Investigation of zirconium-hafnium and rare earth element behaviors as a result of stromatolite-lake water interaction in Salda Lake (Burdur)

Stromatolites are known as the most important and oldest fossil records of life on Earth. Therefore, it is very important to examine them and to know the depositional conditions of the physical-chemical environments in which stromatolites are formed. This study is about Lake Salda, which is surrounded by serpentinite rocks in southwest Türkiye, and it was formed as a closed system in the region. Lake Salda is quite alkaline and dense stromatolite formations are observed in the lake and on the coast. These stromatolites reach 60-70 cm in size in places and exhibit a dense kidney-like structure. Within the scope of this study, water and stromatolite samples were collected separately from ten different points surrounding Lake Salda. Water samples were taken from approximately 30 cm below the surface of the lake and pH, electrical conductivity (EC), temperature and redox potential (Eh) measurements were made on site. In the laboratory, anion+cation, trace and rare earth element analyses (REE) of water samples and major oxide, trace element and all REE analyses of stromatolite samples were carried out. According to the analysis results, Salda Lake Water has an average pH of 9.38, EC of 2.36 mS/cm, and Eh of -1.66 and consists mainly of cations such as Mg, Na, Fe, K and Ca and anions such as HCO3, Cl, SO4 and NO2. Major oxide distributions in stromatolite samples are as MgO, SiO2, CaO, Fe2O3, Al2O3, Cr2O3 and Na2O. Both water and stromatolite samples of Salda Lake have similar distributions in terms of trace element contents and it was observed that the samples were enriched in terms of Ni, Cr and Co according to PAAS and depleted in terms of other elements. Similarly, while the average Zr/Hf ratio in water was 11.8, this ratio was determined as 617 in stromatolites. While the average REE concentration in lake water was 0.078 ppb, this ratio was found as 1.91 ppm in stromatolites. When the REE trend of both water and stromatolite samples in the region was normalized according to PAAS, it indicates an increase from La to Lu. This indicates an enrichment in terms of HREE and MREE in both water and stromatolites, while it indicates a depletion or depletion in terms of LREE. The samples generally show strong negative Ce and Y anomalies and positive Eu anomalies. This indicates that the stromatolites were formed in partially warm lake waters under dominantly oxidizing environmental conditions. In addition, the hydromagnesite composition of the stromatolites in Lake Salda indicates that they were precipitated from waters affected by Mg-rich meteoric waters fed by serpentinite rocks around the lake