Displacive Halite Research Articles

Salt Dissolution in the Permian Flowerpot and Blaine Formations Defines Limits of the Syracuse Basin in Western Kansas and Eastern Colorado

The Syracuse Basin is a large region of about 8,100 mi2 (21,000 km2) in western Kansas and eastern Colorado that is underlain by Permian-age salts in the Flowerpot and Blaine Formations of the Nippewalla Group. Originally thought to be a structural or depositional basin, detailed study around the perimeter of the basin shows that it is a dissolutional remnant wherein the salt beds are dissolved at all places around the basin’s margins. The two main salt units, the Flowerpot salt and the middle Blaine salt, consist mainly of displacive halite in red-brown shales and siltstones (mudstones). The Flowerpot salt is generally 200–300 ft (61–91 m) thick within the basin, but where most or all of the salt is dissolved outside of the basin, equivalent strata are 50–150 ft (15–46 m) thick. The younger middle Blaine salt is typically 45–60 ft (14–18 m) thick in the basin, and equivalent strata are 5–10 ft (1.5–3 m) thick where the salt is dissolved. Five areas selected for detailed study of the dissolution zone around the perimeter of the Syracuse Basin show that removal of about 250 ft (76 m) of Flowerpot salt occurs within horizontal distances ranging from about 930 ft (283 m) to as much as 14 mi (23 km). Structural cross sections show that sub-salt strata dip gently and uninterrupted beneath the dissolution zone, whereas strata above the salt are disrupted and are flexed down by an amount roughly equal to the amount of dissolved salt. This supports the thesis that the salt deposits are a dissolutional remnant and not a structural or depositional basin. In most areas, descending unsaturated groundwater dissolves the shallower middle Blaine salt first and then dissolves the deeper Flowerpot salt. But in two areas, unsaturated groundwater is sourced from a sub-salt aquifer, causing dissolution of the Flowerpot salt first and then the shallower middle Blaine salt. Salt dissolution occurred at different times in different parts of the Syracuse Basin. In most areas, it occurred mainly during the Pliocene–Pleistocene–Holocene Epochs, but locally it started before deposition of the Cretaceous or even from Late Permian through Early Cretaceous time. The original extent of the Flowerpot and middle Blaine salts went far beyond the current extent of the Syracuse Basin. Remnants of both salt units are present in six large regions that extend from the Denver Basin in northeast Colorado and western Nebraska on the north to the Anadarko and Palo Duro basins in Oklahoma, Texas, and New Mexico on the south, a total area of about 115,800 mi2 (300,000 km2). In all these regions, the two salt units have dissolutional limits like those at the perimeter of the Syracuse Basin. Dissolution of subsurface salt units can cause problems when or if underground cavities become so large that the roof of the cavity collapses and the cavity rises to the land surface to form a sinkhole or an area of ground subsidence. Problems can also arise when seismic-reflection surveys cross a dissolution boundary and false images of phantom structures are created in strata below the dissolution zone. Also, drilling through salt units must be done with care so that unsaturated drilling muds and formation waters do not cause cavity development in the salt. Dissolution of salt also can affect the quality of groundwater: Salt-dissolution brine can migrate into fresh groundwater aquifers and even render the water unusable for most purposes.

Deformed displacive halite crystals: Diagenetic or tectonic origin?

ABSTRACT Displacive halite crystals in fine-grained sediments are a common feature of evaporitic sequences worldwide. The crystal habit of halite precipitated from pure aqueous solution under laboratory conditions is a cube: equal side lengths (a = b = c) and rectangular angles (ab = bc = ac = 90°). Crystals with deformed-looking shape appear in mudstone of Permian evaporites of the Eastern Alps. They expose platy, rod-like, parallelepiped-like or rhomb-like shapes. The aim of the study was to explain the origin of these shapes. Samples were taken in the Altaussee, Berchtesgaden, and Hallstatt mines. Representative mudstone samples were scanned by high-resolution X-ray CT, and halite shapes were restored by 3D software. Additionally, 327 euhedral halite crystals were dissected from mudstone and subjected to individual shape analysis. Their sizes range from 3 to 30 mm in thirteen specimens. Crystals are compact, but a slightly platy preference prevails in all samples. Approximately 80% of all objects expose angles > 1° deviating from the right angle, but only ∼ 15% contain angles > 20°. The maximum deviation from the right angle was ca. 33°. Most objects combine a platy shape (a ≈ b ≠ c) with only one angle deviating from the right angle (2× 90°). The acute angle is preferably oriented parallel to the layering. We interpret a primary rectangular crystal growth to platy shapes in the mudstone (reduced fluid circulation). The displacive halite crystals subsequently deformed during compaction of the mudstone. Halite in deformed shapes was replaced by datable polyhalite ca. 15 My after deposition, which rules out deformation during Alpine tectonics.

