Warunki powstania soli retu w zachodniej Polsce: badania inkluzji fluidalnych

Wołodymyr M. Kowalewicz



Lower Triassic evaporite complex was recorded in the Ośno IG2 borehole (Western Poland) at the depth of 1,700 m. The complex is composed of three packets of halite of thickness of 0.5 - 3 m, interbedded by anhydrite and dolomite deposits. I studied fluid inclusions in halite with the aim to obtain a new information about the physico-chemical conditions of salt formation and reconstruction of chemical composition of ocean water in Early Triassic times. In halite grains relics of sedimentary, chevron forms were recorded that contain abundant fluid inclusions - conserved micro-drops of basin brines. Chemical analysis of these inclusions showed that the brines were of sulfate type and the relations between main ions are similar to those recorded in present ocean water although the content of sulfate was slightly higher and of potassium was slightly lower during the Early Triassic times when compared to the recent. Brine concentration is in accordance with the first stages of halite deposition. The conclusion that the brine concentration was relatively low and the source of salt was marine, is supported by bromine data. Results of homogenization of inclusions insedimentary and recrystallized halite indicate that the salts during the postsedimentary stage became overheated. The temperature of homogenization increases downward from 44 to 65°C. Recrystallization of salt took place under the influence of preserved parent brines with slightly changed chemical composition and saturated with gas. If the marine origin of brines in the studied basin is assumed, then the Early Triassic ocean water was characterized by decreased content of sulfate ion. In this respect, it was practically the same as Permian ocean water. Accordingly, a complex of resources which is related to Permian evaporites, may be expected also in Lower Triassic evaporates if they originated in conditions of sufficiently high brine concentration.