Geochemistry of Miocene evaporites from the Askale (Erzurum, Eastern Turkey) area: constraints for paleo-environment

The Askale sub basin hosts Early Miocene evaporites intercalated with clastic sediments and carbonates. Gypsum and anhydrite rich evaporite samples are characterized by high CaO and SO4 contents, and low Na2O, K2O, MgO, and B contents. The Sr contents are 228 = 13100 ppm in evaporite samples, 169 = 992 ppm in claystone, 181 = 60090 ppm in marl, and 15150 ppm in limestone. All the samples are also characterized by enrichment in light rare earth elements (REE) with La-N/Lu-N = 0.667 4.243 and have variable Ce-N / Ce* (0.823 - 1.353) ratios. Measured Eu-N/Eu* values of the samples display strong and variable negative and positive Eu anomalies. 834SCDT and 818O values of gypsum and anhydrite samples have wide ranges from 21.30 parts per thousand to 25.62 %o, and 11.5 parts per thousand to 19.1 parts per thousand, respectively. Most of these values are heavier than expected Miocene marine gypsum composition and may be resulted from reduction and oxidation reactions of sulfide species in brines. Sr-87/Sr-86 ratios range from 0.707475 (Delta(SW) = -169.8) to 0.708175 (Delta(SW) = -99.8), close to and / or slightly lower than an Early Miocene marine isotopic composition. Petrochemical and isotopic data indicate that the Askale basin evaporites developed in subtropical conditions via multiple marine transgressions onto a shallow platform or lagoonal environment.