Acid-saline-lake Systems of the Triassic Mercia Mudstone Group, County Antrim, Northern Ireland

Abstract The Triassic Mercia Mudstone Group of County Antrim, Northern Ireland, is dominated by red beds and evaporites. After only limited study, both marine and continental environments have been proposed previously. Here, we describe these rocks for the first time from core and petrographic observations to interpret depositional environments and conditions, such as water depth, salinity, and aridity. Bedded halite, bedded gypsum, displacive halite, and red siliciclastic mudstone lithologies comprise most (∼ 80%) of the 591.6-m-thick Mercia Mudstone Group in the Gaelectric Carnduff-2 core. Bedded halite consists of chevron and cornet crystals, indicating bottom-growth from shallow surface brines. Bedded-gypsum lithology is composed of halite-replaced pseudomorphs after swallowtail, bottom-growth gypsum crystals. Both bedded halite and bedded gypsum contain dissolution features and are commonly overlain by mud drapes. Bedded-halite and bedded-gypsum lithologies are interpreted to have formed in shallow saline lakes influenced by flooding and evapoconcentration. The displacive-halite lithology is composed of sub-cubic halite crystals, randomly oriented in mudstone, and represents deposition in a saline mudflat. Some mudstones contain ripple cross-lamination, dewatering structures, mudcracks, and rip-up clasts, suggesting shallow surface water and desiccation. Other mudstones are massive (structureless) and may have been deposited by wind. Both of these mudstone units were likely deposited in dry mudflats. Other red mudstones contain soil slickensides, blocky peds, and circumgranular cracks and are interpreted as paleosols. Our observations indicate that the Triassic Mercia Mudstone Group was formed by shallow perennial saline lakes and associated continental environments in an arid climate. Furthermore, lack of carbonates, lack of fossils, and paucity of organic matter suggest acid saline lakes and groundwaters. The Triassic Mercia Mudstone Group is similar to some other Pangean red beds and evaporites. Therefore, we hypothesize that the supercontinent was an arid barren landscape hosting acid-saline lakes.

Contrasting Siliciclastic-Evaporite Strata In Subsurface and Outcrop: An Example From the Permian Nippewalla Group of Kansas, U.S.A

Abstract Geologists tend to expect that rocks as they appear in outcrop are a very good approximation of the same strata in the subsurface. But this is not the case in mixed siliciclastic–evaporite units, strata that contain both a siliciclastic and an evaporite mineral component. Distinct differences in lithologic and stratigraphic descriptions of ancient siliciclastic–evaporite strata exist between outcrop and core. These differences present challenges in stratigraphic nomenclature, lithologic correlation, age determinations, and interpretations about past depositional environments, diagenetic history, and paleoclimate. An example of siliciclastic–evaporite strata is the middle Permian to early Triassic gypsum- and/or anhydrite- (hereby referred to as gypsum/anhydrite) and halite-bearing red beds throughout the midcontinent of North America and equivalent strata from other Pangean deposits. Here, we use core and field observations of the middle Permian Nippewalla Group in Kansas to show the range of similarities and differences in lithologies and thicknesses of specific lithofacies in outcrop and at various depths. For example, the displacive halite lithology, consisting of red mudstones dominated by randomly oriented halite crystals, is abundant in cores and interpreted as saline mudflat deposits. The outcrop counterpart is less common, friable, massive red mudstones with some gypsum/anhydrite pseudomorphs after displacive halite crystals. We interpret these lithologic differences of this saline mudflat lithofacies as the result of excellent preservation of buried displacive halite and late-stage dissolution of near-surface halite. Additionally, bedded halite and intergranular halite cements in siltstones and sandstones are also vulnerable to late-stage dissolution near the surface, further modifying lithologies and thicknesses. Thickness of the Nippewalla Group in the Amoco Rebecca K. Bounds core of western Kansas is 931 feet (∼ 284 meters) thick, but it is estimated to be only half as thick in the outcrop belt of south-central Kansas. To estimate amount of rock lost to late-stage dissolution, we conducted dissolution experiments on displacive halite units from cores, which resulted in 60–95% loss of rock thickness and mass due to dissolution of halite. The unconsolidated red sediment resulting from these dissolution experiments compares favorably with much of the fine massive red siliciclastics that make up the greater part of the Nippewalla Group outcrops. We propose that major lithologic differences resulting from near-surface diagenetic processes must be expected in any evaporite-bearing siliciclastic unit. Besides guiding correlation attempts between surface and subsurface, this knowledge is vital for making accurate interpretations of depositional and diagenetic history of siliciclastic–evaporite units.

