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We describe a new geochemical tool that could provide temperatures of ancient basins in which massive evaporites were deposited: the oxygen isotope composition of fine crystalline quartz found in large halite bodies. Such quartz is well preserved from post-depositional alterations and it can be relatively easily separated. For the purpose of this study, five halite samples were selected from four various evaporite basins, spanning in age from the Early Cambrian to the Late Jurassic. The obtained isotope temperatures refer to locations where evaporites were deposited, i.e. in subtropical zones of the Earth, as it may be estimated from continental distribution during Phanerozoic times. Reasonable temperatures are obtained, with an assumption for the δ18O of brines ranging from − 1‰ to 0‰ during halite deposition. The assumption of higher δ18O values leads to unrealistic temperatures, higher than the homogenization temperatures of fluid inclusions in halite.

The previous study showed that the Zechstein (Upper Permian) anhydrites have about 0.2% strontium with a remarkably small sample scatter. Our study of three lower Zechstein anhydrite units (Lower Anhydrite, Upper Anhydrite and Basal Anhydrite) from West Poland indicate that although often the Sr content is 0.1–0.2%, there are common deviations. In particular, a considerable part (28%) of the studied samples is characterized by lower values (

The study of fluid inclusions in Lower Triassic Rot halite from the Rockensussra 2/83 borehole in northern Germany showed the presence of primary and secondary gas-liquid inclusions. The gas phase in inclusions indicates their stretching due to salt overheating at some postsedimentary stage. The homogenization temperature of inclusions indicates the overheating temperature of about 60–70°C. The overheating is additionally indicated by trails of migration of large secondary inclusions occurring inside chevrons. The major-ion (K, Mg and SO4) composition of inclusion brines was established with the use of ultramicrochemical analysis (UMCA). The results of chemical analyses of brines of primary inclusions in halite from the Rockensussra 2/83 borehole confirm the earlier results for the Rot halite from the Netherlands and Poland. The bromine content in halite is 78–107 ppm, supporting thus marine origin of halite. Brines of primary gas-liquid inclusions are thus representative samples of trapped evaporite water and they may be used for the reconstruction of the composition of Early Triassic seawater. The comparison of our analytical data with the earlier published data and models of chemical composition of seawater during the Phanerozoic which were constructed with the use of the HMW computer program makes it possible to conclude that the Early Triassic seawater was of the SO4-rich type and considering the ratios of major ions it fully corresponded to the Early Permian (Asselian-Sakmarian) seawater. It differed from the present seawater by a slight decrease of Na and Mg ions, a considerable decrease of SO4 ion (by 31%) and an increase of Ca ion (by 36%).

Analyses of primary and early diagenetic fluid inclusions in the halite from the Late Ordovician Mallowa Salt, Canning Basin, Western Australia indicate a Ca-rich composition and high concentration of parent brines in the basin which were close to sylvite and carnallite precipitation. The salt-bearing series in the sampled interval was overheated up to 62 °C. The recorded differences in gas compositions result from the input of several gas sources including dispersed organic matter in the salt series and hydrocarbon deposits in the underlying rocks. The high concentration of the brines in fluid inclusions does not allow quantitative reconstruction of the chemical composition of Late Ordovician parent seawater. Using the information from Early Cambrian and Late Silurian basins as a proxy, however, the new data indicate that Late Ordovician seawater was undoubtedly Ca-rich and, in comparison with modern seawater, had a similar K content, considerably lower Mg content (c. 30%), approximately three times the Ca content and one-third the SO4 content.

Paleokarst developed in sulfate deposits is common, and it is usually formed along the contact with the overlying permeable rocks or it is due to near-surface dissolution of bedded evaporites. In the Lower Werra Anhydrite (Zechstein) of northern Poland the paleokarst cavities are usually filled by bluish semitransparent anhydrite and more rarely by celestite, polyhalite, halite, and carbonate. In small cavities (a few centimeters across), a rim of rod-like anhydrite crystals arranged in narrow bundles occurs, and the inner part of the cavity is filled with a mosaic aggregate of short prismatic crystals of anhydrite and celestite as well as coarse irregular anhydrite. Celestite crystals and fan-shaped aggregates as well as spherulites of anhydrite are rare. In bigger cavities (some ten centimeters across), multiple zones of fibrous anhydrite are arranged in different directions in the middle part of the cavity fill. The innermost parts of large karst cavities remain hollow in some cases, with the cavity walls encrusted by coarse, well-developed crystals of anhydrite and celestite. The karst cavities in the Lower Werra Anhydrite developed in the subsurface by dissolution of CaSO4 strata in halite-rich intervals due to gypsum dehydration water. During gypsum dehydration, dissolution of that halite would have increased the sodium chloride content of the solution and thus the solubility of calcium sulfate. Dissolved calcium sulfate was removed from a leaching zone by diffusion and/or downward flow in interstitial space, and the minerals in karst cavities precipitated from the same solutions as those solutions became oversaturated because of decreases in NaCl concentration over time. This study suggests that karst in sulfate deposits can develop in the subsurface and without uplift and/or near-surface conditions.

