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The AAPG/Datapages Combined Publications Database

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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. Snelson

Author:
Jake Hossack

Structure, Tectonics, Paleostructure

Published 1995 as part of Memoir 65
Copyright © 1995 The American Association of Petroleum Geologists.   All Rights Reserved.
 
Hossack, J., 1995, Geometric rules of section balancing for salt structures, in M. P. A. Jackson, D. G. Roberts, and S. Snelson, eds., Salt tectonics: a global perspective: AAPG Memoir 65, p. 29-40.
Chapter 2
Geometric Rules of Section Balancing for Salt Structures
Jake Hossack

BP Exploration
Uxbridge, Middlesex
U.K.
 
Abstract

 Restored sections provide not only a measure of the viability of structural interpretations but also have the ability to recreate the geometry of the structures through geologic time. Geologists have known for a long time that section balancing is more difficult in salt structures because of the ability of the salt to flow in and out of the plane of section and also to dissolve and thereby violate constant volume considerations. However, the surrounding sediments generally deform by brittle-plastic processes and are less able to flow out of the plane of a properly chosen section. The pragmatic approach is to restore sections by assuming constant-area conditions for the sediment structures alone and to leave the salt area as gaps that may change in area through time. Most restorations of salt structures suggest that throughout long periods of geologic time, salt remains at or close to the depositional surface and that volume reductions of up to 50% are possible in nature.

Salt structures usually involve regional displacements of the salt and its surrounding sediments so that extension in one place has to be balanced by basement extension or cover contraction in another. A key aid to the recognition of contraction and extension is the regional elevation of reference horizons. Generally, salt withdrawal and extensional faulting drop reference beds below regional elevation, whereas salt pillowing , salt sheet formation, and contraction will raise beds above regional elevation. In the Gulf of Mexico, the updip extensional growth faulting and salt withdrawal are balanced by the formation of downdip allochthonous salt sheets and fold and thrust belts, so that the total linear strain across the sediment cover is zero. The extension and contraction are linked by a series of salt and fault welds that lie at several structural levels.

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