Structural and textural characteristics of surface halite crusts of a supratidal, ephemeral halite pan, South Jeddah, Red Sea Coast, Saudi Arabia

Two saline (halite and gypsum) pans have recently developed overlying lagoonal and sabkha sediments in the Şarūm area, south Jeddah, Saudi Arabia, as a result of the construction of an asphaltic road 30 years ago. Structural and textural characteristics of the halite layers reflect their formation during flooding, evaporative concentration, and desiccation stages of the ephemeral halite pan. The flooding stage textures record partial dissolution of the halite crusts, resulting in the formation of truncation surfaces, microkarst pits, pipes, and vugs. Microbial mats can flourish within dissolution vugs, despite the ambient high salinity of the brine. The evaporative concentration stage is characterized by the formation of thick, flat, halite crusts, in addition to isolated masses resembling cauliflowers, mushrooms, and platforms. The halite crusts and isolated masses consist of cumulate rafts and pyramidal hoppers, chevrons, and cornets. Agitation of the brine by waves or currents induced by wind favors the formation of rippled and clastic halite. Desiccation stage textures are represented by polygonal fractures and ridges, chaotic mud-halite filling microkarst pits and pipes, overgrowths, and displacive and efflorescent halite crystals. Field and petrographic studies and major element geochemistry of the brine indicate that the main recharge to the halite pan is from numerous seawater seepage points without direct connection to the Red Sea water or surface drainage. The results of this study provide valuable sedimentological information that could be useful in the interpretation of similar ancient halite.

Magnesite formation by microbial activity: Evidence from a Miocene hypersaline lake

This paper provides an ancient analogue for biologically mediated magnesite in lacustrine hypersaline environments. Thin beds of massive to crudely laminated magnesitic marls occur interbedded with mudstone and evaporite facies deposited in a saline lake-mudflat sedimentary system during the Lower Miocene in the Madrid Basin, Central Spain. Exposure of this succession in a recently excavated tunnel and in collected cores offered a good opportunity to study magnesite precipitates that have been preserved in unaltered conditions by primary evaporitic minerals. Specifically, magnesite arranged as host matrix between and enclosed by displacive halite and glauberite crystals occurs closely associated with abundant microfossils embedded in sheets of organic matter, interpreted as the remains of extracellular polymeric substances (EPS). Even, many magnesite clots are seen to have resulted from the agglutination of fossilized bacterial bodies forming a biofilm. The close and pervasive association of microorganisms and magnesite is used as evidence that microbes played a fundamental role in the precipitation of this mineral. Additional traces of microorganisms and microbial activity observed in magnesite beds include the isotopic ratios in the carbonates, with the δ13C(PDB) value averaging −6.2‰, the presence of carbonaceous film-like structures and the association with patchly-distributed pyrite and celestite minerals. On the basis of the combined sedimentological, mineralogical, chemical and morphological signatures of the magnesitic deposits, it is postulated that carbonate crystals precipitated in microbial mats. Magnesite crystals together with celestite, local barite, and/or pyrite have been also observed to replace silicate and sulphate minerals. It is suggested that magnesite precipitation was biochemically coupled with the early dissolution of the associated sedimentary minerals. Microbes may have used the associated minerals as source of energy and/or of essential elements.

Messinian halite and residual facies in the Crotone basin (Calabria, Italy)

Abstract The Neogene Crotone basin in eastern Calabria contains extensive Messinian evaporite deposits, including thick gypsarenite and halite. The halite deposit reaches a maximum thickness of c . 300 m and in some areas forms relatively small diapirs piercing late Messinian and Pliocene sediments. Halite is strongly modified by folding and recrystallization, but a few primary features are preserved. Four primary halite facies have been recognized: (a) banded halite consisting of folded white and dark bands deposited in a salt pan and/or saline mudflat; (b) white facies, massive halite containing anhydrite nodules, probably formed in a variably desiccating saline lake; (c) clear facies made up of a mosaic of large blocky halite crystals separated by mud, possibly the product of displacive halite growth in a saline mudflat; and (d) breccia facies, a product of dissolution of halite/mudstone/siltstone layers. Residual facies formed from halite dissolution are present as both weld and cap rocks. Weld rocks are thick, undeformed, and composed only of insoluble phases originally included in the salt, whereas cap rocks are thin, strongly sheared and include clasts from the cover rocks.

