Gypsum Layers Research Articles

Weathering crust and karren on exposed gypsum surfaces

The evolution of gypsum bare rock surfaces is the result both of volume changes of the outer rock layer and mass wasting by dissolutional processes. Some unusual weathering processes induce an increase in the volume of the outer gypsum layer, resulting in the development of a “weathering crust” and of characteristic forms such as small ridges and bubbles. However, the more typical erosional forms are dissolutional ones of karren type, which are commonly interconnected, or superimposed upon the previously described forms. In this chapter a classification system is proposed and discussed, within which the magnitude, order and geometry of the different karren forms are outlined, and the related lithofacies and main morphogenetic processes are examined.

Deformation and sedimentation around active Miocene salt diapirs on the Tihama Plain, northwest Yemen

Abstract The Al Salif and Jabal al Milh salt diapirs of Miocene age cut through a 4–5 km thick overburden of Miocene to Recent sedimentary rocks in the southern Red Sea. The Al Salif diapir is part of a north-south oriented diapiric wall which has caused updoming of the overburden and active extensional faulting. The halite is folded into tight to isoclinal subvertical folds, with largescale rafts of interbedded gypsum-anhydrite boudinaged on the fold limbs. There is no evidence for large-scale overburden stoping or injection of salt into overlying faults and fractures, and the upward movement of the salt dome is probably caused by the overburden being forced aside and sliding off the dome. The upper surface of the salt is an undulating smooth surface which was exposed at the sea-floor during the Quaternary. Coral reefs with 14 C ages of 3700 a have been raised up to an elevation of 17 m above present-day sea-level, giving a surface uplift rate of 4.6 mm a −1 . At the Jabal Al Milh diapir, recumbent folding and thrusting are the main deformation features observed in the siltstones and gypsum layers of the overburden. The overburden has been rotated to the vertical at least 200 m from the diapir walls. The folding and thrusting is interpreted to be caused by overflow of salt in a namakier. This study shows that overburden sediments above the Al Salif diapir extended to allow sediments to slide from the salt dome crest by listric faulting, whereas sediments underlying the Jabal al Milh salt glacier were sheared and shortened in the horizontal direction.

Depositional Setting of the Upper Jurassic Hith Anhydrite of the Arabian Gulf: An Analog to Holocene Evaporites of the United Arab Emirates and Lake MacLeod of Western Australia

The Upper Jurassic Hith Anhydrite is a major hydrocarbon seal in the Arabian Gulf region. Outcrops, core samples from the subsurface, and the literature indicate that the Hith Formation is composed mainly of anhydrite. In most locations where a section of the Hith Formation has been measured, this unit contains less than 20% carbonate, much of which is in the form of thin laminations. This lack of carbonate, locally thick layers of salt, and the predominance of anhydrite favor a playa for the setting in which this sediment was accumulated. In fact, much of the Hith has the sedimentary characteristics of the Holocene Lake MacLeod playa of Western Australia, which is dominated by layers of gypsum and halite (what little carbonate that occurs is found in layers at the base o the section). Locally the Hith appears to have accumulated in a sabkha setting, particularly toward central Abu Dhabi where it pinches out into shallow-water, and peritidal carbonate. This sabkha setting is indicated by the interbedded relationship of the Hith anhydrites with these carbonates and the local predominance of horizontally flattened nodules and enterolithic layers of anhydrite. These latter features match some of the characteristic fabrics found in the Holocene coastal sabkhas of the United Arab Emirates. As with the local occurrences in the Hith, the Holocene sabkhas are dominated by carbonates and are divisible into a series of lateral facies belts. These are also expressed as equivalent vertical layers. Traced from seaward to landward, or from the base of the vertical sequence upward these facies are characterized by (1) algal mat, (2) a layer of a gypsum crystal mush (3) active anhydrite replacement of gypsum (4) anhydrite with no gypsum mush, and (5) recycled eolianite and storm-washover sediments.

