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 59

Late Triassic to Early Jurassic climatic change, northern
North Sea region: impact on alluvial architecture,
palaeosols and clay mineralogy
JOHAN P. NYSTUEN*, AUDUN V. KJEMPERUD* † , REIDAR MÜLLER* ‡ ,
VICTORIA ADESTÅL* § and EDWIN R. SCHOMACKER* ǁ
* Department of Geosciences, University of Oslo, 0316 Oslo, Norway (E-mail: [e-mail])
† Idemitsu Petroleum Norge, Fillipstad Brygge 1, 0250 Oslo, Norway
‡ Tullow Norway, Tordenskiold gate 6b, 0160 Oslo, Norway
§ BayernGas Norge, Lilleakerveien 8, 0283 Oslo, Norway
ǁ Statoil ASA, Martin Linges vei 33, 1330 Fornebu, Norway
ABSTRACT
The European continental plate drifted northwards in Late Triassic to Early Jurassic
time. The change in plate position gave rise to a long-term shift from arid/semi-arid to
humid climate in the North Sea region, in addition to a global warming effect of the igne-
ous activity in the Central Atlantic Magmatic Province. In the Tampen Spur area in the
northern North Sea, this climatic change profoundly influenced the development of
alluvial successions represented by the Lunde Formation (Norian-early Rhaetian) and
the overlying Raude and Eiriksson formations (Rhaetian-Hettangian) in the Statfjord
Group. Arid to semi-arid climate during the Norian and early Rhaetian is expressed in
the lower part of the Lunde Formation by ephemeral braided stream sandstones, reddish-
brown entisols/inceptisols and floodplain mudstones characterised by diverse clay min-
eral suites and high feldspar contents. A change towards semi-humid climate in the late
Rhaetian is reflected in the upper part of the Lunde Formation by fluvial sandstones
representing meandering rivers, moderately developed cumulative vertisols and higher
contents of smectite and kaolinite resulting from increased chemical weathering.
Increased production of clays in the hinterland, lowered relief and decreased rate of
sediment supply gave rise to a fining-upward trend with an increasing degree of palaeo-
sol development in the upper part of the Lunde Formation and the lowermost part of the
Statfjord Group. Increasing humidity during the latest Rhaetian and Hettangian is wit-
nessed in the lower part of the Statfjord Group by a change from reddish-brown to green-
ish-grey colour in mudstones, disappearance of calcrete nodules and smectite as the
dominating clay mineral formed on wet floodplains. Quartz-arenitic braided stream
sandstones and kaolinite-dominated floodplain mudstones in the upper part of the
Statfjord Group reveal that humid and warm climate conditions prevailed, with intense
chemical weathering in the hinterland. Monsoonal rainfall gave high surface runoff,
producing sediment-laden discharge within well-drained alluvial fans or plains. Coupled
with low accommodation space, this resulted in a coarsening-upwards trend in the
Statfjord Group, braided-stream sandstones with wide lateral extent and floodplain
mudstones with palaeosols reflecting highly varying degrees of pedogenic alteration.
Allostratigraphic units in the Lunde Formation and the Statfjord Group may have formed
in response to more high-frequency climatic cycles or base-level changes.
Keywords: Palaeoclimate, alluvial architecture, palaeosols, clay mineralogy,
Lunde Formation, Statfjord Group, Late Triassic, Early Jurassic, North Sea.