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Rocks and Minerals

Salt dome

alt dome, largely subsur-
S face geologic structure
that consists of a vertical cyl-
inder of salt (including halite
and other evaporites) 1 km
(0.6 mile) or more in diameter,
embedded in horizontal or
inclined strata. In the broad-
est sense, the term includes
both the core of salt and the
strata that surround and are
“domed” by the core. Similar
geologic structures in which
salt is the main component
are salt pillows and salt walls,
which are related genetically
to salt domes, and salt anti-
clines, which are essentially Salt domes are one of a num- tre or more and may range up
folded rocks pierced by up- ber of kinds of salt structures to more than 10 km. The typical
ward migrating salt. Other whose interrelationships are salt dome is at least 2 km high
material, such as gypsum and (in the subsurface), and some
shale, form the cores of simi- shown diagrammatically in Fig- are known to be higher than 10
lar geologic structures, and all ure 1. “Classic” salt domes de-
such structures, including salt velop directly from bedded salt km.
domes, are known as diapiric by gravitational stress alone. The cores of salt domes of the
structures, or diapirs, from Salt domes also may develop North American Gulf Coast con-
the Greek word )diapeirein,( from salt walls and salt anti- sist virtually of pure halite (sodi-
“to pierce.” The embedded clines, however. In the latter um chloride) with minor amounts
material in all instances ap- case, the development of the of anhydrite (calcium sulfate)
pears to have pierced sur- domes results from superposi- and traces of other minerals.
rounding rocks. Upward tion of gravitational stress on Layers of white pure halite are
flow is believed to have been salt masses that initially devel- interbedded with layers of black
caused by the following: grav- oped due to tectonic stress. halite and anhydrite. German
ity forces, in situations where salt dome cores contain halite,
relatively light rocks are over- Physical Characteristics sylvite, and other potash miner-
lain by relatively heavy rocks Of Salt Domes als. In Iranian salt domes, halite
and the light rocks rise like A salt dome consists of a core is mixed with anhydrite and marl
cream to the surface; tectonic of salt and an envelope of sur- (argillaceous limestone) and
(earth-deformation) forces, in rounding strata. In some areas, large blocks of limestone and ig-
situations where mobile ma- the core may contain “cap rock”
terial (not necessarily lighter) and “sheath” in addition to salt. neous rock.
is literally squeezed by later- The interbedded salt–anhy-
al stress through less mobile The size of typical salt domes drite and salt–potash layers
material; or a combination (including cap rock and sheath) are complexly folded; folds are
of both gravity and tectonic varies considerably. In most vertical and more complex at
forces. cases, the diameter is a kilome- the outer edge of the salt. In
10