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run-off, forced by increased precipitation in the
hinterlands (Nystuen et al ., 1989; Steel & Ryseth,
1990; Steel, 1993; Nystuen & Fält, 1995; Ryseth &
Ramm, 1996; Ryseth, 2001; Goldsmith et  al .,
2003). Differential subsidence, driven by tectonics
and/or by compaction, may account for thickness
variations in the Lunde Formation and the Statfjord
Group in the Tampen Spur area (Fig. 16). Regional
thickness variation is particularly pronounced in
the USG (Fig.  16) and this has been explained by
syn-depositional growth faulting (Ryseth & Ramm,
1996).
Weltje et  al . (1998) pointed out that in most
basin studies changes in depositional stacking
pattern were ascribed to changes in accommoda-
tion driven by tectonics and eustasy, whereas
much less attention was given to the role of sedi-
ment supply controlled by climate. Leeder et  al .
(1998) presented examples of how climate and cli-
matic changes controlled basin infill architecture.
Tectonics as a major factor in the formation of
fining-upwards and coarsening-upwards trends
within the Lunde-Statfjord succession may have
been less influential than previously considered.
The high quartz content of sandstones and mud-
stones in the Statfjord Group (Table 2, Fig. 15)
favours that sand was formed by advanced chemi-
cal weathering of granitic bedrock and not by ero-
sion of juvenile granite or gneiss exposed due to
rapid tectonic uplift. This is supported by the
association of the quartz-arenitic sandstone with
smectite-rich or kaolinite-rich mudstones, prod-
ucts of increased chemical weathering (Fig.  15).
The weathered quartz-rich sand may have been
stored in the hinterlands over long geologic times,
trapped by depositional and/or geomorphic thres-
holds (cf. Schumm, 1977) and then delivered to
the basin by breakthrough of thresholds during
events of very high precipitation and flooding
in Sinemurian times. It cannot be excluded that
tectonic movements in the hinterland may have
affected the run-off pattern.
As pointed out by McKie & Williams (2009), it is
likely that the fluvial systems of the Triassic basins
in the northern North Sea region were terminal
until the onset of the Rhaetian transgression.
However, the Norian-Rhaetian Lunde Formation
has not revealed any signatures of a hydrologically
closed system, in contrast to the underlying
Alke Formation (Lervik, 2006). The difference
in microfloral composition between the Alke and
Lunde formations, recognised by Eide (1989)
and ascribed by her as the result of different
depositional environments (see above), might be
the signature of a change from a closed to an open
fluvial system. Eide (1989, p. 296) further sug-
gested that “local and temporary marginal marine
influence may be reflected in the sporadic pres-
ence of single and questionable specimens of the
acritarch Schizocystia sp” (her Assemblage I, Lunde
Forma tion). Goldsmith et al . (2003) recognised that
both Assemblage II (Alke Formation) and Assemblage
I of Eide (1989) include rare marine and brackish
microplankton and concluded from a regional cor-
relation that the transgression in the North Sea area
started at the sequence stratigraphic surface Tr42,
corresponding to an interval in the upper part of the
Alke Formation/lower part of the Lunde Formation.
The regional unconformity at the base of the
Lunde Formation, documenting the establishment
of large fluvial channel systems (see above), may
represent a change in the Tampen Spur area from
a closed to an open regional fluvial drainage sys-
tem. There is no other candidate surface indicat-
ing such a fundamental shift in type of base level
control in the whole Lunde-Statfjord succession.
The ultimate base level of the Lunde-Statfjord
fluvial system is thus inferred to have been embay-
ments of the sea encroaching onto the northern
North Sea region; Tethys in the south-east and/or
the Borealic Sea in the north. However, shorelines
must have been several hundreds of kilometres
away from the alluvial basin during deposition in
the Rheatian and early Hettangian (Ryseth, 2001;
Goldsmith et al . 2003; Müller et al . 2005; McKie &
Williams, 2009).
Effects of eustatic sea-level fluctuations can
nevertheless be felt up to some hundred kilome-
tres landward from the shoreline (Schumm, 1993;
Shanley & McCabe, 1994; Ethridge et al ., 1998;
Posamentier & Allen, 1999; Catuneanu, 2006).
Repeated rise and fall in relative sea-level during
the Triassic has been documented as transgres-
sive-regressive (T/R) cycles in shallow marine
basins in Arctic Canada, Spitsbergen and the
western Barents Sea (Johannessen & Embry, 1989;
Mørk et  al ., 1989; Glørstad-Clark et  al ., 2010,
2011). Embry (1997) suggested that some of these
cycles were global. The Rhaetian-Hettangian con-
tinental basins in the North Sea region may thus
have been affected by several stratigraphic base
level fluctuations that controlled the rhythmitic
allostratigraphy in the Tampen Spur area. It is
beyond the stratigraphic resolution of the present
biostratigraphic data to correlate high-frequency
cyclic sedimentation in shallow-marine and alluvial
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