Tectonic influence on the Jurassic sedimentary architecture in the northern North Sea with focus on the Brent Group - From Depositional Systems to Sedimentary Successions on the Norwegian Continental Margin - page 391

entirely pre-rift (or post-rift with respect to the
preceding Permo-Triassic phase). Others have
suggested that rifting started during deposition
of the upper Brent Group (Tarbert Formation of
Late Bajocian age; Johannessen et al ., 1995;
Løseth et al ., 2009; Davies et al ., 2000). A few
studies, including Helland-Hansen et al . (1992),
Fjellanger et al . (1996); Færseth (1996) and
Ravnås et al . (1997) have suggested that syn-rift
sedimentation started within the Bajocian Ness
Formation (upper) (Fig. 2). Fält et al . (1989)
pointed to the thick delta plain succession of
the Ness Formation as a possible indication of
syn-sedimentary fault activity.
As stated by Davies et al . (2000), the early phase
of Jurassic rifting is poorly understood due to
subtle rift-initiation indicators. Importantly, fault
activity involved in both the early and main stages
of the Jurassic rift phase would have had a
pronounced impact on the sedimentary infill style,
drainage pattern, facies distribution and shoreline
complexity (e.g. Gawthorpe & Leeder, 2000). In
order to investigate the initiation of the rifting and
the sedimentary response and its potential impact
on Brent Group stratigraphy, a framework of
generic pre-rift to syn-rift models is presented
below.

East
Shetland
Basin

Timescale

Viking
Graben

Horda
Platform

Time
(Ma)

Epoch Age

Draupne Fm

Oxfordian

160

Heather Fm

Callovian

Bathonian

Tarbert Fm

Bajocian

Ness Fm

Etive Fm

Rannoch Fm

Aalenian

Broom Fm

Oseberg Fm

180

Drake Fm

Toarcian

Cook Fm

Pliensbachian

Amundsen Fm

Johansen
Fm

Sinemurian

200

Statfjord Fm

Hettangian

Conceptual pre-rift to syn-rift models

Sandstone Siltstone/mudstone Coal

Nøttvedt et al . (1995) emphasised that rift sys-
tems are generally described by a three-stage
model, where active crustal stretching and fault-
ing (the syn-rift stage) is preceded by a proto-rift
(pre-rift; Fig. 3) and followed by a post-rift stage.
The proto-rift stage is characterised by gentle
basin flexure and minor vertical movements
along pre-existing faults (Gabrielsen et al ., 1990).
The post-rift stage is characterised by sediment
infilling of the basin topography inherited by the
active stretching stage and where minor fault
movements may occur along some of the Jurassic
master-faults (White & McKenzie, 1988; Nøttvedt
et al ., 1995). The rift stages are described below in
more detail.

Fig. 2. Stratigraphic column of the Jurassic northern North
Sea. Modified from Husmo et al . (2003).

is strongly linked to the North Sea dome uplift
and to the late pre-rift and early syn-rift tectonic
subsidence in the northern North Sea. The
'Brent delta' advanced northward as a conse-
quence of the uplift and erosion of the North
Sea dome. It reached as far north as about 62° N,
where its advancement was halted by a combi-
nation of three factors: (1) increased fault activ-
ity and subsidence related to the onset of the
Jurassic rift phase (Ravnås et al ., 1997); (2) a
relative sea-level rise; and (3) exhausted sedi-
ment supply due to an over-extended delta front
(Helland-Hansen et al ., 1992). Several studies
have speculated on the exact timing and dura-
tion of the Jurassic phase of rifting. Some
authors (Jennette & Riley, 1996; Hampson et al .,
2004) assigned the rift-phase to the Late Jurassic,
which renders the Middle Jurassic Brent Group

Generic pre-rift to syn-rift structural models

The Jurassic active stretching evolution of the
northern North Sea has generally been described
as a three-stage structural model, as summarised
below (e.g. Nøttvedt et al ., 1995; Færseth et al .,
1995a; Ravnås et al ., 2000):