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 633

subbasin. The upper part, in contrast, represents
two (or more) relatively stationary channel-fairways,
fixed within sandy overbanks and which fed
smaller and more locally developed frontal splays
or lobe complexes in the adjacent downslope
subbasin, probably via knickpoint channels
incised into the frontal ramp that separated the
two subbasins.

proportion of mass transport deposits (MTDs).
There is sufficient stratigraphic variability in
both the Springar and Egga fan successions to
suggest that each fan system evolved from a
sandy fan dominated by channel-fed lobe com-
plexes to a one increasingly influenced by MTDs
during the final stages of fan development, i.e.
prior to shut-off of sandy supply. The transition
between the two stages was gradual and was pre-
ceded by a marked basinward shift in facies
tracts that can be recognised across the width of
the fan.

Springar and Egga fans - similarities
and contrasts

The Upper Maastrichtian to Danian sandy fan sys-
tems, represented by the Springar sandstones and
the Egga sandstone unit, respectively, can be split
into a lower layered or 'well-organised' sandy fan
(Piper & Normark, 2001), characterised by com-
pensational stacking of lobe storeys and channel
storeys and an upper less-organised to channelised
part defined by a marked basinward shift in facies
tracts (Fig. 13). In an individual subbasin or slope
terrace, the lower part of the two fan systems rep-
resents different fan environments, with the older
Springar sandstones consisting of facies associa-
tions that correspond to more distal environments
than those of the younger Egga sandstone unit.
Thus, the stratigraphic variability in sedimentary
architectures from the Egga sandstone unit to the
underlying Springar sandstones can probably be
viewed as downfan or proximal through central to
distal changes in architectural elements. Such
variability is typical for the various depositional
elements and thereby subenviroments that com-
prise a sandy submarine fan. All or only some of
the facies associations may be present within an
individual mini-basin or slope terrace.
In addition, both fan types evolved stratigraphi-
cally through an early stage of gradual progradation
and infill, followed by a second stage of marked
basinward shifts of facies tracts. Shut-off of sand
deposition in the down-slope subbasin was relatively
rapid for both of the systems. A common evolution
of the two fan systems is envisaged (Fig. 13), which
was probably a response to repeated slope and basin
structural adjustments (discussed below).

Sandy fan - hierarchically ordered lobe
complexes

The lower part of the Springar and the Egga fans
represents the outer to middle and the middle to
inner parts of a channelised sandy fan with supra-
fan lobes, respectively (Fig. 12A; see also Figs 5, 6
and 7). Based on the stacking and partitioning of
facies associations and thus inferred depositional
elements, an organised downfan arrangement of
depositional elements can be discerned, from an
incised slope feeder system through a braided
channelised distributary area, into a lobe-dominated
area. This is terminated downfan by broad and
isolated, mounded to sheet-like lobe features or
beds/bedsets (Fig. 14). Gjelberg et al . (2001, 2005)
and Smith & Møller (2003) in their studies on the
Egga fan system argued for a similar gross deposi-
tional environment, though without recognising
facies tracts that reflect specific architectural
elements or sub-environments. Modern canyon-fed,
sandy fans with similar depositional elements
include the Makassar fan in the Makassar Strait,
off Borneo (Decker et al ., 2004), the Golo fan in the
Tyrrhenian Sea (Gervais et al ., 2004, 2006; Deptuck
et al ., 2008), the Orinoco fan in the Caribbean Sea
(Belderson et al ., 1984; Ercilla et al ., 1998) and the
Pochnoi fan in the Bering Sea (e.g. Kenyon &
Millington, 1995). Outcrop analogues with similar
gross structure and architectural elements include
the carboniferous Ross Formation of western
Ireland (Chapin et al ., 1994; Elliot, 2000; Lien
et al ., 2003), the Permian Brushy Canyon of
western Texas (Beaubouef et al ., 2000; Carr &
Gardner, 2000; Gardner & Borer, 2000; Gardner
et al ., 2003), the Permian Laingsburg and Tanqua-
Karoo systems of south-western South Africa
(Wickens & Bouma, 2000; Johnson et al ., 2001;
Grecula et al ., 2003b; Sixsmith et al ., 2004;
Hodgson et al ., 2006), the Maastrichtian Pab
system of western Pakistan (Eschard, 2003, 2004)

Fan types; distribution and partitioning
of depositional elements

The Ormen Lange fan types can be characterised
as variants on the sandy fan (Piper & Normark,
2001) theme. Two sandy fan sub-types are
recognised: one dominated by channel-fed lobe
storeys and complexes and one with an increasing