Geochemistry and Sr, S, and O stable isotopes of Miocene Abu Dhabi evaporites, United Arab Emirates

This study investigates for the first time the subsurface Miocene evaporite facies (Gachsaran Formation) in Abu Dhabi, United Arab Emirates. Forty-five evaporite rock samples were selected for petrographic, mineralogical, and geochemical investigations and stable isotope analyses to decipher their origin and constrain their age. Secondary gypsum with anhydrite relics dominates the investigated evaporitic rocks, with minor amounts of clays, dolomicrite, Fe/Ti oxides, and celestite. These samples are characterized by their excellent purity and low variability in geochemical composition. The distribution of trace element concentrations is significantly influenced by continental detrital intake. The main focus of the study is to determine the strontium, sulfur, and oxygen stable isotope compositions. The measured Sr-87/Sr-86 values of 0.708411-0.708739 are consistent with Miocene marine sulfates and indicate similar to 21.12-15.91 Ma (Late Aquitanian-Burdigalian). The delta S-34 and delta O-18 values are 17.10 parts per thousand-21.59 parts per thousand and 11.89 parts per thousand-19.16 parts per thousand respectively. These values are comparable to those of Tertiary marine evaporites. The relatively low values of delta S-34 suggest that non-marine water possesses little influence on S distribution. The geochemical composition and Sr, S, and O isotope distributions of the Abu Dhabi gypsum facies from the Gachsaran Formation reveals that their source brines were marine (coastal saline/sabkha) with subordinate continental input.

Automated summary

This study focuses on the subsurface Miocene evaporite facies in Abu Dhabi for the first time. Petrographic, mineralogical, and geochemical investigations were conducted on 45 evaporite rock samples to determine their origin and age. The results show that the samples are predominantly composed of secondary gypsum with minor amounts of other minerals. The stable isotope analysis suggests a Miocene marine sulfate origin with a range of 21.12-15.91 Ma.