JOHNSON, KENNETH S.
Oklahoma Geological Survey, Norman, OK

Abstract: Evaporite Karst in the Southern Midcontinent

Evaporites are the most soluble of common rocks; they are dissolved readily to form the same karst features typically found in limestones and dolomites. Evaporites, including gypsum (or anhydrite) and salt, are present in 32 of the 48 contiguous states, and they underlie 35-40% of the land area. They underlie western Kansas, western Oklahoma, the Texas Panhandle, and eastern New Mexico and Colorado, and locally can be a serious. problem to petroleum exploration and development. In areas, where gypsum crops out (or is less than 30 m deep), or where rock salt is less than 250 m deep, evaporites may be partly or wholly dissolved by unsaturated water. Evaporite outcrops typically contain sinkholes, caves, disappearing streams, and springs. Other evidence of evaporite karst includes surface-collapse features, saline springs, and saline plumes due to salt dissolution. Many evaporites in the deep subsurface also contain remains of paleokarst such as dissolution breccias, breccia, pipes, slumped beds, and collapse structures.

Human activities also have caused development of evaporite karst, primarily in salt deposits. Boreholes or underground mines may enable (either intentionally or inadvertently) unsaturated water to flow through or against salt deposits, thus allowing development of small to large dissolution cavities. If the dissolution cavity is large enough and shallow enough, successive roof failures can cause land subsidence or catastrophic collapse.

At least 30 sites in the United States have reported land subsidence and/or collapse due to human-induced salt karst. Among these sites are Cargill and Panning sinks in Kansas, Wink sink in west Texas, and other sites in the southern Midcontinent. Evaporite karst, both natural and human-induced, is far more prevalent than commonly believed.

AAPG Search and Discovery Article #90921©1999 AAPG Mid-Continent Section Meeting, Wichita, Kansas