Abstract The Permian Basin region, as defined for this chapter, includes all of the Permian basins beneath the high plains of western Texas that lie south of the Red River and Matador Uplifts. It also extends westward into the Southern Rocky Mountain region to include the related Orogrande and Pedregosa Basins in New Mexico. In the central part of the region, surface exposures of the Tertiary Ogallala Formation and other post-Paleozoic strata hide the Paleozoic geology, which includes many anticlinal and faulted structures, sand and shale basins, carbonate banks and reefs marginal to basins, and extensive carbonate shelf areas. On these shelves, carbonates grade into evaporite deposits and eventually into continental clastics. Knowledge of this geology is primarily from wells drilled for oil and gas. Peripheral outcrops of these Paleozoic strata do exist and are important to the interpretation of Permian Basin geology, but many formations and rock facies are known only from the subsurface. With the exception of the two outlying New Mexico basins, petroleum geologists with extensive subsurface experience were selected to write the various parts of this chapter.

Evaporitic deposits ranging in age from Precambrian to Recent are present on all continents and in more than half of those sedimentary basins in which strata of marine origin have been demonstrated to exist. Much of our knowledge of the extent and character of saline materials is a concomitant of exploration for various types of petroleum, and a striking coincidence between the sites of the principal oil-producing provinces and the occurrence of evaporites suggests the possibility of a significant relationship. As with commercial deposits of hydrocarbons, by far most saline deposits are found in the northern hemisphere.

Saline minerals are widely distributed in Spain, particularly in the eastern half of the country. Deposits are in rocks of the Triassic–Early Liassic, late Eocene–Oligocene, and Miocene. Although saline minerals occur in Permian rocks, they are not as well developed as they are in the Permian of northern Europe. The principal deposits are in the Keuper and occur over much of eastern Spain. Rock salt occurs extensively in the subsurface Keuper; outcrops consist of gypsum and marl. The Keuper salt forms salt chimneys or salt domes in the Cantabric trough. Fourteen intrusions are known, and they involve a large volume of sedimentary rock. Original salt movement is believed to be due to gravitational tectonics, later modified by the Hercynian and other orogenies. Salt domes also are known in Andalusia and in the Betic chains. The Keuper also provided the lubricant for gliding and intense folding in the Pyrenees. The salt domes of the Cantabric trough rise through 7000 m or more of sedimentary rocks and are in places exposed, providing spectacular exhibits of diapiric folds. The saline deposits have been extensively exploited for rock salt and brine. Potassium salts and sodium sulphate also have been recovered in limited amounts.

Approximate calculations have been made of the magnitude and form of anomalous masses required to account for the residual gravity anomalies over four diapiric structures in northern Spain. The Orduña diapir has a simple negative anomaly and apparently is caused by a salt intrusion. The Sobrón anticline and the Salinas de Añana diapirs have strong negative anomalies with central positive features; large salt masses apparently caused the negative effects, and intrusions of igneous material, the positive anomalies. The Murguía diapir has a simple, positive anomaly probably caused either by a massive igneous intrusive body which may have replaced a preexisting salt intrusion or by a relatively shallow, lenticular sill.

Based on comprehensive investigations of Dupouy-Camet and extensive oil geological exploration, including geophysics and deep drilling, by the Société Nationale des Pétroles d’ Aquitaine (SNPA), the author describes the main occurrences of diapiric and semidiapiric structure in the Aquitanian Basin of southern France. Included are remarks on the stratigraphy and geological history of Aquitania and a brief discussion of the structural complexities in the north Pyrenean foothills and the Aquitanian “Basin.” The stratigraphy is summed up by means of six columnar sections. A structural sketch map of west Aquitania and the northern Pyrenees illustrates the paleogeographic relationship between the Upper Cretaceous miogeosynclinal shelf of the Pyrenean foreland, the adjacent eugeosynclinal trough marked by a mainly Senonian flysch association, and the axial zone of the Pyrenees characterized by Paleozoic formations and igneous rocks. The last is separated from the eugeosynclinal part by an important thrust fault along the north Pyrenean front. Partly owing to the Pyrenean orogeny, but partly owing to earlier diapiric ascent, the evaporites of the Keuper have developed into numerous diapiric and semidiapiric accidents varying in pattern from sheet diapirism along major fault planes to full-fledged circular salt domes obviously displaying similar genetic conditions as the well-known salt domes of the United States Gulf Coast. Emphasis is placed on the genetic-interpretational aspect of the Aquitanian diapirism and its close association with the various orogenic phases of the area under review. The fundamental problem is whether we are concerned with a phenomenon of buoyancy or if purely orogenic forces account for the accidents observed. In other words, was buoyancy an active tectonic force, or are the intrusions and effusions of evaporites into anticlinal cores and fault planes a result of structural emplacement? There is sound evidence that some diapiric accidents occurred as early as Middle Cretaceous, independent from and definitely preceding the earliest orogenic phase of folding. On the other hand, there is little doubt that the evaporites of the Keuper furnished a gliding horizon that greatly facilitated disharmonic folding, thrusting, and detachment from the substratum in the course of the Pyrenean orogeny. The author concludes that at an early date, buoyancy was an important active force indeed; later the results of orogenic deformation were superimposed onto the early diapiric structure; the combined effect, as presently in evidence, tends to obliterate the early diapirism. An attempt is made to clarify the role of gravitational, tensional, and synsedimentary tectonics as opposed to orogenic-compressive folding. Such gravitational tectonics probably are particularly active and important in areas of diapirism, but may occur anywhere in the sedimentary, i.e. preorogenic, stage. They have often been mistaken as precursory orogenic phases which they are not, but might subsequently be reactivated by genuine orogenic forces.

