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The Caspian Sea is located within the Precambrian Russian and epi-Hercynian Scythian platform and Alpine geosynclinal province. Marine geophysical methods (seismic gravity, magnetic, and electrical) have added many details about its structure and salt tectonics. The ancient age of the Caspian central massif is supported by relationships between the Karabogaz arch and Turkey meganticline. Basically the south Caspian represents a remnant of the ancient Thetis trough; the middle and north Caspian are epiplatforms: The western part is associated with a post-Alpine platform and its foredeeps, with the middle Caspian only recently involved in its subsidence. A series of maps are given, showing the results of various marine geophysical studies. C. E. Sears

Modern seismic methods, which attenuate multiple reflections, demonstrate the existence of consistent diagnostic primary reflections from the deep Lower Cretaceous formations, from key Jurassic formation boundaries and from the base of the salt along the Smackover trend across Texas, Louisiana, and Mississippi. These data make feasible, for the first time, realistic delineation of deep subsurface structure. Typical seismic data along the trend are shown and related to subsurface geology. Certain new concepts in salt tectonics along this trend are indicated. The end of Smackover time was the beginning of the first major period of salt flow with related folding and faulting. The Buckner formation, up to possibly 5000 ft thick, represents backfill and base‐leveling material deposited around Smackover mantles over the pre‐Cotton Valley salt swells. Evidence exists of a mother salt bed up to 6000 ft thick. The possibility exists of Buckner reef growth on top of some Smackover lime highs over salt swells. Salt flow tectonics created rim synclines which tend to preclude migration of hydrocarbons into salt‐generated Smackover closures. Optimum evaluation of Smackover prospects requires determination of age, cause, and magnitude of Smackover closures (including rim synclines if present) plus, if possible, detection of reef buildups.

The North Sea, with its complex geology and rapidly varying seismic velocities, is a highly suitable proving ground for the new digital data enhancement and computational techniques. Record quality is good, although long and short period multiples often mask the desired deeper information (Permian or deeper). Considerable improvement in record quality has been attained by a combination of three or six‐fold stacking and inverse time‐domain or dereverberation filtering (deconvolution), as illustrated in the examples covering a representative selection of structural situations and record types (stratigraphic traps, faults, suspected reefs, and salt tectonics). The contribution of long‐operator time‐domain filtering is the most significant one to date of computer processing since good “brute” stacking can also be attained by analog means if care is taken. In the realm of velocity determination, the computer has been used to improve calculations of expanding spread data, taking into account ray‐refraction and thus providing more accurate interval velocities. Depth computations, using stratigraphy‐correlated multilayer velocity models, and velocity laws derived from these more accurate interval velocities, have been successfully carried out for over 100,000 North Sea “shotpoints” by computer and the results have been computer plotted. Computer programs are currently being perfected for such applications as automated velocity determination, multichannel filtered stacking, data migration, and plotting and contouring.

This paper deals with two salt domes, Monsted and Sevel, located in northern Jutland, and is primarily concerned with the problem of Quaternary salt tectonics and its possible relationship to the Quaternary morphology.

Salt beds with a thickness range of a few feet to 600 ft are common in rocks of Middle Devonian and Permian ages in the northern Rocky Mountain area. Variations in thickness of these salt beds in short horizontal distances require consideration of the hypothesis that the salt-thickness changes are due to post-depositional salt removal by solution and not to original variations in the thickness of salt deposited. Thin, regionally persistent sedimentary units directly above and below the salts prove that, locally, there was little depositional change of salt thickness. Therefore, within the regions of salt deposition, the salt must have been removed after deposition in the present thin or zero salt areas. Local removal of Middle Devonian salt (Prairie Formation) in the Williston basin occurred during later Devonian time and continued through the time of deposition of the Mississippian Lodgepole and Tilston Formations. Local removal of Permian salt (Minnelusa Formation, Opeche Shale, and Goose Egg Formation) in both the Williston and Powder River basins took place near the close of the Jurassic. Compensating deposition took place in the collapse depressions created by underlying salt removal, thus dating the age of solution. In the examples of salt removal described in this paper, a few to several hundred feet of sediment was deposited over the salt before salt removal took place. It is postulated that salt removal was accomplished by the formation of local and regional fracture systems which allowed ascending water to escape from regional aquifers below the salt beds, and that this water dissolved the salt and carried it in solution to the ocean floor. Oil accumulations in some places are related to the formation of local subsidence structures by salt removal. Geologists have postulated the presence of regional lineaments along and above which salt has been removed. Locally, the salt-removal areas may be irregular in size, shape, and distribution, although, as a whole, these areas may occur within a regional band.

