Abstract

Permian salt and associated evaporates within a 20,000-square-mile region in western Oklahoma and the Texas Panhandle are Leonardian and Guadalupean, and possibly Ochoan, in age. This report is concerned chiefly with the subsurface geology of the three principal evaporate sequences, each of which is 300 to 1,000 feet thick and consists mainly of rock salt and salty shale interbedded with anhydrite. These evaporite sequences contain all the rock salt known in Oklahoma. The evaporites occur with red clastic sediments in a sequence 4,000 feet thick, embracing all strata from the base of the Wellington formation to the top of the Dog Creek Shale. Four stratigraphic sections accompanying the report illustrate the distribution and facies relationships of these beds. The youngest evaporites of the region—relatively thin anhydrite beds in the Cloud Chief formation, of possible Ochoan age—are not considered herein.

The evaporites are classed in ascending order as Wellington, Cimarron, and Beckham. Wellington and Cimarron evaporite units known in the subsurface of Kansas are here extended and mapped into Oklahoma and the Texas Panhandle. The term "Beckham evaporites" is a new term that includes (ascending) the Flowerpot salt (new), Blaine anhydrite, and Yelton salt (new). Each evaporite sequence is widely distributed, occurring as eastward-thinning tongues or wedges within the framework of Permian clastic sediments. Together the evaporites have a maximum thickness of 2,500 feet. The evaporite strata, excluding clastics, consist of halite (about 80 percent), anhydrite, and thin beds of dolomite (less than 5 percent). No potassium salts were found or were indicated by investigations for the present study.

The oldest halite-anhydrite sequence in Oklahoma, called the Wellington evaporites, is of Leonardian age and normaly ranges in thickness from 1,000 to 1,300 feet. It is divided into a lower anhydrite-salt unit, a shale unit, and an upper anhydrite unit. The salt in the upper part of the lower unit is equivalent to the Hutchinson Salt of Kansas. Depth to the salt in the Wellingon ranges from 800 feet in northwest-central Oklahoma (Grant County) to 3,900 feet near Elk City in Beckham County. Over an area of approximately 16,500 square miles the average aggregate thickness of salt strata in the Wellington is 225 feet.

Above the Wellington are the Hennessey shales, which are overlain by the Cimarron evaporites. The Cimarron evaporites consist of lower and upper salt units separated by the Cimarron anhydrite and have a maximum thickness of 1,000 feet. The lower salt and Cimarron anhydrite are especially persistent, and the anhydrite is a valuable structural datum. Total thickness of Cimarron salt strata over 13,000 square miles of western Oklahoma is generally 500 feet, and the depth range is between 215 and 2,420 feet. The lower salt unit is noteworthy because it locally consists of massive salt more than 400 feet thick, and thus is probably the thickest salt in Oklahoma.

Red shales above the Cimarron are classed as Flowerpot-Hennessey. They are overlain by the Beckham evaporites (Guadalupean), the youngest salt-bearing strata of western Oklahoma and the eastern part of the Texas Panhandle. The middle unit of the Beckham sequence is the well-known Blaine anhydrite, 150 feet thick, which crops out extensively in western Oklahoma and occurs so persistently in subsurface that it is a valuable stratigraphic datum. Salt beds directly below and directly above the Blaine, respectively called Flowerpot and Yelton, have much less geographic distribution, yet each attains a thickness in excess of 250 feet. The Flowerpot salt has an average thickness of 200 feet and a maximum thickness of 625 feet (including salty shale). It occurs over more than 7,000 square miles of western Oklahoma and is found at depths as shallow as 30 feet in northern Oklahoma, and as deep as 1,655 feet in southwestern Oklahoma in the area north of the Wichita Mountains. The Yelton salt occurs chiefly in Beckham and Washita Counties, Oklahoma, and in Wheeler County, Texas, at depths of 390 to 1,285 feet. Much of the Yelton sequence is massive rock salt, reaching a maximum thickness of 287 feet in the eastern part of Beckham County.

Included in the report are maps showing distribution, thickness, and depth from surface of the principal salt beds.

As outlined by structural mapping at the base of the Blaine anhydrite and of the Wellington evaporites, the major structural feature of the region is the Anadarko syncline. It trends west and northwest across much of western Oklahoma into the Texas Panhandle, its axis following a line just north of the Wichita Mountains. Permian strata on the south limb dip as much as 250 feet per mile, whereas on the north limb they dip 9 to 40 feet, or an average of 20 feet, per mile.

With the exception of the Yelton salt, which occurs in the axial part of the syncline, the Permian evaporites bear no obvious relationship to major structure. Multiple rather than single salt basins were developed for any given sequence, and the maximum salt thickness for one stratigraphic unit does not coincide structurally or geographically with the maximum thicknesses of the other evaporites.

Salt reserves in western Oklahoma are estimated to be more than 21 million million (21,000,000,000,000) short tons. Although much of the salt is thick and nearly pure, the reserves are virtually unexploited. Within the area studied, a small amount of salt is produced from brine wells in the Upper Cimarron salt in Beckham County, and some of the salt beds are used for underground storage of liquefied petroleum gases. Four salt caverns are currently being used, one each in a salt bed of the Blaine anhydrite (Beckham County), in the Flowerpot salt (Beaver County), in the lower Cimarron salt (Beaver County), and in the Lower salt-anhydrite unit of the Wellington (Grant County). Total storage capacity of these facilities is nearly 250,000 barrels.

Future uses of the salt probably will include expanded production for livestock and human consumption, and for such chemical purposes as the production of chlorine, caustic soda, and soda ash. Additional underground storage facilities for liquefied petroleum gases are currently being made in Permian salt beds of Oklahoma. Similar caverns might be made for the underground storage of natural gas, or possibly for the storage of low-intensity radioactive waste materials. A knowledge of the distribution and thickness of salt beds also is useful in the interpretation of seismic data obtained in the exploration for petroleum.