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The AAPG/Datapages Combined Publications Database

AAPG Special Volumes

Abstract


 
Chapter from: M 65:  Salt Tectonics: A Global Perspective
Edited By 
M.P.A. Jackson, D.G. Roberts, and S. Snelson

Author: 
C. J. Talbot

Structure, Tectonics, Paleostructure

Published 1995 as part of Memoir 65
Copyright © 1995 The American Association of Petroleum Geologists.   All Rights Reserved.
 
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.
Chapter 4
Molding of Salt Diapirs by Stiff Overburden
C. J. Talbot

Hans Ramberg Tectonic Laboratory
Institute of Earth Sciences
Uppsala University
Uppsala, Sweden
 
 

 
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 No Disk File and the net increase in relief of salt structures (R = salt rise minus dissolution) at rate No Disk File. Steady kinematic molding ratios, No Disk File/No Disk File, forward model realistic dips of molded salt contacts, a, at particular depths using No Disk File/No Disk File or No Disk File/No Disk File = 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 > No Disk File/No Disk File > 0.01), that is bounded by burial and extrusion. Within this range, aggradation faster than salt can rise (No Disk File/No Disk File < 1) molds tapering (narrowing-upward) top contacts of salt. Accumulation of overburden slower than salt rises (No Disk File/No Disk File > 1) molds flaring (widening-upward) salt contacts. Below this range (where No Disk File/No Disk File < ~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 No Disk File/No Disk File > ~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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