The object of this paper is to describe and explain the formation of salt stock structures in Northern Germany and to contribute in this way to a better understanding of similar phenomena in other parts of the world. The majority of the structures in the North German basin can be directly or indirectly attributed to "halokinesis." This term, proposed by the writer (1957), designates the formation of salt structures, and their structural and stratigraphic implications, which are essentially the result of the autonomous movements of salt under the influence of gravity. Phase-bound tectonic forces play only a minor part. The Permian salt structures of Northern Germany are classified into salt pillows, salt stocks, salt walls, and extrusions along fissures. They are accompanied by primary, secondary, and third-order peripheral sinks. The halokinetic movements have taken place in an essentially continuous and autonomous fashion from the Triassic to the present day. Reckoned throughout long periods of geological time, the absolute rate of flow of the salt averages 0.3 mm. per year.

During a sparker and core-drill program conducted by Shell, salt was cored on 10 prominent structures on the continental slope. Broad salt swells and pillows are typical structures in this region. The Sigsbee scarp appears to be the surface expression of a salt front. A zone of active down-to-the-ocean faults follows the Texas shelf edge. They appear to be related to the flow of salt at depth away from the advancing clastic wedge. Upper Cretaceous through Holocene deep-water sedimentary beds were cored on the continental slope. East of Brownsville the salt is overlain by redbeds of unknown age. Core holes at the shelf edge penetrated deltaic and shoreline deposits of the Pleistocene low-sea-level stages. Submarine slides and turbidity currents carried sediments down the slope and filled deep synclinal basins between the salt uplifts.

The salt anticlines of eastern Utah and western Colorado formed in the deepest part of Paradox basin, a basin developed during Pennsylvanian time and filled by great thicknesses of upper Paleozoic sediments, including a thick sequence of evaporites belonging to the Paradox member of the Hermosa formation. The salt anticlines originated either as tectonic folds or as folds over basement faults soon after the evaporites were deposited, probably in Middle Pennsylvanian time. These structures were parallel to and probably formed concomitantly with the rise of the ancestral Uncompahgre highland, the front of which paralleled rather closely that of the southwest front of the present-day Uncompahgre Plateau. Rapidly accumulating arkosic sediments of the Permian Cutler formation, derived from this highland, probably buried parts of the salt anticlines; elsewhere along the anticlines the salt rose isostatically as rapidly as the sediments were deposited. In places the Cutler was later intruded by the cores of the buried salt anticlines. Parts of the cores were exposed at the surface at least until the Morrison formation was deposited in Late Jurassic, so that the formations pinch out along the flanks of the salt cores. Variations in thicknesses--chiefly thinning--of the Morrison and later Mesozoic formations over the crests of the salt cores indicate that salt flowage was still active after the salt cores were buried. The salt anticlines attained their present form--except for modifications imposed by later collapse of the crestal parts of the anticlines--during the early Tertiary when the rocks of the region were folded, and the salt anticlines were accentuated. End_of_Article - Last_Page 413

The coring of deep-water sediments in the Gulf of Mexico during Legs I and X of the JOIDES program has contributed significantly to our knowledge of the Gulf's geologic history. The nature of Sigsbee scarp is still not known with certainty, but the results of drilling holes 1 and 92 suggest that both "contemporaneous normal faulting" (perhaps overbuilding and downslope movement) and salt tectonics may be involved. Drilling results from holes 3, 85, 87, 90, and 91, indicate that formation of the present Sigsbee plain includes late Neogene subsidence and, prior to the Pliocene, a more westerly source for coarse terrigenous clastic debris than the Mississippi River. The discontinuous record of deep-water sedimentation since the end of Early Cretaceous time, found in holes 86, 94, 95, 96, and 97, suggests a complex structural history of block tilting and faulting for the banks and scarps. This may include a Late Cretaceous seaway, and its reemphasis as the present Yucatan Channel-Florida Strait as late as Pleistocene. Correlatibility of the discontinuities bounded above and below by deep-water sediments may require some more comprehensive explanation than slumping and submarine current removal of s diments. Perhaps worthy of note, is the possibility that the overly publicized recovery of hydrocarbons from Challenger Knoll in the Campeche embayment salt-tectonic province (hole 2) affected the extenders of the JOIDES program, thus helping to make Leg X cruise possible. Drilling during this cruise, in turn, under the influence of changing political winds, contributed to the pollution-scare, thwarting the original Leg X goals. Many of our basic questions have not been answered adequately by JOIDES work, but we are, at least, aware of many more questions. End_of_Article - Last_Page 1699

