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parts of the fan, whilst background sedimenta-
tion dominated by claystone with silt occurred
in inactive areas. The most distal south-eastern
part of the fan was only active in the (maxi-
mum) growth phase of the fan, whereas the
most proximal north-western part of the study
area appears to have been active in the initia-
tion, growth and retreat phases.
4
Sharp channel bends, wide avulsion angles
and large, complex, frontal splays are associ-
ated with structurally confined sand fairways.
aggradation in the north-east-oriented struc-
tural confinements culminated in avulsions
that directed channels back to the more
regional south-east dip direction. The flow
directions into and out of confinements were
thus around 90° different from the flow direc-
tions within confinements. The turns were
accomplished by sharp bends or wide avulsion
angles. Unconfined channels cross substratum
faults and tend to make frequent low-angle
avulsions that originate close to the channel-
splay-transition zone and are a response to
slope advantage on the sides of frontal splays.
5
Flows entered a deeper-floored base level in
the outboard Stord Basin and started to heal
the break in slope by headward erosion and
basinward splay deposition. The slope disequi-
librium was further healed by aggradation of a
levee-confined channel over the frontal splay.
6
avulsions and fan switching appear to have
resulted in a complex stack of channel-frontal
splay pairs, commonly draped by background
sediments deposited over abandoned fan
branches. amalgamation and erosion at the
bases of channels is likely to have promoted
communication between different channel-
splay pairs. Injectites are documented from
core and inferred from abnormal sand thick-
ness in mounds and are expected to connect
sand bodies otherwise separated by shale.
7
an area with large structures formed by post-
depositional sediment remobilisation has been
mapped in the Frøy Field area. The deforma-
tion of the Sele Formation is expressed as
mounds and depressions separated by faults.
The Hermod type well (i.e. 25/2-6) is situated
on a mound, whereas well 25/5-1 is a 'type
well' for the depressions.
8
The severe post-depositional sediment remobi-
lisation over the Frøy Field occurred in the
Early Eocene, probably due to gas seepage to
blocked pockmark craters.
9
Clean sandstone occurs in channels, splays,
injectites and steep-sided mounds. The abun-
dance of clean and mostly homogeneous sand-
stone is attributed to the original sediment
calibre that was delivered to the study area by
feeder channels. The clean sand was remobi-
lised post-depositionally and it is hypothesised
that the deformation was caused by gas escap-
ing from deeper strata to the sea floor.
ACKNOWLEDGEMENTS
We would like to acknowledge Per Øyvind
Seljebotn and Snorre Heimsund who contributed
to the early phases of this study. Ellen Lindland is
acknowledged for technical advice on, and pro-
duction of, all illustrations in this paper. We would
also like to thank Erik Imsland Wathne for sharing
with us documentation of some of his unpublished
work from the Greater Frigg area and for enlight-
ening discussions over some relevant cores. The
authors would also like to express our gratitude to
det Norske Oljeselskap, Bayerngas Produksjon
Norge and Faroe Petroleum Norge for giving their
permission to publish seismic data from Norwegian
Production Licence 414 and for many fruitful dis-
cussions during our years of work in the area.
Gratitude is also expressed to Norwegian Energy
Company for giving us the opportunity to work on
the Hermod Fan. The reviewers Trevor Elliot,
Massimo dall'asta and Jonathan Wonham are
acknowledged for constructive and useful feed-
back which improved the manuscript.
REFERENCES
Ahmadi,
Z.,
Sawyers,
M.,
Kenyon-Roberts,
S.,
Stanworth,
B.,
Kugler,
K.,
Kristensen,
J.B.
and
Fugelli,
E.
(2003)
Palaeocene stratigraphy. In:
The Millenium Atlas:
Petroleum Geology of the Central and Northern North
Sea
(Eds d. Evans, C. Graham, a. armour and
P. Brathurst) pp. 235-259. Geological Society, London.
Baas,
J.H.
(2004) Conditions for formation of massive tur-
biditic sandstones by primary depositional processes.
Sed. Geol.
,
166
, 293-310.
Babonneau,
N.,
Savoye,
B.,
Cremer,
M.
and
Bez,
M.
(2010)
Sedimentary architecture in meanders of a submarine
channel: detailed study of the present Congo turbidite
channel (Zaiango Project).
J. Sed. Res.
,
80
, 852-866.
Bergslien,
D.
(2002) Balder and Jotun - two sides of the
same coin? a comparison of two Tertiary oil fields in
the Norwegian North Sea.
Petrol. Geosci.
,
8
, 349-363.
Blikeng,
B.
and
Fugelli,
E.
(2000) application of results
from outcrops of the deep water Brushy Canyon
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