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 192

Considerations of Triassic precipitation pat-
terns (Sellwood & Valdes, 2006) suggests that
large areas of Pangaea, extending almost to 50º N
and 50º S, were characterised by a large excess of
evaporation, with only short monsoonal periods.
Wetter climates supporting coal formation existed
in higher latitudes to the north and south, particu-
larly during Late Triassic time (Sellwood & Valdes,
2006). Reconstruction of Triassic climates in the
south-west Barents Sea (Hochuli & Vigran, 2010)
also indicates that generally warm and humid
conditions persisted throughout Late Carnian to
Norian times, in contrast to the drier conditions to
the south.
The Triassic to Jurassic boundary seems to asso-
ciate with the establishment of a more humid cli-
mate in the present NW European basins (Hallam,
1985). This climatic change has been related to
north-directed plate-tectonic drift combined with
marine incursions (e.g. Frostick et al . 1992;
Ahlberg et al . 2002). Other studies also suggests
that widespread volcanism and massive release of
isotopic light CO 2 to oceans and the atmosphere
during the initial fragmentation of Pangaea at the
Triassic to Jurassic boundary triggered significant
climatic change and both marine and terrestrial
biological mass extinction on a global scale (e.g.
Hesselbo et al ., 2002, 2007; Schoene et al ., 2010).
The sedimentary successions along the Norwegian
shelf should perhaps reflect such a climatic
change? This point will be addressed below in
relation to the evaluation of possible climatic
controls on deposition.

Hammerfest and Nordkapp basins. Biostratigraphy
data indicate that the cored section is of general
Norian - Rhaetian age. Accordingly, it is a key well
for the understanding of end-Triassic deposition in
the area.
Further to the east, well 7226/11-1 is located on
the Norsel High, in the structural transition zone
between the Bjarmeland Platform and the
Nordkapp Basin. The cored section is dated as
Early Norian to Sinemurian and is a relevant refer-
ence for the Early Jurassic succession in a more
easterly position relative to the other wells. Well
7121/4-F-2H is located in the central part of the
Hammerfest Basin (Snøhvit field) and is a key ref-
erence well for the Early Jurassic (Hettangian to
Early Pliensbachian) depositional systems in the
central part of the Hammerfest Basin. Wire-line
log data from well 7121/5-1 in the central part of
the Hammerfest Basin are included for correlation
purposes. In addition to the core and wire-line
data from the listed wells, some petrographic data
from a separate well on the Bjarmeland Platform
will be discussed.

LATE TRIASSIC TO EARLY JURASSIC
STRATIGRAPHY AND FACIES

Fig. 4 outlines the stratigraphy of Carnian to Early
Pliensbachian strata in the Barents Sea, with cor-
relations to the Halten Terrace offshore mid-Norway
and to the Viking Graben in the North Sea. The
Late Triassic to Early Jurassic succession in the
Hammerfest Basin and adjacent areas in the south-
west Barents Sea comprises strata deposited in
fluvial, marginal marine (paralic) and offshore,
pro-deltaic, environments and are contained
within the lithostratigraphic Storfjorden and
Realgrunnen subgroups and corresponding forma-
tions (Fig. 4; see also Dalland et al ., 1988 and
Mørk et al ., 1999 for definitions). The present
study is entirely related to the upper part of the
Snadd Formation and to the overlying Fruholmen
and Tubåen formations, for which observed for-
mation tops and thicknesses in the studied wells
are listed in Table 1.
The Snadd Formation (Ladinian to Early Norian;
lower part not included in Fig. 4) is widely dis-
tributed across the Barents shelf, with a thickness
commonly exceeding 1000 m to 1200 m (Mørk
et al . 1999). The basal boundary with the underly-
ing unit (Anisian to Ladinian Kobbe Formation;
Mørk et al ., 1999) is defined by an organic

STUDY AREA AND WELL DATABASE

This study is based on core and wire-line log data
from five wells (Fig. 2B), located in and around the
Hammerfest Basin. Environmental interpretations
are based on macroscopic descriptions of approxi-
mately 310 m of core, which are presented on
1:200 or 1:500 scales. Biostratigraphic data are
available for all wells, but stratigraphic age assign-
ments are primarily referred to the Hammerfest
Basin, about which the most detailed records exist.
The stratigraphically oldest described core inter-
val is obtained from well 7222/11-1 in the south-
east corner of the Loppa High (Fig. 2B). Here a
section of Late Carnian age, combined with 3D seis-
mic data, illustrates the nature of the Late Triassic
depositional system. Well 7124/3-1 is located
in the structural transition zone between the