Depositional Basin, Diagenetic Conditions and Source of Miocene Evaporites in the Tuzluca Basin in Northeastern Anatolia, Turkey: Geochemical Evidence

Abstract

The study area is located in northeastern Anatolia and represents a thick sequence (with gypsum, halite, clay, carbonate and siliciclastics) in a Miocene intermontane basin. The purpose of this study is to determine the depositional basin conditions, diagenetic processes and parent brine of the Miocene evaporite deposits (salts and gypsums) in the basin, by using sedimentological properties and geochemical composition. Sedimentological parameters and high positive correlations between some major ion (Fe, Al, and P oxides) and trace element (Zn, Co, Ni, Mo, Ba, and Sr, etc.) concentrations reveal that Tuzluca evaporites accumulated in a shallow terrestrial environment (playa lake-mud flats) exposed to high salinity conditions (Al2O3-Sr/Ba) under the effects of tectonism, diagenesis processes (replacement, dissolution-recrystallization, etc.), intense wave and biological activity (Zn-Fe2O3-P2O5, Ba-Sr-Fe2O3, etc.). The Sr-87/Sr-86, delta S-34 and delta O-18 results of the evaporite minerals also support the view that these evaporites may originate from non-marine water. Also, these values suggest that these may be derived from the dissolution and re-precipitation of ancient marine evaporites. The variable crystal sizes of the evaporites and low delta O-18 values indicate that the salinity and pH conditions in the environment changed from time to time. The high trace element values, positive Ce and Eu anomalies and low delta S-34 value reflect the important contribution of diagenetic and hydrothermal solutions to these evaporites. Some important positive correlations between major ions (Si, Al, Mg, and Ti, etc.), trace (Rb, Th, Pb, Zr, Hf, and Ni etc.) and rare earth elements (La, Ce, Er, etc.), the distribution pattern of REE normalized to MUQ and chondrite, and low delta O-18 values indicate terrigenous detritic input transported into the basin with the contribution of terrestrial waters (river, meteoric, etc.). Also, the presence of fine-grained clay minerals (kaolinite, illite and montmorillonite), which are determined by these relationships and X-Ray Diffractometer (XRD) reveal that the evaporites deposited in the basin were exposed to both humid and hot-dry climates under alkaline conditions.