Evaporite Regions

Evaporites are precipitated in shallow seawater that is evaporating. Usually "evaporite" refers to gypsum (hydrated calcium sulfate or CaSO4•2H2O) or other types of gypsum, such as anhydrite (CaSO4), gypsite, selenite, and others. All are very soluble in water and are rapidly excavated by running water. Some limestone caves have gypsum formations, such as gypsum flowers and selenite needles, which are rarely found in gypsum caves themselves.

Map of Texas Karst and pseudokarst
Map of Texas Karst Regions
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1. Gypsum Plain

The gypsum of the Permian Castile Formation in West Texas contains numerous caves in almost as high a density as the Ellenburger Group in the Llano Region. The Gypsum Plain has very low relief, with little outlet for infiltrating groundwater. Accordingly, most of the caves begin small and become smaller. A few are moderately long (e.g., Crystal Cave and Wiggley Cave, Culberson County) where groundwater can apparently exit to a deeper zone or to a surface valley. A few caves appear to result from artesian flow from the underlying sandstone. Even though the Castile is up to 530 m thick, the lower portion is predominantly anhydrite, and only about the upper 30 m has hydrated to form gypsum. Hydration is partly responsible for the irregular jointing of the gypsum; regional fracture systems have caused some regular jointing. Salt beds at depth are being removed by dissolution and result in broad subsidence sinkholes on the surface (e.g., Wink Sink, Winkler County). The Gypsum Plain extends north into New Mexico near Carlsbad.

2. Northwest Texas

Permian-age gypsum beds up to 7.6 m thick are interbedded with shale and dolomite. Erosion through the Blaine Formation provides an outlet for groundwater that infiltrates its upland exposures. Where the distance from sink to outlet is long, caves are also long if not blocked by collapse or cut by erosion (e.g., River Styx Cave, King County). Some caves form as cut-offs across the bends of surface drainages (e.g., Aspermont Bat Cave, Stonewall County). Artesian salt springs also rise through the gypsum, the result of deep solution of salt beds in the evaporite sequence (e.g., Estelline Salt Spring, Hall County; Salt Spring Cave, King County). The Northwest Texas region extends into western Oklahoma.

3. Kirschberg Gypsum

Gypsum caves are known from the Kirschberg gypsum beds in the middle of the Edwards Group in Kimble, Gillespie, Mason, and Menard counties on the Central Edwards Plateau. The Kirschberg is no more than 6 m thick, and its caves are not extensive. Regional dissolution of the gypsum has resulted in obvious slumping of overlying limestone beds.

Page updated 7/2014. Original page by A. Richard Smith and George Veni.