The Arabic expressions for salt (melah) and gypsum (zebs), frequently used in local geographic descriptions, draw attention to the widespread occurrence of evaporites in North Africa. The principal occurrences consist of variegated red clay containing gypsum and salt alternating with limestone, dolomite, breccia, and cellular dolomite. The evaporite section is predominantly Triassic, but its base may be Permian, and its top frequently extends into the Liassic. The evaporite-bearing sediments often occur as homogeneous masses, lacking any stratigraphic sequence, owing to deformation by plastic flow. A great variety of structural conditions has been noted, including: (1) undisturbed thick stratified evaporites (Saharian shelf in southern Tunisia); (2) salt-bearing laminated beds in the hinge area of important faults and flexures (Nara Bou-Dzer fault in Tunisia); (3) anticlinal features, both gentle domes and narrow anticlines, that have been pierced by a diapiric core of evaporites containing coarse breccia and basalts (Tunisian trough and the Saharian Atlas); (4) clay with intercalated salt and gypsum underlying nappes and thrust sheets, for which the material provided a plastic gliding horizon; and (5) genuine diapirs, with the salt-bearing core injected as a result of gravitational instability owing to the presence of overlying denser sediments (Miocene Cheliff basin in Algeria; Mesozoic Haha trough in Morocco). All but the first (and perhaps last) include phenomena which obviously are related to orogenic deformation by compressive forces; but at least part of the deformation in most cases resulted from gravitational instability and is hence truly diapiric. Thus there appears to be an interaction of diapiric (gravitational) and orogenic structural forces, which probably is characteristic of orogenic areas. Although the Tertiary orogeny had a direct effect on the structure of the evaporites in most places, diapiric movement probably had started by late Cretaceous time. The Tertiary orogeny pressed out some of the diapiric cores and injected the material along overthrusts and faults.

The major deposits of rock salt in Israel occur in the Dead Sea area of the Rift Valley. Here, a practically continuous sequence of salt was found by drillings to a depth exceeding 2700 m in the western, and to almost 4000 m in the eastern part, beneath a thin cover of late Pleistocene sediments. A shallow drill in the center of the southern Dead Sea basin itself penetrated salt to its maximum depth of almost 100 m. The extensive occurrence of salt in this area partly explains the high negative gravity anomaly in this part of the African Rift. At Mount Sdom, on the southwest corner of the Dead Sea, part of the salt mass is exposed on the surface. Mount Sdom, 10 km long and 1–2 km wide, rising 220 m above the present level of the Dead Sea, consists essentially of salt interbedded with sand, shales, anhydrite, and carbonate rocks. It is an uplifted fault block. Its internal structure is that of a compressed and partly overturned anticline truncated on its flanks. Intrusive salt features are essentially absent. A study of the Cl:Br ratio in the salts and associated brines leads to the conclusion that the salt is partly (Mount Sdom) of marine (?) and partly (Lisan Peninsula, southern Dead Sea) of continental origin. The Rift Valley, formed in mid-Tertiary time, was invaded in the Pliocene by the sea. In the following regressive phase, the salt of Mount Sdom was deposited. During most of the Pleistocene, a salt sequence, at least 4000 m thick, was laid down in the area under continental conditions; tectonic subsidence during the Pleistocene is of the same order of magnitude. Concurrently the block of Mount Sdom was uplifted; the last rise of about 100 m took place during the past 10,000 years.