The Zechstein salt deposits of middle and northern Germany were laid down in a sinking basin in which sinking came to an end during the Jurassic, except in northern Germany, where it persisted into the late Tertiary. The beds deposited in this basin were involved in the Saxon mountain-building movements, which contrast with the older, Variscan movements in being intermediate in character between folding and block faulting. The Saxon movements were periodic and not continuous. That the movements were due to compressive thrust is shown by the fact that the "horsts" were uplifted. The salt bodies are found in the form of "salt beds," "salt anticlines," and "salt stocks." "Salt anticlines" are normal anticlines both in the form and inner structure of the salt and in the structure of the sedimentary cover. The "salt stocks" are strongly folded, subcircular to elongated masses of salt which are upthrust into faulted rather than folded adjacent formations. The main theories proposed to explain the upthrust of the salt are three: Lachmann's "atectonic" theory, the "isostatic" theory, and the theory of upthrust by lateral thrust. Lachmann's "atectonic" theory of upthrust of the salt by an inherent autoplastic force is no longer current. The formation of the salt anticlines by the compressive thrust of the Saxon orogenic movements is very generally accepted by German geologists. But as there is every gradation in form between the characteristic salt anticline and characteristic salt stock, as the gradation from one to the other can be followed on the same anticlinal axis, and as with a rare exception the periods of movement in the salt stocks coincide with the periods of the Saxon orogenic movements, it seems reasonable to believe that all have been caused by the same force. The difference in the resulting forms is due rather to the difference in the materials acted upon than to difference in the forces acting. The salt is more plastic and therefore more mobile than the ordinary sedimentary rocks, and is therefore the more easily deformed. Under intensive deformation, it advances far ahead of the other rocks, and thus a salt stock is the extreme form of an anticlinal core. The tectonics of salt upthrust are therefore a phase of the tectonics of mobile materials and are intermediate between the normal tectonics of folding and the tectonics of magmatic intrusion. D. C. B.

This paper follows a companion report on the internal structure of the Grand Saline salt dome, Texas. The Jefferson Island salt dome is a slender column, perhaps several miles high, with nearly vertical walls. The megascopic and microscopic features of the salt are described. Salt layers stand vertically, or nearly so. Where the mine exposures approach the southeastern border of the dome, they strike parallel with it. The interior consists of many large and small folds, ranging from open to isoclinal position of the vertical limbs. Near the border, lenses of sandstone have been folded with the salt. Vertical lineation, shown by distorted halite crystals and preferential orientation of the longest body axes of anhydrite crystals, is common, but there is also coarse-grained, massive salt, locally with large poikiloblasts of halite. The mode of origin of the salt dome is briefly discussed, with special reference to problems of crystal deformation and recrystallization in salt domes, glaciers, and some granitic massifs.

From abstract: The thesis of this paper is that the anhydrite cap rock of salt domes originated by the residual accumulation and consolidation, on top of a salt stock, of sedimentary anhydrite freed from the salt by solution of the top of the stock. This hypothesis is compared with that of origin from a bed of sedimentary anhydrite supposed to have overlain the salt of the salt stock in depth and to have been forced up on top of the stock as it rose. The strongest basis for the hypothesis of residual accumulation is the presence, between the anhydrite cap rock and the top of the salt stock on many salt domes, of a flat solution surface, the "salt table," decapitating anhydrite-bearing folds in the salt. The paper considers other general geologic evidence and internal petrographic evidence with a view to ascertaining to what extent they confirm or at least fit this interpretation.

