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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.

Bromine concentrations in halite, sulfate isotopes (δ34S and δ18O), and major ion concentrations in primary fluid inclusions from three boreholes in the Late Permian Zechstein evaporites have revealed sharp variations in marine derived brines within the Polish sector of the European Southern Permian Basin. The base of the Older Halite (Na2), during the latest Permian, registers a change from sulfate-rich brines, similar in composition to modern evaporated seawater, to sulfate-depleted brines (calcium-rich). This change coincides with a drop in δ34S to values close to + 9‰, not observed in δ18O counterparts. Opposite isotope (δ34S–δ18O) trends through the Na2 unit cannot be explained by changes in restriction conditions. We propose that the change to sulfate-depleted (calcium-rich) brines during halite deposition of the PZ2 (Stassfurt) cycle is related to the overturn of anoxic sulfidic deep-waters from the Panthalassa stratified superocean coinciding in time with the Permian–Triassic mass extinction event. The reconstruction of chemical changes in brines reveals two major evaporite sequences of increasing concentration that do not match the classic lithostratigraphic cycles. The first evaporite sequence (PZES-1) contain the evaporite units of the PZ1 (Werra) cycle, the PZ2 (Stassfurt) cycle, the Main Anhydrite (A3), and the base of the Younger Halite (Na3) of the PZ3 (Leine) cycle. The second evaporite sequence (PZES-2) is represented by almost the entire Na3 unit and the PZ4 (Aller) cycle.

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%).

Fluid inclusions in halite and bitumens in rock salt in Upper Permian Zechstein evaporites in West Poland were studied in locations where the evaporites lie above oil and gas reservoir rocks. The samples were taken from halite intercalated within the Basal Anhydrite; this unit lies above the Main Dolomite which serves as both source rock and reservoir. Samples came from a depth of 2.3–3.2 km. A characteristic feature of the fluid (gas-brine) inclusions was their high methane content together with the occasional presence of bitumen globules of near-spherical form. Geochemical analyses of the bitumen in bulk samples of rock salt (including content and distribution of n-alkanes and isoprenoids, and carbon isotope ratios) suggest an algal origin, similar to that of the oil in the underlying source rocks. For comparison, we studied fluid inclusions in halite from Zechstein evaporites in northern Poland, where hydrocarbon accumulations do not occur in underlying strata and where mostly single-phase (brine) inclusions with a low methane content have been recorded. However, published data indicate that similar inclusions to those occurring in the Zechstein of West Poland (comprising brine with a high methane content, bitumen films and/or oil droplets) are present in other salt-bearing sequences, where their origin is related to the thermal degradation of organic material dispersed within the salt itself. Accordingly, such fluid inclusions in an evaporite succession can only be considered to form a geochemical aureole where the bitumens in the rock salt (including those in the fluid inclusions in halite) can be compositionally linked to those in the associated oil accumulation.

Lower Cambrian salt deposits in the eastern Officer Basin occur in troughs along the western and northwestern margin of the Gawler Craton, and are interpreted to have been deposited in marginal to restricted marine environments. The salt horizons in two drillholes [Manya 6 (373554E, 6938478N: GDA94) and Wilkinson 1 (263545E, 6693435N: GDA94)] were studied utilising multiple techniques including mineralogical investigation, fluid inclusion and isotopic analysis. New data on Br values of 19 salt samples provide evidence of marine origin for the salt. Abundant two-phase (gas – liquid) inclusions and poor preservation of primary inclusions indicate intensive post-depositional recrystallisation. Homogenisation studies of fluid inclusions in halite from Manya 6 suggest that the upper part of the salt-bearing strata (Ouldburra Formation) has been heated to 80°C, whereas the lower part reached even higher temperatures. This heating event may be related to the Devonian – Carboniferous Alice Springs Orogeny. The ch...

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.