Pseudomorphism of gypsum after calcite, a new textural feature accounting for the marble sulphation mechanism

Petrographical investigations were performed on a naturally badly decayed Carrara marble statue covered with a black crust. On thin sections (parallel nicols) the sulphation zone was found to be constituted of two layers: the outer one (0.1–3 mm thick) contained allogenic particles that gave it a dark aspect; the inner one, 150–200 μm thick, looked clear because no allogenic particle could be seen within it. The texture of this clear gypsum layer suggested that it was the consequence of a pseudomorphism process, i.e. transformation of calcite into gypsum without any change in shape or volume of the crystals, even cleavages being conserved. This specificity suggested that the only part of the sulphation zone that could be called “black crust” was the outer dark gypsum layer. Different morphologies observed within the clear gypsum layer were assumed to represent different steps of its formation. These steps would be the following: (1) marble thermal microfracturing; (2) highly localized inward formation of gypsum rims lining the boundaries and cleavages of the calcite crystals; (3) dissolution of calcite grains by sulphuric acid and subsequent formation of hollow gypsum boxwork; (4) precipitation of gypsum within all the voids left, i.e. gypsum boxwork and thermal cracks. The occurrence of pseudomorphism just beneath the stone surface has important implications for stone conservation. Owing to the volume and shape conservation related to pseudommorphism, the surface details of the original sculpture were well preserved under the black crust, despite substitution of calcite by gypsum. Thus, it is suggested that if a clear gypsum layer occurs underneath black crusts on marble statues, it should be conserved when the stone is cleaned.

Early-Holocene geochemical evolution of saline Medicine Lake, South Dakota

Medicine Lake is a highly saline, meromictic, magnesium sulfate, closed-basin lake in northeastern South Dakota. The geochemical, mineralogical, and magnetic stratigraphies of sediments deposited from about 10.8 to 4.5 ka B.P. document the evolution of the saline brine in response to climatic change in the early to mid-Holocene. During the spruce occupation of the Medicine Lake catchment (10.8–10.0 ka B.P.), dark-grey massive basal sediments with low total-sulfur and carbonate content, upwardly increasing organic-carbon content, and high magnetic susceptibility were deposited in a deep freshwater lake. As the vegetation in the area changed from spruce to birch to oak and elm and finally to prairie between 10.0 and 9.2 ka B.P., and as the lake became shallow and salinity increased from 10%, light-and dark-grey calcareous and organic-carbon-rich banded sediments with low total-sulfur content and low magnetic susceptibility were deposited. Previous studies have shown that during the forest/prairie transition the lake then changed abruptly from fresh to saline as it lost a substantial portion of its volume. During the early prairie period (9.2–5.5 ka B.P.), alternating sections of aragonite-rich laminae and grey massive sediments with high total-sulfur content and multiple gypsum layers were deposited in a meromictic environment under conditions of fluctuating lake levels and salinity. Continued aridity during the mid-Holocene (5.5–4.5 ka B.P.) probably maintained the lake at relatively low levels and high salinity as dark-grey generally massive sediments with moderate total-sulfur, carbonate, and organic-carbon content and no measurable magnetic susceptibility were deposited.

Geochemical evolution of Lake Deborah East, prototype salt lake in the relict drainage of the Yilgarn River of Western Australia

Lake Deborah East is a playa lake in the relict drainage of the Yilgarn River. Its surface is covered by a thick salt crust underlain by stratified lacustrine deposits of unconsolidated evaporite minerals intercalated with clay and sand. Halite has formed from groundwater and surface water sources through a continuous process of salt recycling accompanied by rejection of bromide by the crust, and high bromide and bitterns have built up in the brines. The lower part of the sequence was deposited during the Late Tertiary and the top 2 m during the Quaternary. The salt budget indicates prolonged arid periods during which no salt has been added to the lake and suggests additional losses by deflation and overflow during other periods. The distinct layering in the lake, the presence of gypsum and salt layers within the lake sediment, supersaturation of the brines with respect to gypsum and halite at depth, and the distinct pattern of groundwater discharge into the lake, suggest that the mudstone layers at the b...