The American salt-dome problems are divisible into two parallel series, the one comprising problems of description, the other problems of theory. The solution of the latter are of necessity dependent upon solution of the former. The American salt domes consist of subcircular stocklike masses of salt, capped in most cases by limestone and gypsum-anhydrite, intruded into and surrounded by Pleistocene-Eocene or Eocene-Cretaceous sediments which dip quaquaversally away from the salt core. The domes show certain tendencies to alignment. They occur in regions of geologic quiescence where there has been no compressive folding. The Roumanian salt domes are divisible into two groups, the Carpathian-Sub-Carpathian, and the Transylvanian. The Carpathian-Sub-Carpathian domes consist of narrow, elongated, vertical intrusions of the Salifere salt, clays, and marls along anticlinal axes and into a thick series of Pliocene and Miocene sediments. The domes occur on the edge of, and immediately in front of, the Carpathian sheet overthrust and are aligned along structural, mostly anticlinal, axes which reflect the effect of the Carpathian tectonics. If the difference in the structural setting is allowed for, the Roumanian domes closely resemble those in America. Their origin has usually been attributed to some phase of the tangential thrust of the Carpathian mountain-building forces. Krejci recently has raised strong o jection to that theory, and has advanced a tectonic-isostatic theory according to which tectonic thrust is responsible for the localization and initiation of their formation, but the weight of the overlying sediments is responsible for the upthrust of the Salifere core. The Transylvanian domes occur in the Plio-Miocene Transylvanian basin. Although only poorly known, they seem to be very similar in form to the American domes. They are aligned on anticlinal axes which are subparallel to the periphery of the basin. The German salt domes are a phase of the German salt deposits, which are a definitely sedimentary series with a well-defined, persistent, and characteristic section. One of the middle members carries marine fossils, and two members are potash bearing. On account of the extensive mining and exploration for this potash, and on account of the recognizable section in the salt series, the structural deformation of the salt deposits has been worked out in great detail. On the basis of form and structure of the salt deposits there is a complete gradation in type and in space from undeformed sedimentary beds through broad anticlines with slightly swollen cores of salt (Strassfurt type), sharp anticlines where the salt core is starting to pierce the cover (Asse type), to broken End_Page 1227------------------------------ anticlines in which the salt core has been squeezed up between the two flanks (Leine type), or to salt stocks (Hannoverian type) in which a pluglike mass of salt has been intruded for thousands of meters vertically into the overlying sediments. There seemingly can be no dispute that the German salt domes and salt ridges are the result of the plastic deformation and flow of a sedimentary salt series. The salt domes and ridges are aligned along Rhenish and Hercynian anticlinal axes. Many of the domes seem to be at the intersection of axes. The upthrust of the salt cores is attributed to tectonic thrust by Stille, who presents substantial evidence for such a theory. Lachman, Arrhenius, Seidl, and others argue less conclusively for an isostatic upthrust. In view of the evidence of the Roumanian and German salt domes, in addition to what is known about the American domes, it would seem unreasonable to believe that the American salt domes are not the result of the plastic deformation and upthrust of a sedimentary salt series.

More than 300 diapiric structures formed by the intrusion of relatively pure salt are known in Alabama, Mississippi, Louisiana, Arkansas, Texas, Nuevo Leon, Veracruz, Tabasco, and Cuba. In form, the structures are rod-like, domal, anticlinal, and ridge-like. They rise vertically, or nearly so, and increase or decrease with height. Many are capped by residual masses of anhydrite, altered in varied degrees to gypsum, sulfur, and calcite. Modern theory postulates growth resulting from density differences between the salt and surrounding sediments (1) by upward movement of the salt through the overlying sediments in response to gravitational inequilibrium, or (2) by salt structures remaining at an essentially constant level while the surrounding sediments of sedimentary rocks moved downward around them as deposition progressed. Model studies suggest that variations in overburden and faulting are primary causes of the initiation of salt movement. The probable source of the salt in Gulf Coast salt domes is the Louann Salt. It may have been as much as 5,000 ft thick and have had an original volume of 200,000 cu mi. Sediments enclosing salt stocks have varied structural configurations. The strata may be arched, they may be ruptured and pierced by the salt, they may be complexly faulted, or they may be deformed by various combinations of faulting and folding. All the salt structures in the Gulf of Mexico basin probably are of similar genesis.

