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precipitation in hinterland areas during monsoon
seasons. The decrease in CDP upward through the
Lunde Formation and in the lower part of the
Statfjord Group is obviously a function of increased
clay/sand ratio of the sediment load, whereas the
opposite relation explains the increase in CDP in
the upper part of the Statfjord Group. Changes in
sediment supply changed the A/S ratio; a shift
from A/S < 1 to A/S > 1 would have caused a change
from amalgamated to isolated channel belts depos-
its and vice versa .
Properties of fluvial Upper Triassic to Lower
Jurassic sandstone reservoirs in the northern North
Sea region have been reviewed by Diesen et  al .
(1995), Nystuen & Fält (1995) and Lundschien &
Mørch (1998). The climatic control on depositional
architecture, sandstone facies and textural and
mineralogical composition is of great importance
for further exploration for Triassic reservoirs in the
northern North Sea region. The climate, as an
extrinsic control factor on alluvial sedimentation,
has given rise to deposition of allostratigraphic
units of high correlative potential.
gave rise to ephemeral braided streams, enti-
sols/inceptisols with scattered calcrete nodules
and hematite in reddish-brown floodplain mud-
stones, high amounts of detrital feldspar and a
diversified clay mineral suite.
5 In late Rhaetian times, increased precipitation
gave rise to dominantly meander channel belts
in the upper part of the Lunde Formation,
reflecting cyclic changes in hinterland precipi-
tation, whilst paleosols and clay minerals in
floodplain mudstones were controlled by climate
and drainage on the alluvial plain.
6 The Raude Formation represents a marked
climatic change from semi-arid to semi-humid
climatic conditions, reflected by thick mudstone
beds and small single storey channel sandstone
bodies and wetplains with mudrocks dominated by
smectite as clay mineral and generally mottled and
low-chroma vertisols.
7 The Eiriksson Formation reflects a change to
humid climate with quartz-arenitic braided
stream sandstones formed during monsoonal
high runoff and flushing of hinterland storages
of chemically weathered sand and greenish-
grey mudstones dominated by kaolinite formed
in well-drained alluvial fans or plains.
8 Rhythmitic successions of sets of alluvial
allostratigraphic units in the Tampen Spur
area were controlled by cycles of varying
precipitation in the hinterland area, possibly in
combination with changes in base level or dif-
ferential subsidence. Regional correlation of
allostratigraphic successions and their sand-
stone reservoir properties are of fundamental
importance for further hydrocarbon explora-
tion in the continental Upper Triassic-Lower
Jurassic in the northern North Sea.
CONCLUSIONS
1 A long term shift from arid/semi-arid to humid
climate in the northern North Sea region during
the Late Triassic (Rhaetian) to Early Jurassic
(Hettangian-Sinemurian) was primarily related
to drifting of the European continental plate
towards the north and is recorded in the conti-
nental Lunde Formation (Rhaetian) and the
Raude (Rhaetian-Hettangian) and Eiriksson
(Sinemurian) formations in the Statfjord Group.
2 The climatic change had profound influence
on variation in weathering, sediment produc-
tion, runoff and sediment discharge and is
reflected by changes in fluvial style, palaeosol
development and of sandstone and mudrock
mineralogy.
3 Climatic signals and changes in these given by
alluvial style, palaeosols and mineralogy gen-
erally coincide. Responses of the sedimentary
system to the climate change gave rise to a
long-term upward-fining (Lunde Formation)
followed by an upward-coarsening (Stat-
fjord  Group) succession with corresponding
changes in channel belt proportion and alluvial
architecture.
4 During deposition of the lower part of the Lunde
Formation (Rhaetian), arid to semi-arid climate
ACKNOWLEDGEMENTS
The authors would thank the former Saga
Petroleum and the present Statoil for allowing us
to perform this study and giving permission for
publication of the results. We owe gratitude to a
number of people that have been working with the
Upper Triassic and the Lower Jurassic on the
Tampen Spur in the northern North Sea area
through many years for cooperation and a series
of discussions. Two anonymous reviewers have
given very valuable input to the final version of
this paper. We thank Adrian Read for having cor-
rected the English of the manuscript and also for
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