Data on chemical composition of brines in primary inclusions of marine halites and on mineralogy of marine evaporites and carbonates lead to the conclusion that during the Phanerozoic two long-term cycles of chemical composition of seawater existed. During each of those cycles, seawater dominantly a Na-K-Mg-Ca-Cl (Ca-rich) type changed to a Na-K-Mg-Cl-SO 4 (SO 4 -rich) type. Recrystallised halite from the uppermost Neoproterozoic Salt Range Formation (ca. 545 Ma) in Pakistan, contains solitary inclusions indicating SO 4 -rich brines. This supports the concept derived from the study on primary fluid inclusions from the Neoproterozoic Ara Formation of Oman; SO 4 -rich seawater existed during latest Neoproterozoic time (ca. 545 Ma). In contrast, samples of recrystallised halite from the Bitter Springs Formation (840–830 Ma) in Australia contain inclusion brines that are entirely Ca-rich, indicating that basin brines and seawater were Ca-rich during deposition of central Australian evaporites. These combined data supported by the timing of aragonite and calcite seas suggest that during the Proterozoic, significant oscillations of the chemical composition of marine brines, and seawater, occurred, which are similar to those known to exist during the Phanerozoic. It is suggested that Ca-rich seawater dominated for a substantial period of time (more than 200 Ma), at 650 Ma, this was replaced by SO 4 -rich seawater, finally returning to Ca-rich seawater at 530 Ma.

Polyhalite is a common constituent of many ancient evaporite sequences, especially Permian and Neogene ones, that is related to the Na−K−Mg−Cl−SO4 type of marine brines in those time intervals. There are four polyhalite deposits in the Zechstein of northern Poland, and more than ten polyhalite-bearing areas in the adjacent part of Russia, and they are commonly accompanied by K−Mg chlorides. Most polyhalite occurrences are related to the upper part of the Lower Werra Anhydrite and in most cases, polyhalite deposits are concentrated at the sulfate platform close to its boundary with platform slope, where they can pass horizontally into polyhalite beds occurring in the Oldest Halite. The bromine content in samples of the Oldest Halite range from 40–120 ppm and the composition of fluid inclusions in halite are characteristic of halite precipitated from seawater concentrated to the early and middle stages of halite precipitation. The δ18O and δ34S values for sulfates are 10.03‰–13.50‰ and 10.03‰–12.14‰, respectively, and the δ37Cl values for halites from −0.1‰ to +0.4‰ support their marine origin. Bromine distribution in the Oldest Halite and the occurrence of anhydrite intercalations indicate fluctuations of the brine density during the Oldest Halite deposition. The formation of polyhalite was preceded by the syndepositional dehydration of the original gypsum deposit and it appears that the anhydrite was then transformed to polyhalite by reaction with marine brines more evolved than those from which precipitated precursor calcium sulfate minerals. These concentrated brines could have been derived from the evaporation of marine brines and/or inflow of K- and Mg-rich brines that were formed in nearby shallow salt pans occurring in sulfate platform areas and thus sulfate platform areas and adjacent slopes of those platforms were predestined for polyhalite formation.

Thirty nine samples of Lower Cambrian marine sedimentary halite with zoned primary fluid inclusions were analyzed using the UMCA method introduced by Petrichenko (1973) [Petrichenko, O.I., 1973. Metody doslidzhennya u mineralakh galogennykh porid. Naukova Dumka, Kyiv, 91 pp.] in order to determine the contents of K + , Mg 2+ , SO 4 2− and Ca 2+ ions and to interpret the composition of parent seawater. The analyzed samples were from the giant salt basin of eastern Siberia where five major phases of salt deposition can be distinguished, in the Late Vendian (Danilovo) and Early Cambrian (Usolye, Belsk, Angara, and Litvintsevo) basins. Our samples are all from Early Cambrian basins although the largest data set comes from the Angara Basin. The results indicate that Early Cambrian parent seawater was similar in all studied basins and was characterized by lower Mg 2+ and SO 4 2− , and higher Ca 2+ concentrations relative to modern seawater; the concentration of K + in Early Cambrian seawater was similar to that of modern seawater. Accordingly, the seawater in the entire Early Cambrian was Ca 2+ -rich and SO 4 2− -poor. The change of composition of seawater–from SO 4 2− -rich, Ca 2+ -poor in the latest Neoproterozoic to Ca 2+ -rich, SO 4 2− -poor recorded throughout the Early Cambrian–probably occurred within a relatively short time span during the earliest Cambrian (Nemakit-Daldynian) time and caused a rise in Ca 2+ concentrations in the shelf seas leading to the onset of biocalcification and then the Cambrian explosion.

