Eustatic, tectonic and climatic controls on an early syn-rift mixed-energy delta, Tilje Formation (Early Jurassic, Smørbukk field, offshore mid-Norway) - From Depositional Systems to Sedimentary Successions on the Norwegian Continental Margin - page 371

2 and towards the top of sequence 3) and coarse-
grained, sand dominated, fining-upward succes-
sions (more common in sequence 3). Both types of
succession are themselves organised in parase-
quence-set-scale (i.e. 10 m to 15 m thick) units.
Detailed examination of cores and well logs (GR/
RES) by previous workers (Martinius et al ., 2001)
and in this study shows that such parasequence-set-
scale units can be correlated across the Smørbukk
field, thereby allowing the studied succession to be
subdivided into a number of broadly tabular strati-
graphic packages (Statoil reservoir zones A3 and T1
to T6). These reservoir units, which range in thick-
ness from 5 m to 25 m, are bounded by inferred
sequence boundaries and/or significant flooding
surfaces that can be traced regionally (Ichaso, 2012);
thus, each reservoir unit is believed to represent a
time slice with minimal diachroneity.
Within each reservoir unit, gradual lateral
variations in facies occur. Examination of these
facies distributions (Figs 20 to 22) allow the recon-
struction of the temporal evolution of the palaeoge-
ography and sediment-input points as a function of
eustatic sea-level fluctuations and fault movement.
Sediment-input points and dispersal pathways
within each time slice were determined using the
down-system grain-size fining that is expected to
occur in all sedimentary systems (Parker, 1991;
Frings, 2008; Dalrymple 2010), together with the
observed proximal-distal facies trends (Dalrymple &
Choi, 2007). In the determination of these spatial
fining trends, comparisons were made using the
coarsest grain size present, rather than the bulk grain
size of a local succession. This was done to ensure
that differential trapping as a result of spatial varia-
tion in subsidence did not bias the results (Dalrymple,
2010). Detailed examinations were undertaken to
determine whether there was a compensational
style of delta-lobe stacking, whereby younger delta
lobes occupied the topographic low between older
lobes (cf. Straub et al ., 2009; Bhattacharya, 2010).
Such stacking was not detected. Instead, deltaic
units show aggradational and progradational pat-
terns with the finest sediment and most distal facies
toward the S-SW and E-NE parts of the field, indicat-
ing a simple 'layer-cake' stacking behaviour at the
scale of the study area.

by bioturbated sandstones and heterolithics
and storm-dominated lower-shoreface to middle-
shoreface deposits (FA1). This unit lacks channel
deposits and evidence of fresh-water influence.
The moderate to intensely bioturbated, ichnologi-
cally diverse intervals are erosively overlain by
fine-grained hummocky cross-stratified sandstones
forming at least two sandier and coarsening-
upward units (recognisable in core material and
GR/RES well log curves) suggesting deposition of
upward-shoaling successions representing a pro-
gradational or regressive coast/shoreline system.
Locally, toward the north-east, the lowest sandier-
upward succession within A3 is separated from the
upper one by a subordinate flooding surface capped
by a 5 cm to 10 cm thick erosively based medium-
grained to coarse-grained sandstone interpreted as
a lag deposit (FA2) that might have been derived
from reworked coarse-grained fluvial deposits;
elsewhere, this lag is absent. The upper Åre (A3) is
approximately 10 m thick, increasing up to 15 m
towards the NW (Fig. 19, cross section I). HCS beds
are thicker and more common in the central and
northern areas (30% to 60% of the interval by
thickness; Fig. 20A), whereas the southern areas
show a dominance of more intensely bioturbated
deposits (up to 75%) and thinner HCS beds
(Fig. 20A). This facies distribution suggests that the
water deepened toward the south.

Sequence 2: Lower to middle Tilje Fm.
(T1 to T3.1)

The shoreface deposits (FA1) of the upper Åre (A3)
are overlain abruptly by transgressive shelf lags
(FA2) and/or distributary-mouth bar (FA3) depos-
its of the basal Tilje Formation (T1.1.1). In accord-
ance with previous studies, the stratigraphic
contact between the two formations is interpreted
as a hiatal surface (SB2 of Martinius et al . 2001)
based on: 1) the regional extent of the erosive con-
tact, showing low relief and subtle incision towards
the south-west and north-east of the field (Fig. 19);
2) the abrupt vertical change of grain size and facies
from bioturbated and/or very-fine grained wave/
storm-generated sandstones of the upper Åre Fm.
to medium-grained and coarse-grained lags and
pervasively heterolithic deposits of the Tilje Fm.
that show extensive evidence of tidal sedimenta-
tion; and 3) widespread development of a coarse-
grained lag (FA2) at the contact; and 4) the local
presence of Glossifungites beneath the lag, all of
which indicate a depositional hiatus.

Sequence 1: Upper Åre Fm. (A3)

In the Smørbukk field, the uppermost Åre
Formation (reservoir unit A3, the only part of
sequence 1 examined in this study) is dominated