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 614

lower part of the sandy succession in the Slørebotn
Subbasin and on the Gossen High to the south-east
of the Ormen Lange area. This succession has now
been assigned to the Maastrichtian (as opposed to
Danian by Gjelberg et al ., 2001, 2005) and should
formally be included into the Springar Formation,
similar to the Upper Maastrichtian sandstones in
the Ormen Lange area. This re-dating has impor-
tant implications for the tectonostratigraphic
evolution of the area, as well as for reservoir cor-
relations and development (Fig. 4 and see further
discussion below).
The Upper Maastrichtian to Danian has been
divided into two turbidite units or systems (sensu
Mutti & Normark, 1987): 1) the Upper Maastrichtian
Springar sandstones, including the lowermost
Danian Tang Formation sandstones (i.e. the so-called
Våle heteroliths); and 2) the Danian Egga sandstone
unit (Fig. 4). These two turbidite systems represent a
time-span of some 3 to 4 Myr each (Fig. 2B). Both
turbidite systems are draped by pelagic claystones
that can be correlated across the eastern Møre Basin
and onto the Møre Margin and which represent
prolonged intervals of sandstone deprivation and
basinal sediment starvation. The two turbidite sys-
tems are, based on basin reconstructions, seismic
stratigraphy as well as biostratigraphy and ichnofa-
cies studies, interpreted as lower slope sandy fan
systems (following Piper & Normark, 2001). Jointly
they form an overall basinward stepping pattern,
herein attributed to the linked basin margin struc-
turing and slope steepening (see below).

form distinctive classes or units, based on log
characteristics (especially from image logs) that
have been used to classify and differentiate the
uncored sections of the reservoir units. This
approach has proven especially relevant for the
interpretation of the production wells, which are
generally uncored. Image logs have also proven
valuable in identifying amalgamation and erosive
surfaces. In addition, they have helped delineate
the gross orientations of scoured or channelised
surfaces and thereby the general orientation of
the overall channelised or scoured architectural
elements.
The bulk of the sandy facies of the Ormen Lange
cored intervals have a massive appearance
(Table 2; Gjelberg et al ., 2001, 2005; Smith &
Møller, 2003), representing the Bouma (1962)
T a division or one or more of the Lowe (1982) S
divisions. However, faint stratification defined by
vague mineral alignments and alternating inter-
vals of varying grain size populations are present
even in these otherwise apparently massive facies,
as also suggested by image logs. Accordingly, most
of the sandy facies represent alternations of plane
bed traction and migrating ripples and 'megarip-
ples'. In consort, this supports deposition from
sustained flows (e.g. Baas et al ., 2004; Kneller &
Branney, 1995) rather than en masse dumping, for
all of the coarser and sandier lithofacies popula-
tion (Table 2). Sharp, erosive bases testify to flow
erosion, which together with abundant candidate
amalgamation surfaces recognised on image logs,
support the notion that the thicker sandier units
are formed by stacks of amalgamated beds. Bypass
indicators are also provided by granule lag lithofacies,
present both as channel-base/scour-base lags as
well as scoured and rippled bed tops (e.g. see
Kneller & McCaffrey, 2003). Subordinate sandy
facies include varieties of shale-clast conglomer-
ates (Table 2).
The finer-grained lithofacies population con-
sists of different, commonly incomplete Bouma
T abcde turbidite beds (i.e. where only one or some
of the Bouma (1962) divisions constitute the
bed). These beds represent waning and depletive
flow conditions, interpreted to constitute the
peripheral to outer part of turbidite beds, bed
elements and lobe storeys (see below for a fur-
ther discussion of terminology). Rare muddy
sandstones or debrites of hybrid flow origin
(Baas et al ., 2009; see also Haughton et al ., 2009
and references therein) form localised bed or
bedset cappings.

Upper Maastrichtian & Danian sandy
fan reservoir architectures

An extensive dataset, including field-wide 3D
seismic data, 25 exploration and production wells
and a total of 390 metres of core, is available from
the Ormen Lange Field itself. This is supple-
mented by a relatively dense, regional 2D seismic
grid, which allows direct correlation to other 3D
covered areas and wells (some with additional
cores) in the greater Ormen Lange (eastern Møre
Basin) area.

Lithofacies

The core dataset of the Ormen Lange Field (Figs 5
and 6) has permitted recognition of a series of pro-
cess-related 'lithofacies' of the muddier (Table 1)
and sandier (Table 2) depositional units. The
lithofacies identified in core have been grouped to