Late Triassic to Early Jurassic climatic change, northern North Sea region: impact on alluvial architecture, palaeosols and clay mineralogy - From Depositional Systems to Sedimentary Successions on the Norwegian Continental Margin - page 60

INTRODUCTION controlling factor on changes in depositional

style have only been discussed in a few studies
(Perlmutter & Matthews, 1989; Olsen & Larsen,
1993; Van der Zwan, 2002; Feldman et al . 2005).
However, the impact of long-term climatic changes
on palaeosol development has been pointed out
by several authors (Hubert, 1977; Wright, 1990;
Vanstone, 1991; Mack, 1992; Joeckel, 1999;
Ahlberg et al ., 2002). The restricted use of climate
in alluvial models of ancient fluvial deposits
was emphasised by Blum & Törnqvist (2000), who
proposed that much more discussion was needed
on the effects of climate on the stratigraphic record
in general.
The continental Permo-Triassic to Lower Jurassic
succession in the northern North Sea region is
usually thought to record a change in climate from
warm and arid to warm and humid (Evans et al .
2003). This climate change has been attributed to
the northward drift of the Eurasian plate, with
the central northern North Sea position migrat-
ing from about 40 ° N in the Late Triassic (Carnian-
Norian) to about 50 ° N in the Early Jurassic
(Rhaetian-Sinemurian) (Goldsmith et al ., 2003).
Global increase in temperature at the Triassic/
Jurassic transition (Hesselbo et al ., 2002; Bonis &
Kürschner, 2012) may also have contributed to
climatic changes in the northern North Sea area.
Recent studies of the alluvial Triassic of the north-
ern North Sea, particularly dryland depositional
systems, are presented by Müller et al . (2002),
McKie & Audretsch (2005), McKie & Williams
(2009) and McKie et al . (2010).
The present study deals with a rock record com-
prising the Upper Triassic Lunde Formation and
the Lower Jurassic Statfjord Group (elevated to
group status by Lervik, 2006) in the Tampen Spur
area, northern North Sea, particularly in the
Snorre oilfield (Fig. 1). These lithostratigraphic
units are characterised by variously stacked flu-
vial sandstone bodies alternating with units of
floodplain mudstones with palaeosols and clay
mineralogy that change up through the succession
(Nystuen et al ., 1989; 2008; Steel & Ryseth, 1990;
Nystuen & Fält, 1995; Adestål, 2002; Müller, 2003;
Müller et al ., 2004; Kjemperud, 2008; Schomacker,
2008). The object of the present paper is to inte-
grate data on alluvial facies, palaeosols and clay
mineralogy in a synthesis of climatic impact on
basin infill dynamics and alluvial architecture
from Late Triassic to Early Jurassic time in the
northern North Sea (Fig. 1).

Climate is a major factor controlling the sedimen-
tary infill of alluvial basins. River dimension,
channel morphology and fluvial deposits are
related to overall discharge, the run-off pattern
and variation in hydraulic energy, rate of sedi-
ment supply, sediment composition and vegetation
cover; all these variables are controlled and influ-
enced by precipitation and temperature. Tectonics
and eustasy influence base level and thereby
influence accommodation space and sediment
influx. Thus, the depositional style of an alluvial
succession may be the result of complex interac-
tions between climate and other external (extrin-
sic, allogenic) factors as well as internal (intrinsic,
autogenic) factors (Blum & Törnqvist, 2000;
Schumm, 2005; Bridge, 2005).
Alluvial architecture and facies models for
ephemeral dryland streams and perennial streams
of humid climatic regions have been widely
applied to infer palaeoclimate (Miall, 1996; Tooth,
2000; Patterson et al ., 2006; Roberts, 2007;
Howard, 2009); recently, facies models have also
been established for rivers in seasonal tropical
regions (Fielding et al ., 2011).
Palaeosols are particularly important features
for recording palaeoclimate, both in terms of
soil-forming processes controlled by humidity,
temperature, drainage and vegetation, floodplain
dynamics, rate of sedimentation and resulting
alluvial architecture (Retallack, 1986; Kraus, 1987,
1999, 2002; Marriott & Wright, 1993; Tandon &
Gibling, 1994; Bestland, 1997; Hamer et al ., 2007;
Terry, 2007; Moore et al . 2008).
Clay mineralogy represents a third category of
applied palaeoclimate indicators (Blanc-Valleron &
Thiry, 1997; Gingele & Deckker, 2004; Robert,
2004; Suresh et al ., 2004; Wan et al ., 2011).
The architectural style of alluvial basins is the
combined result of several extrinsic and intrinsic
factors operating on various time scales ranging
from some hundreds to several millions of years.
Most studies concerning the impact of climate
on fluvial architecture have dealt with climatic
variations of Milankovitch-scale, or even shorter
duration (Blum, 1993; Yang & Baumfalk, 1994;
Olsen, 1994; Gibling & Bird, 1994; Sinha & Sarkar,
2009). Long-term changes in alluvial architecture
have been related mainly to tectonism and eustasy
(Wright & Marriott, 1993; Leeder et al ., 1996;
Miall 1996). Long-term climate shifts as the main