Salt-mining in Northwestern Europe has afforded significant data on the structure of salt domes. Salt is a relatively plastic rock under pressure, and may "erupt" in a manner analogous to igneous magmas. Highly deformed, clearly traceable key beds in the salt domes of Europe, and progressive changes from slight flowage at the salt outcrops to typical intrusive relations where the salt is deeply buried, afford basis for the conclusion that the European domes are purely tectonic in origin. The cap rock represents the residue of less soluble material in the upthrust salt as solution attacks the rising dome in the zone of active ground-water circulation. The salt domes of Europe are mostly without associated oil deposits, a feature probably due to pre-Eocene erosion which per itted escape of oil from older source beds.

The Rumanian salt domes are confined to the axial portions of sharp anticlinal folds and fracture zones which affect the sedimentary rocks of the region. The anticlines are aligned with the Carpathian axes. Intrusion of the salt has been accompanied by intrusion of thick masses of breccia composed of sedimentary and some igneous rocks of all ages, including types of rock unknown beneath these portions of the mountains. Both salt and breccia have been thrust upward in diaper manner and even overthrust with sharp, recumbent crests. The author believes that the salt in the Rumanian domes cannot be of Miocene age, as has been previously contended, and he argues that the original salt beds from which salt domes have formed, not only in Rumania but universally, are products of the evaporation of the earliest lakes and shallow seas to form on the surface of the primitive earth. These waters were rich in chlorides and other salts taken into solution from the heated rocks of the earth's crust and condensed from the heavy blanket of the earth's atmosphere. Part of the immense quantity of salt deposited in this manner was redissolved in the permanent oceans, but after these had become saturated, the main part of the salt deposit remained, to be covered by the first muds laid down on primitive sea floors. They were thus p otected until movement and pressure squeezed the salt upward as salt plugs. The intrusion of the Rumanian salt plugs is late Pliocene or early Pleistocene.

Internal structures and preferred orientation of halite crystals in Grand Saline salt dome, Texas, and Winnfield salt dome, Louisiana, indicate emplacement of the stocks by successive differential movement of spines and lobes. Differences in intensity of shear folding and varied degrees of preferred orientation in these and other Gulf Coast salt domes suggest that mines within the domes are at different structural levels and that movement of the salt has, in some cases, been very complex. Study of the preferred orientation of bedded salt from Oklahoma showed that it increases with depth.

The salt of the salt domes of some areas is known to be sedimentary. Geological observation of those domes and laboratory experimentation show that salt flows plastically under differential pressure. The German salt domes are known to have been formed by the plastic flowage of the Zechstein salt series. Any type of differential pressure should tend to produce plastic flowage of sedimentary salt whenever certain critical conditions such as those of pressure, temperature, and time have been exceeded. The plausible sources of pressure are two: (1) the static pressure of the overlying sediments; and (2) the dynamic pressure of tangential compression or thrust. Under (1), growth of the dome by upthrust can take place only if the available energy is sufficient both to overcome riction and to uplift the salt core and some sediments against gravity; growth of the dome by downbuilding can take place if the mother salt bed is sinking in earth space; the position of maximum uplift is below that of isostatic equilibrium of the salt core; and the form of the salt dome should evolve progressively through a characteristic series of forms. Under (2), the horizontal dynamic pressure will act indirectly upward through anticlines and downward through synclines in competent beds; and directly through horizontal squeezing of the salt in relatively upthrust cores. The static thrust of (1) will be active and may be more important than the dynamic thrust of (2); the position of maximum upthrust of the salt core may be far above its position of isostatic equilibrium; the form of the domes should be varied. The Gulf Coast domes have been formed by the plastic flowage of sedimentary salt intrusively into the overlying sediments. The evidence for that origin of the domes comes from the structure which is revealed by oil-field drilling, from algal remains in the salt, and from the close similarity of the American salt domes to the German salt domes. The age of the salt is greater than most of the Lower Cretaceous. The motive force of the formation of the domes has been the static weight of the sediments. Growth of the domes has taken place throughout the Tertiary and has taken place on a few domes in the most recent past. There was no dynamic tangential compression in the Gulf Coastal Plain area during the Tertiary and Quaternary; therefore, the motive End_Page 1025------------------------------ force presumably must have been the static thrust of the sediments. Subsidence of the mother salt bed took place almost continuously through the Tertiary and into the Quaternary. The difference between the specific gravity of the salt and of the sediments is small; and the calculated force of upthrust is small, rather too small to overcome friction and to uplift the salt core and some sediments against gravity. Growth of the domes, therefore, must have been largely by downbuilding. Partially corroboratory evidence is given by the concomitant cessation of growth of the Clay Creek dome and cessation of the regional subsidence of the general surrounding area. But some actual upthrust has taken place on the Gulf Coast domes; and, as theoretically expectable, it tends to be greater on the omes of larger diameter. Growth has not continued into recent time on all the domes and has ceased finally at different times on different domes. The law holds crudely that the deeper the dome, the older the time of cessation of growth. The final cessation of growth in general may have been caused by exhaustion of the salt in the mother salt bed, attainment of isostatic equilibrium, frictional freezing of the salt core to the sediments, and, in the case of downbuilding, by cessation of the subsidence. The succession of retrograde movement of the salt core after the cessation of growth is suggested, inconclusively, by the Clay Creek dome. The presence of rim synclines has been suggested by the results of torsion-balance surveys, but has not been identified from geologic data. Rim syncline could be formed: (1) by solution of the flank of the salt, and (2) by the pushing-in of the deep flank of a flaring salt core in the growth of the dome. Overhang of the salt and cap is present in two types: (1) tilting of the vertical axis of the dome, and (2) mushrooming (Barbers Hill). Type (1) is produced perhaps by the seaward flowage of the deeper sediments. The explanations of type (2) are not satisfactory.

