Original Gypsum Research Articles

Genesis of the Middle Miocene stratabound sulphur deposits of northern Iraq

Stratabound sulphur deposits of northern Iraq occur in folded Middle Miocene evaporites overlying Lower Miocene hydrocarbon reservoirs. Rocks hosting sulphur mainly comprise gypsum, dolomitic marl, carbonate mudstones and bioclastic dolomitized limestones, whereas the mineralized rocks are mainly composed of calcite and sulphur. Sulphur was formed by the oxidation of H 2 S produced from gypsum dissolution followed by sulphate reduction in the presence of hydrocarbons. Sulphate reduction occurred in a partially closed to closed system as reflected by the sulphur δ 34 S values of +7‰ to +20‰ (original gypsum +21‰). Host rock carbonates were calcitized by the dissolved carbonate formed by oxidation of the hydrocarbons, which produced low δ 13 C values ( – 14 to – 32‰). Periodic invasion by meteoric water and elevated temperatures produced 18 O-depleted compositions for the newly-formed calcite (down to – 9‰) and dolomite (down to – 7‰), and oxidized the H 2 S produced during sulphate reduction. These sulphur deposits formed through the favourable stratigraphic juxtaposition of gypsum sulphate, brines and hydrocarbons. Tectonically produced fracture permeability in carbonates allowed rising brines from the underlying hydrocarbon reservoirs to mix with laterally migrating and descending, sulphate-bearing meteoric waters and produced the oscillating redox conditions needed for the bacterial reduction of sulphate and the oxidation of sulphide.

Origin of polyhalite deposits in the Zechstein (Upper Permian) Zdrada platform (northern Poland)

Polyhalite deposits in the Zechstein (Upper Permian) of northern Poland occur in the Lower Werra Anhydrite. In the Zdrada Sulphate Platform, the polyhalite appears to be a very early replacement of anhydrite. The replacement was caused by the halite‐precipitating brines which contained potassium and magnesium ions. The formation of polyhalite was preceded by the syndepositional anhydritization of the original gypsum deposit which has often preserved its primary textures. This anhydritization on the platform and its slopes was a reaction of the precipitated gypsum in a hydrologically open evaporite basin, with brines of salt basins adjacent to the sulphate platform. These brines, when nearly saturated with respect to halite, and potassium and magnesium rich, reacted with anhydrite to precipitate polyhalite along the slopes of the Zdrada Platform. The oxygen and sulphur isotopic compositions of sulphate evaporites indicate that marine solutions were the only source of sulphate ions supplied to the Zechstein basin, and that anhydrite was transformed to polyhalite by reaction with marine brines more concentrated than those that precipitated precursor calcium sulphate minerals.

An applied mineralogical investigation of concrete degradation in a major concrete road bridge

AbstractA core of concrete taken from a major road bridge in the Strathclyde Region, Scotland, has been subjected to an applied mineralogical investigation, which involved stable isotope analysis, petrography, X-ray diffraction and scanning electron microscopy.The structure is actively undergoing severe degradation due to mineral growth which is related to chemical reactions between the concrete and pore fluid. The physical growth of minerals causes disfigurement and structural weakening.Pyrite and pyrrhotine hosted by dolerite aggregate appear to have been oxidized, providing sulphate for the deposition of ettringite and minor gypsum, in spheroidal cavities within the cement paste. The rainwater which passes through the structure mobilising sulphate from original gypsum in the paste and oxidizing the iron sulphides is also involved in the further leaching of elements from the cement paste and in the deposition of calcite. The isotopic values of calcites forming a crust on the concrete and a stalactite under the bridge are similar with δ13C= −19‰ PDB and δ18‰= +16‰ SMOW. We suggest that atmospheric carbon dioxide was the carbon source. The carbon isotopic fractionation of −12‰ from atmospheric carbon dioxide of δ13C= −7‰, (O'Neil and Barnes, 1971) can best be explained as due to a kinetic fractionation related to the hyper-basicity of the pore water. The equilibrium formation temperature of about 45°C calculated from the oxygen isotope values and assuming a δ18O value of meteoric water of −8‰ SMOW, is considered unreasonable. The exceptionally low δ18O values are attributed mainly to reaction kinetics and the calcite inheriting its oxygen, two-thirds from atmospheric carbon dioxide and one third from the meteoric formation water (O'Neil and Barnes, 1971). A δ18O value of atmospheric carbon dioxide of +41‰ SMOW and a δ18O value of meteoric water of −8‰ SMOW, lead to a calculated δ18O value for the calcites of +10‰ SMOW. The calcites analysed have a value of +16‰ and this may be due to partial re-equilibration towards a calculated value of +21‰ for calcite in equilibrium with the meteoric water at 20°C.

