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In the Middle Miocene of East Crimea, gypsum evaporites formed in a shallow basin from mixed seawater–nonmarine waters are overlain by marl, siltstone and claystone which contain a few horizons of stromatolitic limestone. The thickness and abundance of the stromatolitic horizons increase up the section. In the siliciclastic portion of the section, a very poor and taxonomically impoverished assemblage of benthic foraminifers (Jadammina, Nonion, Haynesina, Astrononion and Eponides) is recorded. It is typical for a shallow water marsh or lagoon environment with a lowered salinity. Accordingly, the brackish conditions prevailing during gypsum precipitation in East Crimea continued afterwards, although at the end of evaporite deposition the basin became desiccated and then it was rapidly reflooded by brackish water.The impoverished biota and the occurrence of microbialites in the Ptashkino section indicate extremely unfavourable conditions for most living organisms during the deposition of both the terrigenous and carbonate beds. The water salinity thus was probably not only lowered but also anomalous in composition if compared to normal marine water. The occurrence of carbonate stromatolitic horizons is probably related to the periodic shallowing of the basin caused by a drop of the lake water table driven by climatic factors. The resulted changes allowed for a growth of the bizarre microbial-serpulid communities that gave birth to most of the stromatolites.In Karaganian time, the Eastern Paratethys was a huge lake isolated from the Tethys. This lake responded to any climatic fluctuation that in turn might lead to water level oscillations. In humid climate periods, the lake could be open with a surface outflow and, when it was drier, it could be a closed system without surface outflow. Gypsum evaporites and stromatolitic carbonates are clear evidence of strong evaporation in a dry climate that probably induced water level fall in the whole basin. However, all the time the environmental conditions were predominantly brackish, even during gypsum precipitation as suggested by the chemical composition of fluid inclusions in gypsum. Similar conditions may be expected in other evaporite-hosted, predominantly brackish basins, such as some Messinian basins of the eastern Mediterranean, where some evaporites were deposited in the oligohaline to mesohaline conditions typical of the Lago Mare deposits. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

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 chemical composition of fluid inclusions in Manya 6 and Wilkinson 1 samples indicates that parent brines were Ca-rich and SO 4 -poor, whereas modern seawater is SO 4 -rich and Ca-poor. Such a composition is similar to that recorded in the Lower Cambrian halite from the East Siberia Basin. [ABSTRACT FROM AUTHOR]

Abstract: The upper Permian Zechstein Limestone carbonates in the south-western part of the Polish Zechstein basin contain small quantities of organic matter (usually less than 0.1wt% TOC) and have poor hydrocarbon potential. In contrast, the Kupferschiefer shales have excellent hydrocarbon potential with TOC as high as 10.8wt%, predominantly algal type II kerogen. Generally, thermal maturity of the organic matter is 0.6–0.9% vitrinite reflectance, while locally, is as high as 1.45%. The Kimmerian and Laramian tectonic events significantly influenced the regional burial and thermal history. The main subsidence of the Kupferschiefer–Zechstein Limestone complex took place during the Late Permian–Late Triassic period, with additional burial during the Jurassic and Late Cretaceous. Hydrocarbon generation from the Kupferschiefer source rocks occurred from Middle Triassic to Late Jurassic times, reaching maximum rates during the Jurassic. The Cretaceous subsidence had only a minor influence on the maturity and transformation of organic matter. Expulsion started between Late Triassic (in the western part of the study area) and Early Jurassic (in the eastern part), then ceased by the Late Jurassic–Early Cretaceous erosion. The total amount of generated and expelled hydrocarbons from source rocks was small because their thickness was limited. Therefore, Kupferschiefer shales cannot be considered as source rocks for liquid hydrocarbons, but may be a potential source for gas accumulated in the Zechstein Limestone and Rotliegend reservoirs. [Copyright &y& Elsevier]

Study of three halite sections in the Ro¨t Basin from the eastern Netherlands (Twente-Rijn 382 borehole), central Germany (Mardorf 6 borehole) and western Poland (Os´no IG2 borehole) shows that the δ34S values in Ro¨t sulphates of studied samples (27.14–31.98‰) are characteristic of marine sulphates of late Early Triassic. These values fit in the Ro¨t 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 Ro¨t brines correspond to the Na-K-Mg-Cl-SO4 (SO4-rich) chemical type, i.e. the same type that characterises modern seawater. However, the Ro¨t 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 Ja¨necke diagram, the points of the brine composition during deposition of Ro¨t 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 Ro¨t 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. [Copyright &y& Elsevier]

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... [ABSTRACT FROM AUTHOR]

Studies the secular variation in seawater chemistry during the Phanerozoic as indicated by brine inclusions in halite. Analysis of data on chemical composition in primary-bedded halite from many evaporite formations of northern Pangaea; Changes in the compositions of brine which correspond to the chemical evolution of the Phanerozoic ocean.

Abstract: 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-SO4 (SO4-rich) type. Recrystallised halite from the uppermost Neoproterozoic Salt Range Formation (ca. 545Ma) in Pakistan, contains solitary inclusions indicating SO4-rich brines. This supports the concept derived from the study on primary fluid inclusions from the Neoproterozoic Ara Formation of Oman; SO4-rich seawater existed during latest Neoproterozoic time (ca. 545Ma). In contrast, samples of recrystallised halite from the Bitter Springs Formation (840–830Ma) 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 200Ma), at 650Ma, this was replaced by SO4-rich seawater, finally returning to Ca-rich seawater at 530Ma. [Copyright &y& Elsevier]