Earlier studies of individual fluid inclusions in salt minerals of some Devonian evaporite basins showed that the brines in those basins were of chloride type with a high concentration of Ca2+. The genetic significance of this occurrence was subject to different interpretations. We have studied in detail samples taken from the East European Dnipro‐Donets and Prypiac’ evaporite basins aiming to establish the chemical composition of fluid inclusions in studied evaporites and then, using other geochemical information, to establish a geochemical model of the Devonian evaporite basins. Our study showed that salt deposition in the Devonian Dnipro‐Donets and Prypiac’ evaporite basins was because of intensive evaporation of mainly marine brines of chloride type with a relatively high Ca2+ content. In turn, the ratios between Na, K, and Mg corresponded to ratios in recent marine brines. Salt minerals precipitated in bottom water conditions. The occurrence of one‐phase fluid inclusions indicates the temper...

The examination of primary fluid inclusions in sedimentary halite from several Permian evaporite basins of East and Central Europe (Asselian and Sakmarian Dnipro-Donets Basin of Ukraine, Sakmarian Dvina-Sukhona Basin of Russia, Kungurian Solikamsk Basin of Russia, Zechstein Basin of Poland and Peri-Baltic Russia) revealed that the brines were of Na-K-Mg-Cl-SO 4 (SO 4 -rich) chemical type. They are characterized by minor content of SO 4 ions, when compared with modern seawater concentrated to the corresponding stage. The lowest SO 4 content was recorded in the Kungurian; a higher SO 4 content was found in the Asselian and Sakmarian; and the highest content in the Late Permian. The bromine content in halite of the Permian salts of East and Central Europe (mostly 30-160 ppm) correlates with ion concentration in brine inclusions. The marine origin of salt in most of the studied sections is supported by isotopic composition of sulphate sulphur. During salt deposition in every basin, local factors - such as the inflow of surface or subsurface waters, sulphate reduction, and water-rock interaction - have exerted important influences on the K, Mg, and SO 4 ion ratios. However, these changes did not lead to the change of the chemical, SO 4 -rich type that is characteristic for the Permian evaporite basins.

Study of three halite sections in the Rot Basin from the eastern Netherlands (Twente-Rijn 382 borehole), central Germany (Mardorf 6 borehole) and western Poland (Ośno IG2 borehole) shows that the δ 34 S values in Rot sulphates of studied samples (27.14–31.98‰) are characteristic of marine sulphates of late Early Triassic. These values fit in the Rot event shift described in the literature. The bromine content in halite is 32–158 ppm. In the Dutch and Polish sections, relics of sedimentary structures—chevron and hopper—are recorded in halite grains. These structures contain fluid inclusions that were analysed using the ultramicrochemical method of Petrichenko (Petrichenko, O.I. 1973. Metody doslidzhennya vkluchen' v mineralakh galogennykh porid. Kiev, Naukova Dumka, 92 pp.). In the German section, no sedimentary halite structures occur. Because the pressure in the inclusions in recrystallized halite is only slightly greater than atmospheric pressure, these inclusions are presumed to be early diagenetic in origin. The analysis of individual brine inclusions, both in sedimentary and diagenetic forms of halite, shows that the Rot brines correspond to the Na-K-Mg-Cl-SO 4 (SO 4 -rich) chemical type, i.e. the same type that characterises modern seawater. However, the Rot brines differ from the composition characteristic of modern concentrated seawater by a decrease in the content of sulphate ion and an increase in the content of potassium ion. On a Janecke diagram, the points of the brine composition during deposition of Rot halite in Poland, Germany and the Netherlands only show a small range. This suggests a stable composition of basinal brines during the deposition of the halite. At the same time, the relative content of sulphate ion in the Lower Triassic Rot Basin was slightly lower than that in Upper Permian evaporite basins, but higher than that in Lower and Middle Permian and Middle and Upper Triassic evaporite basins. The implication is that the content of sulphate ion in seawater was subject to changes in Permian and Triassic times.

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.

Analysis of data on the chemical composition of primary fluid inclusions (brine inclusions) in primary‐bedded halite from many evaporite formations of northern Pangea shows that during the Phanerozoic the chemical composition of marine brines was oscillating significantly between the Na‐K‐Mg‐Ca‐Cl type and the Na‐K‐Mg‐Cl‐SO4 type. We regard those changes as corresponding to the chemical evolution of the Phanerozoic ocean. The changes correlate in time with earlier suggested secular changes in the mineralogies of marine nonskeletal limestones and potash evaporites. In addition to those secular changes of seawater chemistry, the concentrations of K, Mg, Ca, and SO4 ions in marine brines underwent important changes under the influence of local factors, including rock‐water interaction. These secondary changes did not influence the principal chemical type of the brine characteristic for a given time interval. In the past concentration of the Ca‐ion did not exceed the present concentration in marine water by a...