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 637

represent hyperpycnal flows derived directly
from rivers in flood (Mulder et al ., 2003;
Bhattacharya & MacEachern, 2009). The sus-
tained character of the flows argued to have
deposited most of the sandier facies also favours
direct supply from a fluvial source (Mulder et al .,
2003; Piper & Normark, 2009).
The characteristics of the mass-transport depos-
its (the MTDs), particularly their downslope
transport mechanisms (flow types) and contained
reworking signal, favour initiation as upslope
sediment failures (e.g. see Piper & Normark,
2009). Upslope sediment failure is the most prob-
able origin for both the sandy ('megabeds') and
the muddy (slump units) mass-transport depos-
its, attributed to failure of submarine fans on
upslope terraces or mini-basins and to failure of
the muddy slope substrate itself, respectively.
The co-occurrence of channel-mouth lobes with
mass-transport deposits, also suggest that these
were sourced, at least in part, by re-working of
older (and coarser) upslope lobe deposits or by
flushing of the slope conduits.

as a response to intermittent sediment supply
from the upslope deltaic delivery system(s), which
repeatedly were able to advance to the shelf edge
and deliver their sediment load to the fronting
slope and deeper-water basins. Repeated advances
of the basin-marginal deltaic system(s) were, in
turn, related to basin margin uplift as well as crea-
tion or rejuvenation of hinterland topography.
Initial infilling of slope terraces and mini-basins
smoothed any pre-existing basin floor topography
and promoted the outbuilding of a broad and
channelised braid-plain. Downslope shift of fan
deposition and progradation occurred via fill-spill
processes in upslope mini-basins. Repeated
phases of slope structuring and tilting initially
forced the fan further basinward, but also led to a
change to smaller isolated and more localised
channel-lobe systems, coupled with increased
mass-wasting and gravitational re-sedimentation
along upslope areas. Continued slope structuring
eventually captured the sandy supply from the
basin-marginal delivery systems in more upslope
or basin-marginal (shelfal) subbasins, depriving
the Møre Margin slope and deepwater basin
further to the west of coarse clastic supply.

Late Maastrichtian to Danian evolution
of the Ormen Lange area

Controls on sedimentary architectures

The Ormen Lange area saw repeated outbuilding
and retreat of two fan systems during the Late
Maastrichtian and the Danian (Fig. 12); the
Springar and the Egga fan, respectively. Fan initia-
tion and evolution was in response to preceding
phases of hinterland uplift (see also Martinsen
et al ., 1999, 2005; Sømme et al ., 2009), an uplift
probably already initiated in the Late Campanian
or even earlier. The two phases of fan prograda-
tion both experienced a late stage basinward shift
of facies tracts, herein attributed to an early stage
of gentle structuring and tilting of the basin-
marginal slope area. These mild structural adjust-
ments of the slope represented the initiation
of two renewed phases of linked hinterland
uplift and basinal subsidence, dated to the late
Maastrichtian and late Danian, respectively. The
resultant basin-margin structuring involved gross
basinward tilting and thereby steepening of the
basin's ramp-slope margin. As a result, a terraced
or serrated slope profile formed with slope steps
and subtle mini-basins where slope fans were
deposited.
Hinterland and basin-margin structuring thus
exerted also a first-order control on the fan devel-
opment. Fan initiation and progradation occurred

Large-scale fan evolution

At the largest scale of resolution, the repeated
development of slope fans along the Møre Margin
reflects the ability of the deltaic delivery systems
to advance to the shelf edge and deliver their loads
to the fronting slope and basinal areas. This was
probably promoted by the inferred narrow shelf
that existed during Maastrichtian to Danian time
(Osmundsen & Ebbing, 2008; Sømme et al ., 2009).
Repeated advances and retreats of the basin-mar-
ginal deltas were, in turn, controlled by repeated
basin-margin or rift-shoulder uplift and tectonic
rejuvenation, tied to phases of active rifting within
the western parts of the Møre Basin (Fig. 2). The
development of the fan system along the Møre
ramp margin was the product of sufficient sand
supply to infill and overspill the upslope mini-
basins and terraces and allow progradation of the
sandy fan system down the gently tilted and
mildly structured margin. Changes in fan style
occurred in response to renewed structural read-
justment to the basin and basinward tilting of the
Møre ramp-margin. With time, the increased rate
of structural adjustment and creation of basin
margin topography resulted firstly in the capture