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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.

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.

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.