Paleoproterozoic Stark Formation, Athapuscow Basin, Northwest Canada: Record of Cratonic-Scale Salinity Crisis

ABSTRACT The Paleoproterozoic Stark Formation, a thick breccia unit, formed during the transition from marine to non-marine foreland basin fill in the Athapuscow Basin, Northwest Territories, Canada. Four types of breccia occur in the Stark Formation: (1) bedded breccias at the base of the unit, overlying the basinal facies of the underlying Pethei Group, are interpreted as debris flows, (2) massive chaotic breccias occur in the lower part of the Stark Formation throughout the basin and these are interpreted to be evaporite-collapse breccias; (3) siltstone and mudstone breccia occurs in the upper part of the Stark Formation and is also interpreted as evaporite collapse breccia, though much less evaporite was involved in its formation than the underlying chaotic breccia; and (4) laminar accretionary breccia consisting of laminar carbonate clasts, commonly with flat bottoms and convex-up upper surface geometries; these clasts occur in lenticular pods and are interpreted to form in caves following dissolution of evaporites or carbonates. The widespread presence and abundance of evaporite pseudomorphs (especially halite) in all breccia types, the stratigraphic restriction of the Stark Formation, and irregular filling above this unit indicates that all but the bedded breccia formed by the dissolution and collapse of evaporites. Chaotic breccia directly above underlying Pethei Group shallow-water and deep-water carbonates indicates the evaporates formed across the platform and adjacent deep basin. Foundered megaclasts (up to 1.5 km long and 40 m thick) in basinal settings suggest cumulative evaporite thicknesses on the order of a few tens to a few hundreds of meters. Carbonate clasts in all the breccias contain abundant wave ripples, planar laminations, stromatolites, and ooids. These structures along with a paucity of subaerial exposure features indicates nearly all carbonate deposition in the Stark was subaqueous. Thus, by inference the evaporites in the Stark Formation were also partially subaqueous. Displacive halite pseudomorphs are common throughout all facies in the Stark Formation. Silicified and dolomite-filled halite pseudomorphs are common along the contact between the evaporite-collapse breccia and underlying carbonate platform (Pethei Group) and surrounding large clasts in basinal settings. Silicified hopper crystal casts within deep-water rhythmites of the uppermost Pethei Group indicate precipitation of halite over deep waters. Gypsum pseudomorphs are exceedingly rare, and anhydrite pseudomorphs were not observed. The dominance of halite features in this basin and two penecontemporaneous basins (Kilihigok Basin and Wopmay Orogen) surrounding the Slave Craton suggests that, relative to the present day, seawater at 1.9 to 1.8 Ga was oversaturated with respect to calcium carbonate, had higher HCO3- concentration, and possibly was depleted in SO42-. The dearth of extensive, thick-bedded marine gypsum in the Archean and early Paleoproterozoic can be explained by low atmospheric oxygen content prior to 2 Ga in conjunction with increased carbonate saturation before 1.6 Ga.

Evaporites and siliciclastics of the Permian Nippewalla Group of Kansas, USA: a case for non‐marine deposition in saline lakes and saline pans

The mid‐Permian Nippewalla Group of Kansas consists of bedded evaporites, red‐bed siliciclastics and grey siliciclastics deposited in a non‐marine environment. Lithologies and sedimentary features indicate lacustrine and aeolian deposition, subaerial exposure and palaeosol formation. Grey siliciclastic mudstones characterized by planar and convolute laminations, ostracods, peloids and plant material represent a freshwater‐brackish perennial lake facies. Bedded anhydrites containing gypsum‐crystal pseudomorphs, clastic anhydrite grains and grey mud drapes and partings suggest deposition in saline lakes. Bedded halites consist of chevron and cumulate crystals, dissolution surfaces and pipes and mudcracked microcrystalline salt crusts, which were deposited in saline pans dominated by flooding, evaporative concentration and desiccation. Chaotic halite, composed of red‐bed mudstone and siltstone with displacive halite crystals, formed in saline mudflats. Red‐bed mudstone and siltstone with little or no displacive halite, but with abundant cracking, root and plant features, suggest deposition in a dry mudflat. Red‐bed sandstone, composed of well‐sorted, well‐rounded quartz grains cemented with halite, indicate aeolian and rare shallow‐water deposition. Most deposition took place in halite‐dominated ephemeral saline lakes surrounded by saline and dry mudflats, sandflats and sand dunes. Evaporation, desiccation, flooding and wind played significant roles in this environment. The Nippewalla Group siliciclastics and evaporites represent an evolution from a perennial lacustrine system to a non‐marine, acidic saline pan system in the mid‐continent of North America. The problem of distinguishing between ancient marine and non‐marine evaporites, as well as recognizing those evaporites deposited in acid settings, with detailed field, core and petrographical study of both evaporite deposits and associated sedimentary rocks has successfully been addressed. In addition, interpretations of mid‐Permian palaeoclimate data in the form of short‐term air temperature proxies within longer‐term wet–dry trends have been made. These data provide a new palaeogeographic and palaeoclimatic model for the mid‐Permian of western Pangaea.