Celestite replacements of evaporites in the Salina Group

Replacements of evaporites by celestite were discovered recently at three sites in northwestern Ohio. These replacements are more durable than the original evaporites and provide new paleoenvironmental data for the upper Silurian rocks of the region. The occurrences are situated along the western margin of the Ohio (Cayugan) Basin and appear in the Greenfield Dolomite and in undifferentiated Salina dolostones. The replacements include: lenticular and prismatic crystals of gypsum, nodules of anhydrite and laminar evaporites. The lenticular crystals contain inclusions of carbonate and anhydrite, and are believed to have altered to anhydrite prior to replacement. The prismatic crystals are exceptionally well-preserved, with euhedral, deeply embayed outlines and internally zoned growth bands containing large numbers of inclusions of dolostone and anhydrite. Optical data for the latter crystals indicate that they are oriented replacements of gypsum, and suggest that the original gypsum was unchanged prior to replacement. The nodular and laminar occurrences display features such as chicken-wire and enterolithic structures, and were comprised of anhydrite prior to replacement. Replacement postdates the dolomitization and cementation of the Salina sediments enclosing the evaporites, but occurred prior to deep burial. The rocks hosting the replacements, therefore, did not provide the strontium. The strontium may have been released from dolomitization of the underlying Lockport (Niagaran) beds or from dissolution of subaerially exposed Salina gypsum prior to the middle Devonian.

Correlation of Beds Within Ferry Lake Anhydrite of Gulf Coastal Plain: ABSTRACT

The Lower Cretaceous Ferry Lake Anhydrite is one of the most distinctive, widespread sedimentary units within the Gulf coastal plain. The formation extends from east Texas across southern Arkansas, northern Louisiana, central Mississippi, and southern Alabama, all the way to south Florida where it has been correlated with anhydrite beds of the Punta Gorda formation. The formation consists of alternating carbonates, claystones, and sulfate beds (altered from original gypsum to anhydrite during burial) deposited in a predominantly subaqueous environment within a broad lagoon located shoreward of an extensive reef fringing the shelf edge. Highly resistive anhydrite beds within the Ferry Lake Anhydrite, and within formations above and below, may be correlated across east Texas, Arkansas, Louisiana, and Mississippi, using a network of closely spaced electrical logs. The geographic distribution of these anhydrite beds is variable. Some anhydrite beds may be traced across the entire area, whereas other beds are less widespread. The difference in geographic distribution of these beds reflects the variation in size and configuration of the extensive lagoonal sea in which they were deposited. Water depth, positive conditions around stable areas, subsidence, duration of each evaporitive pulse, and areal salinity variation are among the factors that controlled the thickness of individual beds accumulating within the lagoon. End_of_Article - Last_Page 1428------------

Upper Jurassic Carbonate Deposition, Smackover and Buckner Formations, East Texas: ABSTRACT

