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 211

Götz et al . (2011) examined coal-bearing strata of
Rhaetian to Hettangian age in southern Hungary
and concluded, from microfloral data, that there
was a change to more humid conditions during Late
Rhaetian to Hettangian times, more or less concur-
rent with the increased humidity inferred for the
Lunde to Statfjord transition in the North Sea area.
Götz et al . (2011) also inferred that the climatic
change was sudden and argued that the increase in
humidity could be related to the onset of intensive
volcanism during the initial break-up of Pangaea.
As noted above, this volcanic phase (Central
Atlantic Magmatic Province; e.g. Hesselbo et al .
2007) is associated with global mass extinctions and
increased atmospheric CO 2 concentration, hence
any climatic change induced by this volcanism
should clearly be widespread enough to affect the
climate of the entire Atlantic rift system, including
the strata and basins referred to in this study. For
the Barents Sea area the significantly coarser sand-
stones in the Tubåen Formation, than in the under-
lying strata, can be related to larger fluvial discharge
and increased capacity of rivers to transport coarser
material into the basins. This can clearly reflect a
more humid situation and higher annual precipita-
tion of rain during the Hettangian stage than, for
example, during the Carnian to Late Norian stages.
The data presented in the current study do not
provide any evidence for the actual causes of the
Late Triassic to Early Jurassic climatic changes.
Clearly, a gradual increase in humidity, as inferred
for the Late Norian to Rhaetian Lunde Formation
in the North Sea, can relate to continued north-
wards plate-tectonic drift of the sedimentary
basins, particularly if combined with increasing
proximity to marine environments. However, a
regionally consistent change towards more humid
climatic conditions at the Triassic to Jurassic
boundary, stretching from Iberia in the south to
the Barents Sea basins to the north, is probably
more logically tied to global climatic change (vol-
canism) than to plate tectonic drift, which only
places part of this area to the north of 30° N and
within the more humid climatic zone.

and redistribution of sediment transport routes from
the hinterlands. These changes are not synchronous,
but may eventually have led to more favourable con-
ditions for the development of coarser-grained and
more sand-dominated fluvial systems in the Early
Jurassic Tubåen Formation than in underlying Late
Triassic strata:

1 Contrasting alluvial architectures in Late
Triassic versus Early Jurassic strata indicate that
the generation of accommodation space was
significantly reduced at the Triassic to Jurassic
boundary, thus favouring selective preservation
of sandy, channelised deposits.
2 Comparison of rock accumulation rates from
absolute age assignments accords with limited
deposition and stratigraphic condensation of
Early Jurassic strata relative to the underlying
Late Triassic successions, again indicating that
fluvial reworking and preservation of chan-
nelised deposits should be more typical for the
Early Jurassic strata.
3 Late Triassic to Early Jurassic rejuvenation of hin-
terlands to the south of the Barents shelf can be
inferred from other studies and may have played
an important role in increasing the grain size of
sediment delivered to the basin areas during depo-
sition of the Early Jurassic unit (Tubåen Formation).
4 A re-organisation of transport routes with pos-
sible termination of sediment flux from the
Uralides may be related to the Early Norian
marine flooding and concurrent uplift (rejuve-
nation) to the south, thus changing the mineral
composition of sandy sediment.

Comparison of strata in the Barents Sea area, with
age-equivalent units from the North Sea basins
and the mid-Norway shelf provide additional
knowledge regarding more regional climatic con-
trols on deposition.

5 Whereas warm and humid climatic conditions
persisted in the Barents Sea area during the
Late Triassic (Late Carnian to Norian), warm
and generally dry desert conditions prevailed
to the south. Accordingly, a strong climatic
zonation between a dry desert to the south and
more humid, nearshore, setting to the north
seems to have persisted until the Rhaetian.
6 A significant climatic change to more humid
conditions can be inferred for the Early Jurassic,
with establishment of a seemingly more equa-
ble and wet climate from the North Sea area to

CONCLUSIONS

Based on the discussions above, it appears that chang-
ing depositional styles across the Triassic to Jurassic
boundary in the south-west Barents Sea can, on a
sub-regional scale, be related to a combination of
changing subsidence rates, hinterland rejuvenation