Geoscience Reference
In-Depth Information
(a)
(c)
(b)
Figure 8.4
A halite crust on the floor of Umm as Samim playa in Oman: (a) halite polygons on the playa bed; (b) well-developed
halite crystals in the upper layers of the salt crust; (c) halite efflorescences emerging from pressure ridges between halite polygons.
Halite crusts do not have a lasting effect on the land-
scape owing to their susceptibility to dissolution. How-
ever, halite is important in desert weathering (see Chapter
6) and pedogenesis (see Chapter 7). Saline crusts may
also impact upon aeolian processes by consolidating the
sand on dune slipfaces (Nickling and Ecclestone, 1981;
Nickling, 1984). Halite 'salt scalds' in soils are often as-
sociated with rising saline groundwater tables which, in
some cases, are a function of land management practices
such as removal of vegetation or overirrigation (Chivas,
2007). Understanding the factors that control the forma-
tion of halite crusts can also be of economic significance,
as many petroleum reserves are associated with evaporite
sequences.
precipitated in shallow-water bodies usually grows as
upward-pointing chevron-, cube- or cornet-shaped crys-
tals. Cloudy crystals - some containing poikilitic inclu-
sions - are normally primary precipitates, while clear
crystals are interpreted as secondary diagenetic precip-
itates or syndepositional void-fills (Warren, 2006). Sac-
charoidal textures form during rapid, sporadic halite pre-
cipitation, and occur as bridge cements that consolidate
the host grains in thin salcretes. Halite oolites (halolites)
and pisoids (halopisoids) have also been described in the
shallow Tuz Gol u saline lake of Central Anatolia, Turkey
(Tekin
et al.
, 2006). The halolites are spherical features
ranging from 0.7 to 2.0 cm in diameter, composed of a
nucleus of coarse-grained halite crystals surrounded by
halite-dominated concentric laminae. They form in the
swash zone where halite crystals roll around in halite-rich
mud. Granular crystal textures predominate in phreatic
crusts (Arakel, 1980). Hopper crystals with negative-
crystal brine inclusions are also common (Arakel, 1980;
Lowenstein
8.3.2
Micromorphology and chemistry
Several
distinct
micromorphologies
are
displayed
by
halite deposited in lacustrine and sabkha evaporite se-