Examination of cores from the upper Smackover Formation from 30 wells in east Texas confirms the presence of a belt of blanket high-energy ooid sandstone throughout much of the area. Pockets of lower energy deposits within this ooid grainstone belt are characterized by pellet-Favreina packstones and End_Page 442------------------------------ grainstones and ooid-rhodolite packstones and grainstones. In the easternmost part of the study area, ooid grainstones grade updip into lower energy lagoonal facies including pellet and Favreina wackestones and packstones. These lagoonal deposits are not as widespread to the west. Lower in the Smackover, low-energy skeletal, pellet and oncolite wackestones and packstones dominate. Two cores contain coralgal fragments suggesting nearby reef development. The overlying lower Buckner Formation is composed dominantly of red beds and evaporites deposited in a sabkha setting. The presence of thick red beds in cores from the western part of the study area suggests a strong continental influence. Anhydrite is the major evaporite mineral in the lower Buckner. It is present as displacive mosaic and nodular mosaic masses in red beds and dolomitic mudstones. Partial preservation of some original gypsum crystal outlines provides evidence for lesser amounts of primary evaporite precipitation. Small amounts of halite are present in some lower Buckner red beds and associated with anhydrite to the west. Environments and depocenters within the Buckner are thought to have ben partly controlled by movement of the underlying Louann Salt and by rejuvenati n of basement structures. Major structural influences on Smackover and Buckner deposition or present distribution include the Mexia-Talco fault system, the Sabine uplift, and Louann salt structures. Movement along the Mexia-Talco fault system began in Late Jurassic time and may have affected Smackover and Buckner deposition to an as yet undetermined extent. The extent of the influence of the incipient Sabine uplift on deposition in east Texas has not been determined, although studies to date suggest that it had a significant effect on facies development and on the configuration of the Smackover-Buckner carbonate shelf and associated basin. The major influence of Louann Salt movement on Smackover and Buckner deposition is confined to the western half of the study area. Salt movement began after the close of Smackover time. Withdrawal of Louann Salt into ridges formed a series of strike-trending linear troughs in the western part of the study area. The Buckner Formation thickens dramatically within the linear troughs, suggesting possible salt movement during Buckner time. A second linear zone of thickened Buckner section, apparently unrelated to Louann Salt movement, lies to the northeast of the area of salt structures. This strike-oriented Buckner depocenter is well developed in the east and pinches out to the west. Salt is present within the Buckner in the western part of the depocenter. Cross sections constructed from electric logs and data from core analysis demonstrate these relationships and may help delineate potential areas for hydrocarbon exploration. End_of_Article - Last_Page 443------------

Origin of Precambrian iron-formations in the Lake Superior region

The Precambrian banded, cherty iron-formations in the Lake Superior region were deposited on broad continental shelves, and deposits of the supratidal, intertidal, and subtidal zones can be recognized in the well-known facies of the iron-formations. The supratidal deposits were primarily calcitic, aragonitic, and sideritic muds. Other minerals, in order of decreasing abundance, may have been gypsum, anhydrite, ankerite, dolomite, quartz, apatite, and halite. Intraclasts were produced by desiccation-granulation, and some of this material was redeposited in the intertidal and subtidal zones. The intertidal zone was characterized by the development of extensive algal reefs and digital-sized and larger stromatolitic mounds. Desiccation-granulation and tidal rip of mineralized stromatolites further added to the accumulation of intraclasts. The intertidal zone was the domain of granules that were derived by abrasion and rounding of intraclasts. The original mineralogy of the intertidal deposits was similar to that of the supratidal zone; however, because of photosynthesis, the sea water was oxygenated. Lozenge-shaped grains are considered to be secondary, silicified, and iron-oxide replicates of original gypsum crystals, and, by comparison with recent evaporites, some anhydrite and halite may also have been present. The deposits of the intertidal and subtidal zones are considered to be comparable to the present-day Abu Dhabi complex in the Persian Gulf. Spherical microstructures are abundant and well preserved in the chert of the subtidal deposits. Pyrite, which characterizes these deposits, probably was formed largely by the bacterial reduction of sulfate derived from the intertidal zone. The laminations in the iron-formations resulted from several causes that were controlled by chemical and mechanical processes, such as the rates and localization of the precipitation of calcitic, aragonitic, and sideritic muds and the mechanical breakup and redistribution of these sediments as sand, silt, and mud. These processes resulted in compositional and textural laminations. The diversity of the banded, cherty iron-formations, recognized in the different facies, then, can be explained largely in the diagenetic changes. The large-scale pervasive diagenetic changes were the replacement of calcite and aragonite by chert and the formation of iron silicates by the reactions between ionic silica and siderite and iron-bearing dolomite. Vein-like structures and the development of magnetite along stylolites indicate mobility of iron in late diagenetic stages, and iron-organic chelates are suggested to account for the mobility. Depending on the composition of the laminae and the chemical environment, silicification during diagenesis produced the hematite, magnetite, siderite, pyrite, and mixed-mineral facies.

Zur Bestimmung von Gips in Böden

On the determination of gypsum in soilsThe (020) X‐ray reflection of gypsum at 7,56 Å is nearly specific and may be used for detection and quantitative measurement of the mineral in soil samples. By X‐ray powder diffractometry gypsum can be detected as far down as 0,5% by weight. This limit may be extended down to 0,005% by concentration in the density fraction 2,1–2,5 g/cm3. For quantitative measurements references may be prepared from sample parts by dehydration of the original gypsum and adding known quantities of this mineral. So it is possible to compare samples of nearly identical grain size distribution, and mineral contents. This is important in the powder‐diffractometrical quantitative measurement of a mineral with low hardness and good cleavage where mechanical stress during homogenisation lowers the intensities of X‐ray reflections. Under comparable conditions for sample and reference, gypsum contents can be determined in the range of 0,5 to 20% by weight with an accuracy of ± 3% (relative).