This paper briefly reviews the most important salt deposits of the Middle East. Their stratigraphic and geographic distribution is discussed in relationship to the general geologic history of the area. Recent field studies in Iran have presented new evidence for an Early Cambrian or Proterozoic age of the Hormuz salt. Stable platform conditions on the northeastern shelf of the Arabian Shield and in East Iran favored the development of semiclosed basins with evaporite deposits in Proterozoic (?) time and at repeated intervals in Paleozoic and Mesozoic time, culminating in the Late Jurassic. Their geographic outline is largely governed by old, Precambrian basement trends such as the Oman line and the Qatar line. These trends are essentially north-south and can partly be attributed to a late Precambrian, pre-Hormuz orogeny. The paleogeographic configuration was drastically changed by Alpine diastrophism which developed the Tertiary lagoon of the Persian Gulf and Mesopotamia and separated off the continental basin of Central Iran with its spectacular salt domes and modern Kawir salt wastes. Present salt deposition is displayed on a grand scale in the Great Kawir of Central Iran.

Structural disharmonies between rock masses lying above and below the salt-bearing Lower Fars formation are characteristic of the Alpine foothill folds of the Zagros mountain belt in parts of northern Iraq and southwestern Iran. Most impressive and what appear to be chaotic structural discrepancies have been described from the Iran sector of the saliferous Fars basin, where depositional thicknesses of salt were great. Salt deposits were much thinner in Iraq, and lacked the spectacular disharmonies of the Iran deposits. The typical disharmonic habit in northeastern Iraq is the overthrusting of the northeastern flanks of the long and strongly developed anticlines. Overthrusting has generally been attributed to tectonic compression in the later phases of folding, or to southwestward gliding of the post-salt cover, as a unit, off the rising “high” of the Zagros. Both interpretations are inadequate in some particulars to account for some features of the overthrusts. The thesis is advanced that the overthrusts resulted from gliding adjustments of each synclinal fill to gravitational changes caused by isostatic recovery of the Zagros after the fold-producing orogeny. Overthrusting essentially postdated the completion of folding, being facilitated by decreases in competency of the anticlinal crests as these became deeply eroded. It was controlled by the excess of load in the northeast of each syncline, which resulted from development of high relief during progressive regional tilting.

It is proposed that anticlines and diapirs in the northern part of the Amadeus basin in central Australia were initiated at an early stage in the sedimentary history of the basin and that they continued to grow as the result of salt flowage in response to sedimentary loading during late Proterozoic and early Paleozoic sedimentation. It is further proposed that these structures were accentuated and modified during the Pertnjara orogeny in upper Paleozoic time. However, they were not formed at the time of the orogeny, as was heretofore supposed.

Saline deposits in South America range in age from Cambrian to Recent; they are present in both the mobile Andean belt and in the stable intracratonic basins. Cambrian saline deposits occur in the sub-Andean belt of Bolivia; Pennsylvanian salt is present in the Amazon Basin of Brazil; Permian saline deposits exist in the Andean region of Perú and in the Maranhao Basin of Brazil; Triassic saline deposits appear in south-central Bolivia and northern Argentina; Lower and Upper Jurassic saline deposits occur in the Cordilleran belt from Colombia to northern Chile and Argentina; Lower Cretaceous saline deposits occupy a similar Andean area and also occur in the Sergipe-Alagoas basin of Brazil; Upper Cretaceous and Tertiary saline deposits are present along the sub-Andean belt from Colombia to Argentina. Recent saline deposits include the great and famous “salares” extending from southern Perú into northern Chile and Argentina; the caliche deposits on the arid western slopes of the Central Andes; and also the numerous “salinas” found mainly along the desertic coasts of Chile and Perú. Salt diapirs are common along the Andes, especially in Perú, Chile, and Colombia. In Perú, about 30 large Late Tertiary extrusions of salt and gypsum are known, most of them in the Middle Huallaga region. The salt source in the Huallaga diapirs is not well defined; it could be of Permian, Triassic, or Jurassic age. Most of the diapirs are associated with anticlines or occur along major faults. Those which occur farther toward the less-deformed foreland belt are round or oval in ground plan and are not associated with noticeable faulting, e.g., the Tiraco and Pilluana domes, with diameters of 9 and 6 km, respectively. Their extrusion was caused by tangential orogenic stresses, aided by isostatic components.