Microstructural and microanalytical studies of sulfate attack. I. Ordinary portland cement paste

Portland cement pastes that had been stored for 6 months in solutions of sodium or magnesium sulfate were examined by scanning electron microscopy using backscattered electron imaging and X-ray microanalysis. For a paste stored in Na 2SO 4 solution, successive changes were observed on passing from the unaltered material in the interior towards the surface. These were (1), replacement of monosulfate by ettringite, which was closely mixed with the C-S-H gel, (2), disappearance of calcium hydroxide, partial decalcification of C-S-H and precipitation of gypsum and (3), further decalcification and leaching. Much of the gypsum occurred in veins sub-parallel to the surface, with which were associated cracks. A paste stored in MgSO 4 solution showed broadly similar effects, as well as a largely continuous surface layer of gypsum and brucite, except at the cube edges, where a gel high in magnesia and silica was formed. This was probably cryptocrystalline serpentine. Neither specimen contained massive deposits of ettringite.

Contribution a l'etude des preparations blanches des tableaux italiens sur bois

systematic study of the whole thickness of the ground was carried out on about 50 paintings. The originality of the work consisted in first revealing by back -scattered scanning electron microscopy where two types of coating had been used. The components of each layer were then analyzed by X-ray diffraction and found to be principally anhydrite for the gesso grosso and gypsum for the gesso sottile. According to these results, Tuscan painters used a double white ground until the end of the fifteenth century. The use of a single layer of gypsum was widespread in other Italian schools in the fifteenth century.

Magnesium sulfate attack on portland cement paste-I. Microstructural analysis

The mechanism of magnesium sulfate attack in portland cement and portland cement with silica fume paste was studied by investigating the microstructure and composition of specimens immersed for one year in magnesium sulfate solution. Results are presented in two parts. Part I, presents the microstructure of the pastes. Part II, presents the chemical and mineralogical variations across the specimen together with a proposed mechanism of magnesium sulfate attack. The magnesium sulfate attack resulted in the formation of the “surface double-layer” which was composed of brucite and gypsum layers. In addition, there was a sequential formation of inner gypsum layers resembling the occurence of lisegang bands found in rocks. The surface double-layer was composed of brucite, about 40 to 120 μm thick, and followed by a contiguous layer of gypsum, about 20 to 70 μm thick. Subsequently, up to four internal gypsum layers were deposited at depths of up to 1200 μm from the surface. These layers were parallel to the beam surfaces ranging in thicknesses from 15 to 60 μm. In portland cement with silica fume paste there were almost no inner gypsum layers, instead, massive deposition of dispersed gypsum crystals appeared up to at a distance of about 800 μm from the surface. The attack had apparently influenced the local degree of hydration of the cement constituents; near the surface only residual ferrite and belite crystals were observed, but in the middle, unreacted alite and belite were predominant.

Estudio sedimentológico del Keuper inferior, a partir del análisis de facies, en el sector central de la Cordillera Bética. Algunas consideraciones paleogeográficas

The lower Keuper of the central sector of Betic Cordillera shows a predominance of clays with variegated colours. They have intercalations of thin layers of sandstones (fine grain), gypsum and carbonates. Through sedimentological and stratigraphic analysis we can conclude that these materials are from a systems tract fluviocoastal further more it allows us to distinguish sorne different facies types which characterize the following subenvironments. They are set in a framework of mud flat, found on a vast tidal coastal lutitic plain. Terrigenous sediments (fine sands) from the mainland are deposited on the lutitic plain by ephemeral streams. In this coastal environment there are subenvironments of salt marsh, salt pans, sabkha, coastal lagoons, etc. The distribution in time and space of these facies was mainly controlled by the climate and the frequent incursions of the sea over the coastal plain, facilited by the flat geographical nature of coastline.

Preserving and protecting monuments and historical sites.

