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 345

tracts and sequences) away from the cored wells
was done using gamma-ray (GR) and density neu-
tron (DEN/NEU) well-log curves calibrated using
the cored wells. The reservoir zones defined by
Statoil (Fig. 3) can be correlated directly with these
sequence-stratigraphic units. Thus, facies and envi-
ronmental distribution maps were generated for
each reservoir zone using facies percentages and the
dominant grain size. Stratigraphic cross-sections
(axial and transversal to the field; Fig. 1C) were
constructed using the well logs (datum: Tilje-Ror
formational contact) and the logged cores. The fault
activity-structural maps produced by Marsh et al .
(2010) for Tilje time were integrated with the facies
distribution maps in order to produce evolutionary
tectono-stratigraphic interpretations. Together with
the stratigraphic cross-sections, the architectural
organisation of facies associations and their palaeo-
geographic distribution in a proximal-distal context
are interpreted following Dalrymple & Choi (2007).

deposited rapidly by decelerating turbulent flows,
whereas the inverse grading indicates that disper-
sive pressure operated (Lowe, 1979), or that depo-
sition occurred during waxing flow. Beds that
are poorly sorted with a high matrix percentage
might indicate deposition from high-concentration
sediment flows (Nemec & Steel, 1984), or rapid
accumulation in a setting with abundant sand.

Facies 2: Cross-bedded sandstone

The coarse-grained to fine-grained cross-bedded
sandstones of Facies 2 (Figs 4C, 4D & 4E), forming
fining-upward cosets (up to 2.5 m thick), coupled
with the local presence of herringbone stratification
and paired mudstone layers, indicate deposition by
subaqueous dunes in a setting with moderate to
strong currents and a tidal influence (Dalrymple &
Choi, 2007). The paired and thick-thin alternations
of the mudstone layers in bottomsets of cross-beds
are suggestive of a tidal diurnal inequality (Visser,
1980). Unusually thick (1 cm to 3 cm) homogeneous
mud layers and rip-up mud clasts derived from
such layers (Figs 4D & 4E) occur towards the base of
thick cross-bedded successions, suggesting deposi-
tion from high-concentration, near-bed suspensions
(fluid muds; Ichaso & Dalrymple, 2009). The
upward decrease in the thickness of these mud lay-
ers indicates a vertical reduction of the suspended-
sediment concentration in the water column (cf.
Dalrymple et al ., 2003). Brackish-water conditions
are interpreted from the sparse and low-diversity
trace-fossil assemblage, which is mostly composed
of large-scale vertical burrows ( Diplocraterion and
Skolithos ).

FACIES

In general, the upper Åre and Tilje deposits in the
Smørbukk and Smørbukk South fields are charac-
terised by the following attributes: (1) a pervasive
heterolithic nature; (2) rapid alternation of grain
size between claystone or siltstone and fine-grained
to medium-grained sandstone; (3) dramatic changes
in bedding style and sedimentary structures over
short vertical distances, which imparts a high
degree of variability to the succession; (4) variable
bed thickness with successive beds ranging from
thin-bedded to thick-bedded; and (5) variable bio-
turbation suites composed of mixtures of vertical
and horizontal burrows, with bioturbation indexes
ranging from sparse or weakly burrowed (BI 0 to
1) to intensely bioturbated (BI 5). Within this het-
erogeneous succession, seven lithofacies where
identified (see Tables 1 and 2 for detailed facies
descriptions) on the basis of the characteristics
discussed above.

Facies 3: Current-rippled sandstone

The fine-grained to very fine-grained sandstones
(2 cm to 5 cm thick) of Facies 3, showing current-
ripple cross-lamination (Fig. 4F), are interpreted to
be deposited by slow currents. Most occurrences
show only one direction of ripple migration, but the
common presence of true bipolar cross-lamination
(as indicated by steep lamina dips, in contrast to the
lower dip angles associated with the end-on view
ripple troughs) and the alternation with very thin
(<2 mm) mudstone laminae imply a tidal influence
(Baker et al ., 1995; Dalrymple & Choi, 2007; Van
den Berg et al ., 2007). The occasional occurrence of
low-angle climbing-ripple sets indicates rapid dep-
osition from decelerating flows, probably associ-
ated with sporadic river floods (Ashley et al ., 1982).

Facies 1: Graded and non-graded conglomerate

The unbioturbated, quartz pebble and granule
conglomerates of Facies 1 (Figs 4A & 4B) suggest
the presence of high-energy flows. Single and amal-
gamated, tabular conglomeratic beds (up to 40 cm
thick) commonly show normal and inverse grad-
ing, with no obvious internal lamination. The nor-
mal grading suggests that the conglomerates were