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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. SnelsonAuthor:
C. J. Talbot 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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Talbot,
C. J., 1995, Molding of salt diapirs by stiff overburden, in M.
P. A. Jackson, D. G. Roberts, and S. Snelson, eds., Salt tectonics: a global
perspective: AAPG Memoir 65, p. 61-75. |
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Chapter
4
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Molding
of Salt Diapirs by Stiff Overburden |
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| C. J. Talbot
Hans Ramberg Tectonic
Laboratory
Institute of Earth Sciences
Uppsala University
Uppsala, Sweden |
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Abstract
Although active diapirs
must deform the overburdens they pierce, the shape of passive (downbuilt
or syndepositional) diapirs is formed or molded by their overburdens. Molding
of salt diapirs is simplified here to profiles of diapirs entirely downbuilt
in effectively rigid overburden. The dips of salt-sediment contacts are
shaped by the interaction of two processes: local net accumulation of overburden
(A = deposition minus compaction) at rate 
and the net increase in relief of salt structures (R = salt rise minus
dissolution) at rate  .
Steady kinematic molding ratios, /,
forward model realistic dips of molded salt contacts, a,
at particular depths using /
or /
= tan a/2.
Rising or falling ratios of incremental molding forward model complete
diapir profiles. Conversely, molding histories can be read by backstripping
profiles of downbuilt diapirs.
Salt diapirs are downbuilt
in a field of downbuilding (100 > /
> 0.01), that is bounded by burial and extrusion. Within this range, aggradation
faster than salt can rise (/
< 1) molds tapering (narrowing-upward) top contacts of salt. Accumulation
of overburden slower than salt rises (/
> 1) molds flaring (widening-upward) salt contacts. Below this range (where /
< ~0.01), the top contact of the salt is eclipsed (temporarily buried
to depths from which it can still upbuild) or even occluded (buried below
its critical roof thickness and thus unable to rise again autonomously).
Occluded salt is either dissolved at depth or rises in reactivated diapirs
after exhumation or faulting of overburden that is not rigid. Where /
> ~100, salt emerges like a fountain and extrudes sheets of allochthonous
salt. Extruded salt is recycled back into the ocean by dissolution at the
surface or after burial and reactivation in another cycle. |
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