At the International Association of Engineering Geology symposium held recently in Greece, it was pointed out that the Parthenon has been damaged during the past 2500 years. After surveying natural and man-made damage, including explosions and partial demolition, researchers are suggesting that the monuments may be undergoing continuous damage due to environmental pollution. There is evidence that air pollution has caused substantial harm to monuments on the Acropolis. Air pollution has damaged the interior surfaces of two column capitals. The damage usually occurs as a black crust on carbonate stone surfaces. The damaged areas seem to receive little rain or rain runoff and seem to be formed by sulfur dioxide uptake, in the presence of moisture, on the stone surface. Subsequent conversion of the sulfur dioxide to sulfuric acid results in the formation of a layer of gypsum on the marble surface. Acid precipitation also occurs in Athens, and this may aggravate the air pollution damage.

Paleoenvironment of the Messinian Mediterranean "Lago Mare" from Strontium and Magnesium in Ostracode Shells

Ostracodes from Deep Sea Drilling Project (DSDP) site 376 (Florence Rise, Levantine Basin) in the eastern Mediterranean have been studied to elucidate the environments of the during the Messinian (Late Miocene). Additional ostracode samples from the Lago Mare from DSDP site 372 (East Menorca Rise, Balearic Basin) in the western Mediterranean, andfrom outcrops in the Sorbas Basin in southeastern Spain, the Polemi Basin in Cyprus, and from the Sitia-Lithinais Basin in Crete, were also studied. All samples contained valves of the euryhaline ostracode genus Cyprideis for which the distribution coefficient KD for Sr and Mg is known from analyses of modern specimens grown in the laboratory and from modern field collections. Because the Sr/Ca of ostracode shells is controlled by the Sr/Ca of the host water, and because the MglCa of the shells is controlled both by the MglCa of the water and by water temperature, Ca, Sr, and Mg analyses of individual fossil Cyprideis shells from the Lago Mare indicate the environment in which they lived. Throughout the sequence atDSDP site 376, the water was fresh or close to fresh, exceptfor layers just above the uppermost gypsum layers, at the base of the sequence where water with some marine affinity is recognized. Above these layers, the continental aspect of the Lago Mare water is indisputable. Chemical analyses of single ostracode shells from site 376 and the other sites mentioned above indicate that at no time during the life of the Cyprideis ostracodes was the Lago Mare connected to the ocean. Furthermore, there is no indication that the individual basins of the Mediterranean studied here were in direct connection to one another.

P. G. Fookes, W. J. French, & S. M. M. Rice reply

We are grateful for the comments made by Colin Warren concerning the stratigraphy of the sediments beneath Dubai Dry Dock. Like him we have seen these sediments at various stages in the development of the Dry Dock and elsewhere. The great diversity of strength, particle size, and range of composition of these sediments had to be considered all too briefly in the paper which was already of considerable length. Paragraph 4 of page 118, however, covers most of the points relevant to this diversity. We considered in some detail the relative weighting to be attached to the loss of material as fine particles and loss due to solution of gypsum, concluding that gypsum solution was the main cause of the settlement. The evidence from early cores shows that weak, silty layers of gypsum occurred at depths of about -17.5 and -21mHD. These could not be found in subsequent boreholes. We consider that the main settlement related to the removal of one of these layers (the upper one). More general removal of sulphate also took place but did not appear to lead to settlement of the magnitude recorded because the gypsum was dispersed within stronger rocks. There can be no doubt that gypsum solution has occurred and that the amount of gypsum originally present was of the correct order to account for the settlement observed and the recorded progress of the settlement. We found several thin layers of uncemented carbonate clay and silt in cores taken at various stages in the

Organic geochemical studies of a Messinian evaporitic basin, northern Apennines (Italy) I: Hydrocarbon biological markers for a hypersaline environment