Sedimentology of Ancient Saline Pans: An Example from the Permian Opeche Shale, Williston Basin, North Dakota, U.S.A.

ABSTRACT The mid-Permian Opeche Shale of North Dakota consists of bedded evaporites and red-bed siliciclastics. Detailed core and petrographic study has documented sedimentary and early diagenetic features in order to develop a depositional model, and to refine paleoclimatic data and paleogeographic setting for the late Paleozoic of the U.S. midcontinent. Lithologies and sedimentary features indicate lacustrine, distal alluvial, and minor eolian deposition, subaerial exposure, and soil formation. Bedded halites consisting of chevron and cumulate crystals, dissolution surfaces and pipes, and mudcracked microcrystalline salt crusts were deposited in a saline pan dominated by flooding, evaporative concentration, and desiccation. Bedded halites containing chevron and cumulate crystals but lacking any dissolution or desiccation features formed in perennial saline lakes. Chaotic halite, composed of red mudstone and siltstone with displacive halite crystals, represents saline mudflat deposits. Red mudstone and siltstone with little or no displacive halite but with abundant cracks and root features suggest deposition in a dry mudflat. Red-bed sandstones and conglomerates, composed of poorly sorted, subrounded quartz grains cemented with halite indicate distal alluvial deposition with possible transport by ephemeral streams, sheet floods, and debris flows. Most deposition took place in halite-dominated shallow perennial and ephemeral saline lakes surrounded by saline and dry mudflats. Evaporation, desiccation, flooding, and wind played significant roles in this environment. Therefore, the Opeche evaporites and red beds are representative of an ancient saline pan system. An inland playa setting is favored as a depositional model for the Opeche Shale. The abundance of soil features and halite dominance, as well as lack of nearshore carbonates and lack of restricted marine fossils, suggest a closed-basin nonmarine setting for the mid Permian of the U.S. midcontinent.

Sedimentology of the Cretaceous Maha Sarakham evaporites in the Khorat Plateau of northeastern Thailand

Evaporites of the Cretaceous to early Tertiary Maha Sarakham Formation on the Khorat Plateau of southeast Asia (Thailand and Laos) are composed of three depositional members that each include evaporitic successions, each overlain by non-marine clastic red beds, and are present in both the Khorat and the Sakon Nakhon sub-basins. These two basins are presently separated by the northwest-trending Phu Phan anticline. The thickness of the formation averages 250 m but is up to 1.1 km thick in some areas. In both basins it thickens towards the basin centre suggesting differential basin subsidence preceding or during sedimentation. The stratigraphy, lithological character and mineralogy of the evaporites and clastics are identical in both basins suggesting that they were probably connected during deposition. Evaporites include thick successions of halite, anhydrite and a considerable accumulation of potassic minerals (sylvite and carnallite) but contain some tachyhydrite, and minor amounts of borates. During the deposition of halite the basin was subjected to repeated inflow of fresher marine water that resulted in the formation of anhydrite marker beds. Sedimentary facies and textures of both halite and anhydrite suggest deposition in a shallow saline-pan environment. Many halite beds, however, contain a curious `sieve-like' fabric marked by skeletal anhydrite outlines of gypsum precursor crystals and are the product of early diagenetic replacement by halite of primary shallow-water gypsum. The δ 34 S isotopic values obtained from different types of anhydrite interbedded with halite range from 14.3‰ to 17.0‰ (CDT), suggesting a marine origin for this sulphate. Bromine concentration in the halite of the Lower Member begins around 70 ppm and systematically increases upward to 400 ppm below the potash-rich zone, also suggesting evaporation of largely marine waters. In the Middle Member the initial concentration of bromine in halite is 200 ppm, rising to 450 ppm in the upper part of this member. The bromine concentration in the Upper Member exhibits uniform upward increase and ranges from 200 to 300 ppm. The presence of tachyhydrite in association with the potassic salts was probably the result of: (1) the large volumes of halite replacement of gypsum, on a bed by bed basis, releasing calcium back into the restricted waters of the basin; and (2) early hydrothermal input of calcium chloride-rich waters. The borates associated with potash-rich beds likely resulted from erosion and influx of water from surrounding granitic terrains; however, hydrothermal influx is also possible. Interbedded with the evaporites are non-marine red beds that are also evaporative, with displacive anhydrite nodules and beds and considerable amounts of displacive halite. The δ 34 S isotopic values of this anhydrite have non-marine values, ranging from 6.4‰ to 10.9‰ (CDT). These data indicate that the Khorat and Sakhon Nakhon basins underwent periods of marine influx due to relative world sea-level rise but were sporadically isolated from the world ocean.

