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Abstract
Chapter from: M
65: Salt Tectonics: A Global Perspective
Edited By
M.P.A. Jackson, D.G. Roberts, and S. SnelsonAuthors:
Mike Coward and Simon Stewart Structure, Tectonics, Paleostructure
Published 1995 as
part of Memoir 65
Copyright © 1995 The American Association of Petroleum
Geologists. All Rights Reserved. |
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Coward,
M., and S. Stewart, 1995, Salt-influenced structures in the Mesozoic-Tertiary
cover of the southern North Sea, U.K., in Jackson, M. P. A., D.
G. Roberts, and S. Snelson, eds., Salt tectonics: a global perspective:
AAPG Memoir 65, p. 229-250. |
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Chapter
10
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Salt-Influenced
Structures in the Mesozoic-Tertiary Cover of the Southern North Sea, U.K. |
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Mike Coward
Geology Department
Imperial College
London, U.K. |
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Simon Stewart
Amerada Hess Ltd.
London, U.K.
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Abstract
A structural
model encompassing the southern North Sea Basin west of the Central Graben
has been developed that combines gravity gliding of the postsalt cover
with basement tectonics. The basin differs from many salt basins in that
it forms a closed system. Section construction and balancing through the
cover of the North Sea need to take into account thin-skinned and thick-skinned
extensions and contractions. The North Sea salt formed in Permian time
in two large oval basins separated by the Mid North Sea High. The shape
of these basins reflects variable patterns of thermal subsidence. Subsequent
salt tectonics was governed by local graben structures and by regional
uplift and subsidence.
Rifting initiated during
the Triassic and allowed reactive and locally passive diapirs to develop
in the postsalt cover. In the southern North Sea, the Dowsing graben system
in the cover is offset from the Dowsing fault zone below the salt. This
offset in extensional structures probably relates to the salt thickness
and to the position of the surface hinge line that controlled the onset
of gravity gliding in the postsalt section. Gravity gliding of the cover
into the Triassic-Jurassic Sole Pit trough and away from zones of rift
flank uplift was associated with Late Jurassic-Early Cretaceous extension
in the Central North Sea; gliding caused asymmetric compressional pillows
to develop downslope. Gravity spreading of the cover during the Late Cretaceous-early
Tertiary was associated with tilting during thermal subsidence of the southern
North Sea Basin, enhanced by pulses of tectonic inversion in the southern
North Sea basement. The resultant glide tectonics formed new small grabens
upslope and compressional pillows downslope. Where the compressional pillows
were eroded sufficiently or faulted later, the salt broke through the thinned
cover to produce new active and then passive diapirs, which drained the
pillows to produce new rim synclines. |
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