Nutrient cycling in grazed pastures. II. Further observations with [35S] gypsum

The incorporation of sulphur-35 (35S) into the wool of sheep grazing radioactive pasture was measured in two successive experiments on the same site following application of [35S]gypsum. Equilibrium between the applied sulphur and sulphur present prior to the application was established at different rates with different rainfall. After 3 years the sulphur from the original gypsum application was still being turned over in the soil-plant-animal system, there had been no change in the total soil sulphur, and a large portion of soil sulphur did not enter the sulphur cycle. A diagram of a proposed sulphur cycle in grazed pasture is given, and the assumptions made are discussed.

Modern Evaporite Deposition and Geochemistry of Coexisting Brines, the Sabkha, Trucial Coast, Arabian Gulf

ABSTRACT Near Abu Dhabi, Trucial Coast, diagenetic evaporite minerals are developed within an accumulation of detrital Pleistocene sands and Recent carbonate sediments which form a supratidal flat (sabkha) 8 miles wide. Field studies were carried out by the author and his co-workers of Imperial College in 1964. A further visit to the Trucial Coast was made by the author in 1967 under the auspices of the Dry Lands Research Institute, Riverside. A study of 260 interstitial brine samples showed that the distribution of the evaporite minerals, which include gypsum, anhydrite, dolomite, and balite, is largely controlled by the hydrology of the area. Interstitial brines within the sabkha sediments are replenished with sea water by abnormally high tides and storm surges. These surface waters, which soak down into the sediments, are concentrated both by solution of soluble salts and by evaporation. The subsequent equilibration between brines and host sediments leads to precipitation of aragonite, gypsum, and halite; alteration of gypsum to anhydrite, and dolomitization of carbonate sediment. A direct correlation exists between the frequency and extent of flooding, the mineral phases developed, and the chemical composition of interstitial brines. Flooding of a 2- to 3-mile wide belt roughly concentric to lagoon margins, occurs at monthly or longer intervals. In this belt, a surface gypsum crystal mush up to 12 inches thick is present which, landwards, is overlain and progressively replaced by anhydrite. Dolomitization is extensive toward the landward margin of this zone. From the lagoon laterally across the 2- to 3-mile wide belt to its landward margin, chlorinity increases from 44 to 155; sulfate concentration rises from 6 to 17 gm/kg and then falls to less than 3 gm/kg; the Mga2+/Ca2+ mole ratio increases from 5.3 to 35 and then decreases to about 4. Concentration of these components decreases with in reasing depth below the sediment surface. Gypsum is the stable calcium sulfate mineral in contact with brines of chlorinities less than 145 and anhydrite at chlorinities greater than 145. An additional 5-mile wide zone is flooded only at 4- to 5-year intervals. The original gypsum crystal mush in this zone is completely replaced by up to a 12-inch thick layer of chicken-wire mesh structure anhydrite, and the carbonates are highly dolomitized. Interstitial brines are Saturated with NaCl at chlorinity 160 and specific gravity 1.20. These brines contain less than 1 gm/kg sulfate and have Mg2+/Ca2+ mole ratios of about 4. In this zone, constant Mg2+/Ca2+ values with increasing magnesium concentration suggest that there has been an approach to mutual equilibrium between brines and evaporite-carbonate minerals. The remaining 1 to 2 miles at the landward margin of the sabkha are underlain by Pleistocene sands and are not flooded by marine waters. Ground waters in this zone are in part terrestrial in origin. Inland across this zone, chlorinity decreases from 160 to 107; the sulfate concentration is 2 gm/kg and the Mg2+/Ca2+ mole ratio averages 3.5. Locally, anhydrite is hydrated to gypsum where brine chlorinity is less than 145. Processes of gypsum precipitation and dolomitization are essentially restricted to the 2- to 3-mile wide belt close to the lagoon margin. In the mid-sabkha, equilibrium conditions probably prevail between brines, diagenetic minerals, and host sediments. Diagenesis at the landward margin of the sabkha is in part retrogressive. Both a progressive and a retrogressive diagenetic facies can be visualized as moving out with the progradation of the shore line. The similarity between the stratigraphy and mineralogy of some Ordovician, Silurian, Pennsylvanian, and Jurassic evaporite sequences and the sabkha on the Trucial Coast suggest that evaporites of supratidal origin may be more common in older evaporite rocks than previously realized.