Alate halite in the late Permian Rotten Marl of Tees-side, north-east England

SUMMARY Scattered delicate, unusually alate crystals of displacive halite occur in the late Permian Rotten Marl of north-east England. Where they intersect, they locally give rise to complex networks of thin vein-like halite sheets. The alate halite appears to have been formed after compaction of the host sediment was complete or nearly so, but before it became brittle enough to fracture.

Water Table Controlled Syndepositional Alteration Textures and Fabrics in Salt Pan Halite: Modern Analogues and Ancient Examples

At the Devil's Golf Course, Death Valley, CA, vadose zone and phreatic zone alteration of subaqueously accumulated halite produces characteristic textures and fabrics that are recognizable in ancient salt pan halite (Late Permian Salado Formation) exposed in a shaft at the Waste Isolation Pilot Plant. Water table depth and duration control fabric type. The crystal size of surficial halite is reduced by hygroscopic alteration. Efflorescent crusts extend the capillary fringe to the surface along vertical permeability pathways. When the water table is shallow, planar dissolution in the vadose zone removes all or most halite from successive thin depositional sequences and progressively disrupts strata consisting of clay or sulfate into irregular strata, stringers, isolated blebs, and, ultimately, 'blebby' laminae. With a deeper water table, point dissolution occurs along vertically oriented permeability pathways (e.g., polygonal margins) producing characteristic textures. Vertical pits, pipes, and macropores form first. Then the surface becomes slightly hummocky as point solution pathways to the water table widen and coalesce. A complex terrain of spires, hummocks, and columns develops and exhibits characteristic pods and lenses of fine halite surrounded by and containing solution lags of insoluble material. Relief is reduced by solution, and lenses and pods of fine halitemore » become smaller and less common. Ultimately, halite is entirely removed leaving only insoluble material. Halite cements grow in the phreatic zone. Halite passively fills voids in more mechanically competent halite. Displacive halite cements dilate fabrics within less competent bedded halite. These textures can be integrated into an idealized lithologic sequence for ancient salt pan halite.« less

Diagenesis of Saline Pan Halite: Comparison of Petrographic Features of Modern, Quaternary and Permian Halites

ABSTRACT Petrographic studies of modern saline pan halites (Saline Valley, CA; Salina Omotepec, Baja California, Mexico) and Quaternary shallow-buried (0-200 m) halites (Saline Valley, CA; Bristol Dry Lake, CA; Searles Lake, CA; Qarhan saline pan, Qaidam Basin, China; Lake Uyuni, Bolivia) show that the diagenetic modification of halite begins contemporaneously with deposition, is most intense within the upper few meters of burial, and is essentially complete within the first 45 m of burial. Halite crusts from modern saline pans that have undergone repeated episodes of flooding, evaporative concentration, and desiccation contain abundant syndepositional diagenetic features. These mature modern halites are dominated by dissolution textures and fabrics (formed during flood stages) and cementati n textures (formed during desiccation stages). Interlayered mud beds contain varying amounts of displacive halite crystals. At shallow burial depths, halites retain many textural features of mature modern saline pan halite. Halites below the first few meters are no longer susceptible to dissolution from floodwaters but continue to be cemented by clear halite. Within the first 10 m of burial, cementation reduces the porosity of halite crusts to less than 10%. The remaining pore spaces are completely filled by burial depths of approximately 45 m. Displacive growth of halite in muds continues at shallow-burial depths and is probably limited to the first few tens of meters of burial depth. The mechanisms for cementation and displacive growth of halite at shallow-burial depths probably include (1) evaporative concentration of groundwater brines and (2) cooling of surface brines when they sink below the sedime t surface. Undeformed halites from the Permian Salado and Rustler Formations of New Mexico contain delicate syndepositional textures and abundant clear halite cements that are comparable to those observed in modern saline pan halites and shallow-buried halites. The Permian halites are interpreted to have undergone a depositional and early diagenetic history similar to the modern and Quaternary analogs. Complete cementation of saline pan halites at shallow burial depths has important implications for the origin of saline formation waters in sedimentary basins. Parent evaporite brines may not be stored in the pores of halite rocks and later expelled during burial compaction if the rocks are cemented early, and tightly crystallized halite rocks may also impede the downward migration of dense syndepositional brines.

