Articles
Publication Date: 2025
Carbonates and Evaporites (08912556)40(2)
The continental closed basin playas often serve as the discharge point of regional water flow systems and the evolution of brines and salts in these areas is a response to fluctuations in recharge or evaporation. This research discusses the geochemistry, brine type, and evaporite minerals of the Jandaq and Khur sabkhas located in the Great Kavir, Iran. The sabkhas consist of four main sub-environments: sand flats, mud flats, saline mud flats, and salt pans. Samples of brine, primary and secondary salt were collected and analyzed for their pH, major cations and anions, mineralogy. Brines of the sabkhas are moderately acidic and the low pH of the brines is likely due to the oxidation of Fe sulfides present in the green marl deposits. The quantities of Na+, Cl- and SO42- are lower in the brines than in the salts, while the amounts of Mg2+, Ca2+, K+ and Sr2+ are higher in the brines. The average contents of major cations in the primary salts are higher than those in the secondary dendritic salts, and the primary salts of the Jandaq sabkha have higher contents than those of the Khur sabkha. Halite is the primary mineral formed under natural conditions, and tachyhydrite may form during the final stages of concentration. The ionic strength and sum of Na+, K+, Ca2+, Mg2+, and Cl- quantities increase with evaporation, while pH decreases from the precipitation stage to desiccation stage. Carbonates in the pH range of the brines mostly exist as HCO3-. SO42- occurs in the secondary dendritic salts, primary salts, and brines, respectively, in order of abundance. The brine of the salt pan is of Na-(Mg)-Cl type. The brines are supersaturated with respect to calcite, aragonite, dolomite, and halite, indicating precipitation of these minerals. However, the brines are undersaturated with respect to barite, gypsum, sylvite, and celestite. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2025.
Publication Date: 2025
Journal of Stratigraphy and Sedimentology Researches (20087888)41(3)pp. 71-91
Dam reservoirs serve as suitable places to settle sedimentary materials carried by rivers. Pollutants absorbed into these sediments may lead to water contamination, increased aquatic animal mortality, and loss of biodiversity. Potentially toxic elements (PTEs) are classified as highly hazardous pollutants due to their long persistence in the environment. Due to their destructive effects on humans and the environment, it is important to examine sensitive and special areas for contamination with them. Therefore, spatial zoning of these pollutants in surface sediments of aquatic ecosystems is very effective in identifying the entry routes and determining their origin, as well as in identifying sedimentation conditions and determining sensitive zones for pollution reduction management. The sampling of surface sediments with the aim of zoning the sediments of the Zayandehroud Dam reservoir in terms of the level of contamination with PTEs based on geochemical indicators was carried out from 20 stations in this lake in December 2022. Then, the physical and chemical variables of the sediments were measured, including pH, EC, Eh, percentage of moisture, bulk density, dry density, grain size, percentage of organic matter, percentage of calcium carbonate, and concentrations of 26 elements. The results showed overall increasing changes in pH, bulk density, dry density, percentage of organic matter, percentage of calcium carbonate, and sand-sized particles from the dam crest to the lake entrance, while the percentage of moisture and Eh showed an overall decreasing trend. Only some elements, including silver, arsenic, chromium, copper, nickel, and lead, exceeded the US sediment quality guidelines (ERL and ERM) at some stations, among the 26 elements measured in the 20 surface sediment samples. Which was found towards the dam crest for arsenic and lead, chromium except for a few points, nickel and copper were found throughout the study area, and silver was found towards the lake entrance. Also, the Enrichment Factor (EF) of lead and copper was lowest at the lake entrance (EF<2) and increased towards the dam crest, and there was also very high enrichment (EF= 20-40). The EF of silver showed the highest enrichment (EF> 40) at one station at the lake entrance. The Geoaccumulation Index also showed non-polluted (Igeo < 1) to slightly polluted (Igeo = 1-2) for cadmium and antimony in the entire study area, and slightly polluted (Igeo = 1-2) for silver towards the lake entrance and for lead near the dam crest. The PLI index based on total elements showed pollution (PLI>1) only near the dam crest. © 2025 University of Isfahan.