The Elk Point salt beds of the Prairie Provinces were deposited in two distinct, but connected, basins: the Alberta Basin to the northwest and the Saskatchewan basin to the southeast. Deposition began earlier in the Alberta Basin, resulting in the formation of two salt beds which have no equivalent in the Saskatchewan basin. Later, in Elk Point time, waters moving southeastward were apparently progressively concentrated so that carbonates and anhydrite are common to the northwest, whereas salt and potash predominate to the southeast. Subsurface solution of the salt beds in the Saskatchewan basin began in Devonian time and continued intermittently until at least late Cretaceous time, resulting in the formation of many anomalous structures. Exploitation of the salt beds and related brine springs began with the earliest settlement of the area and continued until the present. In recent years, the potash salts of Saskatchewan have been intensively explored, and commercial production is under way.

Thick salt deposits are present in the Middle Pennsylvanian Paradox Member of the Hermosa Formation in the Paradox Basin of southeast Utah and southwest Colorado. Data suggest that the original thickness of these deposits was from 5000–6000 feet. Locally, however, these deposits have been subjected to intense deformation and flow, resulting in thicknesses as great as 14,000 feet. Each salt bed is part of a series of partial and complete evaporite cycles which show a lateral and vertical change in facies. Varve counts in the salt beds give an indication of deposition rates of time-equivalent carbonate beds. Black sapropelic shales are interbedded with the salt beds. It appears that the euxinic environment in which the shales were deposited persisted during the deposition of salt. An understanding of the stratigraphy of the salt deposits has made possible a more complete depiction of early tectonic events involving the salt basin. These studies indicate that many of the salt anticlines in the basin were formed along trends of originally thick salt beds, and that upward growth of these anticlines possibly began during the late stages of salt deposition.

Upheaval Dome is a breached domal structure that is surrounded by a well-developed rim syncline; it lies in the rugged canyonlands of southern Utah, near the western margin of the Paradox Basin. Strata that range in age from Permian to Jurassic are exposed in the dome and all have been deformed by the forces which produced the feature; about 3000 feet of Pennsylvanian salt beds underlies the area of the dome. The origin of Upheaval Dome has not been established, but the following hypotheses have been advanced: (1) it is a cryptovolcanic feature; (2) it is a simple salt dome; (3) it was formed by meteorite impact; (4) unloading of overburden through stream erosion resulted in the upward migration of the salt; and (5) it is a salt dome produced by multiple salt movements resulting from local diastrophism and igneous intrusion. The author suggests that the dome is the product of salt flowage resulting from differential pressures which were produced by differential compaction of the sediments over and on the flanks of a buried hill, or monadnock, on the Precambrian basement complex.

Throughout most of late Permian time the southeastern Permian Basin was part of a shallow barred lagoon located in an area of high evaporation and low rainfall. Refluxion to the open sea farther west was slowed by the intervening Capitan barrier reef during Guadalupian time, but free surface influxion of sea water occurred. Dolomite and sand deposition during Grayburg time yielded to precipitation of anhydrite and halite in early Queen time. Deposition of fine-grained sand and clay from a lowland lying to the east and south alternated with anhydrite and halite during Queen and Seven Rivers times. A maximum of 550 feet of Queen and 600 feet of Seven Rivers sediments accumulated. During Yates time 150 feet of fine-grained sand was spread across the area. Clastic deposition was interrupted at the beginning of Tansill time, during which 15–50 feet of anhydrite and halite were precipitated. Regional uplift followed, and 20 feet of shale of Castile (?) age accumulated. After the sea returned, halite deposition ensued throughout Salado time except for short periods of polyhalite accumulation and one period of widespread anhydrite precipitation during which the Cowden Member was deposited as far east as Coke County. Emergence and local erosion of Salado salt occurred in early Rustler time. Final transgression of the Permian sea allowed the marine deposition of 80 feet of Rustler sand and anhydrite and 100 feet of Dewey Lake sand. The sea then withdrew, ending Permian deposition in West Texas.

Maps of layering visible in salt mines in Texas and Louisiana salt domes show intricate patterns of shear and flow folds. This layering, which is now dipping steeply, is believed to be original sedimentary bedding. Petrofabric studies on halite and anhydrite in Grand Saline salt dome demonstrate that the direction of motion was steeply upward and essentially parallel to the fold axes as determined in the mine mapping. Halite petrofabric studies also show cubic as well as dodecahedral glide planes. Structural mapping and petrofabric studies show that the domes rose to their present positions as a series of separate elements (spines, pencils, etc. ) rather than as single large entities. This theory of differential uplift of the Texas and Louisiana salt domes has been corroborated from structural mapping of sedimentary rock units surrounding the dome.