Fluid inclusion analysis, geochemical characteristics of Jurassic carbonates: Case study from High Zagros Zone, Kohrang area, SW Iran

The Surmeh Formation with the age of Jurassic composed of shallow-water limestones and dolomites. The study area is located in the southwest of Iran in the Chaharmahal and Bakhtiari Province. Petrographic observation of the Surmeh Formation reveals the presence of several different of cement types related to various diagenetic environments. This study attempts to determine the temperature of cement precipitation, the salinity of the fluid from which the cement precipitated and the diagenetic environments. Bivariate plot of Th (temperature of homogenization) and Tmice (temperature of final ice melting) show distinct areas for each cement. In addition, the petrographic observation and fluid inclusion data (Th and Tmice) revealed that timing of precipitation of 5 different types of coarsely-crystalline cements in this successtion, began with meteoric diagenesis and then affected by deep burial diagenesis. All of fluid inclusions exhibit two-phases (liquid-vapour phase), which the liquid ratios is more than vapour ratios. In this research, petrographic evidence, elemental, oxygen and carbon isotope values indicate that aragonite was the original carbonate mineralogy in this formation. Bivariate plots of Sr/Ca versus Mn values, also illustrate that Surmeh carbonates were affected by non-marine diagenesis in a closed to semi-closed system.