Climatic and tectonic controls on Triassic dryland terminal fluvial system architecture, central North Sea - From Depositional Systems to Sedimentary Successions on the Norwegian Continental Margin - page 48

has been noted in the Early Carnian of the mid-
Norway region (Müller et al ., 2005), extending to
southern Norway (Paul et al ., 2009), which would
lend some support to this model. This mechanism
of basin margin uplift has been appealed to as
an on-going process by Kozur & Bachmann (2010),
in which the brief episode of Schilfsandstein
drainage is attributed to a period of unusually
high precipitation on a persistently uplifted rift
flank. However, the persistence of westward
fluvial drainage into the central North Sea
from Fennoscandia would indicate that if the
Schilfsandstein rivers did indeed drain south-
ward then this brief departure from the typical
drainage pattern would potentially require an
equally brief tectonic deflection. In the absence
of conclusive evidence that drainage flowed
directly southwards off the Fennoscandian
region it is also plausible that this Fennoscandian
drainage, which traversed the central North Sea
from Anisian to Early Carnian times, was
extended in the Late Ladinian and Middle
Carnian via the Norwegian-Danish Basin into
the Southern Permian Basin, at which point it
began to flow southwards towards Tethys.
However, although both models are plausible,
there is little evidence of an abrupt change to
more humid facies in the central North Sea to
support a correlation of Erfurt and Schilfsandstein
formation fluvial facies into the time equivalent
Ladinian-Carnian Joanne Sandstone Member
(except possibly in the Norwegian-Danish Basin;
Lindström et al ., 2009). This paucity of humid
facies would suggest either that there was no
expression of these climatic changes in the central
North Sea or that the time equivalent section is
absent due to erosion or non-deposition and is
instead represented by an unconformity or hiatus.
This might be explicable for the Middle Carnian
pluvial event if it followed Cimmerian 1 rifting
and large areas were eroded by uplifting fault
blocks (although hangingwall areas might be
expected to have preserved some record). However,
there is no comparable record of tectonism in
the Late Ladinian which could explain the
absence of humid facies indicators for the broadly
similar Erfurt Formation drainage. The absence
of diagnostic facies may therefore be a result of
non-deposition and erosional bypassing during
these episodes. In both cases the Erfurt and
Stuttgart formation fluvial systems temporarily
drained towards a marine base level and were
commonly widely incised across the Southern

Permian Basin, suggesting that Tethys at this
time represented a lowered base level compared
to the preceding endorheic drainage contained
within the Southern Permian Basin. Further
upstream, in the central North Sea, it is also likely
that the fluvial profiles were similarly incised,
with conditions of even less accommodation than
the basins to the south. The record of the Late
Ladinian and Middle Carnian pluvial events in
the central North Sea may therefore be entirely
degradational as a result of fluvial incision across
the region towards a lowered marine base level.
Whilst subsequent backfilling in the Southern
Permian basin took place under on-going humid
conditions, backfilling further north in the central
North Sea may not have occurred until later when
the regional climate had reverted to dryer condi-
tions and the central North Sea converted to an
endorheic drainage with its own internal geomor-
phic base level.

DISCUSSION

Deposition of the Skagerrak Formation occurred
as terminal fluvial systems which debouched
into an arid central North Sea region (Fig. 19).
Discharge was seasonal, with flood waters dissi-
pating through evaporation and transmission
losses towards distal playa and sabkha (when the
Southern Permian Basin was marine influenced).
During pluvial episodes these terminal systems
expanded as a result of increased flood frequency
and/or magnitude and dry season runoff was
sufficient to maintain year-round vegetation and
burrowing organisms. Only during two major plu-
vial episodes, in the Late Ladinian and Middle
Carnian, did the fluvial systems expand outside
the central North Sea region to reach Tethys
as exorheic systems. A variety of mechanisms
have been proposed for these pluvial events,
including rift flank uplift to form an orographic
barrier which captured moisture-laden monsoon
circulation (Kozur & Bachmann, 2010), orogenic
events altering atmospheric circulation patterns
(Hornung & Brandner, 2005) and increased injection
of CO 2 during volcanic episodes (Korte et al .,
2005; Galfetti et al ., 2007b; Feist-Burkhardt et al .,
2008). Of these mechanisms volcanism is probably
the most likely process to have induced the rela-
tively abrupt climatic swings seen in these
Triassic successions, although whether these
resulted in cooling (Feist-Burkhardt et al ., 2008)