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 610

Normark, 2009). The resultant gravity flows,
whether short-lived and surge-like or sustained
but with spatially and temporarily variable flow
patterns (e.g. Kneller, 1995; Kneller & Branney,
1995), may travel the steeper slope portions via
focused routes such as canyons or deep channels,
through a network of shallower channels, or as
near-complete, unconfined flows (e.g. Reading &
Richards, 1994). The slope topography, which
may vary from unconfined through stepped to
ponded (e.g. Meckel et al ., 2000; Booth et al .,
2002; Prather, 2003), normally changes through
time as a result of the complex interplay between
basin margin sedimentation and consequent shelf
and slope progradation and slope topography cre-
ation due to structuring of the basins margins.
Slope steps or subbasins may be connected through
erosional knick-point channels (Pirmez et al .,
2000; Kneller, 2003; Heinö & Davies, 2007), via tor-
tuous corridors (Smith, 2004), or some combina-
tion of the two. Basin margins of deep-water active
basins, such as foreland-basins, rift-basins and
immature passive margins, display most, if not all
of these complex slope types and morphologies,
which commonly leads to the trapping of coarse
sediment within slope terraces and subbasins, nor-
mally with a complex fill-spill, bypass and backfill
depositional pattern.
The reservoirs of the giant Ormen Lange Field
(Fig. 1; Møller et al ., 2004), are contained within
deep-marine, lower slope turbidite systems within
the Upper Maastrichtian Springar Formation and
the Danian Egga sandstone unit of the Tang
Formation (Fig. 2). These reservoirs have previ-
ously been interpreted as basin-floor turbidites
sourced by an inferred deltaic system (Gjelberg
et al ., 2001, 2005; Sømme et al ., 2009) and as
canyon-fed slope turbidites, with the canyons tap-
ping into a shelfal sand source (Smith & Møller,
2003). These previous accounts interpreted the
Ormen Lange reservoirs as lower slope or inner
basin-floor sandy fan systems (following Piper &
Normark, 2001), developed as laterally extensive
channelised lobe to sheet systems with a rela-
tively simple forestepping to backstepping infill
pattern (Gjelberg et al ., 2001, 2005) coupled with
some compensational stacking of individual tur-
bidite complexes (Smith & Møller, 2003).
The aim of this contribution is firstly to present
an update of the Ormen Lange depositional model,
based on new information from additional produc-
tion wells and new field and analogue studies.
The focus has been on placing the Ormen Lange

reservoir development into a basin-scale context,
with emphasis on spatial and temporal changes in
slope turbidite architectures as a response to slope
topography and structuring. Secondly, a hierarchi-
cal subdivision of the Ormen Lange reservoirs is
proposed, based on integration of sedimentologi-
cal, ichnological and biostratigraphical studies. A
novel approach applying detailed sedimentology
with ichnofacies and microfacies studies has
allowed for characterisation and distinction of
surfaces embedding reservoir or depositional ele-
ments at various scales, analogous to studies of
turbidite systems in outcrops and at the modern
seafloor or in the shallow subsurface. Thirdly, an
attempt is made to further decipher the potential
controls on the reservoir development at various
scales, as inferred from detailed studies of the
Ormen Lange reservoirs combined with an inte-
grated tectonostratigraphic evaluation of the
greater Ormen Lange area.

Geological Setting

The Ormen Lange Field is located in the south-
eastern part of the Møre Basin (Fig. 1; Blystad
et al ., 1995); that is, at the transition from the Møre
Basin proper to the Møre Margin to the south-east
(Grunnaleite & Gabrielsen, 1995). The Møre Basin
formed in response to Triassic, Middle to Late
Jurassic and Late Cretaceous to Early Palaeogene
rifting (Brekke, 2000; Færseth & Lien, 2002), with
most of its present structural configuration reflect-
ing intense Late Jurassic rifting and subsidence.
Late Cretaceous and Early Palaeogene rifting was
focused along the western margin of the Møre
Basin, where tilting and compartmentalisation of
fault-blocks occurred from the Coniacian until
continental break-up commenced in the earliest
Eocene (Fig. 2). In the eastern part of the Møre
Basin, Late Cretaceous to Early Palaeogene rifting
resulted only in minor reactivation of the deeper
Jurassic structures (Grunnaleite & Gabrielsen,
1995; Færseth & Lien, 2002; Osmundsen & Ebbing,
2008) and associated drape-folding of the sedi-
mentary cover over these deep-seated structures.
The stepwise fault-block rotation in western Møre
Basin and drape folding in eastern Møre Basin
appear to have formed in response to a series of
rift phases that can be recognised across the Mid-
Norway deepwater area.
The Møre Margin, which formed the eastern part
of the Late Jurassic rift basin (Grunnaleite &
Gabrielsen, 1995; Jongepier et al ., 1996; Osmundsen