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at this level and it is likely that this mid-Judy
Sandstone Member event was the combined
product of one or more Anisian pluvial episodes,
combined with local climatic humidification asso-
ciated with the marine flooding of the Muschelkalk
seaway (Fig. 18) and marks a major change in the
Fennoscandian sediment supply to the basin. This
contribution was sustained through the Ladinian
and Carnian as the subsequent progradation of
the Joanne Sandstone Member and marks a major
departure from the more regional dominance of
Keuper Formation and Mercia Mudstone Group
playa environments.
did occur, but not in a cyclical or repetitive
manner that can be correlated over large distances.
Although evidence of base level fall is limited, pos-
sible exceptions may be during the Late Ladinian
and Carnian pluvial events, when Fennoscandian
drainage reached Tethys and incised Erfurt and
Stuttgart formation fluvial systems drained across
the Southern Permian Basin towards an initially
lowered marine base level (Aigner & Bachmann,
1992; Kozur & Bachmann, 2010). The expression of
these events in the central North Sea, however, is
not clear-cut.
Erosional by-pass of exorheic fluvial systems?
Base level
The Late Ladinian and Middle Carnian are
characterised regionally by evidence of a wide-
spread increase in humidity and fluvial run-off
(Simms & Ruffell, 1989, 1990; Hornung
et al
., 2007;
Bachmann
et al
., 2010; Kozur & Bachmann, 2010),
with the main expression in the Southern Permian
Basin being the regional development of the flu-
vio-deltaic Erfurt (Lettenkeuper) and Stuttgart
(Schilfsandstein) formations (Geluk, 2005; Kozur
& Bachmann, 2010). These deposits record the
drainage off Fennoscandia of large, southward
flowing, incised river systems (e.g. Shukla
et al
.,
2010; Fig. 19D) which supported widespread
riparian vegetation (Visscher
et al
., 1994). The
local evidence of brackish facies and tidal influ-
ence (Kozur & Bachmann, 2010; Bachmann
et al
.,
2010; Shukla
et al
., 2010) indicates that the rivers
reached Tethys as exorheic fluvial systems and in
the Carnian supplied sufficient clastic detritus to
precipitate a 'reef crisis' (Hornung
et al
., 2007).
Provenance data (Köppen & Carter, 2000; Paul
et al
.,
2008) indicate derivation from the Fennoscandian
and Caledonian basement region of western
Norway - the same region from which the west-
ward draining Skagerrak Formation streams
flowed. Regional maps of the incised channels
of these fluvial systems in Germany typically
project the southward drainage pattern north-
wards directly onto the Fennoscandian Shield in
a departure from the typical westward drainage
seen towards the central North Sea. If this change
in drainage is genuine it is conceivable that in the
Early Carnian the Cimmerian 1 extensional epi-
sode induced sufficient rift flank uplift of the east-
ern margin of the central North Sea to divert the
Norwegian drainage away from the central North
Sea and southward to directly enter the Southern
Permian Basin. Widespread basin margin uplift
A definition of geomorphic base level within ephem-
eral, terminal systems is problematic because in
many cases the fluvial discharge fails to reach the
terminus of the fluvial system due to evaporation
and infiltration. However, over geological time
scales the ultimate base level for endorheic systems
must be the playa or lake floor, depending on the
balance of runoff versus evaporation/infiltration and
of sediment supply versus subsidence (cf. Nichols,
2007). Low runoff will result in distal fringes domi-
nated by aeolian processes (and preservation
dictated by water table fluctuations; Kocurek &
Havholm, 1993), with increasing runoff leading to
an increasing dominance of fluvial facies, until run-
off exceeds evaporation and transmission losses and
perennial lakes form. At this point lake level fluctu-
ations dominate the fluvial architecture within the
basin in a similar manner to coastal plain systems.
In general the Triassic fluvial systems appear to
have drained towards a desiccated playa floor in
which geomorphic base level changes would have
largely been the product of a changing balance
between sediment supply and subsidence, with
the former dictated by climatic changes in the
headwaters of the fluvial system and the latter by
regional thermal subsidence, episodic extension
and more localised salt movement. There is little
evidence of fluvial incision in the form of readily
identifiable incised valleys or mature interfluve
palaeosols (e.g. Fig. 15C), suggesting that the sys-
tems were dominantly aggradational in character
(Fig. 15B) and did not experience systematic, high
frequency base level fluctuations in the same
manner as fluvial systems discharging into peren-
nial lakes or marine water bodies. Mature calcic
palaeosols and major lags of reworked calcrete
occur locally, indicating that terracing and incision
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