The Cuanza basin is in northwestern Angola on the Atlantic Coast of West Africa. This basin is about 300 km. long north-south and 170 km. wide east-west, and contains an Early Cretaceous carbonate-evaporite sequence and a Late Cretaceous and Tertiary argillaceous-arenaceous sequence. The Precambrian crystalline basement is partly covered by extrusive rocks and granite-wash type sediments. Surface and subsurface sediments of the basin consist of Lower and Upper Cretaceous, Paleocene, Eocene, and Miocene strata. Occurrences of oil and gas have been reported in almost all of the stratigraphic units in the Cuanza basin, and there is major production from the Cretaceous rocks. Study of these hydrocarbon occurrences and of the geological history of the basin shows that close relationships exist between sources, migration, and entrapment of oil, and environment of deposition controlled by the basement and salt tectonics. During Early Cretaceous time, subsidence of the central part of a restricted basin determined the regional cyclical deposition of a carbonate-evaporite sequence providing a favorable situation for genesis and entrapment of oil. Thus, the deposition during Aptian time of a very fine crystalline limestone, interbedded with argillaceous limestone and overlain by an oolitic sandy calcarenite, itself underlying evaporites, had an important influence on the subsequent extent of oil accumulations in the Binga Formation. During Aptian-Albian time, differential subsidence on the western margin of the basin caused lateral interfingering of back-reef calcarenite, argillaceous carbonate, and evaporite. This interfingering is believed to be related closely to oil accumulations in this area. Very i portant vertical development of reef deposits in the Longa area is related to lateral migration of the underlying Massive Salt, which flowed with the help of the excess of weight introduced by the growing reef. On the eastern margin, upper Albian reef buildups capped by marine shale also provided a favorable situation for generation and accumulation of oil. During Late Cretaceous and Tertiary time, a major basement flexure or fault zone appears to have been associated genetically downdip with deposits that accumulated with greater thickness than elsewhere. This flexure and the loci of maximum deposition moved eastward during Late Cretaceous and Paleocene, then westward during Eocene and Miocene. These thick formations, which are mainly argillaceous-arenaceous and which were deposited partly in deltaic and lagoonal environments, grade westward into thinner marine deposits and eastward into thinner continental deposits. During each particular epoch corresponding with a stabilization of this moving flexure, favorable conditions for genesis of hydrocarbons seem to be related to these transitional environments. Oil production is located above the Massive Salt at the crest of salt anticlines, and one small oil field has been discovered below the Massive Salt along a ridge of the Basement Complex in a pinch-out of sandstones between Precambrian mica-schist below, and salt above.

