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of dryland ecosystems in the central North Sea
was not driven by runoff from distant, wetter
regions but by discharge sourced from local, basin
margin catchments which experienced sufficient
precipitation during the dry season to prevent the
central North Sea region becoming fully desic-
cated, evaporitic and unable to support plants and
animals. This perennial runoff within a region
broadly characterised as one of net evaporation
occurred during pluvial pulses when the basin
margins experienced a departure from widespread
aridity towards a more semi-arid dry season with
groundwater flow and a wet season characterised
by flooding and overland flow.
the Smith Bank and Bunter formations (up to
600 m thick) do not differ markedly over the
c. 5 Ma of Early Triassic time from 'normal' Mesozoic
terrestrial rates (Sadler & Strauss, 1990). However,
the more widespread nature of the Bunter and
Sherwood sandstones across north-west Europe
compared to younger Triassic fluvial systems
suggests that during pluvial episodes, with suf-
ficient water to transport sediment, dispersal of
large volumes of sand-prone detritus was possible
(McKie & Williams, 2009).
Anisian and Ladinian pluvial events are poorly
expressed in the strontium isotope record, sug-
gesting that these events were of insufficient
duration or magnitude to disturb Tethyan seawa-
ter chemistry, but the major Carnian pluvial event
is marked by a minor
87
Sr/
86
Sr increase reflecting
the widespread development of exorheic fluvial
systems which drained into Tethys, terminated
carbonate production and precipitated a Tethyan
'reef crisis' (Hornung
et al
., 2007). Increasing
values through the Late Triassic are interpreted
to reflect increasing erosion of the Cimmeride-
Indosinian orogens, marking the closure of the
Palaeotethys (Korte
et al
., 2003), but could plausi-
bly have some enhancement from climatically
induced runoff.
The
87
Sr/
86
Sr data provide a record of major
trends in sediment yield into Tethys which high-
light continental-scale sediment supply pulses
in the Early Triassic, Carnian and Late Norian-
Rhaetic by exorheic rivers. However, this record
provides only limited insights into the behaviour
of endorheic systems in basins like the central
North Sea or the higher frequency supply pulses,
which might be expected given the evidence of a
highly variable climatic record. These events may
be more subtly expressed. For example, the upper
part of the Anisian Judy Sandstone Member shows
an abrupt increase in vegetation cover and pro-
portion of channel-fills, marking a major increase
in sediment supply into the basin, availability of
year-round soil moisture and expansion of the flu-
vial catchments into Fennoscandia (McKie, 2011).
This event is composite in nature, being marked
initially by a facies and provenance change from
terminal splay to cross-stratified fluvial depos-
its indicative of well organised, Fennoscandian,
channel systems, followed by a change in flood-
plain style from barren playa mudstones to rooted
floodplain mudstone with calcrete (Fig. 4A). The
onset of palynological recovery from the Skagerrak
Formation (Goldsmith
et al
., 1995) broadly occurs
Sediment yield
The Triassic mudstones across the region are
generally lacking kaolinite and smectite (Ruffell
et al
., 2002; Jeans, 2006) and the sandstones are
typically arkosic to lithic arkoses in composition
and highly feldspathic (10% to 50%), indicating a
dominance of mechanical weathering in source
areas subject to long term aridity. The pluvial
episodes do not appear to have been of sufficient
duration or intensity to significantly modify the
weathering products, except during the Middle
Carnian pluvial phase when kaolinite became epi-
sodically more abundant (Simms & Ruffell, 1990).
Although sediment supply to these basins rarely
reached Tethys or the Muschelkalk seaway,
87
Sr/
86
Sr data from these marine basins (Korte
et al
.,
2003) may provide an indication as to the broader
conditions of sediment yield during pluvialisa-
tion by exorheic river systems across the region,
which can be compared to the nearby endorheic
basins (Fig. 18). These data indicate three major
episodes characterised by marked increases in
sediment yield. An Early Triassic increase is likely
to reflect increased weathering and erosion result-
ing from widespread devegetation during the
recovery from the end Permian extinction, with
the subsequent long-term reduction in yield broadly
corresponding to the Anisian recovery and resump-
tion of sediment binding by plants (Newell
et al
.,
1999; Korte
et al
., 2003). Evidence for this high
sediment yield appears to be lacking in the central
North Sea, which may be due to several factors,
including the general aridity of the region and
infrequent sediment supply. Although it would be
tempting to ascribe Early Triassic halokinesis to
unusually rapid sediment loading, the long-term
sedimentation rates for the interval comprising
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