Interfingering of evaporites and red beds: An example from the Queen/Grayburg formation, Texas

Interbedded red sandstone, siltstone, mudstone, anhydrite and halite comprise the Queen/Grayburg formation (Guadalupian) of the Palo Duro Basin. These deposits accumulated in a 28,000 km 2 epicontinental basin that was characterized by regional aridity and episodic, nearly basinwide influx of marine-derived hypersaline waters. In each of several recurrent progradational cycles a variety of environments developed in this basin including eolian dunes, interdune areas, sand sheets, saline mud flats, and broad, shallow expanses of marine-derived brine (salinas). Siliciclastic sources were in the west and northwest whereas brines were derived from the south and southwest. Eolian dune deposits are represented by medium- to high-angle (15–35°) cross-stratified, fine-grained sandstone. Interdune areas accumulated flat- to low-angle bedded, wind-rippled strata, which are moderately to well sorted, fine-grained sand with frosted grains and illuviation structures. Sand sheets are characterized by deposits of horizontally bedded, rippled to massive, well-sorted, very fine-grained sandstone with illuviation structures. Sheetwash deposition on sand sheets and mud flats produced sandstones and siltstones with graded bedding, ripples with mud drapes, and intraclasts, and also flaser-bedded siltstones and mudstones deformed internally probably by haloturbation. Saline mud flats produced admixtures of mud and coarsely crystalline halite (chaotic halite-mudstone) and were located on the margins of regionally extensive hypersaline environments (salinas) in which bedded anhydrite and halite were precipitated subaqueously. Queen/Grayburg facies are cyclic and occur in characteristic vertical sequences that comprise, from base to top, bedded anhydrite, bedded halite, chaotic halite-mudstone, fine-grained clastics with displacive halite, siltstone and mudstone with deformed ripples, and eolian clastics. The sharp contacts between these shallowing-upward sequences suggest that transgressions were rapid.

Multiple Applications of Dipmeter Curves for Analyzing Evaporite Formations: Examples from Paleogene of Bresse Trough, France

The microresistivity curves recorded by dipmeters give much diverse information about evaporitic formations because these curves have a fine vertical resolution (approximately 1 cm) and show the very high contrast in resistivity between evaporites (with high resistivity) and clay and carbonate rocks, which are porous and conductive. Examples are taken from the Paleogene salt sequence and its overlying formations of the Bresse Trough in southeastern France. The consistency of the 4 to 8 dipmeter curves allows clear recognition of different salt facies (primary salt, secondary salt, and mixed patches of clay and carbonate within displacive halite layers) and sulfate facies (massive anhydrite, nodular anhydrite, etc). The correlation of thin continuous carbonate and clastic beds using resistivity curves discloses, with a high degree of precision, the geometry of the various formations between wells. Examples show the detection of small-magnitude halite dissolution (a few meters vertically) and the lateral effect of anhydrite hydration. In this paper, a method is proposed for determining structural dip of salt beds by computing dip angle and azimuth of thin conductive beds within the salt using the DUALDIP computer program. A frequency distribution plot of these dip angles and azimuths gives a good indication of the dip of the salt beds.

Paleoenvironments of Lower Cretaceous DeQueen Formation of Southwestern Arkansas: ABSTRACT

The Lower Cretaceous DeQueen Formation crops out in a narrow sinuous band extending east-west from Pike County, Arkansas, to near Broken Bow, Oklahoma. Natural exposures are poor, but quarrying has exposed excellent vertical sections of the formation about 75 ft (23 m) thick at several localities. The DeQueen is composed of a lower sulfate facies and an upper sandstone-limestone-shale facies. The lower facies which is correlated with the subsurface Ferry Lake Anhydrite, is about 40 ft (12 m) thick. It is 60% gypsum and 40% dark shale, with minor interbedded mudstones. The upper facies, which is also about 40 ft (12 m) thick, is unconformably overlain by Upper Cretaceous clastic sediments. The upper facies is predominantly shale, with interbedded thin beds of sandstone, sa dy limestone, and celestite. This facies is equivalent to the lowermost beds of the Mooringsport Formation of the subsurface. The environments of deposition of units within the lower sulfate facies have been interpreted from a sparse faunal assemblage, sedimentary structures, and trace fossils. However, the most intensive study has been concerned with the more richly fossiliferous beds of the upper facies of the DeQueen. Present in this unit are well-preserved pseudomorphs of displacive halite hoppers, calcite pseudomorphs after gypsum, and preserved intrastratal gypsum nodules. Oscillation ripples, current ripples, and a variety of trace fossils are very common in these beds also. Body fossil assemblages range from a less diverse restricted pelecypod-ostracod assemblage to a more diverse gastropod-pelecypod-ostracod-serpulid worm assemblage. Marine and terrestrial vertebrates are also common in these upper eds. All of the above information has been incorporated with subsurface data in order to reconstruct the local and regional depositional framework of the DeQueen and its subsurface equivalents. A better understanding of the depositional environment of these rocks will promote interest in, and may lead to the development of, undiscovered hydrocarbon reserves within less-well-known downdip areas. End_of_Article - Last_Page 535------------

