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Group Sequence Stratigraphy in the Northern North Sea: A Model for Cook
Tihomir Marjanac and Ronald
The Dunlin Group in the northern
North Sea, consisting of the Johansen, Amundsen, Burton, Cook, and Drake
formations of late Sinemurian-
Toarcian age, hosts important hydrocarbon
reservoirs in the Cook Formation sandstones. The Johansen Formation is
associated with a relative fall of sea level and is interpreted to be a
large sandstone delta confined within a broad incised valley at the base
of the group. During a later stage of relative sea level rise, the finer
grained Amundsen and Burton formations were deposited. The overlying Cook
Formation consists of four sandstone tongues, each of which is characterized
by a lower zone of sharp-based, upward-coarsening, thinly bedded shoreface
sandstones and siltstones (reflecting forced regression during falling
relative sea level) and an erosively based upper zone of thin tidal flat
and thick deltaic/estuarine sandstones (reflecting lowstand incision, as
well as initial progradation and subsequent transgressive backfill of estuaries
during relative sea level rise). The Drake Formation shales were deposited
during continued relative sea level rise. Several types of erosional surfaces
are recognized within the studied succession: (1) sequence boundaries occur
at the base of the Johansen Formation and within the Cook Formation, and
represent the bottoms of incised valleys that truncate the underlying
1997. The American Association of Petroleum Geologists. All rights reserved.
received May 4, 1995; revised manuscript received March 27, 1996; final
acceptance September 12, 1996.
of Geology/Paleontology, University of Zagreb, 10000 Zagreb, Croatia.
of Geology/Geophysics, University of Wyoming, Laramie, Wyoming 82071.
paper was part of the sequence stratigraphy research project at the University
of Bergen, Norway, and is a product of studies on the architecture of Lower
Jurassic shelf sandstones of the northern North Sea. The work was sponsored
by STATOIL through a VISTA fellowship awarded to T. Marjanac, and this
support is gratefully acknowledged. We are grateful to D. Mellere and L.
M. Falt for discussion and encouragement during the work. We also thank
Else Lien for drafting the sections and Jane Ellingsen for reprographs.
Constructive criticism from D. Nummedal, J. Webb, and K. T. Biddle on the
final version of the manuscript is much appreciated.
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