Sedimentation at the Jurassic–Triassic boundary, south-west Barents Sea: indication of climate change - From Depositional Systems to Sedimentary Successions on the Norwegian Continental Margin - page 210

indicate some water deficiency in the parent soil
and also oxidising conditions. Accordingly, some
evidence exists for slightly drier climatic condi-
tions in the Late Triassic than in the Early Jurassic
successions in the Barents Sea.
The Late Triassic climate further to the south is
apparently very different. As described above,
palaeographic reconstructions generally assume
that north-west Europe, including the North Sea,
was positioned at a palaeolatitude of approximately
40° N during the Late Triassic, approximately
12° south of the Barents shelf (Golonka, 2007).
Widespread occurrence of red beds with pedo-
genic carbonate (calcrete) throughout the Triassic
strata in the north west European basins, coupled
with climatic circulation models, generally point
towards very hot and arid conditions, with a short
wet season (e.g. Sellwood & Valdes, 2006) and flu-
vial systems entering the basins are thought to
drain into terminal playa lake systems (McKie &
Williams, 2009).
However, following Nystuen et al . (this vol-
ume), a gradual increase in humidity can be
recorded from Late Norian to Rhaetian strata
(Lunde Formation) in the North Sea area, reflected
by significant changes in clay mineralogy and by a
change from mainly ephemeral stream deposits
and associated red beds in the lower Lunde
Formation, to more perennial fluvial systems in
its the upper parts. Nystuen et al . (this volume)
related this gradual change in climate mainly to
continuous continental drift, with a steady north-
wards shift of e.g. the Viking Graben (Fig. 1) to
approximately 50° N in the Early Jurassic. Other
studies have also indicated that marine incursion
from the south may have contributed to a more
humid type of climate during the latest Triassic
(Rhaetian) in the North Sea area (Ahlberg et al . 2002).
For the Late Triassic on the Halten Terrace,
Müller et al . (2005) stated that the Carnian halite
units (Fig. 4) were precipitated from marine waters
in a warm and arid climate. They also inferred a
semi-arid setting for overlying Norian red beds,
very similar to the inferred climatic condition in
the North Sea area. This contrast between arid cli-
mates to the south and more humid climates to
the north (Barents Sea) during the Late Triassic
seems to relate to palaeogeographic variations,
particularly in palaeolatitude, with a humid cli-
matic zone to the north of a prevailingly dry zone
to the south.
Humid conditions and high ground-water lev-
els in the Late Triassic strata in the Barents Sea

area can also be related to deposition in closer
proximity to marine environments. The sedimen-
tary facies of the Snadd Formation are indicative
of frequent marine incursions (e.g. Fig. 6) in the
delta plain and palaeogeographic models (e.g.
Riis et al . 2008; Glørstad-Clark et al . 2010) show
the existence of marine systems immediately to
the north and west of the interpreted delta plain
of the Snadd Formation. General proximity to the
Boreal ocean, as opposed to inland desert condi-
tions to the south, should clearly be favourable for
a more humid climate on the Barents shelf than,
for instance, in the North Sea area, which appar-
ently was located well away from marine waters
and within inland basins of a major continent.
However, the desert basins to the south may have
been partly connected to the Boral Ocean to the
north through the Atlantic rift, particularly during
deposition of the Carnian halite on the Halten
Terrace (Fig. 1), which has been related to marine
incursions from the north (Müller et al ., 2005).
In contrast to the inferred climatic zonation in
the Late Triassic, the Early Jurassic climate seems
to be humid and rather equable between the
North Sea basins and the Barents Sea area. In the
south-west Barents Sea, the fine-grained part of
the Tubåen Formation seems to be totally domi-
nated by grey beds and associated coal, which
is indicative of completely water saturated and
predominantly reducing conditions. In the North
Sea, coal-bearing grey beds are frequently
observed in the upper part of the Statfjord
Formation (Steel & Ryseth, 1990; Ryseth, 2001).
Likewise, common coal-bearing strata in the
time-equivalent (Hettangian) lower part of the
Åre Formation on the Halten Terrace (Morris
et al . 2009) also accords with a humid climate.
This widespread change to a wetter climate
across the Triassic to Jurassic boundary on the
Norwegian shelf may relate to continuous north-
wards continental drift (e.g. Frostick et al . 1992;
Nystuen et al . this volume). However, the turn-
around to more humid conditions is apparently
common to many European basins. For instance,
Hesselbo et al . (2007) noted that marine platform
carbonates in Iberia (Spain) record a change from
arid to humid climate at the Triassic to Jurassic
boundary. Based on plate reconstructions plac-
ing this part of the western Tethys in the equato-
rial belt south of 30° N during Rhaetian to
Hettangian times (Golonka, 2007), it seems
unlikely that continental drift alone can explain
the climatic change.