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used to constrain the distribution and timing of
fault activity during the Early Jurassic to earliest
Cretaceous rifting stages in the Åsgard develop-
ment area. Corfield & Sharp (2000) suggest that
rifting was initiated during the early Jurassic
(top Åre Formation time) and was characterised
by distributed deformation along blind faults
(oriented NE-SW) within the basement and by
localised deformation along the major Smørbukk
and Trestakk normal (westerly dipping) faults
within the cover (Fig. 1C). During Tilje deposi-
tion, these faults caused slow tectonic subsidence
and the formation of local shallow depocentres
occurring to the west of the Trestakk Fault and
east of the Smørbukk Fault (Marsh
et al
., 2010).
The early syn-rift (rift-initiation stage) Tilje depo-
sition was succeeded by a large-scale rift-climax
stage, during which middle-upper Jurassic folds
and Early Cretaceous grabens developed at an
oblique angle to the main faults (Marsh
et al
., 2010).
deposits sandstone (> 90 : 10 sandstone : mud-
stone ratio); (2) sand-dominated heterolithics
(60 : 40 to 90 : 10 sandstone : mudstone), (3)
mixed sand/mud heterolithics (40 : 60 to 60 : 40),
(4) mud-dominated heterolithics (0 : 90 to
40 : 60) and (5) mudstone (< 10 : 90).
2
Bed thickness and bedding style: Individual
layers were described using the standard
bed-thickness classification of Ingram (1954) as
laminae (<1 mm thick), very thin-bedded (1 mm
to 3 mm), thin-bedded (3 mm to 10 mm),
medium-bedded (10 mm to 30 mm), thick-bed-
ded (30 mm to 100 mm) and very thick-bedded
(>100 mm). Bedding styles were described fol-
lowing Reineck & Wunderlich's (1968) classifi-
cation, which includes the classic flaser, wavy,
lenticular and pin-stripe types. The terms bed,
bedset (group of similar beds), amalgamated
(similar beds with no intervening material of
different type) and tabular (nearly planar bed-
ding surfaces that are parallel to each other)
were used following the definitions in
Collinson & Thompson (1982).
3
Grain-size and sedimentary structures: For
grain-size descriptions, the standard Wentworth
size-class nomenclature was used. The primary
sedimentary structures used included those
produced by currents, waves and mixed-energy
conditions (e.g. Dumas
et al
., 2005), as well as
both deformational and biogenic structures.
4
Degree and type of bioturbation: Descriptive-
genetic ichnological classifications (Pemberton
et al
., 2001) were used for the recognition and
interpretation of ichnofacies, with application
to the recognition of depositional settings
(MacEachern & Bann, 2008). Bioturbation-
index values were described following the
Bann
et al
. (2008) classification.
METHODOLOGY
Core material from nine wells that penetrate the
upper Åre and Tilje formations in the Smørbukk
field (production blocks 6506-11 and 6506-12)
was examined and logged in detail (i.e. at the cen-
timetre to decimetre scale), in order to define the
different facies (F) and facies associations (FA).
The sedimentary facies were distinguished on the
basis of lithology, physical sedimentary struc-
tures, sand-mud ratio, degree of bioturbation and
the specific trace-fossil assemblage present.
Heterolithic facies are particularly common in the
study interval and are especially challenging to
subdivide in a meaningful way. Heterolithic
deposits within the Tilje Formation have been
described in the past using traditional schemes
such as flaser, wavy and lenticular bedding
(Dreyer, 1992). Recently, Martinius
et al
. (2001)
used a facies classification based on variations of
the intralayer characteristics of the heterolithic
units such as: grain size and sorting, structures in
the coarse-grained layers, trace fossils and ichno-
fabrics, grain size and thickness variability, fre-
quency of occurrence and stratigraphic position.
In this work the heterolithic deposits were classi-
fied based on the following characteristics:
Use of all of these criteria has the potential to pro-
duce an unwieldy number of facies. Therefore, in
this work, classification of heterolithic deposits
was focussed at the decimetre to metre scale, whilst
paying close attention to details at the mm-scale to
cm-scale. This allowed us to have a smaller num-
ber of facies than previous authors.
Using the cored wells and the environmental
interpretations derived from the facies associations,
a sequence-stratigraphic analysis of the succession
was undertaken using the standard Exxon-based
approach (cf. Catuneanu, 2006; Ichaso, 2012).
Correlation of the stratigraphic units defined in this
way (parasequences, parasequence sets, systems
1
Sand/Mud ratios: The proportions of sand-
stone and mudstone are used to create a
fivefold subdivision of the heterolithic
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