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 629

(A)

(B)

Fig. 12. Conceptual reservoir architectures for the organised (A) and less organised, or channel-mouth lobe (B) types of
sandy fans.

accompanied by a change from a more distal to a
more proximal facies association. In contrast, the
upper fining-upward and thinning-upward trend is
defined by the reverse change in facies associa-
tions. The motifs are underlain as well as capped
by thicker mudstone intervals, commonly of mixed
turbiditic-hemipelagic and pelagic origin. The
motifs are interpreted to represent stacks of turbid-
ite beds that jointly form the peripheral to the outer
parts of a series of relatively wide and low-relief
turbidite lobes; hence, the term 'lobe storey' is used
for these metre-scale bedsets. These lobe storeys
probably developed in the distal or outer (i.e.
downfan) areas of the sandy fan environments
(Fig. 12A; cf. Piper & Normark, 2001). Notably, the
thicker lobe storeys also contain the more proximal
facies association, that is, they comprise both lobe
fringe and peripheral facies tracts. The layered
development of the Springar sandstones in the
Ormen Lange area form the downslope equivalents
to thick and sandy packages in upslope subbasins,
such as the Sløreboth Subbasin (Fig. 4). These
upslope successions are uncored, but from well
logs appear similar to the Egga sandstones.
The upper part of the Springar sandstones, includ-
ing the so-called Våle heteroliths (Gjelberg et al .,
2001, 2005; Smith & Møller, 2003), consist of a
variably developed package with marked changes in
sediment architecture across the Ormen Lange

subbasin. Abundant, thick-bedded sandstones of
possible debris-flow origin stack in an apparent
disorganised, but compensational manner in the
southern part of the subbasin. In the central to
northern part of the Ormen Lange subbasin, thick
channel storey packages are present, commonly with
interbedded slump units derived from upper slope
settings (Fig. 12B). These channel storeys translate
down-fan (or downslope) into relatively coarse-
grained central and peripheral lobe deposits,
probably representing isolated channel-mouth lobes.
The channel-fills and lobe deposits are organised
in gross fining-upwards and thinning-upwards
and coarsening-to-fining-upwards or thickening-to-
thinning-upwards motifs, representing single-storey
channel-fills and lobe storey successions, respec-
tively. It is tentatively postulated that a single-storey
channel-fill translates down-fan into a single lobe
storey motif, linking erosional-depositional events on
the proximal fan to lobe formation and growth further
down the depositional slope. The disorganised stack
of megabeds, in contrast, appears to have formed by a
series of gravitational re-sedimentation events. Their
contained palynomorphs suggest derivation by
reworking of upslope Upper Maastrichtian sands,
probably via gravitational collapse of unconsolidated
turbidite deposits. The Upper Maastrichtian in the
Slørebotn Subbasin is locally top truncated, with
deep, seismically visible gulley-fills incised into the