Evaporitive Limestone: Its Generation and Diagenesis: ABSTRACT

The Calcare-di-base is the only significant carbonate facies of the upper Miocene evaporites of Sicily. It was deposited within an exceedingly saline but marine water body adjacent to older, exposed carbonate terranes which surround the depositional basin. This somewhat dolomitic limestone is commonly cavernous or brecciated at outcrop and contains numerous zones of evident halite dissolution. It also interfingers with thin gypsum stringers in many areas and overlies diatomites of variable thickness. Based on petrographic and isotopic studies, it appears that this limestone was produced by diagenetic processes from an origininal aragonitic mud containing displacive halite hoppers and massive halite zones. Regional variation in carbon-13 (^dgrC13 from 0 to 49 pp PDB) and oxygen-18 (^dgrO18 from +6 to -5 ppt PDB) can be tied to variations in the mineral content of the original sediment and to later diagenetic waters and their organic content. The very negative carbon-13 values and the presence of native sulfur are indicative of the calcitization of gypsum, the by-product of the life processes of sulfate-reducing bacteria. These bacteria utilize part of the available and commonly copious organic matter associated with both the carbonate and with the diatomite. Inversion of the original aragonite to calcite has resulted in expulsion of strontium from the carbonate crystal lattice and the formation of celestite (SrSO4) which now fills the voids left by the dissolution of halite, and the associate pore spaces. End_of_Article - Last_Page 988------------

ORIGIN OF DOLOMITE MOTTLING IN ORDOVICIAN LIMESTONES FROM SASKATCHEWAN AND MANITOBA

ABSTRACT Dolomite-mottled limestones (and fully dolomitized equivalents) are widely distributed in epeiric successions and constitute the greater part of the Ordovician Yeoman and lower Red River Formations of southern Saskatchewan and Manitoba. In Manitoba they are exploited as building stone (Tyndall Stone) and in this rock the mottles are branching cylindrical structures, composed of dolomite and containing meniscus-filled burrows, that are set within an undolomitized biomicrite matrix. Late diagenetic (Devonian?) dolomitization of mottle-matrices has generated colour-mottled dolomites. Control of dolomitization patterns by burrows and the preferential dolomitization of aragonitic skeleta are insufficient evidence for concluding that dolomitization was penecontemporaneous. The resemblance of mottles to burrow-systems (Spongeliomorpha), and the eccentricity of contained burrows (among other evidence) indicates mottles are replaced burrow-fills, not envelopes of dolomitized sediment around burrows. The relations between mottles, contained burrows and dolomitized fossils indicate that the original sediments underwent extensive synsedimentary lithification and were further modified by multigeneration burrowing, internal sedimentation (as a consequence of burrowing activities), and early-diagenetic dissolution of skeletal aragonite. These processes created a markedly heterogeneous sediment comprising magnesian calcite (?) - cemented matrices that surrounded unlithified sediment-fills of burrows and skeletal aragonite molds. This heterogeneity was exploited by dolomitizing brines causing preferential replacement of the unlithified and more permeable parts of the sediment. Anhydrite pseudomorphs after later-diagenetic halite crystals are restricted to dolomite mottles. This restriction indicates that, when halite grew, the burrow-fills (now mottles) were still unlithified and could be displaced. This implies a persistence in time (until late diagenesis) of the sediment heterogeneity -- a conclusion of importance when attempting to date the dolomitization process. Dolomitization may have occurred at the time overlying Herald (upper Red River) evaporites were deposited, by reaction of the sediments in the still-permeable Yeoman burrow-networks with refluxing magnesium-rich brines capable of precipitating halite. However, the stratigraphic distribution of mottle-dolomitization does not lend support for this interpretation. An inferred resemblance between some environmental variables in ancient epeiric carbonate-depositing environments and those of Holocene deep-water, semi-enclosed basins suggests that the Ordovician sediments may have been largely composed of magnesian calcite. It is believed that magnesium released during stabilization of these magnesian calcites allowed dolomitization of the more permeable parts of the sediment, perhaps early in the diagenetic history. Such dolomitized sediment remained unlithified to allow the late diagenetic growth of displacive halite crystals. End_Page 480------------------------