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top of the unit. Final shut-off of fan deposition was
again relatively rapid and left the Ormen Lange sub-
basin deprived of coarse-grained siliciclastic sedi-
ments until renewed progradation in the early
Selandian of the basin marginal slope and deposi-
tion of the so-called 'Lista Fan' (Gjelberg
et al
., 2005).
This rapid return to a sediment-starved basin prob-
ably led to clay-dominated and mud-dominated fills
of the channels incised into the uppermost part of
the Egga sandstone unit (Figs 10 and 11).
Upslope, the Egga sandstone unit is represented by
channel-fill and potential inter-channel facies associ-
ations, capped by channel-mouth lobes; the latter
equivalent to the spill-cap of Gardner
et al
. (2000,
2003). In further upslope mini-basins (e.g. the
Slørebotn Subbasin), the Egga sandstone unit is rep-
resented by a high net-to-gross sandstone unit, again
with seismically identified channel-fills defined by
both erosional and constructional architectures. By
contrast, these are shallower and wider than are those
incised into the underlying Springar sandstone.
Candidate lobe storeys form the uppermost part of the
Egga sandstone unit in such settings. Notably, the
Egga sandstone unit terminates against an arcuate
fault-plane along parts of the outboard edge of the
Slørebotn Subbasin, suggesting local removal of the
unit by late-stage gravitational collapse.
Stratigraphic development: The Egga fan repre-
sents the renewed arrival and infilling of a sandy
fan in upslope mini-basins or slope terraces,
followed by bypass and overspill into the neigh-
bouring, downslope subbasin, such as the Ormen
Lange subbasin (Fig. 13C). In the Danian, the Ormen
Lange subbasin was positioned on the lower part of
the slope. Initial-stage fan development was charac-
terised by deposition of a series of isolated, chan-
nel-mouth, coarse-grained lobe storeys that infilled
and overtopped the depositional topography pro-
duced during the late stage of Springar fan develop-
ment. This initial or 'fan-arrival stage' was probably
coupled with early aggradational infill (?backfill) of
the lower stretch of the slope conduit(s) or channel
fairways. As the inherited topography became dep-
ositionally smoothed, the subsequent phase of fan
development was one of progradation (see also
Gjelberg
et al
., 2005), paralleled by the continued
backfilling and onlap onto the slope of the proxi-
mal, channelised part of the Egga fan. As a result, an
expansion of the Egga sandy fan probably occurred,
with upslope partitioning of the coarser inner fan
facies tracts, the development of a fairly extensive
channel-dominated and lobe-dominated central or
mid-fan area and an outbuilding, lobe-dominated
outer fan area. In turn, this produced an apparent
backstepping stacking pattern in the inner, proxi-
mal parts of the Ormen Lange subbasin, whereas a
forestepping stacking pattern developed in the
outer, more distal part of the subbasin. The central-
fan or mid-fan area is dominated by alternating
channel-fills and lobe storeys, which probably
reflects compensational stacking of lobes (Fig. 10),
as well as short-lived, intermittent outbuilding and
retreat of the distributary channel fairway.
Intermittent shut-off of sandy supply left the Egga
fan dormant for some time in the Ormen Lange sub-
basin, before a new phase of fan progradation (rep-
resented by the upper part of the Egga sandstone
unit) occurred. During this stage, the channel-dom-
inated area was rapidly shifted basinward and
accompanied by a southward shift of the main
sandy channel fairway. A sandy, broad 'braid-plain'-
type channel-belt developed across the southern
part of the Ormen Lange subbasin. However, the
northern part of the subbasin was dominated by
individual or narrower channel-belts flanked by
sandy inter-channel or channel overbank areas; the
latter dominated by crevasse sub-channels and
splays (Figs 12 and 13D). The southern and north-
ern channel-fairways fed laterally separate, frontal
lobe complexes in the adjacent, downslope subba-
sin or terrace to the west and northwest, respec-
tively. However, both channel-fairways probably
originated from a common upslope feeder system
or slope conduit to the south-east. The basinward
shift in facies tracts recorded by the upper part of
the Egga sandstone unit was accompanied by
increased sediment instability in the uppermost
part of the unit, related to tilting of the slope and
basin floor (see below). Eventually, the basinward
tilting of the slope area resulted in gravitational col-
lapse of the Egga sandstones along the outer edge
of upslope mini-basins, leading to ensuing
downslope re-sedimentation of relatively coarse-
grained sandy material.
Thus, a change from the laterally extensive mid-
fan area present across the greater part of the
Ormen Lange subbasin (represented by the lower
part of the Egga sandstone unit) to an inner, poten-
tially braided fan environment and finally to
isolated inner fan channel-fairways in the upper
part of the Egga sandstone unit, is envisaged.
The lower part of the interval represents a sandy
fan environment with suprafan lobes and intra-
lobe channels that shifted laterally or avulsed
across the fan surface (e.g. see Decker
et al
., 2004),
periodically spilling downslope into the next
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