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 339

Eustatic, tectonic and climatic controls on an early syn-rift
mixed-energy delta, Tilje Formation (Early Jurassic,
Smørbukk field, offshore mid-Norway)

AITOR A. ICHASO and ROBERT W. DALRYMPLE
Department of Geological Sciences and Geological Engineering, Queen's University,
Kingston, Ontario K7L 3 N6, Canada

ABSTRACT

The Early Jurassic Upper Åre and Tilje formations are an important mature hydrocarbon
reservoir in the Smørbukk field, offshore Mid-Norway. The Tilje Fm. was deposited in a
tide-influenced deltaic setting during an early syn-rift tectonic stage within a NE-SW ori-
ented half-graben sub-basin. The deltaic deposits rest erosively (SB2) over the Upper Åre
shoreface units and are arranged vertically in two major sequences that show a diverse
range of heterolithic facies preserving tide, combined-flow and wave-generated structures.
The first sequence, consisting of the lower-middle Tilje (reservoir zones T1 to T3.1), is
composed of stacked, coarsening-upward and sanding-upward distributary mouth bars,
delta-front and prodeltaic deposits. This interval shows a complex vertical alternation of
more proximal tidal-influenced and medial wave/storm-influenced successions that
locally record seasonal variations in river discharge. The lower-middle Tilje facies distri-
bution suggests overall N-NW to SE progradation of 'lobe-shaped' deltas, oblique to the
regional structural grain. The second sequence (reservoir zones T3.2 to T6; middle-upper
Tilje) rests erosively (SB3) over the delta-front deposits of the underlying sequence. The
sandy lower part of the upper sequence is capped by a regional flooding surface that marks
the transition from the Tilje Fm to the marine Ror Fm. The middle-upper Tilje is composed
of proximal tidal-fluvial distributary-channel and point-bar successions with abundant
fluid-mud deposits. The top of the Tilje is mainly composed of medial-distal channelised
heterolithic mouth bars and mixed tide-wave delta-front deposits. The propagation of
blind normal faults within the study area and the generation of isolated syn-depositional
shallow hanging-wall depocentres exerted a subtle control on the sediment-entry points,
the thickness of sedimentary successions and the direction of delta progradation. Two
main tectonic pulses are recognised, both of which are responsible, in whole or in part, for
the two main sequence boundaries recognised in the succession. The first caused an abrupt
change from wave-dominated to tide-dominated sedimentation, whereas the second is
reflected in an abrupt change in the sediment-transport pathways in the study area.

Keywords: Tilje, Delta, Tide, syn-rift, Early Jurassic, Norway.

INTRODUCTION dominated successions (both estuarine and deltaic;

Martinius et al ., 2005) that were deposited in a mid-
palaeolatitudinal location (between 49° N and
53° N; Doré, 1991) and had a warm climate with
strong seasonal differences in temperature and
rainfall (Hallam, 1994). The mid-upper Åre
Formation (Svela, 2001; defined by the first fully
marine deposits within the Halten Terrace succes-
sion) and the entire Tilje and Ile formations
(Fig. 2A), in particular, contain the main intervals

In the Mid-Norwegian shelf (Fig. 1), Early Jurassic
Sinemurian and Pliensbachian sediments (Brekke
et al ., 2001; Fig. 2A) were deposited in a seaway/
rift-basin setting (Halten-Trøndelag Basin; Fig. 2B)
during the opening of the North Atlantic Ocean, at
a time of significant eustatic sea-level rise (Hallam,
1988; Surlyk, 1990). These deposits are charact-
erised by a series of tide-influenced and tide-