Plot of δ^l8O of brines versus δ¹⁸O_SO4 for the investigated sulfates: blue dots represent gypsum and red polyhalite isotopic compositions. “Trend 1” indicates the thermal event affecting both anhydrite/gypsum and polyhalite δ¹⁸O_SO4: “trend 2” shows that subsequently crystallization water of gypsum was replaced by meteoric water at low temperature. δ¹⁸O_SO4 values are the same range for both minerals, gypsum and polyhalite, suggesting that thermal overprint shown by “trend 1” affected both to similar extent. Isotherm calculation was done according to Zeebe (2010). Blue horizontal line represents Permian oxygen isotopic composition in sulfates precipitated from seawater.