This paper describes the occurrence and significance of hydrocarbons present in two bituminous marl layers and one distinct gypsum layer from a Messinian sedimentary basin, where hypersaline conditions prevailed. Several new compounds were detected and tentatively identified: of these 20R and 20S 4α, 24-dimethyl-5α(H),14β(H),17β(H) and 20R and 20S 4β,24-dimethyI-5α(H),14β(H),17β(H) cholestanes; 4-methylspirosterenes; 4,4-dimethyl-5α(H),14β(H),17β(H) pregnanes and homopregnanes are discussed in this paper. Several of these compounds might be considered as biological markers for a (hyper)saline environment. The short side chain 4-desmethylsteranes, 5α(H),14β(H),17β(H), 5α(H),14β(H),17α(H) and 5α(H),14α(H), 17α(H) pregnanes and homopregnanes, are the most abundant compounds in the extract from the gypsum sample. It is suggested that in this case these compounds do not reflect the stage of diagenesis but are related to certain organisms exclusively occurring in hypersaline environments. In addition the very low pristane/phytane ratio, often considered as an indicator for anoxicity, could also be interpreted as a useful indicator for hypersalinity.

Inversion of marble sulfation—reconversion of gypsum films into calcite on the surfaces of monuments and statues

This work combines our observation that the details of marble statues that have already been lost from the calcite surface are preserved in the gypsum layer, with our research on the mechanism of marble sulfation, to lead to a consolidation of the gypsum, transforming it back to calcium carbonate (calcite) using carbonate ions in solution. Our research shows the mechanism of the conversion of gypsum to calcite, the rate determining steps being the desorption and diffusion of CO2−3 We found that the reproduction of the surface detail and the improvement of the mechanical properties was very satisfactory.

Anatomy of a Modern Marine Sabkha in a Rift Valley Setting, Northwest Gulf of California, Baja California, Mexico: ABSTRACT

An extensive sabkha, 100 by 20 km (62 by 12 mi), caps Holocene siliciclastic tidal flats along the coast of Baja California in the northwest Gulf of California structural trough. This sabkha, bounded on the west by alluvial fans, is a complex of sand flat, saline mud flat, gypsum-halite pan, and supratidal mud flat subenvironments. The sand flat, transitional between the fans and the sabkha, consists of horizontally to wavy laminated sand washed onto the flats by sheetfloods from the fans under upper-flow-regime conditions. The sand flat passes into saline mud flats characterized by massive mud crowded with discoidal gypsum crystals grown within the sediment, destroying the layering. This intrasediment growth of gypsum is driven by evaporative pumping of brine from a shal ow subsurface brine body. A gypsum pan occupies a wide, shallow depression within the saline mud flat. After storm flooding (either marine or meteoric) the pan becomes a temporary saline lake with an algal mat overgrowing a siliciclastic storm layer. Precipitation of gypsum needles from the open lake brine and bottom growth of gypsum prisms produce a gypsum layer that mimics the algal mat topography. Evaporation of the lake leads to (1) vadose diagenetic growth of gypsum that distorts and polygonally disrupts the gypsum layers (2) deposition of a surface halite layer in the center of the pan. These layered pan deposits are the evaporites of the sabkha. Seaward of the saline mud flats are supratidal mud flats underlain by millimeter-thick laminites with deep prism cracks, sheet cracks, an scattered gypsum discoid crystals. Pervasive mud cracking during long periods of nondeposition completely disrupts layering, creating a massive arid soil. A beach ridge separates this sabkha complex from the burrowed and ripple cross-laminated intertidal sediments. End_of_Article - Last_Page 460------------

Morphologies of Gypsum on a Modern Sabkha: Clues to Depositional Conditions: ABSTRACT

