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 375

muds and low to moderate bioturbation) mouth-
bar types.(cf. Dalrymple & Choi, 2007; Tanavsuu-
Milkeviciene & Plink-Björklund, 2009).

lobe facing toward the SE. The coarsening-upward
trends, coupled with the increase of vertical
thickness in southern and north-eastern areas of
the Smørbukk field, with interpreted low-angle
clinoforms (dipping 2 to 5 degrees) in well-log
correlation panels (Fig. 19, cross sections I and II),
suggest delta-front progradation toward the SW
and NE.

Lower Tilje (T1.2)

The distributary mouth-bar (FA3) deposits of Tilje
1.1 (T1.1.2) are overlain by channelised distribu-
tary mouth-bar (FA3) and tidally influenced delta-
front deposits (FA4) of reservoir zone T1.2 (Fig. 19).
Locally, the E and NE parts of the study area
show basal mud-dominated heterolithics with
intense bioturbation and a moderately diverse
mixed Cruziana-Skolithos assemblage, indicative
of relatively distal settings compared with the
upper deposits of T1.1.2. This indicates that the
contact between T1.1 and T1.2 is a significant
flooding surface. The T1.2 interval (10 m to
15 m thick) is recognised in GR well logs as two
broadly coarsening-up packages that are variably
developed (Fig. 3). The channelised mouth-bar
deposits (FA3) consist predominantly of fine to
very-fine sandstone and are more bioturbated than
the basal deposits of T1.1.1. The mouth bars of
T1.2 in the north and central areas are composed
mainly of mixed sandstone-mudstone heterolith-
ics showing both current and combined-flow
structures, locally interbedded with intensely bio-
turbated sandstones. These deposits change later-
ally (SW and NE; Fig. 20D) and vertically into
tidally influenced delta-front deposits (FA4) that
lack channels and show intense bioturbation.
Mudstone-dominated heterolithics, showing
wave influence, occur locally toward the SW,
forming stacked coarsening-upward and thicken-
ing-upward successions (3 m to 5 m thick). The
trace-fossil suites also show a gradational change
from a low-diversity mixed Cruziana-Skolithos
assemblage in the central area to a more diverse
facies-crossing Cruziana-Skolithos assemblage (cf.
MacEachern & Bann, 2008) toward the NE and SW.
Overall the T1.2 interval shows fewer terminal
distributary channels and storm-influenced depos-
its than the lower stratigraphic intervals. Tidal
currents are the dominant depositional process in
the delta-front area. Sedimentological observa-
tions, facies and trace-fossil distributions within
T1.2 suggest the dominance of heterolithic mouth
bars with localised terminal distributary-channel
deposits towards the NW, whereas the SW and NE
areas show tidally influenced proximal to medial
delta-front deposits. This distribution (Fig. 20D)
suggests a delta-lobe configuration with the delta

Middle Tilje (T2 to T3.1)

The base of zone T2, which is 16 m to 25 m thick, is a
high-order flooding interval that marks a marine
incursion followed by renewed progradation. It is
characterised by the presence of local marginal-
marine to normal-marine lags (FA2), where the thick-
est deposits (up to 15 cm thick) occur toward the
SW and the eastern parts of the field. This basal lag
commonly consists of coarse-grained cross-bedded
reddish sandstone (similar of the basal T1.1.1 lags).
Locally, the thickest marine lags show interbedding
with sandstone and intensely bioturbated (high
diversity) heterolithic deposits forming a 60 cm thick
overall upward-thinning succession. These deposits
are commonly overlain by 2 m to 3 m thick, proximal
prodelta units (FA5). This distinctive sharp-based
mud-dominated deposit has been used by Martinius
et al . (2001) as a regional stratigraphic marker (Fig. 19)
that is characterised by a shift from low to high GR
readings (Fig. 3) and, in density-neutron separation,
from fine sandstones to mixed mudstone-sandstone.
These prodelta deposits (FA5) show sanding-upward
and coarsening-upward successions that consist
of pinstripe mudstones and lenticularly-bedded,
wave-dominated heterolithics, locally preserving evi-
dence of tidal, river flood and storm deposition.
The prodeltaic unit (FA5) is commonly overlain
by storm-influenced (FA6) and wave-influenced
(FA7) delta-front deposits, which typically show a
series of correlatable coarsening-up successions
(visible in GR/RS well-log curves; Fig. 3) and com-
monly thicken toward the SW and NE of the field
(Fig. 19 cross sections I and II). These deposits
include a variety of heterolithic facies; however,
lenticularly wave-dominated and mixed sand-
stone-mudstone wavy bedded varieties are most
common. These heterolithics generally become
thicker bedded and sandier upward and locally
are interbedded with thick unbioturbated HCS
beds. These deposits lack channels. The facies
distribution maps (Fig. 21A) indicate that HCS
beds are thicker and more common in the central
and NW parts of the field; the abundance of HCS