The Ormen Lange turbidite systems: sedimentary architectures and sequence structure of sandy slope fans in a sediment-starved basin - From Depositional Systems to Sedimentary Successions on the Norwegian Continental Margin - page 636

likewise display compensational stacking of the
lobe storeys. The smaller dimensions and coarser
sediment of the inferred isolate channel-mouth
lobes are consistent with deposition from smaller
volume, sand-laden flows, potentially with short
run-out distances from feeder channels (or slope
conduits), which lead to narrow and elongate, pos-
sibly more tongue-like bodies (e.g. see Baas et al .,
2004; and cf. Mulder & Alexander, 2001; Al Ja'aidi
et al ., 2004). The component facies suggest deposi-
tion from initial sand-laden, hyperconcentrated
surge-type flows that later changed into more sus-
tained flows (e.g. see Deptuck et al ., 2008).
Slump-blocks consist of laminated and biotur-
bated upper slope mudstones that are slump-
folded and sheared. Slump blocks also show that
they were thrust faulted and normally faulted
whilst still in an unconsolidated state, most prob-
ably during downslope transport. They normally
occur interbedded with channel-fill storeys and
represent intermittent upslope gravitational mass-
wasting events.
Megabeds comprise thick, single storey, mas-
sive or dewatered sandstones. The lithofacies
characteristics suggest deposition by frictional
freezing and points to deposition from highly con-
centrated, possibly unchannelised flows. Bed
geometries are probably in the form of elongate,
narrow and thick tongue-like bodies, although the
potential for an unchannelised origin could sug-
gest a broader, lobe-like geometry. Nevertheless,
the poor correlation potential of packages contain-
ing 'megabeds' argue against laterally extensive
sheet geometries and therefore against deposition
from some exceptionally large flows.
Deformed units consist of sheared and thrust-
faulted, normally faulted, slump-folded and dis-
rupted beds or units, of which the parent
architectures appear to have been originally
medium-bedded to thin-bedded, layered facies
tracts. Deformation typically occurred while the
sediment was still unconsolidated, most probably
shortly after deposition and prior to deposition of
the overlying, undeformed strata. Deformation
was probably gravitationally triggered, although
only short distances of post-depositional remobili-
sation are inferred, in contrast to the interbedded
slump blocks of upper slope origin. Thus, the
deformed units were subject to penecontempora-
neous in situ soft-sediment deformation, probably
on an unstable slope.
The inner fan region of the MTD-influenced fan
was dominated by channel-belts and inter-channel

areas with unstable overbank units (deformed cre-
vasse splays and sub-channels units), as well as
mass-transport deposition from slides, slumps and
'megabed' flows. This passed downslope into a
mid-fan area dominated by lobes and terminal
parts of megabed flows and finally into an outer fan
area where only the occasional large flows were
able to reach and deposit their sediment load.
Unstable basin-floor conditions were present along
the entire fan profile. The background environment
was dominated by pinstripe-bedded mudstones,
suggesting a change to increasingly stressed envi-
ronments, induced by a combination of reduced
oxygenation and increased sedimentation rates.

Sediment feeder and delivery system(s)

The sandy facies, despite having a predominance
of fine-grained to medium-grained sand, consist
of varying and different grain sizes and textures
(e.g. from fine to pebbly material; from angular to
subrounded; and from poorly to well sorted) and
include abundant detrital glauconite and cham-
osite (see also Gjelberg et al ., 2001, 2005; Smith &
Møller, 2003). Grain size and bed thickness varia-
tions indicate that the mechanisms responsible
for delivering sediments to the fronting basin var-
ied in magnitude and frequency. The textural
characteristics suggest mixing of first cycle and
reworked sediment. Organic material, including
plant remains and coal/coaly claystone clasts are
abundant in the interbedded claystones and also
occur as minute clasts in some sandier facies. The
presence of plant fragments in both turbiditic
mudstone and sandstone facies favour direct sup-
ply from a paralic or non-marine hinterland, with
limited littoral and shelf storage. Jointly this sug-
gests deltaic delivery systems, most probably
from rivers in flood (see discussion below; see
also Martinsen et al ., 2002, 2005; Sømme et al .,
2009), with some reworking and re-sedimentation
of former deltaic, shallow-marine and shelfal
sandstones. This is also supported by the charac-
ter of the basal mudstones and sandstones of both
lobe storeys and some single beds. Such units
commonly show a subtle to pronounced coarsen-
ing-upward trend in the underlying turbiditic
mudstones, which in turn are erosively truncated
by the scoured basal surface of the overlying
sandstones that commonly have a thin basal
coarsening-upwards zone themselves. This is
indicative of deposition from flows with increas-
ing flow strength and velocity, typically argued to