The Viséan evaporites of the Windsor Group in the Moncton Subbasin at the western limit of the Maritimes Basin of eastern Canada represent an important stratigraphic sequence to study in determining changes in the chemistry of marine brines. Seventeen samples of halite have been selected for fluid inclusion study. The chemical composition of inclusion brines was examined using the Petrichenko method of glass capillaries with applied ultramicroanalytical techniques. The results of the study indicate that the conditions of evaporite deposition in the Windsor Basin differed from those recorded in other Phanerozoic basins and that the history of the Windsor Basin brines was characterized by changes in the chemical composition of the brines. It was also found that there existed continual unfavourable conditions for the day-and-night zonality in chevron halite crystals and for the origin of relatively large (>50 µm) fluid inclusions and that the gas content was low not only during the deposition but also during the diagenesis of potash deposits. The chemical composition of the Viséan waters of the Moncton Subbasin at the beginning and end of deposition of the Windsor Group evaporite sequence was controlled by the predominating waters of nonmarine origin; during the potash deposition the controlling factor was chloride-type marine waters. In general, the geochemical data support the concept of Carboniferous evaporite basins with Na–K–Mg–Ca–Cl-type brines.

The development of basal Zechstein (Wuchiapingian) strata inSW Polandindicates the existence of a diversified relief inherited after the flooding of the pre-existing depression by the transgressing Zechstein sea. The deeper parts of the basin were the place of development of thin basinal Zechstein Limestone showing sedimentary condensation manifested by bored and encrusted grains and thick evaporites (mostly halite), and in shallow parts Zechstein Limestone reefs followed by thinner evaporite sequences (dominated by anhydrite) occur. The analysis of 3D seismic sections showed that instead of three conventionally recognized evaporite units of stratigraphic potential in the PZ1 cycle, five units occur (from the base to the top: Lower Anhydrite, Lower Oldest Halite, Middle Anhydrite, Upper Oldest Halite, Upper Anhydrite). In a particular place their number may vary from two (Lower Anhydrite at the base of the PZ1 cycle and Upper Anhydrite at the top of the PZ1 cycle) to five. There are two complexes of Lower Anhydrite occurring throughout the platform and basinal zones showing deepening-upward (transgressive) trend. The halite sedimentation in the deepest parts of salt basins began shortly after the deposition of the upper Lower Anhydrite complex while in the sulphate platform areas the sulphate deposition lasted still for a long time. The Lower Oldest Halite deposits occur in the depressions. Between the halite basins, anhydrite platforms occur, and the thickness of anhydrite platform deposits is smaller than it is observed in salt basins. The Upper Oldest Halite in turn is recorded above the anhydrite platform. The two halite units represent different phases of development of halite basins. The Lower Oldest Halite basins are related to the pre-Zechstein depressions, although in some cases their syndepositional subsidence was controlled by reactivation, during the deposition of basal Zechstein strata, of former faults. In turn, the Upper Oldest Halite basins used the accommodation space created due to anhydritization of the Lower Anhydrite deposits composed originally of selenitic gypsum. The 3D seismics evidences that the PZ1 evaporites inSW Polandhave been deposited in far more complex and dynamic system than it was assumed before.

In the middle Miocene Badenian gypsum basin of the Carpathian Foredeep, west Ukraine, three main zones of gypsum development occur in the peripheral parts of the basin. Zone I consists entirely of stromatolitic gypsum formed in a nearshore zone. Zone II is located more basinward and is characterized by stromatolitic gypsum in the lower part of the section, overlain by a sabre gypsum unit. Zone III occurs in still more basinward areas and is characterized by giant gypsum intergrowths (or secondary nodular gypsum pseudomorphs of these) in the lowermost part, overlain by stromatolitic gypsum, sabre gypsum and then by clastic gypsum units. Correlation between these facies and zones has been achieved using lithological marker beds and surfaces. Of particular importance for correlation is a characteristic marker bed (usually 20–40 cm thick) of cryptocrystalline massive gypsum occurring in zones II and III. The marker was not distinguished in zone I, possibly because this bed is older than the entire gypsum section of that zone. These new results strongly suggest that the deposition of giant gypsum intergrowth facies and stromatolitic gypsum facies was coeval. In some sections of zones I and II, limestone intercalations have been recorded within the upper part of the gypsum sections. Considerable scatter of the δ18O and δ13C values of these limestones indicates variable diagenetic overprints of marine carbonates, but a marine provenance of the limestones is confirmed by microfacies analysis. Some of the limestones are coeval with an intercalation of gypsarenitic, mostly laminated gypsum occurring in the sabre gypsum unit of zones II and III. Badenian gypsum formed in extremely shallow-water to subaerial environments on broad, very low relief areas of negligible brine depth, which could be affected by rapid transgressions. Stable isotope (δ34S, δ18O) studies of the gypsum demonstrate that the sulphate was of sea-water origin or was derived from dissolution of Miocene marine evaporites. Investigations of individual inclusions in the gypsum indicate decreased water salinity when compared with modern marine-derived, calcium sulphate-saturated water. Groundwater influences are indicated by high calcium sulphate contents of the brines in the evaporite basin. The chemical composition of Badenian waters was thus a mixture of relic sea water (depleted in NaCl), groundwater (enriched in calcium sulphate) and surface run-off.

