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et al
., 2003) as rifting propagated from the Tethys
Sea to the south (Fig. 1) and the Boreal Ocean
to the north. Rifting between Greenland and
Fennoscandia, beginning in the latest Permian to
Early Triassic (Wignall & Twitchett, 2002; Seidler
et al
., 2004; Müller
et al
., 2005), propagated south-
ward along the Atlantic seaboard of the UK and
western Ireland, onshore UK and East Irish Sea
(Stolfová & Shannon, 2009) and into the northern
and central North Sea (Steel & Ryseth, 1990).
Northward directed rifting propagated into the
Southern Permian Basin and central North Sea
from the Tethyan margin via the Polish Trough
(Geluk, 2005). The location and trend of these rift
basins was influenced strongly by the structural
grain of the Precambrian basement, position of
former Variscan thrusts and the location of pre-
existing Carboniferous and Early Permian basins
(Peacock, 2004). Two dominant basin orientations
developed, controlled by north-west to south-east
oriented Arctic-Atlantic extension and north-east
to south-west extension related to the opening of
Neotethys. This resulted in a broadly orthogonal
fault pattern across the region (Coward, 1995).
Earliest Triassic deposition commonly infilled
remnant Permian rift topography (Stolfová &
Shannon, 2009), but as the break-up of Pangaea
progressed two main extensional pulses occurred
in the late Early Triassic and in the early Late
Triassic which can be identified from the Southern
Permian Basin to mid-Norway (Geluk, 2005;
Müller
et al
., 2005). These generated the wide-
spread Hardegsen and Early Cimmerian uncon-
formities, although it is likely that these episodes
were not precisely synchronous across the region
(e.g. Hounslow & McKintosh, 2003). As a result of
these events, the Permo-Triassic basin-fills com-
monly show a broadly half-graben form (although
this is commonly masked by subsequent Jurassic
rifting which may not have the same fault polarity)
and contain a fill showing multiple extensional
episodes across migrating fault arrays (Tomasso
et al
., 2002; Stolfová & Shannon, 2009). In the cen-
tral North Sea there has also been widespread
denudation of the Triassic during Middle Jurassic
thermal doming (Underhill & Partington, 1993)
and footwall/rift flank erosion during Late Jurassic
rifting (Erratt
et al
., 1999). However, regional sec-
tions locally give a general sense of a deeply
truncated half graben wedge (Fig. 3A and B),
with the active basin-bounding faults probably
located on the eastern, Norwegian, margin (Faerseth,
1996; Erratt
et al
., 1999).
In the central North Sea, mobilisation of the
underlying Zechstein Group halite due to sedi-
ment loading, faulting and dissolution resulted
in the formation of salt withdrawal minibasins
(Fig. 3C, D). The most prominent of these appear
to be Early Triassic in age and filled by Smith
Bank Formation mudstones. Stewart & Clark
(1999) and Penge
et al
. (1999) note the local-
ised presence of an intra-Triassic unconformity
separating the main episode of differential mini-
basin subsidence from the younger Skagerrak
Formation. Whilst these authors suggest that this
unconformity may be Anisian to Norian in age, it
is likely that this boundary, which occurs close
to the Smith Bank-Skagerrak formation bound-
ary, represents the late Early Triassic Hardegsen
Unconformity recognised across the Southern
Permian Basin (Geluk, 2005), Wessex Basin
(Hounslow & McKintosh, 2003), East Irish Sea
(Colter & Barr, 1975) and Cheshire Basin (Evans
et al
., 1993). Higher in the succession, Archer
et al
. (2010) note the presence of an unconform-
ity within the Carnian Joanne Sandstone Member.
This unconformity, which shows onlap by the
Jonathan Mudstone member, probably represents
the Early Cimmerian I unconformity which,
although widely recognised in the Southern
Permian Basin (Geluk, 2005) and towards the
Ringkøbing-Fyn High (Clausen & Pedersen, 1999),
is not well represented in the deeply truncated
central North Sea succession where there is
limited preservation of Carnian and younger
sections.
DEPOSITIONAL SETTING
On a regional scale, the facies architecture of the
Skagerrak and Smith Bank formations in the cen-
tral North Sea is dominated by dryland fluvial
deposits. To the south, crossing the mid-North Sea
and Ringkøbing-Fyn highs and entering the
Southern Permian Basin, the Triassic succession
becomes more mud-prone, with episodic marine
incursions recorded by carbonate and evaporite
facies (Michelsen & Clausen, 2002; Geluk, 2005).
This facies transition records the downstream
(Fig. 2B) terminal shale-out of the Skagerrak
Formation fluvial systems into playa and coastal
sabkha facies. In addition to this regional facies
transition, there is a fundamental stratigraphic
change in depositional character between the
Early and Middle to Late Triassic successions in
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