The mode of deposition of the mother salt bed from which the salt domes of the Gulf Coastal Plain arose is discussed. Deposition of the salt in a restricted basin during Permian time is postulated, the deposition taking place under the conditions of Branson's "modified bar theory." The Castile sea of the Delaware Basin area of West Texas is though to have been the first of the "barred basins" necessary under the Branson theory. The mechanics of the growth of the salt plugs of the Gulf Coastal Plain is discussed. The motive force for the intrusion of the salt plugs is attributed to the static weight of the overlying sediments, resulting in a buoyancy effect caused by the difference in density between the salt and the sediments.

The surficial sediments of an area of the upper continental End_Page 1895------------------------------ slope in the Alaminos Canyon area, Gulf of Mexico, indicate sand input from the ancestral Colorado-Brazos and Mississippi River systems. The clay minerals in the area were derived from indeterminate sources and were incorporated in coarse samples through resuspension of former sediment. Vermiculite, as well as tubular hallaysite, were identified in clay samples. The first mineral is unreported in the northwest Gulf, and the latter is only known from the Mississippi delta in the northwest Gulf area. The "hummocky" nature of the bathymetry in the area resulted from salt diapirism and scouring by tractive and/or density flow. Sand-size sediment was transported to the area from river systems by longshore drift during the Holocene transgression or through channels still identifiable on the present continental shelf. The lineation of one of these features, the Outer Colorado-Brazos Channel, is probably due to salt tectonics and not the result of a barrier spit as previously reported. End_of_Article - Last_Page 1896

The recent studies presented by Schmalz indicate that it is possible for significant thicknesses of salt to be deposited in a deep-water environment. This hypothesis makes it possible to propose a relatively simple model for the Gulf of Mexico which accounts for the distribution of the deep-water salt structures including the Sigsbee Knolls, the diapiric structures on the northern continental slope, and possibly the anticlines of the western Gulf. However, most recent geophysical data indicate that a thick salt layer is not present across the Gulf of Mexico basin. These data suggest that the Sigsbee scarp represents the southernmost extent of the salt of the northern Gulf region and that the trend of the Sigsbee Knolls and domes is the northern extent of the migration of alt from south Mexico. On the basis of the assumptions that the Gulf of Mexico is an old basin and that our interpretation of the new data is correct, an alternate hypothesis is proposed to explain the salt-structure distribution. It is suggested that the following series of events took place: (1) salt was deposited along the marginal areas of the basin; (2) sediment accumulated above the salt and subsequently subsidence occurred; (3) salt ridges and stocks formed and salt migrated downdip into the deeper parts of the basin, as a result of overburden pressures; and (4) in areas of carbonate buildup, competency of the carbonate material prevented formation of salt piercement structures; instead, horizontal migration of salt toward the deep basin seems to have taken place.

Small folds and fractures (thrusts) up to 50 feet apart that have produced polygonal patterns in the Bonneville salt crust, western Utah, are believed to be caused by the annual expansion of the salt crust due to the growth of salt crystals within the salt layer plus the effect of increased summer temperature. It is suggested that these strain systems are caused by positive (compressional) isotropic planar stresses developed within the salt layers of the salt crust.

In south Texas, there are three known salt domes, Palangana, Piedras Pintas, and Falfurrias; three possible domes, Sal del Rey, Sal Vieja, and Chapeno; and two much less probable domes, Smith Corkill and La Lomita. The structure of Palangana, fairly well known from drilling, is that characteristic of an American salt dome, and is distinctly reflected in the topography. Palangana has no production. At Piedras Pintas, the salt and cap have been drilled into, but not much is known in regard to the structure of the dome. Piedras Pintas has a small, shallow oil field. Both domes gives evidence of the very great upthrust of the salt. On the basis of the evidence afforded by the German salt domes, the origin of salt domes is the plastic deformation of sedimentary salt beds. The rigin of salt domes is the plastic deformation of sedimentary salt beds. The origin of the cap, such as is present at both Palangana and Piedras Pintas, has not been satisfactorily explained, although several plausible theories have been proposed. At Falfurrias, the salt has not been encountered, but the presence of a characteristic salt-dome mound and characteristic cap rock indicate the presence of a salt dome. Sal del Rey and Sal Vieja are saline lakes whose topography in a general way is similar to that of a central-depression type of salt-dome mound. The lakes, however, are more probably due to wind activity with concentration of normal surface waters in the wind-scooped basins. Chapeno suggests salt-dome structure in the presence of sulphur deposits. La Lomita is a mound near the R o Grande, and Smith Corkill is a group of chalcedonic knobs.

