Abstract:

The Aşkale 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 LaN / LuN = 0.667 - 4.243 and have variable CeN / Ce* (0.823 - 1.353) ratios. Measured EuN / Eu* values of the samples display strong and ariable negative and positive Eu anomalies. δ34SCDT and δ18O values of gypsum - and anhydrite samples have wide ranges from 21.30 ‰ to 25.62 ‰, and 11.5 ‰ to 19.1 ‰, 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. 87Sr / 86Sr ratios range from 0.707475 (ΔSW = −169.8) to 0.708175 (ΔSW = −99.8), close to and / or slightly lower than an Early - Miocene marine isotopic composition. Petrochemical and isotopic data indicate that the Aşkale basin evaporites developed in subtropical conditions via multiple marine transgressions onto a shallow platform or lagoonal environment.

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