengths
and growth pattern, as further presented below.

Structural control on channel and splay
evolution

C1S makes a 90° turn towards the left (in a down-
stream direction) and splits into two almost parallel
branches close to a substratum fault. Both branches
run parallel to the fault (i.e. north-eastward) for