The Middle Badenian anhydrite sections in the central part of the Carpathian Foredeep consist mainly of interbedded laminated anhydrite and anhydrite breccia. These facies display features characteristic of redeposited sediments such as distortions due to slumping, erosional boundaries, and graded-bedded laminae. Lamination in laminated anhydrite is rarely regular and often accompanied by disruptions. The predominance of clasts of laminated anhydrite combined with the observed brecciation of laminated anhydrite indicates that a short distance for transport and even in situ reworking were common. A high degree of convolution indicates that some reworked sediments were unconsolidated when they moved, but in many cases they were probably at least partly lithified. This is evidenced by the anhydrite breccia consisting of clasts of laminated anhydrite as well as the brecciation in situ. The resedimentation processes have not been related to regional bathymetrical differences as indicated by minor differences along seismic profiles. A great deal of redeposition within the basin centre of the Middle Badenian evaporite basin combined with the in situ brecciation suggests that the triggering mechanism for redeposition could be earthquakes. They generated mass flows and eventually turbidites, so that earlier deposited grains could be redeposited. This implies that in other evaporite basins the laminar facies might be at least partly related to redeposition and not necessarily to changes of surface brine concentration as usually supposed.

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.

Primary gypsum is the main evaporite mineral in the middle Miocene (Badenian) of the West Ukraine. The lower part of the gypsum sequence is built of autochthonous gypsum while the upper part is composed of allochthonous gypsum that formed following a major, tectonically induced, change in basin morphology. This change resulted in the destruction of the gypsum deposited on the margins of the basin and formation of redeposition features. Autochthonous gypsum facies were deposited in two main environments: (1) giant gypsum intergrowths precipitated from highly concentrated brines; (2) very shallow subaqueous gypsum deposited in a vast brine pan. The brine pan was characterized by a facies mosaic that reflects an interplay of concentrated brines from the central part of the evaporite basin and diluted brines due to the influx of continental meteoric waters. The facies continuum, microbial gypsum - bedded selenite - massive selenite - sabre gypsum, indicates increasing salinity of the brine with time. This type of facies pattern has been established in recent salinas that are analogous to Badenian gypsum in their lateral facies changes. However, the pattern of facies distribution with respect to the open sea in the Badenian basin is opposite to that found in recent salinas. The pattern of the Badenian gypsum facies in the Ukraine indicates that facies repetition may have been related to climatically controlled salinity changes and not to depth changes, as is commonly used to explain the repetition of sulphate facies in a vertical succession.

Potash evaporites of the lower Miocene Vorotyshcha Suite are sandwiched in salt breccias in the Ukrainian part of the Carpathian foreland basin. These breccias have traditionally been interpreted as tectonically deformed units related to the overthrust nappes of the Carpathians. Most clasts consist of intrabasinal sandstone, marlstone, halite, and anhydrite, but exotic clasts consisting of rocks that are characteristic of the Carpathian flysch rocks are also present. Breccia beds are intercalated with salt layers containing chevron crystals and cubic hopper crystals, and some layers are composed of detrital salt. These salt layers rarely display graded bedding or cross-lamination, and continue over great distances. There are also slump structures associated with the bedded salts. The salinity in the Vorotyshcha Basin was extremely high, but intermittent inflows caused brine dilution so that it could maintain halite precipitation for a long time. During long periods of evaporative concentration and reduced inflow, brines in the basin could reach the sylvite saturation level so that potash chlorides and sulfates started to precipitate. The potash precipitated subaqueously. On the basis of evidence from the study of fluid inclusions, the depth of the brine is interpreted to have been 20-30 m, in agreement with the supposed brine stratification in a basin subjected to influxes of sediment-laden waters. The breccias are debris-flow deposits. They are commonly tectonically deformed, but analysis of the relation of breccias to evaporites suggests that both were formed in water ten to a few tens of meters deep. It therefore seems that halite breccias in other foreland basins could have had a sedimentary origin.