Gypsum is the dominant evaporite mineral across the Holocene marine sabkha of the northwest Gulf of California, Baja California, Mexico. This sabkha is a complex of mud flats and saline pans in which gypsum occurs as layers and isolated intrasediment crystals. Six distinct morphologies of gypsum were found: flat plates, acicular prisms, bladed prisms, blocky prisms, blocky hemipyramids, discoidal hemipyramids. Flat plates (< 0.5 mm wide) and acicular prisms (< 1 mm long), in the form of radiating clusters and interpenetrating twins, crystallize at the brine-air interface during the temporary saline lake stage of the pan. These tiny crystals settle out on the bottom of the pan as a cumulate layer. Bladed prisms (0.5-1.5 mm long) nucleate on this cumulate layer and gr w upward as vertically oriented prisms (commonly swallowtail twins) making a grass-like layer. Blocky prisms (up to 2 cm long), barrel-like in shape with swallowtail twin terminations, are found as pendant cements in shelter vugs formed by buckling of the gypsum layers of the pan. Blocky hemipyramids (up to 1 cm across) are found as a loose mush making a diapir-like mound beneath m-scale polygonal cracks in the layered gypsum of the pan. These clear, blocky hemipyramids grow diagenetically in the vadose zone during the dry stage of the pan when evaporative pumping draws subsurface brine up along the polygonal cracks. Discoidal hemipyramids (up to 2 cm long) occur as isolated crystals. clusters of crystals, and rosettes within the siliciclastic sediment of the mud flats surrounding the an. They are of vadose and phreatic origin. Gypsum morphologies clearly vary with depositional conditions across this sabkha and this finding should allow us to use morphological variation in gypsum as a sensitive interpretative tool for ancient evaporites and evaporitive sediments. End_of_Article - Last_Page 460------------

The investigation of the effect of gypsum on foundation design

In East and Middle Anatolia, where several heavy industrial plants are planned to be constructed, vast areas are covered by gypsiferous layers. In this investigation, geotechnical properties of the gypsum layer, encountered at the Sivas IVth Iron and Steel Complex Site, are investigated and an attempt is made to propose solutions to some of the geotechnical problems anticipated at the site. In the research several physical, chemical and engineering properties of gypsum, the changes caused by the environmental conditions on its mechanical behaviour and crystal structure, its stress-strain-time behaviour and effect on foundation concrete are investigated and recommendations on the precautions to be taken are presented.

Measuring the hydraulic conductivity of soil adjacent to tile drains in a heavy clay soil in The Netherlands

The hydraulic conductivity, K sat, of soil adjacent to tile drains in heavy clay soils was measured at twelve locations with a new technique. This technique involves excavation of a cube of soil (25 cm × 25 cm × 25 cm) in situ around a tile fragment. Cutting of the tile leaves it protruding from the cube for ∼5 cm on two sides, also when covering five sides of the cube with a layer of gypsum outside the pit. Flow rates from the tile are measured for two conditions: (1) infiltration into the layer which was previously the lower horizontal soil surface of the cube; and (2) infiltration into the upper surface. The cube is turned upside down to allow the first measurement. The open surface is then covered with gypsum. The cube is turned upside down again and gypsum is removed from the upper surface of the cube (which is the original upper surface of the cube in the pit) to allow the second measurement. The first measurement mainly characterizes undisturbed soil below the drain, the second characterizes soil above the drain (fill). Dye is added to the percolating water to trace patterns of water movement, using micromorphometric techniques. Flow rates are transformed to K sat-values by using an electrolytic analog model. Measured K sat-values below the drain had median values of 10 m/day and agreed well with those measured in undisturbed soil at comparable depth, indicating that there are no changes due to either system construction or system operation. The median K sat for fill above the drain was 5 m/day. The conclusions reached pertain to three types of drains, e.g., one fired-clay pipe and two types of plastic pipe. The dye studies showed that water movement occurred almost exclusively along larger planar voids (cracks), and hardly along channels (rootholes). Water-conducting voids were below 2% by volume.

Bilan hydrique dans le Sud-Tunisien: I. Caractérisation expérimentale des transferts dans la zone non saturée

A detailed study of water movement in a multi-layered bare soil is presented. The main objective was to determine the possibilities of water table recharge by natural rains in semi-arid zones (south Tunisia). Systematic measurements of the soil water balance, using neutron probe and tensiometers have been run during infiltration and redistribution of water in a monolithic soil. The water was applied at the soil surface at a constant rate by a rain simulator. In Part I the following points are developed: experimental analysis of the processes of infiltration and redistribution and determination of the hydrodynamic properties for each layer of soil during the redistribution of water without and with evaporation through the soil surface.It is notably shown that water table recharge is possibly due to the high values of hydraulic conductivity of a gypsum layer located at a depth of 90 cm. This is of particular interest since until now this layer was considered to be impermeable.