Proposes that the Cornish and Devon granite masses in southern England have risen due to gravity difference with a more rigid overburden, and in so doing have been a factor in the probable crustal foreshortening between south Wales and the Brest peninsula, France. The series of events is considered analogous to "salt tectonics."

A geophysical study of the continental slope and rise off Angola shows the presence of two basement ridges under the sedimentary prism. These ridges are the continuation of onshore basement highs, or parallel to them. The continental rise deposits are built up behind the outermost of these ridges; the deposits of the onshore Cuanza basin and its northward offshore equivalent behind the innermost one. The sedimentary sequences in both zones have a parallel history of evaporite deposition followed by diapirism. Two separate phases of salt tectonics can be distinguished which propagated eastward with time from their western terminal basement ridges. The relative ages of the onshore and offshore sequences cannot be established at this time. The offshore diapir province has a width of more than 300 km and extends possibly from the Congo Canyon in the north to near the Walvis Ridge in the south.

The plastic deformation of salt formations is reviewed to evaluate the possibility of diapiric processes affecting salt beds used for radioactive waste disposal. In a geological sense, rock salt is characterized by a marked mobility as a result of its ability to deform under relatively low stresses. Examples are known of salt formations deformed by tectonic forces, but the typical diapiric processes are essentially due to gravitational forces. In the initial phase, salt deformation is caused by differential loading of the salt bed; only after salt flowage has resulted in thickening of the low pressure zones of the salt bed does the density difference between salt and sediment contribute to the deforming stress. Salt diapirs are usually large structures, and to furnish the necessary large volume of salt, a mother bed of great initial thickness must be presumed. No minimum depth seems to exist for the plastic deformation of salt; however, the plasticity of salt increases with depth as a result of the increasing temperature. The rate of salt deformation is critical in relation to the required containment time for plutonium-contaminated waste. A few authors maintain that diapiric processes proceed at a catastrophic rate, but the geologic literature indicates that most geologists believe salt diapirism to be a relatively slow process and geologic evidence seems to support strongly the majority view. It can be concluded that, in the final stage of salt intrusion, rates of diapir growth as high as a few millimeters per year are possible, and in the initial phase of plastic deformation of the salt bed, flow rates should be markedly lower. In relation to the safety of radioactive waste containment, the risk of excessive deformation can be kept acceptably low if the disposal formation meets the following requirements: (1) bedded salt located in a geologically stable area; (2) subhorizontal salt beds exposed to very limited differential loading; (3) thickness of the salt beds of the order of 100 to 300 m; and (4) depth of the salt beds between 300 and 700 m.

Salt deposits occur in two areas in western Pakistan: one near Kohat west of the Indus River, and the other in the Punjab Salt Range between the Indus and Jhelum rivers (lat. 35° N.; long. 71°–74° E.). The Salt Range is the south-facing scarp of the Potwar Plateau. The plateau is formed by a great thickness of sedimentary rocks which have been thrust southeastward between two wedges of the Indian Peninsula toward Kashmir and Waziristan. The strata in the Potwar basin (whose southern border is the Salt Range) are gently folded in the south but progressively more intensely folded and faulted in the north. The Salt Range exposes a good sedimentary succession but has a long gap between the Cambrian and the Upper Carboniferous, and short gaps below the Upper Jurassic, below the Eocene, and below the Upper Oligocene. The Saline Series with its associated salt, marl, gypsum, dolomite, and oil-shale beds is exposed all along the Salt Range. The salt beds attain a maximum thickness of 800 feet. The salt appears massive except where it includes marl and gypsum bands which show very complex folding. The Saline Series occupies various stratigraphic positions, and its contacts with the other formations are highly disturbed and brecciated, presumably as a result of thrusting. The controversy regarding the age of the Saline Series, whether Cambrian or Eocene, will probably not be settled without the aid of new techniques, for the observable geologic features can be used to support either side of the controversy.