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

Author:
Mark G. Rowan

Structure, Tectonics, Paleostructure

Published 1995 as part of Memoir 65
Copyright © 1995 The American Association of Petroleum Geologists.  All Rights Reserved.
 

Department of Geological Sciences and Energy & Minerals Applied Research Center
University of Colorado
Boulder, Colorado, U.S.A.

Seismic interpretation and section restoration are combined with recent models of salt deformation to describe the geometry and evolution of allochthonous salt from the central Louisiana outer shelf and upper slope. Scattered salt bodies are connected by a complex system of diachronous salt welds or remnant salt having two end-member geometries: (1) regionally extensive, subhorizontal sheets bounded by north-dipping (counter-regional) feeders and characterized by common listric growth faults that may accommodate significant extension; and (2) elliptical depressions bounded by dipping salt welds and arcuate growth faults that accommodate little extension.

Most salt bodies in the study area were emplaced at or near the sea floor and grew by downbuilding (passive diapirism). Reactive and active diapirs are rare. The former are confined to the updip margins of shallow salt sheets, and the latter may occur basinward of major salt-withdrawal minibasins. Many salt bodies along the downdip margins of sheets have been modified by contraction.

Two end-member evolutionary models account for the range of observed structural styles. In "counter-regional" systems, which are more typical of the shelf, salt rises through south-leaning feeder stocks and flows both downdip and along strike to form allochthonous sheets. In "salt stock canopy" systems, which are more typical of the upper slope, bulb-shaped salt stocks expand outward and form salt canopies. Subsequent gravitational collapse and sedimentary loading form bowl-shaped minibasins, from which salt is displaced into allochthonous tongues and remnant salt bodies.