Étude par microscopie optique et radiocristallographie des sulfates de calcium semihydratés

The comparative study of the textures of the three calcium-sulfate-hemihydrates (α, α low pressure and β), by optical microscopy observation on thin layers, allows us to consider that liquid water is the recrystallisation medium of the hemihydrate during dehydration of gypsum. Diffractometer patterns of these three varieties differ in the intensity of the lines. According to the texture of the original gypsum, the α variety crystallizes either in thin needles or in large elongated crystals having their axis parallel to the (010) planes containing the water molecules of the dihydrate. The three hemihydrates (α, α low pressure and β) may be considered as structuraly identical, the β form showing a very porous submicronic texture.

Compaction Phenomena in Gypsum and Anhydrite: ABSTRACT

End_Page 628------------------------------Anhydrite can be precipitated from natural brine in the presence of gypsum in the temperature range of 60°-70°C. Below this temperature range and within the anhydrite stability field, the rate of growth is extremely slow. Growth of gypsum in brine in the presence of anhydrite within the gypsum stability field is rapid. Recent anhydrite in the Persian Gulf in general occurs above the free-water level in supratidal sediments. It is postulated that this anhydrite is formed in the dark sediments during the hottest summer days and is preserved throughout the year in the partly dry sediments because of lack of water. However, at temperatures below approximately 23°C. in the presence of sea water which has been evaporated to precipitate halite, or at higher temperatures in les concentrated brine, the anhydrite will be dissolved and gypsum will precipitate. Thus, with burial of a few feet below the free-water level, any surface anhydrite should be dissolved easily and gypsum precipitated, at least during winter, at any known mean annual temperature. Only gypsum would be carried into the subsurface, despite the fact that anhydrite may have formed at or near the surface. This gypsum, and all original gypsum, will be replaced by anhydrite with burial to a depth of 500-2,000 feet, depending on the salinity of the subsurface water and on the geothermal gradient. During this stage, there will be at least a 38-per cent volume reduction of the solid. It is unlikely that this volume will be compensated by addition of anhydrite from an outside source because of the gene ation of abnormal fluid pressure and, thus, outward water flow during the gypsum-anhydrite replacement. Anhydrite in the subsurface commonly is devoid of pore space, indicating additional compaction. Therefore, ancient anhydrite sections must represent approximately one-third of their original depositional thickness. Because much of the volume reduction is delayed, the compaction and any dissolution of evaporites provide a mechanism for increasing and perpetuating the subsidence of an established evaporite basin in addition to and after its tectonic history. End_of_Article - Last_Page 629------------

The Effect of Gypsum on Core Analysis Results

Published in Petroleum Transactions, AIME, Volume 216, 1959, pages 221–224. Abstract The presence of gypsum in samples subjected to standard core analysis introduces serious errors in the measurement of water saturation and porosity. The magnitude of these errors, depending upon the type of analysis procedure used, has been evaluated experimentally and theoretically. Water-saturated pore volumes determined by vacuum distillation or retort procedures may be too high by as much as 48 per cent of the volume of gypsum present. The maximum error in this value determined by Dean-Stark extraction with toluene is 36 per cent of the gypsum volume. If pore space is measured by a Boyle's law type porosimeter the maximum error due to gypsum is 38 per cent of the original gypsum volume present. The conscientious core analyst may eliminate the errors caused by gypsum by either of two methods. He may apply suitable corrections for the water of crystallization removed from gypsum, or take special precautions to prevent dehydration of gypsum during core cleaning and analysis procedures. These alternatives are discussed and methods for obtaining reliable core analysis data are proposed. Introduction Gypsum (CaSO42H2O) occurs as a common mineral in many of the world's sedimentary basins. In addition to its presence as primary bedded evaporitic deposits, it is often found as secondary replacement zones and pore-fillings in host rocks. That it may cause false indications in porosity, both on neutron logs and in standard core analysis, has been generally recognized. False porosity interpretations from neutron logs result because the chemically bound water in gypsum attenuates neutrons as effectively as free water. Errors in core analysis result when gypsum is dehydrated prior to or during the analysis. Vacuum retort procedures used by many laboratories to determine fluid saturation and porosity effect a complete removal of water of crystallization from gypsum. The crystal water, distilled and collected with free water from the sample, is counted as water-saturated pore space.