Salt structures continue to attract attention as petroleum traps and as storage vessels for wastes or fuels. Drawing on field studies, experiment, and theory, we examine the megascopic structure and large-scale dynamics of salt structures.
Salt flowage can transform a tabular salt body into nondiapiric rollers, anticlines, and pillows; into diapiric walls, stocks, massifs, and nappes; and into extrusive domes and salt glaciers. These structures distort at widely variable strain rates of 10−8 s−1 to 1016 s−1, with a comparatively restricted range of dominant wavelengths of 7–26 km.
Buoyancy is an ineffective diapiric mechanism unless the salt structure has pre-existing relief of at least 150 m beneath a denser overburden of terrigenous clastics. Differential loading is a far more effective mechanism in the early stages of diapirism and commonly results in asymmetric salt structures. Gravity spreading modifies the shape of salt structures with negative buoyancy. With a heat-induced density inversion, thermal convection may lead to internal circulation and stirring of a still-tabular salt body. At least four mechanisms may form broad bulbs on mature salt stocks. Consideration of the effective viscosity contrast between salt and its cover suggests that mature stocks may have stems much more narrow than is commonly envisaged.
Salt tectonics is classified here on the basis of change of gravity potential energy that promotes or retards salt flow. Halokinetic movements can be initiated, succeeded, retarded, or accelerated by regional tangential forces that stretch, wrench, or compress sedimentary basins.